Aspects of the Breeding Biology of the African Penguin on Bird Island, Algoa Bay

Aspects of the breeding biology of the African Penguin on Bird Island, Algoa Bay

By

Mark Shaun Ralph

Submitted in fulfilment of the requirements for the degree of Magister Scientiae in the Faculty of Science at the Nelson Mandela Metropolitan University

Submitted: January 2008

Aspects of the breeding biology of the African Penguin on Bird Island, Algoa Bay

By

Mark Shaun Ralph

Submitted in fulfilment of the requirements for the degree of Magister Scientiae in the Faculty of Science at the Nelson Mandela Metropolitan University

Submitted: January 2008

Supervisor: Dr. N. Klages Co-supervisor: Prof. T. Wooldridge

Aspects of the breeding biology of the African Penguin on Bird Island, Algoa Bay ACKNOWLEDGEMENTS Since the initiation of the project in 1992, Marine and Coastal Management (MCM) provided the primary financial support. The National Research Foundation provided additional financial support, together with the University of Port Elizabeth, in the form of a Grant Holder bursary through Prof. T. Wooldridge during 2002 and 2003. Mr Lucius Moolman and Mr Nollie Bosman of South African National Parks provided generous support with regard to permits for the research on Bird Island and provided accommodation at penguin colonies under the administration of the Greater Addo Elephant National Park. Transport to the island was provided by Eugene Swart and Richard Dodgson from MCM and Mrs Gea Groenehof and Mr Lloyd Edwards of Raggy Charters.

I am greatly indebted to my supervisors, Dr Norbert Klages and Prof. Tris Wooldridge, for their guidance, expertise, support and encouragement. Additionally, Dr Norbert Klages, Sean Rohm and Steve Ndzube provided an extensive database that formed the foundation on of this research. The results in Chapter 4 and 5 were solely derived from this database.

I am grateful to Dr David Schoeman and Mr Danie Venter for their assistance with the biological statistics during this study. Prof. Tris Wooldridge, Prof. Graham Kerley, Dr Sharon Haschick and Dr Philip Whittington provided the background information and additional literature. Evert Jacobs of SRK Consulting assisted with the GIS mapping. Hugh van Niekerk of the South African Weather Service kindly gave relevant temperature, wind and rainfall data. Dr Caroline Goodier of the University of KwaZulu-Natal, Mr John Holland and Mrs Pat Smailes kindly proof read the dissertation. Ms Robyn Greyling of Bayworld provided numerous opportunities in assisting with rehabilitation efforts. I extend my gratitude to those individuals that have assisted me on Bird Island, notably: Mike Spies, Wayne Sharp, Phil Whittington, Norbert Klages, Bruce Dyer, Nollie Bosman, Tony Tree, Evert Jacobs, Julie Nelemans and Debbie Ralph. The completion of this dissertation was only possible through continued support and encouragement from Ms Nicola Holland.

I dedicate this research to the late Dr Dave Hartley, and his wife, Crystal Hartley, who have dedicated their lives to saving the African Penguin.

May the African Penguin grace our hearts and our oceans for many years to come.

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TABLE OF CONTENTS ACKNOWLEDGEMENTS ...... i TABLE OF CONTENTS ...... i LIST OF TABLES ...... iv LIST OF FIGURES ...... iv GLOSSARY ...... v ABSTRACT ...... vi

1 GENERAL INTRODUCTION ...... 1 1.1 Breeding distribution ...... 1 1.2 Population trends ...... 4 1.3 Population trends in Algoa Bay, Eastern Cape ...... 5 1.4 Factors inhibiting breeding of the African Penguin ...... 6 1.4.1 Human disturbance ...... 7 1.4.2 Introduced exotic species ...... 8 1.4.3 Extreme weather conditions ...... 9 1.4.4 Predation and inter-specific competition ...... 10 1.4.5 Parasites and diseases ...... 11 1.4.6 Oil spills ...... 12 1.4.7 Fisheries ...... 13 1.5 Rationale for the study ...... 16

2 STUDY AREA ...... 17 2.1 General introduction ...... 17 2.2 Geology of Algoa Bay ...... 18 2.3 Climate of Algoa Bay ...... 19 2.3.1 Weather at Bird Island ...... 19 2.4 Flora of Bird Island ...... 20 2.5 Avifauna of Bird Island ...... 21 2.5.1 The Cape Gannet ...... 22 2.5.2 The Kelp Gull ...... 22 2.5.3 Roseate and Antarctic Terns ...... 23 2.6 The history of Bird Island ...... 23 2.7 Conservation of the Algoa Bay Islands ...... 24

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3 NEST DISTRIBUTION ...... 25 3.1 General introduction ...... 25 3.1.1 Habitat at the nest site ...... 25 3.1.2 Topography of the islands in Algoa Bay ...... 26 3.1.3 The breeding cycle of penguins in Algoa Bay ...... 28 3.1.4 Rationale ...... 28 3.2 Methodology ...... 29 3.2.1 The mapping of Bird Island ...... 29 3.2.2 Description of the habitat types ...... 31 3.2.3 Census data acquisition ...... 35 3.2.4 Data collection ...... 36 3.2.5 Maximum density of penguin nests ...... 36 3.2.6 Statistical treatment ...... 37 3.3 Results ...... 39 3.3.1 Relocation of birds to favourable habitat ...... 39 3.3.2 Nest count and density trends in habitats receiving complete and no shelter ...... 40 3.3.3 Additional criteria determining nest site selection ...... 45 3.4 Discussion ...... 48 3.5 Conclusion ...... 53

4 BREEDING SUCCESS AND CLUTCH SIZE ...... 54 4.1 Introduction ...... 54 4.1.1 The annual breeding cycle ...... 54 4.1.2 Egg incubation and chick-rearing stages ...... 55 4.1.3 Mortality of offspring at the nest ...... 55 4.1.4 Clutch size and breeding success ...... 56 4.1.5 Parental expenditure required in breeding ...... 56 4.1.6 Asynchronous breeding theories...... 57 4.1.7 Rationale ...... 58 4.2 Methodology ...... 59 4.2.1 Study location ...... 59 4.2.2 Drawbacks to the study ...... 59 4.2.3 Data collection ...... 59 4.2.4 Classification of nests ...... 60 4.2.5 Statistical data analysis ...... 60 4.3 Results ...... 61 4.3.1 Data collection ...... 61 4.3.2 Survivorship summary at the incubation and chick-rearing stages ...... 61 4.3.3 Drawbacks to the statistical analysis of the data ...... 63

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4.3.4 Survivorship comparisons between the breeding stages...... 63 4.3.5 Clutch size during the incubation stage relative to the breeding attempt ...... 64 4.4 Discussion ...... 66 4.5 Conclusion ...... 68

5 GROWTH IN CHICKS ...... 69 5.1 Introduction ...... 69 5.1.1 Chick classification ...... 69 5.1.2 Chick development ...... 69 5.1.3 Dietary demands of chicks ...... 71 5.1.4 Rationale ...... 71 5.2 Materials and Methods ...... 72 5.2.1 Data collection ...... 72 5.2.2 Drawbacks to the study ...... 72 5.2.3 Growth models and data transformation ...... 72 5.2.4 Statistical treatment ...... 74 5.3 Results ...... 75 5.3.1 Data analysis ...... 75 5.3.2 The best fit growth curve ...... 75 5.3.3 Statistical treatment ...... 75 5.4 Discussion ...... 86 5.4.1 Aspects of growth between the chick groups ...... 86 5.4.2 Growth rate and survival of chicks ...... 87 5.4.3 Growth rate used as an indicator of environmental conditions ...... 88 5.5 Conclusion ...... 89

6 GENERAL CONCLUSION ...... 90

REFERENCE LIST ...... 93

APPENDICES ...... 106 Appendix A: Nest Distribution ...... 106 Appendix B: Chick Growth...... 111

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LIST OF TABLES Table 1.1: Nest counts of long-term breeding colonies for the African Penguin. 2 Table 3.1: The extent of the mapped areas on Bird Island. 31 Table 3.2: Descriptive statistics of the mean nest density for the shelter types. 41 Table 3.3: Nest density (m²) recorded for each locality. 43 Table 3.4: Post-hoc Tukey p-values and Cohen’s d practical significance values for mean nest density for each locality. 44 Table 3.5: Descriptive statistics of nest density within coastal and inland localities. 45 Table 3.6: Descriptive statistics for mean nest density during the breeding periods. 46 Table 4.1: Descriptive statistics of nests and clutch size (eggs laid) during peak and replacement breeding attempts. 65 Table 5.1: Mean aspects of growth recorded per chick type. 76

LIST OF FIGURES Figure 1.1: The distribution range of the African Penguin & colony size. 3 Figure 1.2: Time-line illustrating the global decline of the African Penguin population 4 Figure 1.3: Recent regional population trends in African Penguins. 5 Figure 1.4: Trends in active nests counts for Algoa Bay. 6 Figure 1.5: Annual harvests from the South African pelagic and demersal fisheries. 14 Figure 1.6: Estimated sardine & anchovy biomass relative to annual catches in SA. 15 Figure 2.1: Islands of Algoa Bay. 18 Figure 2.2: The seasonal appearance of vegetation on Bird Island. 21 Figure 2.3: The breeding density of the Cape Gannet on Bird Island. 22 Figure 2.4: Kelp Gulls scavenging on regurgitated fish. 22 Figure 2.5: The full breeding plumage of the Roseate Tern and the Antarctic Tern 23 Figure 2.6: The Bird Island lighthouse with the gannet colony in the foreground. 24 Figure 2.7: View of the houses on Bird Island from the south and east. 24 Figure 3.1: Penguin nests on the rocky topography of St Croix Island. 26 Figure 3.2: Aerial view of Bird Island showing its flat topography. 27 Figure 3.3: The mapped localities including the six sub-divided surface localities. 30 Figure 3.4: A typical burrow nest. 32 Figure 3.5: Nests and breeders deserting nests seeking maximum shade. 33 Figure 3.6: Calculation of the shaded extent behind the house locality. 33 Figure 3.7: Breeders found nesting in the open. 34 Figure 3.8: The elevated rocky outcrop found in the Surface 6 locality. 34 Figure 3.9: Nests utilising rocks to receive partial shelter. 35 Figure 3.10: Maximum nest density within the optimal habitat behind the guano sheds. 37

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Figure 3.11: The relocation of breeders from nests found in the open to sheltered nest sites temporarily provided in the form of cardboard boxes. 39 Figure 3.12: Nest counts recorded for habitats receiving complete and no shelter. 40 Figure 3.13: Nest density recorded for habitats receiving complete and no shelter. 41 Figure 3.14: Mean nest density for the three types of shelter. 42 Figure 3.15: Mean nest density for each habitat locality. 44 Figure 3.16: Mean nest density for localities along the coast and inland of the island. 45 Figure 3.17: Mean nest density between the three breeding periods for each locality. 47 Figure 4.1: Survival and failure history of offspring per clutch type during breeding. 62 Figure 5.1: The stages of breeding at the nest. 70 Figure 5.2: Mean aspects of growth comparisons per chick type. 78 Figure 5.3: The plotted von Bertalanffy growth curve of the mean weights of chicks from groups A, B, C up until mean fledging day and/or mean day of death. 80 Figure 5.4: Extrapolated growth periods from the overall growth curves of the three chick groups illustrating day 1 - day 30 and day 31- mean fledging day. 81 Figure 5.5: Mean growth rate comparisons of the growth constants determined from the von Bertalanffy growth equation over the entire growth period for each chick type. 83 Figure 5.6: The von Bertalanffy growth curve of the mean weights for chicks from Groups A, B, C as well as the upper and lower 95% confidence intervals of the means for those chicks that died. 84 Figure 5.7: The critical time and weight that influences the survival of chicks. 85

GLOSSARY Clutch: Total number of eggs laid during one breeding attempt; Brood: Offspring (i.e. chicks) that are cared for during one breeding attempt; Fitness: The condition of a bird relative to its body size determined by weight gained.

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ABSTRACT It is important to the survival of the Africa Penguin ( Spheniscus demersus ) population that breeding at the nest site is successful and that large numbers of chicks are fledged into the breeding population. Nest distribution on Bird Island is not random and locality preferences for breeding exist. Although it seems that sufficient area exists on Bird Island for penguin nests, it can hardly be considered as suitable to optimise breeding. During prolonged heat conditions, breeders relocated to nest sites that were sheltered. Nests that were below ground in burrows was the only habitat that did not suffer nest desertion whilst all the other habitat types (including those that were sheltered) experienced 2-3 fold declines in nest numbers. Nest density and the selection of suitable nest sites are significantly influenced by the stage of breeding that the majority of birds are in, yet nests that are shaded, well-ventilated and protected seem to be the most preferred sites for breeding.

Adults that attempt to breed are considered to then be in a healthy condition and will usually lay a double clutch (Randall 1983). The frequency of double clutches being laid during the peak breeding attempt was significantly higher compared to the replacement one. Breeding failure was fairly similar to breeding success during the incubation stage for nests with double clutches however, was substantially higher in single clutches. The growth rate of chicks was best fit to the von Bertalanffy growth curve in 90% of the cases. The overall growth rate of chicks from double broods was faster than that from single broods, however was not significant. A-chicks maintain a high growth rate until they fledged. Yet, the sibling B-chick recorded the lowest weight of the successfully fledged chicks and up until day 30 recorded a similar weight to those chicks that failed to fledge. Contrary to findings of Randall (1983), chicks from single broods delayed fledging, recorded the lowest overall growth rates and experienced the greatest weight loss of all groups, yet fledged successfully. In order for chicks to fledge successfully, they need to obtain a weight of 1060 g before day 30.5 in their growth cycle to avoid death due to starvation later on. Single chicks that are raised from a double clutch, fledged more often than chicks raised from a single clutch. Un- fit or ill-adapted breeders that are marginal in their capabilities of raising offspring, already manifest in a small clutch size and offspring unable to obtain adequate weights during the initial stages of growth.

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1 GENERAL INTRODUCTION 1.1 Breeding distribution The African Penguin ( Spheniscus demersus ) is the only species found on the African continent and is distributed along the coastlines of South Africa and Namibia (Crawford et al. 1995a). The African Penguin probably bred at 37 localities in the past (Crawford et al. 1995a), yet it is probable that only 29 breeding colonies remain (Crawford et al. 1995b, Kemper et al. 2001). At present the breeding population is distributed from the northernmost locality of Sylvia Hill, on the edge of the Namib Desert (Simmons & Kemper 2003), to the easternmost locality of Bird Island in Algoa Bay, Eastern Cape. Additional localities exist (i.e. two cave colonies located south of Sylvia Hill), however, active breeding has yet to be confirmed (Simmons & Kemper 2003).

African Penguins breed primarily on islands (Randall 1983, Crawford et al. 1995b) where they are less vulnerable to mainland predators. A cave colony (Sylvia Hill) along the Namibian coastline, two colonies (Boulders Beach and Stony Point) along the Western Cape coastline of South Africa, and, very recently, a fourth mainland colony located at the De Hoop Nature Reserve (Underhill et al . 2006) are the only mainland breeding colonies (Loutit & Boyer 1985, Simmons & Kemper 2003). Mainland predators have colonised some islands in the past viz. Marcus Island (Saldanha Bay) and Bird Island (Lamberts Bay) for example. These are connected to the mainland by man-made cause-ways (Cooper et al. 1985) and breeding penguins are now vulnerable to mainland predators. At present, mainland predators are absent from all islands in Algoa Bay.

Of the global population of African Penguins, two major population strongholds exist and both are found in South Africa. Nest counts conducted during 2001-2002 at all the breeding localities (Table 1.1 and Figure 1.1) found the Western Cape accommodating the main stronghold (54%), followed by the Eastern Cape accounting for 37% of the remaining nests (du Toit et al. 2003a). More recent counts reflect a breeding shift, with each of the two provinces recording 40% of the global population (Nel et al. 2003). The remaining 20% of the population is distributed among the other breeding colonies.

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Table 1-1: Nest counts of long-term breeding colonies for the African Penguin (du Toit et al. 2003b).

Locality Number of Active Nests Date of Count Bird Island, Lamberts Bay 15 2001 Marcus Island 114 March-June 2001 Malgas Island 55 March-June 2001 Jutten Island 1 338 March-June 2001 Vondeling Island 649 March-June 2001 Dassen Island 21 409 March-June 2001 Robben Island 6 723 March-June 2001 Boulders Beach 1 054 March-June 2001 Seal Island, False Bay 52 November 2000 Stony Point 111 March-June 2001 Dyer Island 2 088 March-June 2001 South Africa – Western Cape 33 608 (~54% of global nest counts)

Jahleel Island 538 May 2000 St Croix Island 16 950 March-June 2001 Brenton Rock 32 May 2000 Seal Island, Algoa Bay 345 March-June 2001 Stag Island 24 March-June 2001 Bird Island, Algoa Bay 5 376 March-June 2001 South Africa – Eastern Cape 23 265 (~37% of global nest counts)

South African Total 56 873

Hollams Bird Island - 1990 Oyster Cliffs 250 February 2002 Sylvia Hill 45 January 2000 Mercury Island 2 822 2000/2001 Ichaboe Island 1 345 2000/2001 Halifax Island 462 2000/2001 North Reef 1 2000/2001 Possession Island 359 2000/2001 Pomona Island 1 2001/2002 Plumpudding Island 67 2000/2001 Sinclair Island 75 2000/2001 Namibian Total 5 431 (~9% of global nest counts)

Overall Total 62 304

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Saldanha St Helena Bay Marcus I. Malgas I. Saldanha Mercury I. 33 o Jutten I. Langebaan Lagoon C 26 o Dassen I. Vondeling I.

Robben I. Ichaboe I. Cape Town 34 o Dassen I. Seal I. Halifax I. C Boulders False 18 o Bay Luderitz Cape Point Stony Point S NAMIBIA North Reef 27 o B Dyer I. Possession I.

o o o Walvis 35 18 19 Bay Pomona I.

Hol lams Bird I. Jahleel I. Seal I. Oyster Cliffs Stag I. 25 o D St Croix Sylvia Hill Plumpudding I. I.

Mercury I. Luderitz o Brenton Bird I. 34 Rock Sinclair I. Port A A 15 o Elizabeth 26 o Algoa Bay

Durban 30 o 30 o SOUTH AFRICA

MAP KEY Bird I. Lambert’s Breeding - Counts Bay East > 16 000 – 22 000 nests London C Port > 1 000 – 7 000 nests Mossel Elizabeth Cape Town Bay > 500 – 1 000 nests > 100 – 500 nests B D 35 o > 0 – 100 nests recent breeding cessation Towns 15 o 20 o 25 o 30 o E

Figure 1-1: The distribution range of the African Penguin (after Shelton et al. 1984) and their respective colony size (du Toit et al. 2003b).

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1.2 Population trends In 1900 it is likely that there were 1.4 million penguin adults on Dassen Island (Western Cape). By 1956, the overall population had declined to 300 000 adults (du Toit et al. 2003b). By the late 1970s the population had decreased to 222 000 adults. A further population decline of 19.4% followed (Whittington et al. 1999a) with only 179 000 adults recorded in the 1990s (Crawford et al. 1995b). The population recovered to 201 000 adults in 2000 as a result of increased abundance of sardine and anchovy stocks in South Africa (Crawford 1998a cited in Ellis et al. 1998, Crawford et al. 2001b, Wolfaardt et al. 2001). However in 2001, the global African Penguin population relapsed into a state of decline and recorded 163 500 adults. Of this total, approximately 27 500 adults (17%) were recorded in Namibia and 136 000 adults (83%) in South Africa (du Toit et al. 2003b).

Overall, the population trend of the African Penguin continues to decline (Shelton et al. 1984, Crawford et al. 1995b, Whittington et al. 1999b). The South African population meets the conservation criteria of ‘vulnerable to extinction’ and the Namibian population is already ‘endangered to extinction’ (Barnes 2000, BirdLife International 2000, du Toit et al. 2003b, Hockey et al. 2005). The population trend of the African Penguin on a global and regional scale as described above is represented in Figure 1.2 and in Figure 1.3 respectively.

14

12

10

8

6

4

2 Nest Count (100 000s)

0 1900 1956 1970 1990 2001

Time-line (years)

Figure 1-2: Time-line illustrating the global decline of the African Penguin population.

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60000

50000

40000

30000 Breeding pairs Breeding 20000

10000

0 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

South Africa Western Cape

Eastern Cape Namibia

Figure 1-3: Recent regional population trends in African Penguins. (Data obtained from Marine and Coastal Management seabird censuses). The disjointed line (i.e. Eastern Cape) is a result of data deficient years and hence these trends cannot be accurately depicted.

1.3 Population trends in Algoa Bay, Eastern Cape The St Croix and Bird Island groups in Algoa Bay are collectively colonised by a major stronghold of African Penguins (Crawford et al. 1995b, Crawford et al. 2001a). The number of breeding pairs recorded at these two island groups shows that since the 1990s, the St Croix Island group has continued to record higher numbers of active nests than that of the Bird Island group. The latter has remained relatively stable except for recent declines (2005 to 2007) of 3 545 to 818 breeding pairs. In contrast, the St Croix Island group increased from 3 005 to 4 363 breeding pairs during this time (2005-2007). This increase in breeding pairs in comparison to the regional total decline of 17 000 pairs recorded between 1993 and 2005 is considered negligible. Overall, and in particular during 2004 to 2005, the breeding population in Algoa Bay has declined. At present (2007), the breeding penguin population in Algoa Bay stands at 5 181 pairs, with 16% located on Bird Island and 84% on the St Croix Islands (Figure 1.4).

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25000

20000

15000

10000 Breeding pairs Breeding

5000

0 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Eastern Cape St Croix Island Bird Island

Figure 1-4: Trends in active nests counts for Algoa Bay. (Data obtained from Marine and Coastal Management seabird censuses and from Dr Klages). The disjointed lines are a result of data deficient years and hence the trends cannot be accurately depicted during these periods.

1.4 Factors inhibiting breeding of the African Penguin The reasons for the significant decline in the African Penguin population are well known. Past impacts included colony disturbance and habitat destruction through guano exploitation and egg collecting activities (Frost et al. 1976a). This resulted in the decline of the global population by 90% (Crawford et al. 2001a, Crawford et al. 2006). Guano exploitation activities were banned in 1969 (Frost et al. 1976b) however, more recently, competition with commercial fisheries for pelagic fish as well as an increased occurrence of oil spills (two major oil spills in 1994 and 2000) have also contributed to the decline (Crawford et al. 2001b). Penguin survival is also affected by intra-specific and inter-specific competition for space and food, predation, parasitism, disease and climate change. These identified threats are discussed below, while specific threats that affect the Bird Island population are further elaborated on in Chapter 3.

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1.4.1 Human disturbance Breeding birds are extremely sensitive and easily disturbed. In the past, breeding penguins on Bird Island were continuously disturbed by human activities on the island that involved the collection of guano and penguin eggs. Similarly, the potential exists for tourists and research activities conducted on the island to disturb breeding penguins.

a) Egg collecting Harvesting of African Penguin eggs probably began soon after the Europeans settled in the Cape (Westphal & Rowan 1971). In the space of 32 years (1897–1930) approximately 15 million eggs were collected from the breeding colonies (Frost et al. 1976b). Inevitably, this led to a decline in the African Penguin population and resulted in egg harvesting being banned in 1967 (Shelton et al. 1984).

b) Guano scraping In addition to the disturbance caused by egg collecting, breeding of the African Penguin was also severely impacted by the commercial harvesting of guano (Rand 1963, Berry et al. 1974). The African Penguin historically dug burrow nests in the guano substrate that covered most of the islands. However, the activity of guano scraping forced birds to nest on the surface or burrow into a less stable sandy substratum neither of which is ideal for breeding. Surface nests are exposed to aerial predators and extreme weather conditions, whilst the burrow nests are likely to collapse (Frost et al. 1976a, Cooper 1980, Wilson & Wilson 1989). Guano scraping has ceased on all South African islands, but the altered substratum with its related effect on breeding success, persists.

c) Research studies In field ornithology, the impact of field investigations is similar to the more overt impacts caused by non-scientific human activities such as tourism and general recreational activities (Whittington et al. 1999b). Adverse effects of field research activities are most commonly associated with nest visits, aircraft surveillance, working in or passing through sensitive areas and approaching breeding birds. Responses of species to any activity may vary between species, and what may be consequential for one is inconsequential for another (Whittington et al. 1999b).

At some localities (i.e. Boulders Beach), African Penguins show remarkable tolerance to humans, whereas at other sites (i.e. Seal Island in Algoa Bay) birds are easily disturbed (Whittington et al. 1999b). The breeding cessation of penguins at four former colonies has been the result of disturbance related activities (Crawford et al. 1995b).

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d) Helicopter disturbance Helicopter use is often the safest and most convenient way to access the islands. However, the use of helicopters can cause serious disturbance to wild birds if unregulated, and can negatively impact on seabird feeding efficiency, energy budgets, breeding success and survival (Rounsevell & Binns 1991). Klages & Whittington (2006b) also documented additional impacts on seabirds as a result of helicopter use and include:

alteration to characteristic of breeding habitat;
deterrence of birds from settling to breed;
desertion of colony sites by all or part of a breeding population;
increased destruction or predation of un-protected eggs and chicks;
increased mortality of young chicks from predation;
trampling or disorientation;
reduced number of young birds fledging; and
a reduced fledging weight.

The impacts listed above contribute to a lower juvenile survival and may even be implicated in long-term population declines (Harris 2001 cited in Klages & Whittington 2006b). Bird Island in Algoa Bay has a history of helicopter access to transport personnel when the lighthouse requires maintenance or when South African National Parks (SANParks) officials stay on and patrol the island. Due to Bird Island serving as a breeding, nursing and roosting ground for large numbers of threatened and endangered seabirds, the probability of it becoming a major tourist attraction is made possible by commercial helicopter access. In order to mitigate any disturbance that may be caused by these operations on the breeding seabirds, detailed management and implementation plans should be adhered to (Klages & Whittington 2006b).

1.4.2 Introduced exotic species The invasion of ecosystems by exotic species is currently viewed as one of the most important causes of biodiversity loss. Particularly vulnerable, are islands that offer an abundance of resources but lack natural enemies. This favours the successful establishment of introduced species that is often to the detriment of the natural occurring specie. Mammals are one of the most important taxa responsible for invading islands. Rats, cats, goats, rabbits and pigs have been responsible for most of the damage caused to isolated ecosystems (Courchamp et al. 2003).

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Bird Island has been invaded by a number of exotic species in the past viz. rabbits, mice and cats. Of the three alien species introduced, rabbits (the European species: Oryctolagus cuniculus ) posed the most formidable threat to the breeding success of the island seabirds. Rabbit numbers were controlled by the availability of their food, a green spinach-like plant (Mesembryanthemum aitonis ) which grows seasonally over the island. As a result of the overgrazing of the vegetation by the introduced rabbits, penguin chicks no longer received shelter from the vegetation and suffered increased mortality due to aerial predation and heat stress. The rabbit population on Bird Island was eliminated in 1990 when concerted and successful eradication efforts were introduced (Urquart & Klages 1996). The only exotic mammal species to have invaded and not yet been eradicated from Bird Island, is the common house mouse (Mus musculus ). The population on Bird Island is considered small (Klages, pers. comm .).

1.4.3 Extreme weather conditions Storms, drought, flooding, fire, heat waves and global climate change are all identified as threats to the African Penguin population and other seabirds (du Toit et al. 2003b). Storms and flooding may result in nest desertion, eggs being washed away and chicks drowning (Randall et al. 1986). Drought events increase the risk of fires on islands that have woody, herbaceous and grass vegetation. Global warming is also likely to increase the frequency of these extreme events (du Toit et al. 2003b). This is especially pertinent at Boulders Beach and Robben Island where African Penguins are reliant on the abundant Acacia thickets that provide shelter for nesting birds (Whittington et al. 1999b).

Penguins are adapted for life in extremely cold conditions. They have insulating fatty deposits that prevent hypothermia. These adaptations result in them becoming over- insulated whilst breeding on land, especially for those species that live in warm temperate regions such as the African Penguin (Griffin 2005). In southern Africa, peaks in temperature are experienced during the summer (January – March). This coincides with the first peak breeding attempt of penguins in the Eastern Cape (Crawford et al. 1990, Crawford et al. 1995b). At such times, African Penguins may be exposed to temperatures exceeding 30°C. They can reduce the effects of heat stress by nesting in habitats that provide shelter from the sun (vegetation cover, man-made structures, behind rocks and in burrows). However, as a consequence of the past removal of guano on Bird Island, penguins are largely forced to nest on the surface. These birds are more likely to suffer from heat stress and record lower breeding success than sheltered breeders (Frost et al. 1976a).

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1.4.4 Predation and inter-specific competition Island habitats provide protection and isolation for penguins from mainland terrestrial predators. For penguin colonies found on the mainland, a broad spectrum of mainland predators such as leopards, Black-back jackals, rats, cats, mice and snakes prey on breeding birds. However, terrestrial predators have colonised islands in the past because of human developments such as man-made causeways, these include Marcus Island and Bird Island (Lamberts Bay) (Cooper et al. 1985). Mainland predators are presently absent from all islands found in Algoa Bay, although Jahleel Island is close to the Ngqura port, and it is possible that they may now invade the island. Island predators (excluding introduced species) are limited to the Sacred Ibis ( Threskiornis aethiopicus ), Great White Pelican (Pelecanus onocrotalus ), Kelp Gull (Larus dominicanus vetula ) and the Cape Fur Seal (Arctocephalus pusillus).

a) Kelp Gulls Kelp Gulls prey on unprotected eggs and small penguin chicks (Cooper 1974). Most of their takings constitute scavenging on deserted clutches, infertile eggs and dying chicks. Gulls have also learnt to capitalize on disturbance, preying on eggs and chicks that are temporarily exposed when parent birds take fright due to human presence. The Kelp Gull population in southern Africa has increased by 105% since 1982 (Crawford & Hockey 2005). This increase is likely the result of human related activities viz. guano scraping and commercial fishing operations.

In the early part of the 20 th century, guano scraping caused disturbance to breeding birds, resulting in the desertion of nests by adult penguins. Kelp Gulls preyed on the exposed eggs and small chicks (Whittington et al. 2006). For this reason, Kelp Gulls were heavily persecuted and shot by the guano collectors (Crawford 1997). However when guano collection ceased in the 1960s, so did the persecution of the Kelp Gull. This resulted in the slow recovery of the gull population. In the latter part of the 20 th century, gull numbers had substantially increased primarily as a result of easily accessible food in the form of human wastes, fish offal and discarded by-catch (Whittington et al. 2006). The elevated Kelp Gull population in Algoa Bay is especially noticeable on Seal Island, where the largest colony in Algoa Bay is found and is competing for space with breeding African Penguins (CSIR 2001).

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b) Cape Fur Seals Following the cessation on the exploitation of the Cape Fur Seal in South Africa in the 1980s, numbers have increased substantially (Butterworth & Wickens 1990). Numbers have also increased in Namibia (du Toit et al. 2003b), even though sealing is still practised. Isolated incidences of predation of Cape Fur Seals on penguins have been reported on southern African islands since the early 1900s, but predation intensity has dramatically increased since the 1980s (du Toit et al. 2003b). Expanding seal herds have displaced large numbers of penguins at breeding localities, including Hollams Bird Island, Mercury and Sinclair Islands (Crawford et al. 1989, Steele & Hockey 1990). Penguins compete with Cape Fur Seals for breeding space (Crawford et al. 1995b) and for prey (Whittington et al. 1999b). These are the probable reasons for breeding cessation of penguins at five former colonies (Crawford et al. 1995b). Approximately 4 000 Cape Fur Seals colonise Black Rocks which is in close proximity to the Bird Island Group (Klages et al. 2003).

c) Other influencing factors In addition to the mainland predators listed above, marine predators such as the Killer Whale (Orcinus orca ) and Great White Shark ( Carcharodon carcharias ) also occasionally prey on penguins. African Penguins also compete with other seabirds for breeding space. At Bird Island, penguins have been displaced from a portion of prime breeding habitat by the Cape Gannet (Morus capensis ) (Ralph, pers. obs.).

1.4.5 Parasites and diseases Colonial nesting birds such as the penguin are suitable hosts for parasites. Large concentrations of parasites are frequently observed at colonies where avian nest sites are frequently utilised during subsequent breeding attempts (Rothschild & Clay 1952, Marshall 1981). Heavy infestations of parasites can cause breeders to desert their nests (Loye & Zuk 1991) and if they harbour arboviruses, could also cause illness and death of seabirds (Nutall 1984, Morgan et al. 1985). African Penguins contract a diverse array of diseases resulting from ecto- and endo-parasites. Fleas (i.e. Paraphsyllus longicornis ) and ticks (i.e. Ornithodoros capensis ) are the common ecto-parasites, whilst cestodes (i.e. Tetrabothrius lutzi and T. eudyptidis ) and nematodes (i.e. Contracaecum variegatum ) are the common endo-parasites. The disease types that affect seabird colonies are broad and are covered in detail in Ellis et al. (1998).

Under normal conditions healthy penguins can tolerate the presence of parasites. However, when parasitic infestations at the nest site are combined with other sub-optimal breeding conditions (i.e. limited food availability, heat stress, predation etc) acting on breeders,

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the cumulative impact may inhibit a breeder’s tolerance. Artificial penguin nest shelters were found only to be utilised by breeders during one breeding season as a result of tick infestations within the nest site. In addition, Kemper (2006) recorded prevalent infestations of ticks within the buildings of Halifax Island, a likely reason as to why these areas are void of any penguin nests. Similarly, the guano-sheds on Bird Island are accessible and would provide sheltered nest sites to breeders, however they rarely utilize these areas for breeding (Ralph, pers. obs. ). The subject of disease in African Penguins is data deficient, although the potential exists for disease to cause major catastrophic population declines (Whittington et al. 1999b).

1.4.6 Oil spills Oils spills affect all marine species, but penguins are particularly vulnerable to this form of pollution because they cannot fly (Erasmus et al. 1981, Morant et al. 1981, Erasmus & Wessels 1985, Birrel 1995). Penguins are contaminated by floating oil when they surface to breathe. The penguin feather structure and alignment is specialised to combat heat loss and water penetration (Webb & King 1984), therefore allowing the penguin to remain warm and dry in colder water. Penguins preen their plumage whilst on land realigning their feathers and maximising their retention of heat. When feathers become oiled, insulation properties of the feathers are lost and oiled birds suffer from hypothermia (Erasmus & Wessels 1985). Birds that preen their contaminated feathers ingest oils resulting in dehydration and death (Eastin & Murray 1981). The incidences of oil pollution are more frequent and probable for penguin breeding colonies located within proximity to ports. The four largest penguin colonies are Robben and Dassen Islands north of the Cape Town port and St Croix and Bird Islands north of the Port Elizabeth and Ngqura ports respectively. To highlight the severity that oil spills have had on penguin numbers in the past, major oil spills and the resultant casualties in penguin numbers are listed below:

The ‘Apollo Sea’ sank in 1994 near Dassen Island where 10 000 penguins were oiled. Only 5 213 penguins were cleaned and released;
An unidentified oil spill in 1995 near Dyer Island affected 1 200 penguins;
The sinking of the ‘Treasure’ between Robben and Dassen Island in 2000, affected 19 000 penguins (11% of the total population) with 16 163 penguins being cleaned and released;
923 penguins were oiled in 1985 as a result of the sinking of the ‘Kapodistras’ at Cape Recife; and

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Approximately 1 100 penguins were oiled when the ‘Cordigliera’ sank off the Transkei coast in 1996 and oil washed southwards into Algoa Bay.

Since 1968, approximately 50 000 penguins have been recorded oiled. Of these, 31 500 penguins (18% of the global population at that time) were recorded oiled between the years 1991-2001 (Nel & Whittington 2003).

1.4.7 Fisheries The downward trend of the African Penguin population has been ascribed to one predominant factor, prey scarcity. The scarcity of prey influences the ability of breeders to sustain their food requirements and that of their chicks (Crawford et al. 1990, Crawford et al. 2006). African Penguins feed on a variety of prey species notably: fish, squid and crustaceans (Crawford 1998b). Sardine ( Sardinops sagax ) and Anchovy ( Engraulis japonicus ) form the major component of a penguin’s diet in the South African waters. These prey species are also important in the diet of other seabirds, notably the Cape Gannet ( Morus capensis ) and Cape Cormorant ( Phalacrocorax capensis ) (Crawford 1998b).

a) The South African fishery More than 4 500 commercial fishing vessels work the nearly 3 000 km of South African coastline (Jones 2002). The principal species of shoaling fish caught by the pelagic fishery are anchovy, sardine and Red-eye Round Herring ( Etrumeus whiteheadii ). Demersal deep- sea trawlers bring in Hake ( Merluccius sp .), Snoek (Thyrsites atun ), Mackerel ( Scomber japonicus ), Monkfish ( Lophius sp .) and sole ( Austroglossus pectoralis and Solea bleekeri ). The most important species caught in the handline fishery is Chokka squid ( Loligo vulgaris ). In addition, this type of fishery also catches many other species (Jones 2002).

South Africa exports about 80% of its annual fish catch. The industry hit a peak in 1988 when close to 1 million tons was harvested, with 74% (671 415 tons) of the catch comprised of pelagic fish, 22% (200 515 tons) from the demersal catch and the remainder (4%) comprised of other catch types. During the 1990s catches dropped to half a million tons due to the collapse of the fish stocks as a result of fishing pressure. Up until 1999, fish stocks remained low with catches from the South African fisheries totalling 571 924 tons. With reference to Figure 1.5, the pelagic fishery accounted for 65% (375 370 tons) and the demersal fishery 31% (179 578 tons) of this total catch (Jones 2002).

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1000000

900000

800000

700000

600000

500000

400000

300000

200000

100000

0 Date 1988 1989 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Pelagic Demersal Total

Figure 1-5: Annual harvests from the South African pelagic and demersal fisheries (Data obtained from Jones 2002).

b) The catch of the pelagic fishery The demersal fishery is the most valuable sector of the fishing industry in South Africa due to its generated income (R500 million per annum). However, it is the pelagic fishery that dominates in terms of volume of fish caught (primarily anchovy, sardine and Red-eye Round herring). The pelagic catch fluctuated between 350 000 tons and 450 000 tons (1975 to 1990), dropping to 214 000 tons by the end of 1991 (Government Gazette 2005). About two-thirds of the total pelagic catch is derived from sardine and anchovy (Jones 2002).

c) Sardine and anchovy trends in South Africa and Namibia Sardine was abundant during the 1950s and the 1960s, where 3.7 million tons and 9.8 million tons were harvested by fisheries in the South African and Namibian waters respectively. This over-fishing practice resulted in the collapse of the South African sardine fishery in the mid 1960s, followed by the collapse of the Namibian sardine fishery in the 1970s (Crawford 1998b). Over the following two decades (1970-1990), the sardine catch in South Africa and Namibia totalled 1.2 million tons and 4.5 million tons respectively (Crawford 1998b). Furthermore, the sardine catch in Namibia continued to decline between 1990 and 1995, with 170 000 tons of fish in total being caught. The scarcity of sardine had a devastating effect on the African Penguin population in Namibia, the numbers of which have continued to decline (Crawford 1998b, du Toit et al. 2003b).

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Anchovy was first exploited by the South-African purse-seine fisheries in the 1960s with anchovy contributing the most volume to the catch compared to other fish species. Acoustic surveys in South Africa estimated that the anchovy stocks were healthy, totalling approximately 0.98 and 1.75 million tons between 1984 and 1988. Anchovy continued to dominate the purse-seine catch, with 90 000 tons being caught in 1994 alone (Crawford 1998b). Anchovy became an important fish sustaining the diets of many seabirds during the period when sardine stocks were low. However, anchovy stocks declined from 0.5 million tons in 1994 to 0.2 million tons in 1996. This decline was experienced in both Namibia and South Africa (Crawford 1998b).

With sardine and anchovy stocks reaching diminished levels during the mid 1990s, stern fish management practices and catch restrictions were implemented in South Africa. In 2000, sardine and anchovy abundance in South Africa had increased to peaks of approximately 1.5 million and 4 million tons respectively (Figure 1.6).

4.5 7

4 6

3.5 Catchtons)000 (100 Fish 5 3

2.5 4

2 3

1.5 2

1 Available tons) Fish (million Stock

1 0.5

0 0 Date 1984 1986 1988 1990 1992 1994 1996 1998 2000

Sardine Catch Anchovy Catch Sardine Biomass Anchovy Biomass

Figure 1-6: Estimated sardine and anchovy biomass in relation to annual catches in South Africa (redrawn from Jones 2002).

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d) Over-fishing and its effect on the African Penguin The marine fishes of South Africa have been exploited on a commercial scale for more than 100 years. This intensified during the last 50 years as a result of better fishing gear (Penny et al. 1989). As a result, every type of fishery in Algoa Bay is either under severe pressure or is in a state of collapse (Griffiths 1997a, b, 2000). The crash of the sardine stocks as a result of over-fishing has contributed to the decline of the African Penguin population (du Toit et al. 2003b). Crawford et al. (2006) recorded that penguin pairs fledged on average 0.46 chicks per annum when available fish stocks were less than 2 million tons and 0.73 chicks per annum when fish stocks are in excess of 2 million tons. These levels of breeding success are inadequate to sustain the African Penguin population in the future (Crawford et al. 2006). An aggravating factor in the vulnerability of penguins to over-fishing is the fact that they are central place foragers and thus are restricted in foraging distance compared to birds of flight.

1.5 Rationale for the study The specific nature of the threats affecting the survival of the African Penguin has shifted in the past 100 years. The effects of egg collecting and guano scraping brought the species to the brink of extinction during the first half of the 20 th century. The legacy of these unsustainable practices still persists due to the loss of the guano substrate and thus the inability of breeding penguins to dig burrows. This has led to penguin nests becoming more exposed to heat stress and predation by Kelp Gulls. In the closing years of the 20 th century, oil catastrophes, together with the effects of over fishing, have become the major inhibiting factors driving the decline in the population numbers of the African Penguin. Crawford et al. (1995b) have thus stated that if the rate of decline of the African Penguin population continues unabated, they could become extinct by 2040. Although efforts are underway to address the present shortages of fish and to ensure that adequate prey stocks exist in the future, it is also imperative to the survival of the African Penguin population that ample numbers of chicks are being fledged and that breeding at the nest site is successful. The null hypothesis that clutch size has no influence on either breeding failure or growth rate of chicks formed the primary focus behind this study.

Forty percent of the global African Penguin population is resident in the Eastern Cape (Nel et al. 2003). St Croix Island and Bird Island populations contribute to the bulk of this total (du Toit et al. 2003b). A comprehensive study on the St Croix Island breeding population has already been documented by Randall (1983). The smaller Bird Island colony is not well studied and the present investigation is aimed at filling this gap.

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2 STUDY AREA 2.1 General introduction Algoa Bay is the most eastern, and largest, of several log spiral-shaped bays on the south- eastern coast of South Africa. The dominant oceanographic feature of the region is the warm Agulhas Current (Goschen & Schumann 1988) which flows southwards. The bay coastline is predominantly comprised of surf-swept beaches that extend for 90 km between the headlands of Cape Recife in the west to Woody Cape in the east (Lubke & de Moor 1998).

Five rivers enter Algoa Bay of which the Swartkops River and the Sundays River are the most important. These estuaries serve as important nursery areas for fish, and their wetlands and salt marshes act as natural filters (Whitfield 2000). Port Elizabeth, the largest city in the Eastern Cape, dominates the western shores of Algoa Bay. Construction of a major industrial port (Ngqura) at the mouth of the Coega River (approximately 20 km north of Port Elizabeth) is presently nearing completion. The eastern area of Algoa Bay is dominated by the large Alexandria coastal dune-field. This part of the Algoa Bay coastline is sparsely populated as most of it forms part of the Greater Addo Elephant National Park.

There are two island groups in Algoa Bay. The St Croix Island group consists of Brenton, Jahleel and St Croix Island (collectively known as the Islands of the Cross) and the Bird Island group (Bird, Stag and Seal Islands and Black Rocks). The St Croix Island group is located 4 km from the mainland near the Port of Ngqura. St Croix Island has a maximum elevation of 53 m and is 12 ha in size (Figure 2.1), while Brenton and Jahleel are considerably smaller with areas of 1 and 2 ha respectively. The latter two islands do not rise more than 20 m above sea level.

The Bird Island group is located 47 km east of the St Croix Island Group (Randall 1983) and 66 km from Port Elizabeth. Stag and Seal Islands are joined at low tide by a single rocky ridge (Courtenay-Latimer & Gibson-Hill 1946) and are in close proximity to and separated from Bird Island by a shallow (~2 m) channel that is approximately 450 m wide (Randall et al. 1981). Bird Island rises to approximately 9 m above sea level and measures 19 ha in size (Stewardson et al. 2001), whilst Stag and Seal Islands are small, flat rocky outcrops.

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Figure 2-1: Islands of Algoa Bay (photos by N. Klages). Top Left: Jahleel Is. Top Right: St Croix Is. Bottom Left: Black Rocks in the foreground colonised by Cape Fur seals. Lying in the distance are Seal and Stag I. Bottom Right: Bird Is.

2.2 Geology of Algoa Bay The Eastern Cape region is under-lain by the soils of the Cape Supergroup. Both island groups in Algoa Bay are comprised of Table Mountain Group quartzites (Bremner & Day 1991). The islands of the St Croix Island group have a rugged topography and relatively little soil. The surface substrate of the Bird Island group is made up of pebbles and stones that are interspersed by coarse sand and shell fragments (Figure 2.1) (Lubke & de Moor 1998). Owing to the presence of a large colony of Cape Gannets, the soils of Bird Island are mostly ornithogenic in origin.

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2.3 Climate of Algoa Bay The Eastern Cape experiences wide variations in temperature, wind and rainfall as a result of it being located at the transition of several climatic regimes. These variations are largely determined by topographical features (movements of air masses, altitude, mountain orientation and distance from the Indian Ocean) associated with specific areas within this transitional region (Siegfried 1977). It experiences subtropical summer conditions associated with the Transkei and Natal coasts, and temperate winter conditions associated with the Western Cape (Kopke 1988 cited in Lubke & de Moor 1998).

In broad terms, the Algoa Bay climate is described as warm and temperate. Climatic conditions between localities in Algoa Bay differ (Kopke 1988 cited in Lubke & de Moor 1998). Schumann et al. (1991) and Jury (1994) describe weather conditions around Bird Island to be different to localities found along the coastline of the mainland. This is as a result of the island’s low-lying position (Stewardson et al. 2001). However, localities associated with this region generally experience high summer temperatures which are cooled by maritime air and cool winter temperatures that are warmed by winter maritime air (Schultze 1965 ). Seasonal variability in the surface heat fluxes and mass transports of water, are the primary factors influencing temperature structure in Algoa Bay (Goschen 1991).

2.3.1 Weather at Bird Island Weather records for Bird Island are incomplete, as the weather station on the island has been mostly in-operational since 1989 (Stewardson et al. 2001). Therefore, the weather experienced at Bird Island has been described through the summary of numerous sources, notably from Heydorn & Tinley (1980), Stewardson et al . (2001), Klages un-published data, and temperature data recorded over 21 days during this study.

Bird Island experiences a bi-modal wind regime. Both westerly and easterly winds dominate during summer but only westerly winds dominate during winter (van Niekerk, pers comm ). Wind speeds of the predominant seasonal wind generally exceed speeds of 15 m/s. Easterly winds, derived from over the Indian Ocean, are associated with warm conditions. These often become more pronounced during the afternoons and tend to give rise to thunderstorms (van Niekerk, pers comm ). During winter the predominant south-westerly wind or sea- breeze is extremely cold as it is associated with cold fronts that originate from the Southern Ocean and result in small variations in air temperature (van Niekerk, pers comm ). Land breezes, or berg winds, occur from the N-NW and are most frequent in winter. They also form an important component of local winds at Bird Island (Roberts 1990, Goschen 1991) and result in large variations in air temperature (Stewardson et al. 2001).

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On Bird Island, mean maximum temperatures (~26°C) peak during summer (February) and mean minimum temperatures (~13°C) are lowest during winter (July). The diurnal temperature range is more variable during winter than in spring and summer as a result of land/sea breezes (Stewardson et al . 2001). Under berg wind conditions, or when the cool maritime breeze is absent, Bird Island can experience air temperatures in the high twenties, occasionally rising well over the thirties (Burger & Scorgie 1998) and temperatures in the forties have been recorded. This was experienced during February 2003 of this study and resulted in the desertion of 33% (422 nests) of the African Penguin nests on Bird Island (Ralph, pers. obs. ).

The Eastern Cape falls in a transitional region between summer rainfall associated with the KwaZulu-Natal and Transkei coasts and winter rainfall associated with the Western Cape (CSIR 2001). An unpredictable rainfall pattern occurs in the Algoa Bay region, with no clear seasonal trend being recorded at Bird Island (Stewardson et al. 2001, Klages un-published data). Stewardson et al. (2001) recorded a peak in rainfall (~50 mm) for Bird Island during June and September. Similarly, Klages (un-published data) recorded rainfall highs during September (~74 mm), yet also during January (~65 mm) and a peak rainfall in December (~92 mm). Annual rainfall for Bird Island is generally in the order of 461-600 mm (Klages un-published data).

2.4 Flora of Bird Island The occurrence of plant cover on Bird Island is highly variable. After a wet spell the entire island is extensively covered in vegetation except for the gannetry where trampling excludes plant growth completely. After a few dry months, the island appears virtually barren (Figure 2.2). Mostly a higher vegetation cover is found in winter in comparison to summer. The vegetation is comprised of 33 plant species, of which 13 are indigenous to the island (Powell 1994). Vegetation on Bird Island is governed by succulent annuals and no woody plants exist there. Succulent plants provide no shelter from the sun for breeding penguins. The most commonly found plant species are Mesembryanthemum aitonis , Tetragonia decumbens, Malva parviflora and Chenopodium glaucum (Powell 1994). During summer when succulent vegetation is dehydrated it serves as an important nesting material for many of the bird species resident on the island.

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A B

D

C

Figure 2-2: The seasonal appearance of vegetation on Bird Island. Figure A and B shows vegetation growth after sufficient rains and Figure C and D illustrates the dried out vegetation during the summer periods.

2.5 Avifauna of Bird Island Only a few terrestrial birds breed on the island and include the House Sparrow ( Passer domesticus ), Cape Wagtail ( Motacilla capensis ) and the Speckled Rock Pigeon (Columba guinea ). The majority of bird species on the island are seabirds and those associated with the shoreline. Six of the seven islands in Algoa Bay are important bird areas, as they are utilised by more than 5 000 waterbirds, including threatened and vulnerable species (Barnes 1997). Five important species are associated with the seabird component, notably: the Cape Gannet, Kelp Gull, Roseate Tern ( Sterna dougalli ), Antarctic Tern ( Sterna vittata ) and the African Penguin. Four of the five species breed on Bird Island (Antarctic Terns occur during winter but do not breed) with only the African Penguin and Roseate Tern also breeding on St Croix Island (Ralph, pers. obs ). A limited area of 19 ha is available for all breeding birds on Bird Island (Stewardson et al. 2001). Breeding domains of each species are restricted on the island and thus inter-specific competition for breeding space is infrequent. At present, enough space is available should the populations of the four species increase (Ralph, pers. obs .).

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2.5.1 The Cape Gannet The Cape Gannet colony on Bird Island, Algoa Bay (Figure 2.3), is the only colony on the south-eastern coast of South Africa and supports almost 40% of the global Cape Gannet population. Depending on the population size of this colony it can occupy between 3.6 and 5.5 ha of Bird Island (Chapter 3) and can reach almost 100 000 breeding pairs (Crawford et al. 2007). In terms of area occupied and in terms of numbers, the Cape Gannet is the most prominent seabird on Bird Island.

Figure 2-3: The breeding density (left) of the Cape Gannet (right) on Bird Island.

2.5.2 The Kelp Gull The Kelp Gull (Figure 2.4) is widely distributed throughout the Southern Hemisphere. The gull population in Algoa Bay totals approximately 2 000 birds, and has increased by approximately 71% since 1982 (Whittington et al. in press). Gulls breed on all three islands of the Bird Island group, with 24, 47 and 22 pairs recorded on Bird, Seal and Stag Islands respectively (Klages & Whittington 2006a). The increased gull population has led to increased inter-specific competition for breeding space and increased predation on the African Penguin (Klages & Whittington 2006a).

Figure 2-4: Kelp Gulls scavenging on regurgitated fish.

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2.5.3 Roseate and Antarctic Terns Roseate Terns (Figure 2.5) have a wide global distribution and occur in scattered pockets throughout the North Atlantic, Pacific and the Indian Ocean. The species is endangered (250 pairs) in South Africa where it is the third rarest seabird (Tree 2005a). All the Algoa Bay islands are used as roosts for the Roseate Tern during the non-breeding season. At the start of breeding during the winter, the Roseate Terns breed in amongst the Mesembryanthemum aitonis south of the lighthouse on Bird Island and a small satellite breeding colony is also found on St Croix Island, however the latter has mostly been unsuccessful (Tree 2005a). The Antarctic Tern (Figure 2.5) is only a winter migrant to South Africa. Antarctic Terns arrive in South Africa in late April when they commence with moult. Peak numbers of 4 000 birds are recorded in July-August on Bird Island (Tree 2005b). The global population of Antarctic Tern is approximately 45 000 breeding pairs (du Toit et al. 2003b). The Algoa Bay islands, and in particular Bird Island are globally important areas for these species (Tree 2005a, b).

Figure 2-5: The full breeding plumage of the Roseate Tern (left) and the Antarctic Tern (right) (photo by N. Klages) .

2.6 The history of Bird Island Two hundred years of guano and egg exploitation have resulted in the human disturbance on the Algoa Bay islands. From 1885, all the guano that had accumulated over centuries on the island was exported as fertiliser, thus robbing the penguins of important nesting material (Urquhart & Klages 1996). As a result of Bird Island’s flat topography, many ship wrecks occurred around the islands rocky shores (Urquhart & Klages 1996). To prevent this, the Bird Island lighthouse (Figure 2.6) was constructed in 1852 on the island’s southern side.

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Figure 2-6: The Bird Island lighthouse with the gannet colony in the foreground.

The houses on the islands were inhabited when guano exploitation occurred, however at present they are in a state of disrepair. The houses and guano sheds (Figure 2.7) are located on the northern edge of the island. Penguins utilise the shadow cast from these structures as an alternative shelter for nests to guano (Ralph, pers obs ).

Figure 2-7: View of the houses on Bird Island from the south (left) and east (right).

2.7 Conservation of the Algoa Bay Islands In 1981 the St Croix Island group, and an area of sea within 500 m surrounding each island, was the first marine island reserve to be proclaimed in South Africa (Government Gazette 1981). The Bird Island group was declared a marine protected area in 2004 (Government Gazette 2005) and has been included within the Greater Addo Elephant National Park. To ensure that these Marine Protected Areas are enforced and protected, officials from South African National Parks reside on Bird Island. The houses on St Croix Island are vacant. Conservationists focus their efforts on Bird Island where abalone poaching is presently rife.

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3 NEST DISTRIBUTION 3.1 General introduction The existence of the African Penguin is determined by its adaptability and survival to a life spent feeding at sea and breeding on land. The aquatic environment in which penguins spend more than half their lives in has a thermal conductivity 30 times greater than that of air (Frost et al. 1976a). The capacity for increased heat loss within the relatively cold marine environment, potentially poses a bioenergetic problem for these endotherms which must maintain body temperatures higher than that of the ocean in order to survive. Penguins have overcome this problem by supporting thick layers of sub-dermal fat, a dense water-proof plumage and counter-current arterio-venous heat exchange (Stonehouse 1967). These adaptations allow penguins to be well suited to the oceanic environment, but pose over- insulation problems whilst breeding on land.

3.1.1 Habitat at the nest site Given the availability of suitable habitat to be utilised in nest sites, breeding penguins will relocate to these (Crawford et al. 1994). According to Frost et al. (1976a), penguins rely on the burrow type nest to overcome heat stress and associated over-insulation problems experienced from high temperatures above ground. Burrow nests remain cool during the day and warm at night compared to exposed surface nest sites where the opposite is experienced (Frost et al. 1976a, Frere et al. 1992). Various studies (Frost et al. 1976a, Randall 1983) have also shown that burrow nest sites are favoured from a breeding perspective and recorded a higher fledging success compared to exposed surface nests. The quality of the nest habitat thus influences the breeding success of penguins (Randall & Randall 1981). However, the prevalence of colonial breeding among seabirds, and the attractiveness of established colonies to prospectors, suggest that potential benefits such as predator deterrence (Birkhead 1977) and knowledge of habitat suitability (Boulinier & Danchin 1997) outweigh costs such as competition for nest sites (Potts et al. 1980), increased prevalence of disease and parasites (Boulinier & Danchin 1996) and predator attraction (Brown & Brown 1996). The net advantage of colonial breeding to seabirds could be great, as when faced with intense competition for limited nest sites within established colonies, potential recruits make use of lower-quality nest sites (Ashmole 1962, Potts et al. 1980, Kildaw 1999) or may even defer from breeding, rather than colonizing unoccupied habitat that is often available nearby (Porter & Coulson 1987, Olsthoorn & Nelson 1990, Kildaw 1999). Forbes & Kaiser (1994) stated that prospective breeders will pioneer new colonies only when the cost of joining an established colony exceeds that of the knowledge barrier.

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The knowledge barrier is defined as the uncertainty in regard to the breeding quality of the unoccupied habitat. In summary of these findings, breeding success of penguins is thus largely determined by habitat of a nest site.

The type of habitat that is available for use within penguin nest sites differs between the island localities of South Africa. For instance, Robben Island offers penguins large trees under which to shelter, a habitat type virtually absent from all other islands. The two island groups located in Algoa Bay differ remarkably in topography and habitat.

3.1.2 Topography of the islands in Algoa Bay The topography and hence the associated habitat types available to nesting birds on the St Croix Island group, is remarkably different to that of the Bird Island group.

a) The St Croix Island Group The Islands of the Cross have a rugged rocky topography and are almost devoid of any vegetation. Nesting habitat is therefore restricted to shelter behind the rocks on the steep slopes or on the flat areas, which are preferred (Figure 3.1). The absence of plants on the island restricts the choice of nesting material for breeders and most nests are primarily comprised of feathers, small pebbles and the dried out remains of dead chicks and adults (Ralph, pers. obs. ).

Figure 3-1: Penguin nests on the rocky topography of St Croix Island.

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b) The Bird Island Group In contrast to the St Croix Island group, the Bird Island group, and in particular Bird Island, has a fairly flat topography. For ease of reference to certain areas on Bird Island, the names of areas on the island are illustrated in Figure 3.2. With relevance to this study, special mention is made of the Headman’s House and Guano sheds/stores that are located on the islands northern side; “Newton’s Well” located towards the western side of the island; the Gannetry found in the central areas expanding across to the islands eastern edge and the Atlas House and Light House located to the south of the island. Numerous pathways (constructed and patrolled by SANParks) extend across the island and are kept clear of breeders. Unlike St Croix Island that offers nesters only rocky terrain, Bird Island offers various habitat types viz. rocky areas, low-growing shrubbery, bare ground, burrows and the shelter provided by the old guano-shed and houses. The only topographical feature that extends across the entirety of Bird Island are the numerous, small (~15 cm in diameter) pebbles.

Stink Bay Gabion Jetty Old Slipway Headman’s House

Guano Stores

Bunk House

Newton’s Well

Washing Rock Gannetry

Heli Pad

Atlas House Lighthouse

Anchor Big Bay Bay

Figure 3-2: Aerial view of Bird Island showing its flat topography.

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3.1.3 The breeding cycle of penguins in Algoa Bay Off the coast of South Africa, the main breeding period for the African Penguin is from January to September with most birds usually commencing with moult from October through to January (Randall 1989, Crawford et al . 1995b). Sardine is abundant in the Eastern Cape from March to June coinciding with the rearing of penguin chicks from the peak breeding attempt (Randall & Randall 1981). In the Western Cape, the foraging range of breeding penguins is approximately 11-15 km, yet breeders are required to forage farther (~40 km) from their colonies in the Eastern Cape (Wilson 1985a, Heath & Randall 1989).

In spring, maturing anchovy join spawning shoals over the Agulhas Bank and may not be readily abundant within the in-shore waters of the south coast where penguin colonies are located. Penguins breeding on Bird Island commence with moult as early as September, a time when the sardine migrate up to KwaZulu-Natal (Crawford et al . 2002). Randall & Randall (1981) recorded that the availability of fish in the vicinity of penguin breeding colonies determines the time when peak breeding attempts commence. Birds are able to forage farther off-shore on feeding trips before and after moult than whilst rearing chicks (Crawford et al . 2002). Penguins that emigrate (usually pre-mature breeders) are to some degree able to adjust the timing of their moult in order to take advantage of favourable breeding conditions elsewhere (Underhill & Crawford 1999).

3.1.4 Rationale For most of the penguin breeding localities in South Africa, with a few exceptions (e.g. Dassen Island), the past guano exploitation activities have left the islands almost entirely barren of guano. This is especially evident on the Algoa Bay islands (except for a few small isolated areas) and thus breeders can no longer seek shelter from the sun by digging burrows. The continued existence of the African Penguin is largely determined by the number of juveniles that fledge and ultimately breed. It is therefore important to understand the associated interaction between the nest site, available habitat and the possible causes of breeding failure. This study attempts to determine whether penguins select specific habitats for nesting based on the degree to which they are sheltered from the sun. Bird Island was selected as the study site as a result of the numerous habitat types available to breeding penguins in which a comparative study like this could be undertaken.

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3.2 Methodology

3.2.1 The mapping of Bird Island Stewardson et al. (2001) measured Bird Island to be 19 ha in area. For the purposes of this study, it was necessary to quantify the extent of available area offered to nesting penguins as Bird Island is also utilised by other seabirds. The periphery of the island was considered to be the area above the high-tide mark that remains dry and protected from the tide. A global positioning system (Garmin eTrex Vista Cx) was utilised to map the island’s periphery and available nesting areas for the penguins. These coordinates were transposed onto the latest (2006) aerial photograph provided by SANParks and the extent of the various areas determined in square meters. The extent and position of each mapped area is illustrated in Figure 3.3 and was mapped according to three categories viz:

Complete shelter - The habitat type that provides complete shelter to nesting birds is only found at specific localities on the island (i.e. behind the houses and in burrows);
Partial shelter - Habitats that provide partial shade to nesters are found in two areas on the island largely comprised of rocks. Although, depending on how “partial” shade is defined, this shelter type could also be considered to occur across the broader island extent. Due to the inability to accurately quantify partial shelter in this study, it is not considered for further analysis. It has however been mapped for further reference;
No shelter - Nests found in the open. These surface areas extend across most parts of the island and were thus further sub-divided into six localities.

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Figure 3-3: The mapped localities including the six sub-divided surface localities (S1 – S6). ‘ BI’ in the caption refers to Bird Island.

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The area of Bird Island inclusive of all areas available to breeding penguins and those areas that are excluded (i.e. surface area utilised by structures, pathways, Roseate Tern breeding areas and the gannet colony) totalled 19.1 ha. The large Cape Gannet colony can utilise up to 5.6 ha of the island area and due to their densely packed nests provide little available space for penguins to burrow and exploit this guano rich area. Of the remaining 13.5 ha, a further 6.3 ha is not accessible to breeding penguins as a result of the following:

Areas found within the gannet colony (where juvenile gannets congregate);
Areas used by Roseate and Antarctic Terns for breeding, roosting and resting; as well as
All the man-made pathways and structures.

Thus, only 7.2 ha is considered available for breeding penguins and the available breeding space within each mapped area is illustrated in Table 3.1 below.

Table 3-1: The extent of the mapped areas on Bird Island.

Locality Area (m²) Percentage Total area (i.e. mapped island area) 191 157

Area not available to penguins: 119 311 62.4  The Gannetry 55 893 29.2  Areas used by breeding terns & gulls, human pathways 63 418 33.2

Area available to penguins: 71 845 37.6 Habitats receiving complete shelter 6 075 3.2  Houses 1 931 1.0  Burrows 4 144 2.2 Habitats receiving partial shelter 1 659 0.9  Rocks 1 659 0.9 Habitats receiving no shelter 64 111 33.5  Surface 1 10 573 5.5  Surface 2 12 859 6.7  Surface 3 3 432 1.8  Surface 4 29 284 15.3  Surface 5 6 727 3.5  Surface 6 1 235 0.6

3.2.2 Description of the habitat types Specific results for aspect and distance from the sea between the habitat types were not documented other than broadly classified as those areas along the coast and those that were inland (i.e. did not border on to the ocean). Apart from this, aspect was considered to be similar across all the habitat types on Bird Island due to the islands flat topography. It should be noted that the south-eastern side of the island (surface 5 and surface 6 localities) has a slightly acute slope towards the south which is more pronounced in the latter.

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a) The burrow locality The only area found on Bird Island allowing penguins to construct burrows is located in the central region that borders to the south of the gannetry and is referred to as the “burrows locality”. Due to the predominant south-westerly winds, gannets frequently fly over the burrow locality during take-off and landing. Thus, the occurrence of gannet excrement falling within this locality as compared to any other locality on the island is higher. The accumulated guano has allowed penguins to burrow into the substrate and to nest below ground obtaining complete shelter from the sun. The total area that could be utilised for burrow type nests equates to 0.414 ha. A typical burrow nest that has been constructed within the guano substrate is illustrated in Figure 3.4.

Figure 3-4: A typical burrow nest.

b) The house locality The above ground nests that receive complete shelter from the sun are those located within the shadow of the houses and derelict guano sheds, referred to as the “house locality”. The shaded areas located behind the structures found in the south are inaccessible to penguins due to the boundary walls. Although penguins primarily utilised shaded areas directly behind a structure (Figure 3.5), the total shaded areas (including the east and west sides of the building) that could also have been utilised by breeders in avoidance of heat stress conditions (i.e. 10:00 am-2:00 pm) was determined (Figure 3.6). It was determined that a structure with an approximate height of 4 m would cast a shadow 6 m away between 10:00 am and 2:00 pm. Therefore, the sheltered areas as a result of the structures in the north that could be used by breeding penguins was calculated to be 0.193 ha.

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A B

Figure 3-5: Nests (A) and breeders deserting nests (B) seeking maximum shade.

Noon 2pm 10am

HEIGHT

sunset sunrise

6m shadow Figure 3-6: Calculation of the shaded extent behind the house locality.

c) The surface localities Bird Island is primarily open, barren and void of any burrowing substrate (viz. guano) or vegetation. Pebbles are interspersed with coarse sand and shell fragments that make up the island substrate (Lubke & de Moor 1998). This is impenetrable to penguins constructing burrows. Breeders thus nest on the surface (Figure 3.7). At the onset of rain, the barren landscape becomes covered with low-growing shrubs that provide no additional shade to nesters. However, when dried these serve as important nesting material. The surface localities appear the same but they were still tested against one another to identify whether differences in their properties hidden from overt human view were present.

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Figure 3-7: Breeders found nesting in the open.

The total extent of the surface habitat available to penguins is 6.41 ha. For the purpose of this study where nest distribution was determined across the island, the large surface area was sub-divided into six smaller localities in accordance with their position on the island. The sub-divided surface localities are referred to as the “surface 1” through to “surface 6”. With regard to aspect, the only locality that is noticeably different between the surface sub- localities and compared to the overall flat topography of Bird Island is surface 6. This locality has a raised rocky outcrop and is found on the south-eastern edge of the gannetry (Figure 3.8).

Figure 3-8: The elevated rocky outcrop found in the Surface 6 locality.

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d) The rocky locality Numerous penguins attempt to seek shelter behind the pebble ridden landscape of Bird Island. Unlike St Croix Island, these rocks are small and provide penguins with brief periods of shelter. The only true rocky feature on Bird Island that provides nesters with either morning or afternoon shade is a 20 m wall, referred to as Newton’s Well . Penguins are also found breeding within the crevices of the high-tide rock on the island’s western edge. This area is not often flooded by the incoming high-tide as the water-mass in this area is relatively calm due to the shallow ocean floor of the Bird Island channel. Both rocky areas receive partial shelter from the sun (Figure 3.9) and incorporate a total area of 0.166 ha. For the purposes of this study, partial shelter could not be quantified and thus nest counts within the rocky habitat were excluded from the analysis.

Figure 3-9: Nests utilising rocks to receive partial shelter.

3.2.3 Census data acquisition Numerous census methods viz. grid-square, strip and moult counts (further elaborated on in Randall 1983) can be used for counting adult penguins from which total nest number or colony size at a specific time can be determined. However, when using these techniques the nest number that is determined can be negatively influenced by certain drawbacks associated with each technique. Collectively, these factors may include the breeding stage at which a population may be in, seasonality, time of the day and statistical error incurred through modelling and calculations. In order for nest density and nest distribution to be determined accurately, exact nest counts were required in this study.

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3.2.4 Data collection Census counts were obtained from 1993 to 1994 and also during 2002 to 2003/2004 on Bird Island. During 1993 to 1994, each mapped habitat type was subdivided into smaller grid squares (400 m² each) in which nest counts took place. Categorical counts of nests in increments of 25 were estimated for each grid square i.e. 25; 50; 75; 100; 125 and so forth. The 1993-1994 data sample (collected by Dr Klages) was not originally intended for mapping nest densities but was used to understand nest distribution over the island on a broad scale at that time, hence the reason for the categorical counts of nests being recorded. The 1993-1994 preliminary nest distribution study revealed that it was possible that nest distribution on Bird Island was in fact not random. In order to quantify the results further, the 2002-2004 study required exact nest counts for each mapped locality be obtained. Because nest counts were taken in the months of February, March, May, August, September and December in the 1993-1994 study, the same months were used in the counts taken during 2002-2003. This ensured that although the count techniques differed, other factors such as seasonality remained constant between the comparisons of the two study periods. As a result of strict access restrictions imposed on the islands, further counts could only be recorded during February and November of 2003 as well as for February and June of 2004.

Active nests were counted as per the methodology discussed in Crawford et al . (1990). Researchers slowly moved along the perimeter of the mapped habitat areas (eliminating any disturbance on nesting birds) using binoculars and a tally counter. This method was considered more suitable than other census techniques (i.e. moulting counts or modelling) due to the less probability of errors being recorded. Only nests that were deemed to be active (i.e. adults found defending a nest or the presence of eggs or chicks within a nest site) were counted. Chicks that were found in crèches where it could not be visually determined from which nest they came, were not considered in the census counts. Thus, census results in this study are likely to be an under-count compared to the annual census counts conducted by MCM for Bird Island.

3.2.5 Maximum density of penguin nests In order to substantiate whether the nest densities recorded for the various habitats were meeting maximum carrying capacities within the available space, it was necessary to determine the amount of area required for one penguin nest in relation to a neighbouring nest. Regardless of season, the area within the shadow of the houses and guano sheds was always densely packed with African Penguin nests and therefore was used to determine the maximum nest density. During February 2006, active nests clustered behind the guano sheds

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totalled 201 occupying an area of 127 m² (Figure 3.10). Thus on Bird Island, each nest (if not backing onto a structure) requires a minimum area of 0.6 m² (i.e. 1.58 nests per m²). An area of 71 845 m² on Bird Island is available for African Penguins to breed and therefore, the island could potentially accommodate 113 515 nests.

Figure 3-10: Maximum nest density within the optimal habitat behind the guano sheds.

3.2.6 Statistical treatment In order for nest count comparisons to be made between habitats of unequal size, a common parameter was required. Hence, nest density (nests per m²) was used for all comparisons. The likelihood of factors (i.e. prey availability etc) that may cause delays in breeding could differ between months and years for any given locality. Thus nest density recorded between months for each locality was considered non-conformant for homogeny and were not pooled in the statistical comparisons i.e. pseudoreplication of the observations does not apply. The one-way ANOVA was used to identify whether significant differences (determined at the p <.05 at the 95% confidence interval) occurred and in the cases where significance was obtained, post-hoc bivariate tests (either Scheffé or Tukey) were used to distinguish where the significant differences occurred. Tukey post-hoc tests were utilised where the sample size (n) was equal across the criteria tested and Scheffé post-hoc tests used where it was unequal. The degree of significance from a practical perspective was further quantified using the Cohen’s d test and quantified either as small (> 0.2), moderate (> 0.5) or a large (> 0.8) practical significance. Further research with a larger sample may elaborate on the in- significant result of p-values recorded within the reportable interval (.05 < p < .10).

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The null hypothesis that nest density within a habitat is independent of the type of shelter that a habitat receives was tested. Under the null hypothesis, the variance recorded from within-groups is assumed to be the same as the variance recorded between-groups. For example, the variance in the nest density recorded between the habitat types that receive complete shelter from the sun and those that receive none (between-group criteria) is assumed to be similar; likewise between localities that are either sheltered and between the localities that are not sheltered (within-group criteria).

In order for ANOVA statistical tests to be conducted, the tests require data to be of normal distribution. Regression analysis of the recorded nest density data was of non-normal distribution (R² = 0.585) and therefore all results were linearly transformed (R² = 0.989), as illustrated in Table 1 and 2 of Appendix A. All statistical tests reflect the findings of the transformed data referred to as ‘ln-density’. In order to provide substantiating support for the nest density findings recorded, nest density trends relative to locality type, locality distribution and breeding period were also analysed.

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3.3 Results

3.3.1 Relocation of birds to favourable habitat During the study, the weather experienced in February 2003 on Bird Island was different to that experienced in similar summer months. February 2003 recorded four consecutive days of prolonged heat and no wind. Temperatures in excess of 40°C over these four days were recorded (Ralph, pers. obs). The heat impact was compounded by the absence of the usually present, cool sea-breeze. As a result, 33% of the colony deserted their nests with the colony declining from 1263 to 843 nests. A preliminary study was also undertaken during this time to investigate whether breeding penguins would relocate their nests or move away (if eggs were present) if a better suited habitat for breeding was provided. Fifteen cardboard transport boxes, offering no air movement through the box (due to only one open side) were randomly placed around the surface area. Within 20 minutes, adult penguins with chicks occupied 14 of the 15 boxes (92%) and breeder with eggs alongside the box (~2 m away) relocated itself into the box for shelter and would return to its nest at the sight of gulls. The shelter that the boxes provided compared to the exposed surface nest sites that the birds were using seemed preferred (Figure 3.11).

Figure 3-11: The relocation of breeders from nests found in the open to sheltered nest sites temporarily provided in the form of cardboard boxes.

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3.3.2 Nest count and density trends in habitats receiving complete and no shelter Nest counts for each of the habitat localities throughout the sampling period were recorded and are represented in Table 1 and Figure 1 in Appendix A. Due to the complex nature of these data, the nest counts are graphically illustrated in Figure 1 as a proportion of the percentage of the total counted nests. A summary of the general trends in nest counts recorded within the habitat localities that received complete shelter (houses and burrows) and those that received no shelter (surface 1 to surface 6) from the sun is illustrated in Figure 3.12.

The combined habitat space that received no shelter (i.e. 6.4 ha) in relation to that which received complete shelter (0.61 ha) from the sun, was ten times larger as well as supported a larger number of nests. With reference to Figure 3.12, the two shelter types followed the same trend across the sampling period for most of the time. During the usual breeding cycle, peak nest counts are recorded during the peak breeding attempt, with less numbers of nests being recorded in the replacement breeding attempt and least during moult. This was the case for the 1993-1994 period however, the 2002 to 2004 period differed. Following the heat wave event in February 2003, nest count peaks were recorded during the moulting period, a time when most breeders usually are moulting and preparing for their peak breeding attempt.

4500 4000 3500 3000 2500 2000

Nest CountsNest 1500 1000 500 0

4 5 2 4 94 94 9 02 02 03 04 99 9 00 0 03** 0 0 1 199 19 1 2 20 2 0 2 2 g p c p c 2 n e e b Mar 1994 May Au S De Feb 19 Mar 2002 May Aug 2002 S De e Nov Feb 2004 Ju Feb 2003*F Total Nest Count Complete Shelter No Shelter

Figure 3-12: Nest counts recorded for habitats receiving complete and no shelter.

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When the actual nest counts recorded within the habitat localities are expressed as nest density (Figure 3.13), the sheltered localities recorded overall greater nest densities than those areas that received no shelter. In comparison with the expected maximum nest density limit determined as 1.5 nests per m², sheltered habitats ranged from 0.004 to 0.08 nests per m² and for the non-sheltered habitat type from 0.004 to 0.06 nests per m², thus neither habitat recorded the calculated maximum carrying capacity.

0.100 4500 0.090 4000 0.080 3500 0.070 3000 0.060 2500 0.050 2000 0.040 1500 0.030 Censuscount 0.020 1000

NestDensity (Nestsper m2) 0.010 500 0.000 0

4 2 94 94 94 95 02 02 02 9 9 9 9 0 0 03* 3** 004 19 19 20 20 20 2 2004 y b 1 y 20 200 v 2003 n b o Mar 1 Ma Aug 1994 Sep 1 Dec Fe Mar 2 Ma Aug 2002 Sep Dec N Feb Ju Feb Fe

Count in Mapped Area No Shelter - density Complete Shelter - density

Figure 3-13: Nest density recorded for habitats receiving complete and no shelter.

The descriptive statistics of the nest density data analysed between shelter types is represented in Table 3.2. The number of observations recorded for each shelter type is the total number of months over the census period. Within the complete shelter group, the houses (0.0564 nests per m²) was the only locality to record a higher mean nest density compared to the overall nest density (0.0256 nests per m²), with both the burrows (0.0148 nests per m²) and surface (0.0223 nests per m²) shelter types recording below.

Table 3-2: Descriptive statistics of the mean nest density for the shelter types. Shelter Type n Mean SD Min Median Max SEM Surface (no shelter) 96 0.0223 0.0347 0.0000 0.0121 0.2931 0.0035 Houses (shelter above ground) 16 0.0564 0.0427 0.0093 0.0507 0.1761 0.0107 Burrows (shelter below ground) 16 0.0148 0.0118 0.0000 0.0154 0.0446 0.0030 Overall 128 0.0256 0.0357 0.0000 0.0139 0.2931

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One-way ANOVA tests (Figure 3.14) recorded significant differences between nest density and shelter type (F = 14.157; p < .0005; df = 2; n = 128). Post-hoc Scheffé tests quantified with the use of Cohen’s d found large significant differences between the higher nest density in the house locality compared to the nest densities recorded for both the surface (Scheffé p < .0005; Cohen’s d = 0.95) and burrow localities (Scheffé p < .0005; Cohen’s d = 1.16). No significant difference was recorded for the nest density between the burrows and surface localities (Scheffé p = .081). However, this p-value is in the reportable interval (.05 < p < .10) and further research with a larger sample may elaborate on these findings.

0.080

0.070

0.060

0.050

0.040

0.030

Mean Nest DensityMean (m2) 0.020

0.010

0.000 Surface Houses Burrows

Figure 3-14: Mean nest density for the three types of shelter.

The null hypothesis that nest density is independent of the type of shelter that a habitat provides to nests is therefore rejected. However, nest density does not seem to be solely determined by the degree to which a habitat provides shelter to nests from the sun. If this were the case, density within the complete shelter type would record equally high densities, however, the study found significantly higher nest densities in the house locality compared to the burrow locality. Therefore it would seem that other properties relative to a habitat also influence nest site selection even between habitats of the same shelter type.

Nest density was determined for each habitat locality (represented in Figure 2a, b of Appendix A). With reference to this and as represented in Table 3.3, the mean nest densities of the house locality (0.0564 nests per m²) and the surface 6 locality (0.0536 nests per m²) were the only localities to record higher values than the overall mean density (0.0256 nests per m²). The burrow locality features low on the list recorded within the eight localities.

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Table 3-3: Nest density (m²) recorded for each locality.

Total nest Location S1 S2 S3 S4 S5 S6 Burrow Houses count Mar 1994 0.017 0.012 0.022 0.013 0.015 0.081 0.018 0.078 1200 May 1994 0.017 0.012 0.022 0.010 0.007 0.081 0.018 0.078 1075 Aug 1994 0.009 0.006 0.007 0.004 0.011 0.020 0.006 0.039 525 Sep 1994 0.002 0.002 0.007 0.002 0.011 0.020 0.006 0.013 275 Dec 1994 0.009 0.012 0.000 0.003 0.004 0.000 0.000 0.013 400 Feb 1995 0.017 0.012 0.022 0.013 0.026 0.020 0.018 0.078 1200 Mar 2002 0.060 0.056 0.075 0.044 0.092 0.293 0.035 0.176 4359 May 2002 0.008 0.006 0.022 0.011 0.063 0.054 0.045 0.104 1434 Aug 2002 0.011 0.009 0.015 0.004 0.030 0.028 0.018 0.054 808 Sep 2002 0.012 0.002 0.003 0.013 0.011 0.004 0.006 0.068 792 Dec 2002 0.036 0.016 0.013 0.019 0.001 0.023 0.002 0.025 1266 Feb 2003 0.015 0.008 0.010 0.016 0.034 0.096 0.018 0.042 1263 Feb 2003 0.006 0.008 0.003 0.012 0.025 0.041 0.018 0.015 843 Heat wave Nov 2003 0.017 0.010 0.009 0.024 0.004 0.008 0.003 0.065 1232 Feb 2004 0.004 0.017 0.017 0.004 0.026 0.023 0.013 0.009 712 Jun 2004 0.007 0.010 0.009 0.005 0.025 0.065 0.011 0.048 783

Descriptive statistics of nest density per locality

Mean 0.0154 0.0123 0.0160 0.0123 0.0242 0.0536 0.0148 0.0564 0.0256 N 16 16 16 16 16 16 16 16 128 SD 0.0142 0.0122 0.0172 0.0105 0.0238 0.0703 0.0118 0.0427 0.0357 Min 0.0024 0.0019 0 0.0017 0.0015 0 0 0.0093 0 Median 0.0116 0.0103 0.0117 0.0113 0.0198 0.0259 0.0154 0.0507 0.0139 Max 0.0602 0.0555 0.0746 0.0441 0.0919 0.2931 0.0446 0.1761 0.2931 SEM 0.0035 0.0031 0.0043 0.0026 0.0059 0.0176 0.003 0.0107 0.006

One-way ANOVA tests reveal that significant difference exists for nest density between the different localities (F = 27.13; p < .0005; df = 7; n = 128). Post-hoc Tukey tests and Cohen’s d practical significance tests were further conducted to identify where the significant difference occurred (Table 3.4). These tests reveal that the significant difference for nest density between localities exists only for the house and surface 6 localities in comparison to the others.

In addition to the house locality, the surface 6 locality also recorded large significant differences with the surface 1, surface 2, surface 3 and surface 4 localities as well as to the burrow locality. Surface 6 and surface 5 localities recorded no significant difference between their mean densities. The sheltered burrow locality recorded no significant differences with the other surface 1 to surface 5 localities (Figure 3.15). The surface 6 locality experienced the greatest variation in nest density in comparison to the other less variable localities. With the variation in nest density taken into account, the surface 6

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locality still recorded significantly higher nest densities. Variance within the other localities is far less than the surface 6 locality suggesting that nest densities (i.e. nest counts) remained fairly constant throughout the year in these localities. It is substantiated that the large variations in nest density recorded between the localities is a result of maximum nest density (i.e. preferred habitat) being influenced by a combination of criteria and not primarily by the shelter a locality receives. Therefore, additional criteria were further investigated in an attempt to clarify the results.

Table 3-4: Post-hoc Tukey p-values and Cohen’s d practical significance values for mean nest density for each locality. Values underlined denote significant results. Tukey p-values Surface Surface Surface Surface Surface Surface Burrow House 1 2 3 4 5 6 Surface 1 0.984 0.999 0.949 0.995 0.013 1.000 0.0004 Surface 2 0.087 0.900 1.000 0.718 0.0007 0.995 0.0001 Surface 3 0.015 0.102 0.804 1.000 0.047 0.999 0.002 Surface 4 0.087 0.001 0.102 0.577 0.0004 0.978 0.0001 Surface 5 0.247 0.334 0.232 0.334 0.096 0.987 0.004 Surface 6 1.070 1.157 1.055 1.158 0.824 0.009 0.976

Cohen’s d values d Cohen’s Burrows 0.019 0.068 0.034 0.069 0.265 1.089 0.0003 Houses 1.149 1.236 1.134 1.236 0.902 0.078 1.167

0.080

0.070 )

2 0.060

0.050

0.040

0.030

Mean Nest Density (m Density Nest Mean 0.020

0.010

0.000 Surface 1 Surface 2 Surface 3 Surface 4 Surface 5 Surface 6 Burrow s Houses

Figure 3-15: Mean nest density for each habitat locality. Standard error bars denote 95% confidence intervals.

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3.3.3 Additional criteria determining nest site selection Nest density between the localities based on their position relative to the shore (i.e. proximity to the sea) and in respect to breeding stages (i.e. peak, replacement, moulting periods) were further tested.

a) Coastal versus Inland localities The null hypothesis that nest site selection and therefore nest density is uninfluenced by the localities position to the waters edge is tested. With reference to Table 3.5 and Figure 3.16, the near-water localities (Surface 1, 3, 4, 5 and Surface 6) recorded a higher mean nest density (0.029 nests per m²) across the sampling period in relation to the inland localities (Surface 2, Houses and Burrows) where mean nest density was 0.025 nests per m². Results from the one-way ANOVA found no definite significance between the higher nest density recorded for localities found nearer the water’s edge in comparison to the lower nest density for those localities found further inland (F = 3.157; p = .078; df = 2; n = 120). Thus the null hypothesis is not disproved. However, this p-value is in the reportable interval (.05 < p < .10) and further research with a larger sample may elaborate on these findings.

Table 3-5: Descriptive statistics of nest density within coastal and inland localities.

Locality distribution N Mean SD Min Median Max SEM Near-water or Coastal 45 0.029 0.034 0.000 0.013 0.176 0.005 Inland 75 0.025 0.038 0.000 0.015 0.293 0.004 Overall 120 0.026 0.036 0.000 0.014 0.293 0.040

0.035

0.030

0.025

0.020

0.015

Mean Nest (m²) Density 0.010

0.005

0.000 Coast Inland

Figure 3-16: Mean nest density for localities along the coast and inland of the island. Standard error bars denote 95% confidence intervals.

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b) Breeding period With reference to Table 3.6, density of nests was compared between the usual, initial peak breeding attempt (January to end of March), replacement breeding (April to September) period and the moulting period (October to December). In addition, the relationship between breeding period and individual habitat localities is also explained. The null hypothesis that nest density between the three breeding periods is no different was tested. One-way ANOVA tests reveal that a significant difference in nest density exists between the three breeding periods (F = 12.922; p = .0005; df = 2; n = 111). Data from the heat stress event was omitted from the analysis due to its isolated occurrence. Post-hoc Scheffé tests and Cohen’s d tests found that the higher nest density recorded within the peak breeding period (0.0369 nests per m²) in comparison to the replacement (0.0213 nests per m²) and to the moulting periods (0.0132 nests per m²) was significantly small (Scheffé p = .002; Cohen’s d = 0.44) and moderate (Scheffé p = .001; Cohen’s d = 0.66) respectively. An almost significant difference was recorded in nest density between the replacement and moulting breeding periods (Scheffé p = .057).

Table 3-6: Descriptive statistics for mean nest density during the breeding periods. Breeding period n Mean SD Min Median Max SEM Moulting 24 0.0132 0.0144 0.0000 0.0099 0.0647 0.003 Replacement 56 0.0213 0.0233 0.0017 0.0111 0.1036 0.003 Peak 48 0.0369 0.0498 0.0029 0.0182 0.2931 0.007 Overall 128 0.0256 0.0357 0.0000 0.0139 0.2931

Of the mean nest density recorded within the eight localities (Figure 3.17), the surface 6 locality recorded the highest density during the peak breeding period (0.0925 nests per m²) followed by the house locality (0.0663 nests per m²). However, the surface 6 locality did experience greater variance about the mean compared to the house locality. All the other localities recorded a lower nest density. Overall, all localities recorded their highest nest densities in the peak breeding period, except the surface 1 locality where peaks (0.0206 nests per m²) were recorded during the moulting period. During the replacement and moulting periods, the house locality had the highest nest density. Except for the surface 1, 2 and 4 localities, all the localities recorded a high density of nests during the replacement period in comparison to the moulting period.

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0.14

0.12 ) 2 0.10

0.08

0.06

0.04 Mean Nest Density (m

0.02

0.00 Surface 1 Surface 2 Surface 3 Surface 4 Surface 5 Surface 6 Burrow Houses

Peak Replacement Moult

Figure 3-17: Mean nest density between the three breeding periods for each locality. Standard error bars denote 95% confidence intervals.

One-way ANOVA tests reveal that a significant difference in nest density existed between localities and breeding periods (F = 1.921; p < .0005; df = 14; n = 128). It has already been determined through post-hoc tests where the significant differences exist for the breeding periods (as discussed above) as well as for the various localities (i.e. Table 3.4). Nest density and the selection of suitable localities are significantly influenced by the stage of breeding that the majority of birds are in.

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3.4 Discussion In order to attain standardization in the statistical results, comparisons would usually occur between datasets where the observation periods and collection methods are similar i.e. either grouped per sampling category as in the case of the 1993/1994 dataset or as per the count techniques used. However, in this study they are compared regardless of how the counts were collected as the discrepancies incurred in nest counts between the two techniques are considered to have had negligible influence on the trends of nest density. This is based on previous findings by Crawford et al. (1994) where breeders were found to use optimal breeding habitat first.

Potential factors that influence breeding success at the nest are likely to differ between similar months, or even days. This is why annual census data can fluctuate considerably depending at what stage of breeding the individuals are in and when the census is conducted. To illustrate why data between similar samples cannot be pooled and why nest density comparisons can be made between time periods regardless of whether factors inhibiting breeding occurred or not, the following supportive argument is provided: Penguins breeding in the Eastern Cape generally have a defined moulting season and are synchronized with breeding after their moult (Randall & Randall 1981). However, breeders that fail during their first breeding attempt may lay a replacement brood whilst other birds are still raising chicks from the first breeding attempt. It is therefore difficult to record precise nest counts for each month from a once off visit to a colony. Illustrative of this is that in February 2003, 1 267 nests were recorded and four days later the number of active nests had declined to 845 nests (Ralph, pers. obs.).

The number of breeding African Penguins on Bird Island over the past 15 years has fluctuated yet on the whole has remained relatively constant. Peak nest counts of approximately 5 300 and 4 350 nests have been recorded more recently during the consecutive years of 2001 and 2002. The heat stress event experienced in Algoa Bay during February 2003 resulted in the total nest number on Bird Island declining by 33% and similarly, St Croix Island declined to 9000 nests from a total of 17 000 nests that were recorded in 2001. Maximum temperatures at Bird Island usually peak during February (Stewardson et al. 2001) and in the absence of the summer, cool sea breeze (Schultze 1965) can rise well into the high thirties or forties (Burger & Scorgie 1998) which was the case during the heat wave event of February 2003. This event provided the perfect opportunity to investigate whether breeders would relocate to a more favourable habitat if it became available. The study found that breeders relocated from the surface nest sites to the artificial,

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poorly ventilated boxes in 92% of the cases. Nest desertion and relocation to more sheltered nests as a result of heat stress has also been recorded in other penguins, the Yellow-eyed Penguin ( Megadyptes antipodes ) and the Galapagos Penguin ( Spheniscus mendiculus ) (Boersma 1975, Seddon & Davis 1989). The nests of the burrow locality in this study were the only nests not abandoned whilst all the other habitat types experienced up to 2-3 fold declines in nest numbers. The majority of Bird Island nesters occur in the open where usually low fledging rates are recorded in comparison to sheltered nests (Frost et al. 1976a). Alternative shelter should thus be considered. Other studies have recorded similar results, for example: those conducted by Crawford et al. (1994) where concrete-piping was used as breeding habitat for penguins. Griffin (2005) compared differences in temperatures at different nest sites (underneath the canopy in permanent shade, in a burrow, in the open or within an artificial nest box) on Robben Island. Variations in temperature remain more constant within burrow type nests compared to other nest types (Griffin 2005). However, nests that were completely shaded still recorded rising temperatures during the day as a result of reduced air circulation at the nest site (Griffin 2005). Temperature differences in artificial nest sites compared to those that were shaded were smaller on windy days (Griffin 2005), suggesting that preferred nest sites for breeders are not always those that are shaded but those that are also well ventilated.

If it is considered that well ventilated nests are preferred to those that are sheltered, then on Bird Island nests that are exposed to the south-westerly sea breeze (Stewardson et al. 2001) should be preferred. However, it is then surprising that the burrow locality recorded no declines in nest density during the heat stress event (i.e. no sea breeze effects). The poorly ventilated cardboard boxes at the surface habitat induced breeders to relocate from surface nests to the artificial habitat. Both burrows and the box habitats provide nesters with shelter from the sun, but are also both poorly ventilated. Griffin (2005) recorded that artificial nest boxes had smaller temperature variations compared to habitats that were sheltered yet well ventilated. Thus, it is likely that prolonged utilisation of the cardboard boxes (if wind were present) would have resulted in penguins deserting the boxes. Griffin (2005) also found that burrow nests recorded a more constant temperature that was slightly lower than experienced in non-sheltered nests on the surface. In the absence of ventilation, the burrows sheltered from the sun would be preferred as was recorded during the heat stress event. During times of prolonged heat stress conditions and no sea breeze, especially during the hottest period of the day (i.e. 10:00 am – 2:00 pm), the number of breeders that can receive shelter behind the houses is limited. It is thus concluded that during summer if the cool sea breeze is absent,

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permanently sheltered habitats are preferred and in cases where the sea breeze is present, well ventilated localities are preferred.

In the months after February 2003, trends in nest counts on Bird Island were irregular with peak counts being recorded during the moulting period when usually this would be a time when most birds had completed breeding (Randall 1983, Crawford et al. 1995b). The irregular pattern experienced by breeders illustrates the disruptive nature that an unusual weather event can have on a colony’s breeding pattern. The changed breeding pattern resulted in penguins attempting to raise their initial clutches during autumn and winter, a time when their prey (sardine and anchovy) are no longer abundant within their foraging range (Randall & Randall 1981, Crawford et al. 2002). The disruption could greatly have influenced chick survival due to lack of food (Wilson 1985a, Heath & Randall 1989). In the years after 2003, St Croix Island breeders continued to decline from 9 116 to 2 653 nests. In contrast, Bird Island showed an increase from 926 to 3 203 nests. Latest nest counts (2007) showed that the St Croix Island breeders had increased to about 4 700 nests and Bird Island breeders had declined to 818 nests. As determined from this study, 113 000 penguin nests could be accommodated on Bird Island but the actual nest counts recorded are much lower. Although the St Croix and Bird Island penguin colonies are located only 47 km apart (Randall 1983), breeding patterns differ.

Factors that could influence breeding success may be spatially classified as either broad or specific to a population or colony respectively. Effects on breeding due to broad factors such as guano and egg exploitation, breeding disturbance, weather, oil pollution and prey scarcity are considered to influence various colonies within a region. However, the difference in the nest count patterns recorded between the Bird and St Croix Islands are ascribed to factors that are specific to the colonies (Siegfried 1977, Grundlingh 1983, Stewardson et al. 2001), potentially the result of weather associated with the positioning of the two island groups.

Breeders on Bird Island primarily have the choice to nest in two shelter types, those that are completely sheltered behind the houses and those within burrows, or to nest in the open with no shelter. Various studies (Frost et al. 1976a, Randall 1983) have shown that burrow type nests, artificial nests (Crawford et al. 1994, Griffin 2005) and nests that are completely sheltered from the sun are more favourable for breeding success than open nests (Frost et al. 1976a, Frere et al. 1992). Confounding factors such as age, breeding experience and predation intensity makes it difficult to quantify the importance of shelter in nesting success (Frere et al . 1992). However, breeding success is considered to be largely influenced by the suitability of the habitat within the nest site, more specifically, the degree of shelter

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that the nest receives from the sun (Frost et al. 1976a, Randall & Randall 1981, Randall 1983). In contrast, the results from this study do not completely support these findings.

Broad comparisons of nest density between the two types of sheltered habitats (burrows and the shade behind the houses) and those localities found in the open, recorded significant differences between the house and the other two localities (surface and burrows). No significant difference was recorded between the surface and burrow localities. Mean nest density was no different between the above ground shelter locality (houses) and the open surface 6 locality. Both recorded significantly higher nest densities compared to the other surface localities (except comparisons between the surface 6 and surface 5 localities) and with the burrow locality. The only similar finding recorded in this study compared to previous studies is that when wind was absent, the burrow locality did not suffer nest declines.

Penguins on Bird Island seem to select favourable breeding habitats and thus nest distribution is not random across the island. However, habitat suitable for breeding is not primarily determined by the degree of shelter that a specific habitat type provides to a nest. Further analysis indicated that the periphery of the island compared to inland localities showed higher nest densities, although differences were not significant. Thus, nest site selection relative to its distance from the sea is not the principal influencing factor determining the selection of a nest site. Further analysis of the nest density patterns within the different localities during the three breeding periods (peak, replacement and moulting) showed a significance difference between the high nest counts recorded during the peak breeding period relative to the replacement and moulting periods more so in the house and surface 6 localities. However, during the replacement and moulting periods the nest density at the house locality was higher than any other locality. The relatively high nest densities recorded during the moulting period on Bird Island (especially within the house locality) could be the result of breeders delaying their moult. This is thought to be the result of birds either still breeding or an abundance of prey availability during this time. Generally during October to December, the amount of sardine within the inshore waters is scarce (Heath & Randall 1989). However, the breeding cycle of sardine may have been disrupted as a result of its over-exploitation by the Algoa Bay fishery in the past (Penny et al. 1989, Griffiths 1997a, b, 2000) causing the sardine to be numerous during the time when the penguins should be commencing with moult. It is more likely though that the delay in moult by breeders was due to the disruption in their breeding during the peak breeding attempts from the consistently high summer temperatures.

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Supportive reasoning (without quantitative evidence) for the nest density patterns experienced on Bird Island is further provided.

a) Parasites In regards to the nest site, Kemper (2006) showed that artificial nest shelters only proved successful for one breeding season on Possession Island, as ticks invaded these shelters and penguins did not reuse these shelters. Artificial nest boxes were only favoured for penguin breeding when the presence of parasites had been artificially controlled or were absent (Kemper 2006). Although a number of derelict guano sheds exist on Bird Island that could be utilised as nesting areas for penguins, they refrain from doing so. Information on parasitism for Bird Island is scarce, but it is possible that parasite infestation or poor ventilation leads to the rejection of these potentially favourable breeding sites.

b) Predator deterrence Kelp Gulls prey on seabird eggs and chicks (Cooper 1974). The numbers of Kelp Gulls are increasing on Seal Island, Algoa Bay (CSIR 2001), which could lead to an increased predation on penguin chicks and eggs (du Toit et al. 2003b). The large Cape Gannet colony that resides on Bird Island directly borders on to the surface 6 locality. Although also a target for Kelp Gull predation, the densely packed nests may act as an additional predatory deterrence to attacking gulls (Crawford et al. 2007) on nearby penguin breeders. This may explain the nest site preference for the surface 6 locality compared to other surface localities.

c) Optimal habitat for breeding Habitat selection results in animals living in a restricted set of environmental conditions (Partridge 1978 cited in Seddon & Davis 1989). Selection of environment, though once thought to be mediated by the recognition of specific physical features (Hilden 1965), is now believed to be due to choices made in relation to various hierarchically ranked criteria (Klopfer & Ganzhorn 1985 cited in Seddon & Davis 1989). Given the availability of suitable habitat that could be utilised for nest sites, breeding penguins will relocate to the more favourable habitats first (Crawford et al. 1994). In this study, optimal nest density calculated for Bird Island did not occur, even within the more preferred surface 6 and house localities. Forbes & Kaiser (1994) concluded that prospectors will pioneer new colonies only when the cost of joining an established colony exceeds the cost of the knowledge barrier. As a result of the nest density (i.e. an indication of habitat preference) changing between localities in relation to breeding period (time of the year) as well as during events of abnormal weather conditions, an uncertainty seems to exist among breeders on Bird Island as to what and when respective habitats are most suitable for breeding.

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3.5 Conclusion Suitable breeding habitat exists on Bird Island for penguin breeders, but suitability is not principally determined by the degree of shelter that a habitat type may provide to nests. This is supported by the fact that nest density within the sheltered burrow habitat was no different to the majority of surface localities. The maximum nest density on Bird Island was determined as 1.58 nests per m² and was never reached within any of the localities. This supports the argument that certain habitats on Bird Island may be preferred as a result of factors influencing the colony at any one time. Due to the fluctuation of nest density recorded between the habitats relative to time of the year and breeding stage, no one habitat can be considered as preferred for breeding. What has been ascertained from this study is that locality preferences exist for breeders on Bird Island and that nest distribution is not random. It is suggested that suitable breeding localities are not chosen primarily as a consequence of avoidance from the direct rays of the sun but equally important are nest sites that are well ventilated.

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4 BREEDING SUCCESS AND CLUTCH SIZE 4.1 Introduction African Penguins devote approximately nine months of the year to breeding. This allows time for breeders to attempt to successfully raise two broods before the onset of the annual moult (between October and January). Breeding within a colony is usually synchronized during their peak breeding attempt (January to March) which normally coincides with high summer temperatures (Crawford et al. 1990, Crawford et al. 1995b). The presence of chicks (March to May) from the peak breeding attempt also coincides with the availability of their prey (sardine) within their foraging range (Crawford & Shelton 1978). This is as a result of the annual sardine migration from the South Western Cape (Crawford & Shelton 1978) up to the KwaZulu-Natal coast. Chicks raised in replacement broods do not benefit equally in quantity of food supplied to them from their parents due to the sardines having already migrated past their foraging range. Thus chicks from replacement broods have less chance of survival than chicks from the first breeding attempt (Crawford et al. 1995b, Crawford et al. 1999). African Penguins show a decreased tendency to lay replacement broods following the first breeding attempt (Randall 1983). However, even in times of poor food availability, some adult pairs are able to fledge chicks (Randall 1983, Coulson & White 1958 cited in Adams et al. 1992). Adult foraging and breeding experience may thus be the determining factors for chick fledging success, especially during periods when unfavourable conditions for breeding exist.

4.1.1 The annual breeding cycle Unlike many other seabirds, African Penguins can have an extended breeding season. The stage of breeding within any colony differs as a result of breeding pairs initiating and possibly failing at different times. The annual life cycle for any adult will broadly involve an annual moult followed by one or more breeding attempts (Ralph, pers. obs.), the latter generally occurring after breeding failure. Replacement breeding differs between localities. Western Cape colonies rarely lay replacement clutches, however, the colonies in the Eastern Cape frequently do so (up to four) (Hockey 2001). Indefinite breeding attempts are constrained by breeders having to moult. Hockey (2001) is a popular synthesis of the primary literature governing the breeding cycle of the African Penguin and has therefore been used only to provide background information on this topic.

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4.1.2 Egg incubation and chick-rearing stages About three weeks after a pair has reunited, the female lays her eggs. Like most birds, Spheniscus penguins have an asynchronous breeding strategy whereby chicks within a brood hatch (often of different weights) at different times (Boersma & Stokes 1995). African Penguins usually lay two eggs (Randall 1983) with fewer than 1% of breeders laying one egg (William & Cooper 1984) and rarely are three eggs laid. The mean clutch size is about 1.86 eggs (Crawford et al. 1999). The first egg laid (A-egg) is on average 4.6 g (range 0-12 g) heavier and hatches 2.1 days earlier (range 1-4 days) than the second B-egg (Williams & Cooper 1984). After approximately 40 days of incubation, the eggs hatch (Hockey 2001).

Depending on the hatching order, chicks are classed in three categories. A-chicks and B- chicks are from the same clutch. The A-chick hatches first approximately 3 days prior to that of its sibling B-chick (Crawford et al. 1999). The C-chick is the only chick to hatch from a 1-egg clutch. As a result of the first chick hatching prior to that of its sibling it obtains a developmental head-start and acquires a greater initial weight (Seddon & van Heezik 1991a). Chicks only gain full control over their body temperature once they are 15 days old, and thus parents have to feed, guard and keep the chicks warm. Adults remain at the nest until the chicks are approximately 30 days old and then both adults depart to forage at sea in order to sustain the demanding food requirements of their growing chicks (Hockey 2001). Chicks left alone on land form crèches along with other similarly aged chicks. The biggest threat to these older chicks is them not receiving sufficient food. A six week old chick can demand up to half a kilogram of fish a day. In addition, each adult has to catch 300 g per day of fish to sustain itself (Hockey 2001). Juvenile African Penguins have a less than 10 % chance of surviving their first year at sea. Their first weeks at sea, learning to forage, are the most critical for their survival. The better the body condition of a chick when it fledges the better its survival potential during its first weeks at sea. Body weight at fledging could be an important indicator of chick survival (Seddon & van Heezik 1991a).

4.1.3 Mortality of offspring at the nest Breeders desert their nests more frequently when high temperatures together with windless conditions are experienced (Crawford et al. 1999). Prolonged heat stress conditions can result in the breeding failure of the entire colony (Randall 1989). Although theoretically raising two broods in succession is possible, it is unlikely when breeders have to accommodate unfavourable conditions whilst attempting to raise their chicks (Crawford et al. 1999).

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The most common factors of hatching failure are: egg destruction during adult penguin fights, nest desertion as a result of nest flooding, heat stress and predation of the eggs and chicks primarily by the Kelp Gull (Randall 1983). Factors that cause nest failure usually differ between island colonies and factors significant in one season may be insignificant in the next (Randall 1989). Two distinct stages exist in the growth of the chick where mortality factors differ. Chicks are at greatest risk of death between the age of 0-34 days (Seddon & van Heezik 1991a). Of all the types of nests, the surface recorded the lowest reproductive success and highest chick mortalities as a result of heat exposure, drowning, burrow collapse, accidental death within the nest and predation by Kelp Gulls (Seddon & van Heezik 1991a). Mortality of larger chicks aged from 42-90 days is almost entirely a result of starvation.

4.1.4 Clutch size and breeding success Breeding success in the colonial living penguin may be hampered by the complexity with which many factors influence reproductive success (Davis & McCaffrey 1986). Breeding failure differs between breeders at colonies in the Western and Eastern Cape. In a study conducted at Robben Island, only 48.6% of nest pairs successfully hatched eggs of which only 19.3% successfully fledged chicks (Crawford et al. 1999). In a clutch size study conducted on St Croix Island, 12% of broods with a two-egg clutch fledged both chicks and recorded a fledging success rate of 0.37 chicks per nest (Randall 1989). Although, no difference in fledging success was found between successful first time breeders and successful replacement breeders (Crawford et al. 1999), chicks that fledged during the first breeding attempt were in better condition (i.e. weight) than fledglings from the replacement broods (Randall 1983, 1989, Crawford et al. 1999).

4.1.5 Parental expenditure required in breeding Seabirds live in variable environments with large annual fluctuations in breeding conditions. Under poor conditions (i.e. lack of food availability) the offspring produced may have achieved a lowered weight compared to those chicks produced under favourable breeding conditions. Although adult seabirds have a small storage of nutritional reserves that can be used to supplement themselves, even a small reduction in their body weight may have dramatic effects on their survival (Velando 2001). When conditions are favourable the breeding adults can quickly replenish their depleted fat reserves as well as provide sufficient food to their chicks thus increasing both the breeder and offspring’s chances of survival (Erikstad et al. 1998). Depending on how favourable the conditions are for breeding, female birds are able to adjust their clutch size, egg size and egg investments at the time of egg-

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laying (Ankney & MacInnes 1978, Boutin 1990, Bolton et al. 1992). Parental care involves substantial energy expenditure by the parents (Clutton-Brock 1991) and for many species physiological stress peaks during the chick rearing stage (Bryant & Westerterp 1983). The physiological stress involved with breeding is greatly increased during adverse conditions especially during periods of poor food abundance (Yorio & Boersma 1994). Breeding adults investing energy into fledging their chicks simultaneously need to ensure that they maintain physiological survival condition to ensure breeding success in the future (Partridge & Harvey 1985, 1988). Therefore, the degree of investment that breeders are able to place in their offspring is governed by the breeders’ body condition. Poor body condition may force them to reduce their investment in their offspring in an effort to avoid jeopardizing their future survival (Wright & Cuthill 1989, Chastel et al. 1995, Erikstad et al. 1997, Olsson 1997) or cause them to abandon their breeding attempt (Dearborn 2001). Williams & Croxall (1991) found that in most cases where nests were deserted, the breeders weighed less than those adults that bred successfully.

Edge et al. (1999) found that Yellow-eyed Penguins (Megadyptes antipodes ) that raise a single clutch gained weight more rapidly and were in a better condition than those that were raising a two-egg clutch. During favourable feeding conditions Yellow-eyed Penguins (Edge et al. 1999) as well as the African Penguins (Seddon & van Heezik 1991b) will deliver food at rates regulated in accordance with the begging of their chicks (Bengtsson & Ryden 1981, Stamps et al. 1989). Under non-favourable breeding conditions, parents of a single-chick brood are able to invest more energy into ensuring their own survival and reproductive potential in the future than parents raising a two-chick brood (Edge et al. 1999).

4.1.6 Asynchronous breeding theories Avian breeders adopt numerous reproductive strategies in order to enhance the survival of the species and are broadly discussed by numerous hypotheses notably: brood reduction, peak load reduction, dietary diversity, hurry-up, sex ratio manipulation, sibling rivalry and the insurance hypotheses (Hahn 1981, Forbes 1991, Stinson 1979 cited in Stoleson & Beissinger 1997). The likelihood of chicks of different sizes hatching asynchronously, results in a competitive advantage for the first-hatched chick (Seddon & van Heezik 1991b). This is a basis for subsequent brood reduction (i.e. a situation where the second-hatched chick only survives in years when it can receive adequate food once the older chick has been satisfied). The benefit of having at least one chick survive is that similar sized chicks would have a greater chance of equally starving (Forbes 1991) due to neither being able to dominate the feeding (Lack 1966, 1968, Hahn 1981, Stoleson & Beissinger 1997).

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4.1.7 Rationale The survival of the African Penguin is dependent on chicks successfully fledging and becoming breeders. Therefore, an understanding of breeding failure and when it is most likely to occur is vital in focussing conservation efforts.

Counting active nests, in conjunction with the proportion of successful nesters within a colony at any one time, provides valuable information used in assessing the overall breeding capabilities of a colony. This is based on the assumption that the sample monitored could be used to reflect breeding failure across the entire colony. This very rarely is the case as a result of factors causing breeding failure usually being different between island colonies, and factors significant in one season may be insignificant in the next (Randall 1989). As a result of the complexity associated with standardizing these factors causing breeding failure at the nest, the breeding failure results determined cannot be used as a representation of breeding failure across the Bird Island colony, since nest densities varied across the island and between nest types (as determined in Chapter 3). This study tests the null hypothesis that breeding failure is independent of clutch size.

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4.2 Methodology

4.2.1 Study location Penguins breeding on Bird Island utilize five different habitats as nesting sites, viz. surface, vegetated, rocky, burrows and those nesting behind the houses (as discussed in Chapter 3). Surface type nests experience the greatest breeding failure of all habitat types due to heat exposure (Frost et al. 1976a). Since the island is comprised mostly of surface habitat, breeding failure is most likely to be maximal at these habitats as compared to other habitats. Penguin breeders that utilise open nest sites that were found in front of the research houses (i.e. surface 1 locality) were considered the most appropriate locality to conduct the study. Breeders within this area are habituated to human presence and therefore any breeding failure observed at these nest sites were most likely not the result of human disturbance.

4.2.2 Drawbacks to the study It is important to acknowledge that breeding failure recorded in this study could have been the result of single or numerous factors perhaps acting frequently or once-off on the study area. It is also not possible to evaluate how breeding and foraging experience of adults may have influenced breeding. Knowing the breeding histories of individual breeding pairs would have been an advantage, together with knowledge of all the abiotic and biotic factors that could potentially have influenced breeding. In order to acquire this knowledge would have been an extremely complex task, one that would have required substantially more sampling time than the two-year period dedicated to this study. Therefore, findings from this study do not represent long term trends regarding breeding success at surface habitats on Bird Island and cannot be used to generalise breeding trends across similar habitats within the colony (Whittington et al. 1999a).

4.2.3 Data collection All nests observed within this study were monitored continuously from egg laying up until the eggs hatched and the clutch size of the nest determined. Breeding success at the nest site within the surface 1 locality on Bird Island was determined through the monitoring of breeders at fortnightly intervals (due to restrictions on island visitation) irrespective of breeding attempt and time of year. Only breeders with flipper bands were considered for observation. As a result of the A-chick always being larger in size in comparison to its sibling B-chick (Williams & Cooper 1984), clutch size as well as mortality within the nests for the incubation and chick-rearing stages could be recorded. Due to limited observational time, it was not always possible to determine reasons for breeding failure during the chick-

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rearing stage. In cases where the temporary flipper bands had become dislodged from the chicks, and the hatching order of the chicks from a double clutch could not be determined, these nests were discarded from the analysis. Chicks were considered to have successfully fledged when they had at most a 5 cm diameter of down feathers left on their napes. No control was deemed necessary in this study, as a result of monitoring being observational from an adequate distance away from the nest, breeding disturbance was thus considered negligible. In addition, when the age of the chicks and the clutch size within the nest had been determined, the apparent nest success calculated in this study reflected the true nest success rate and therefore Mayfield’s ‘at risk’ concept (Mayfield 1961) was of no relevance.

4.2.4 Classification of nests Chick classification and clutch size within this study was defined following Williams & Cooper (1984). In addition, a single chick that had survived from a 2 chick nest (as a result of the death of the other chick) irrespective of whether it was the A or B-chick was then referred to as an E-chick. Also, if only one of a two-egg clutch hatched, the survivor was referred to as a D-chick as its origin was still different from that of a C-chick.

4.2.5 Statistical data analysis Statistical analysis of the data was done using cross tabulation contingency tables testing for independence (as a result of unequal counts being recorded between years and the number of various clutch size nests). Significance was considered at p < .05. Where significant differences were recorded, Cramer’s V practical significance was determined in order to quantify the degree of significance obtained. A two-tailed T-test assuming unequal variance (as a result of different egg counts being recorded between breeding periods) with an alpha level of 0.05 was used to determine whether a significant difference existed between the mean egg number laid between peak (January – May) and replacement (June-November) breeding periods. In order to determine the practical significance of the T-test result, the Cohen’s d test statistic was determined. No statistical programmes other than Microsoft Excel (1997) were used in the data analyses.

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4.3 Results

4.3.1 Data collection Of the 225 nests monitored within the surface 1 locality over the two-years (587 observational days in total), 36 nests in total were excluded from further analysis as a result of chicks being absent from ten of the nests, and thus the breeding status of the nest was undetermined, and twenty six nests were not utilized for breeding and deemed ‘in-active’. Hence, 189 nests accounting for 357 eggs were used for statistical analysis in this study. As a result of continuous observation during the incubation stage, the number of eggs laid during summer and winter could also be determined. The percentages reflected below were calculated from the number of offspring that either successfully hatched or fledged accordingly.

The random selection of the nests that were monitored within the study area revealed that 87.8% (166 nests) of breeders laid 2-egg clutches, 11.6% (22 nests) laid a 1-egg clutch and 0.6% (1 nest) laid a 3-egg clutch (Figure 4.1). Only one of the three egg clutch hatched and soon afterwards (within 14 days), the chick had failed to fledge. As a result of the lack of replicate nests observed with a 3-egg clutch, this sole record was discarded from analysis.

4.3.2 Survivorship summary at the incubation and chick-rearing stages Of the 22 nests with a 1-egg clutch, only 5 chicks hatched (23%) of which only one chick fledged. Of the 332 eggs laid in the 166 nests with a 2-egg clutch, 69 nests successfully hatched both eggs (41.6%). However, 67 nests (40.4%) with 2-eggs failed to hatch either of the eggs and thirty (9%) of the nests hatched only one of the two eggs laid.

Within the nests with a 2-egg clutch, 7 nests (10.1%) successfully fledged both their chicks (i.e. 14 chicks in total). Complete breeding failure of both the chicks (i.e. 74 chicks in total) was recorded in 37 of the nests (53.6%). Twenty five (18.1%) of the fifty chicks that hatched from a 2-egg clutch failed to fledge (i.e. E-chicks). Of the 30 single chicks that successfully hatched from their 2-egg clutches, a very high proportion fledged successfully (28 D- chicks). Of the total number of 2-egg clutch nests that successfully hatched both their chicks, 10% of the chicks fledged with their siblings and 38% of the chicks fledged alone (Figure 4.1).

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Undetermined Active Nest # Inactive Nests

10 189 26

1-Egg Clutch # 2-Egg Clutch # 3-Egg Clutch #

22 332 3 (11.6%) (87.8%) (0. 6%) INCUBATION

17 134 30 2 HATCHING

5 138 30 1

REARING CHICK CHICK

4 74 25 2 1 FL

EDGING 1 14 25 28 0

C - Chick AB - Chick E - Chick D - Chick ABC - Chick

KEY: KEY - Deaths - Alive - Deaths - Alive

Figure 4-1: Survival and failure history of offspring per clutch type during breeding.

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4.3.3 Drawbacks to the statistical analysis of the data In order for the data to be pooled and represented across the two-year window, homogeny needs to be derived. Testing for homogeny within this study is complicated by the fact that numerous criteria that influence breeding would need to have been considered for each nest. These criteria could include: micro-climate, predation intensities, parasitism, clutch size nests in incubation and fledging stages, between peak and replacement breeding periods as well as ensuring that the timing of breeding was similar between the years of 1993 and 1994. Assuming that the above mentioned criteria had been monitored, the foraging experience of the breeders could not have been accurately determined in association with the potential factors inhibiting breeding at any one time. It is understood that homogeny was required prior to the pooling of the data. However, as discussed above, this was an impossible task given the time-frame of the study. An attempt was made to limit the degree of uncertainty with regards to factors potentially influencing breeding at the nest sites, by excluding nests that were found along the periphery of the surface 1 locality. Thus only nests found within the centre of the surface 1 locality were selected. It should be noted, that this study has been conducted under the broad and unlikely assumption that all factors potentially influencing the outcome of breeding at the monitored nests were similar. Therefore, the statistical analyses of the results have not taken homogeneity into consideration.

4.3.4 Survivorship comparisons between the breeding stages A cross tabulation contingency table (testing for independence) was used to determine whether the high failure of broods within the incubation and chick-rearing stages is influenced by clutch size. The null hypothesis that failure at the incubation stage is independent of clutch size was tested. A large significant difference was found for the higher proportion (77%) of brood failure within 1-egg clutches (17 eggs) in comparison to the smaller proportion (40.4%) of failures (yet larger number) accounted for within 2-egg clutches (134 eggs) ( χ2 = 6.39; p = .0114; df = 1; n = 294; Cramer’s V = 0.147).

With relevance to brood failure at the chick-rearing stage, the null hypothesis that brood failure was independent of clutch size was also investigated. No significant difference in brood failure was recorded between the 4 C-chicks (80%) that failed to fledge from the 5 nests with 1-egg clutches in comparison to the 74 chicks (53.6%) that failed to fledge from the total number of chicks (88 chicks) that hatched from 2-egg clutch nests (χ2 = 0.058; p = .8; df = 1; n = 93; Cramer’s V = n.a).

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Of the 5 C-chicks that hatched, 4 chicks (80%) failed to fledge, however of the 30 D-chicks that hatched, only 2 chicks (7%) failed to fledge. The null hypothesis that brood failure is independent of nests with the same clutch size was tested. A significant difference (χ2 = 16.22; p = < .0005; df = 1; n = 35; Cramer’s V = 0.68) was recorded between the larger number of C-chicks that failed to fledge in comparison to single clutch D-chicks that also failed to fledge. Therefore, brood failure during the chick-rearing stage is determined by the clutch size of the nest in which the chicks are raised and the null hypothesis is rejected.

Irrespective of clutch size, breeding failure at the incubation and chick-rearing stages was compared based on the null hypothesis that breeding failure was independent of the stage at which breeding occurred. A small significant difference ( χ2 = 4.28; p = .035; df = 1; n = 527; Cramer’s V = 0.09) was found between the higher brood failure (106 of 174 chicks) recorded during the chick-rearing stage as opposed to the incubation stage (183 of 354 eggs)

4.3.5 Clutch size during the incubation stage relative to the breeding attempt A two-tailed T-test assuming un-equal variance was used to test the null hypothesis that the mean egg number laid is independent of the breeding attempt in which it is laid (i.e. peak breeding attempt is from January – April and the replacement breeding attempt is from May- November).

With reference to Table 4.1, a highly significant difference yet moderate practical significance (t = 5.04; df = 125; p = < .005; Cohen’s d = 0.69) was recorded for the higher mean egg number laid within the peak breeding attempt (1.88 eggs/nest) as compared to the replacement breeding attempt (1.40 eggs/nest). A greater frequency of 1-egg clutches were laid during the replacement breeding attempt compared to the peak breeding period where mostly 2-egg clutches were laid. In addition, the replacement breeding period also showed an elevated number of inactive nests (24 nests) where breeders made provision to breed (i.e. building nests) yet failed to lay any eggs. The peak breeding attempt recorded only 2 inactive nests, and the occurrence of 1-egg and 3-egg clutches was less.

Overall, for every egg laid, 49% of eggs successfully hatched which resulted in only 19% of chicks fledging. The incubation and chick-rearing stages accounted for 51% and 61% of clutch failure respectively.

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Table 4-1: Descriptive statistics of nests and clutch size (eggs laid) during peak and replacement breeding attempts.

Percentage of Nests with: Peak Replacement Total Count nests No eggs (inactive nests) 2 24 26 12.0 Single clutches 12 10 22 10.2 Double clutches 103 63 166 77.2 Triple clutches 0 1 1 0.46 Total eggs 218 139 357

Descriptive statistics

Total nests 116 99 215 100

Mean (eggs per nest) 1.88 1.40 1.66 SD or variance 0.12 0.77 0.69 Observations 116 99 215

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4.4 Discussion The chick-rearing stage is a time when parental care involves substantial energy expenditure (Clutton-Brock 1991) and physiological stress on breeders peaks during this time (Bryant & Westerterp 1983). Breeders that attempt to raise chicks are inhibited from maintaining their own body condition as a result of foraging excursions being restricted by time spent at the nest (Partridge & Harvey 1985, 1988). It is more difficult for breeders to maintain their own body condition whilst attempting to raise two chicks instead of one chick as a result of the additional food demands placed on the breeders (Edge et al. 1999). For this reason, it is thus expected that failure within a 2-chick brood would occur more frequently than in a 1-chick brood. On the contrary, no significant difference was found in the proportion of brood failure between 1 and 2-chick broods during the chick-rearing stage in this study. Reasons for this may be that breeders raising 2-chicks are generally in better body condition and thus more fit than those raising a single chick. Even with the greater breeding demands placed on adults raising 2-chicks, they are able to persist longer with breeding than those raising a single chick. In support of this argument, Williams & Croxall (1991) found that breeders that deserted nests weighed less than those that successfully completed breeding. Breeders that were well maintained (weight) were found to invest more energy into their offspring (i.e. heavier eggs not necessarily more clutches) than those that were not (Wright & Cuthill 1989, Chastel et al. 1995).

African Penguins live in variable environments where large annual fluctuations in breeding conditions and prey abundance occur (Randall 1989). Breeders are therefore required to ensure that their own survival is not compromised whilst attempting to ensure the survival of their offspring. It is expected that African Penguins will usually lay a 2-egg clutch (Randall 1983) and during non-favourable conditions for breeding it is more likely that a higher frequency of single clutches are laid (Williams & Cooper 1984). Breeders of single clutches are able to invest greater amounts of energy into the one egg compared to those that lay two. Therefore, it would be reasonable to assume that, those breeders that raise only one offspring should succeed at fledging their chick more often than those attempting to raise two. However, this was not supported by the results recorded in the chick-rearing stage of this study.

Chicks originating from a nest with only a single chick failed to fledge more often than the single chicks that originated from a 2-egg clutch. This suggests that breeders that attempt to breed are already considered to be in healthy condition and would thus lay a 2-egg clutch (Randall 1983). Breeders in poorer condition may reduce their breeding efforts in order to

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avoid jeopardizing their own survival (Chastel et al. 1995, Erikstad et al. 1997, Olsson 1997) and hence may only lay a single clutch (Ankney & MacInnes 1978, Boutin 1990, Bolton et al. 1992). Breeders that are already under-nourished at the start of breeding would probably not have the expected nutritional reserves to sustain themselves during breeding (Yorio & Boersma 1994, Velando 2001). This is perhaps why breeders in a poorer condition with a single egg or chick are more likely to abort breeding sooner than those in a healthier condition (Dearborn 2001). This is supported by the fact that a significant difference was recorded in the higher proportion of failures in 1-egg clutches as compared to 2-egg clutches.

Breeding success may be hampered by the complexity and frequency with which many inhibiting factors (i.e. food availability or gull predation) could occur (Davis & McCaffrey 1986, Randall 1989). For example, a significant difference was recorded in the higher frequency of 2-egg clutches being laid during the peak breeding attempt as opposed to the replacement breeding attempt. Peak breeding attempts of the African Penguin in the Eastern Cape occurs from January – May which coincides with the abundance and availability of their prey resource (Crawford & Shelton 1978). Breeders raising chicks during a peak breeding attempt are able to optimise the favourable breeding conditions as opposed to replacement breeders that cannot (Crawford et al. 1995b, Crawford et al. 1999). Chick survival is thus greatly influenced by the breeding period in which they are raised (Randall 1983, 1989, Crawford et al. 1999) and by the condition in which they fledge (Seddon & van Heezik 1991a). From the results derived in this study, and in respect to the supporting documentation, the condition of the breeders may reflect how favourable the food stock conditions are and hence the likelihood that a nest will be successful. Ideally, clutch success between breeding periods in relation to the factors affecting breeding should have been monitored, but given the infrequent monitoring of the nests in this study, this was not possible. Therefore, no attempt has been made to correlate the findings with the factors inhibiting breeding for this study.

A greater proportion of nests in this study hatched eggs (60%) and fledged chicks (32%) in comparison to the 48.6% and 19.3% respectively recorded at Robben Island (Crawford et al. 1999). At Bird and St Croix Islands, fledging success of 2-chick broods was similar, with 10% (0.2 chicks per nest) and 12% (0.37 chicks per nest) recorded respectively (Randall 1989). Of the nests with a 2-chick brood that fledged only one of the two chicks, 78% was recorded in this study in comparison to the higher 90% recorded in the Western Cape (Hockey 2001).

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4.5 Conclusion The results obtained during the short time-frame in which this study was conducted cannot be used to elaborate on the theories governing asynchronous breeding in African Penguins (Stoleson & Beissinger 1997). However, further reasoning is provided.

When fish stocks are abundant and accessible to breeders during their peak breeding attempt, proportionately more breeders will lay 2-egg clutches. This is due to the breeders being in a better body condition compared to breeders in a replacement breeding attempt. Penguins attempting to breed when food stocks are less abundant (i.e. replacement breeding periods) may only have enough energy to attempt to raise a single clutch, if that. Breeding failure was fairly similar to breeding success during the incubation stage for nests with 2- eggs however, breeding failure was substantially higher in nests with 1-egg. Breeders attempting to raise a single clutch from the start are already in a poorer body condition and thus are potentially more ‘aware’ that their own survival may be jeopardized by investing too much energy into breeding. Thus, breeders that are more physically fit for breeding can allocate enough energy into raising a 2-chick brood without jeopardising their own fitness and perhaps are thus more devoted towards raising their offspring than breeders of 1-chick broods. Breeders that are under-nourished and attempting to raise a single clutch may be spending longer periods of time foraging to enhance their own fitness. This could inevitably lead to both breeders extending their foraging trips resulting in nest desertion and clutch failure (Davis 1982, 1988, Groscolas 1990, Dearborn 2001). Of course, breeders of double clutches can afford to lose half their brood without completely failing. Contrary to the above argument, penguins will usually lay two eggs (Randall 1983) regardless of whether adequate food stocks exist or not, simply because eggs are ‘cheap’ to produce. Hence, the theory that the number of nests with double clutches is a reflection of how healthy the breeders are, may be incorrect.

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5 GROWTH IN CHICKS 5.1 Introduction

5.1.1 Chick classification African Penguins adopt an asynchronous breeding strategy (Seddon & van Heezik 1991b). Penguins usually lay two eggs (Randall 1983) with fewer than 1% of nesters laying one egg (William & Cooper 1984) and rarely are three eggs laid. Chicks that hatch from 2-egg clutches are classified as A-chicks (those hatching first) and B-chicks (those hatching second) (Randall & Randall 1981, Crawford et al. 1999), whilst chicks that hatch from a solitary egg are classified as C-chicks.

5.1.2 Chick development The breeding stages and chick development at the nest site are illustrated in Figure 5.1. Under favourable growth conditions, downy chicks are fully brooded from the age of 0 to 5 days. From 6 to 10 days the downy chicks are covered and protected by the adult. The downy chicks’ eyes open at 11 to 15 days and a secondary down (brown above, white on the face, throat and belly) starts to develop. They now become more active and are only partially covered by the adult. By the age of 16 to 20 days, the secondary down is complete and provides a thickened thermal down. The chicks are now relatively active. At 21 to 25 days, the secondary down is fully developed and the chicks show aggressive hiss vocalisation and pant when heat stress is experienced. Chicks have now attained full thermo-regulatory capacity, weighing approximately 400 g (Erasmus & Smith 1974). At the age of 26 to 30 days, the chicks are left unattended while the adults forage. Chicks also gather in crèches of 5 to 10 chicks. At the age of 31 to 35 days the contour feathers start to grow beneath the down and at age 36 to 40 days the chicks begin to lose their down. At 61 to 65 days they have completely lost their down and have grown into full juveniles (also called “blues”). Fledging usually occurred between 75 to 80 days (Seddon & van Heezik 1991a).

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F

A

B E

C D

Figure 5-1: The stages of breeding at the nest. Reproduction (A), incubation (B), a newly hatched chick (C), the guard stage of chicks younger than 30 days (D), the crèche stage where chicks older than 30 days huddle together (E) and a juvenile prior to fledging from the nest (F).

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5.1.3 Dietary demands of chicks Hatchlings from the Western and Eastern Cape generally weight about 72 g (Randall 1983, Williams & Cooper 1984). In a 2-egg clutch, the first chick to hatch generally recorded a hatching weight 12 g higher than that of the second (Williams & Cooper 1984, Seddon & van Heezik 1991a, Boersma & Stokes 1995). However, Randall (1983) found no difference in hatching weights of chicks from 2-egg clutches in the Eastern Cape. Hatching asynchrony influences the ability of the younger chick to compete for food due to its smaller size relative to the older chick. This is especially noticeable in the growth of the chicks during periods when prey is limited. During favourable breeding conditions, the older chick will fledge earlier enabling the B-chick to then feed undisturbed and fledge soon afterwards (Seddon & van Heezik 1991b).

Chicks experience maximum growth from 15-30 days old following which their growth rate gradually slows down until they fledge (Moreno et al. 1998). Growth rates in chicks were higher for chicks from single broods as opposed to chicks competing for food in double broods (Moreno et al. 1994). Chicks that are older than 30 days require a substantial amount (~500 g/day) of food to sustain their growth (Hockey 2001). Chicks that receive adequate (quality and quantity) quotas of fish experience faster growth rates and can fledge as soon as 60 days old. Chicks that receive less than adequate amounts of food experience slower growth rates and can fledge as late as 130 days of age (Hockey 2001).

Variations in fledgling time and weight are correlated to seasonal availability of fish (Ainley & Schlatter 1972, Randall 1983, Wilson 1985a). The long fledging period that can be experienced by African Penguin chicks allows them to recover from unfavourable breeding periods during their time at the nest (Randall 1983).

5.1.4 Rationale The number of chicks that survive after fledging is important for the future recruitment of juveniles into the breeding population. Penguin chicks that are able to grow quickly and fledge with a higher weight have a better chance of survival. The overall growth rate of the chick whilst at the nest site may influence its overall survival potential before and after fledging. Thus, this study compares growth rate, weight and fledging time of chicks from single and double broods on Bird Island. Growth rate comparisons between A, B and C- chicks can thus be made.

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5.2 Materials and Methods

5.2.1 Data collection During a two-year period (1993-1994), Dr N. Klages monitored chick growth on a daily basis. Chicks from single and double broods were monitored. Nests were individually marked in the surface 1 locality (refer to Figure 3.3) to ensure that specific nests could be re- visited. Chicks were measured at the same time every day with the monitoring of weights being completed before the afternoon feed. Chicks were marked with temporary flipper bands (cable ties). Each temporary flipper band had a unique number and was removed just before chicks were due to fledge. The weigh-in was done with the use of a Salter Spring Scale (Thermoscale Model 235 SA), accurate to 100 g. The monitoring of chicks continued daily throughout the chick rearing stage until chicks were considered to have fledged or had died. Chicks were considered to have fledged when they had a < 5 cm patch of down on their napes. No control was undertaken since it is impossible to monitor growth rate in chicks without disturbing chicks or the nest site. Chicks were monitored in batches of 20 nests at a time with some degree of overlap between batches. For example, when chicks from one batch of 20 nests were 30 days old, a new batch of 20 nests was selected.

5.2.2 Drawbacks to the study The drawback to this sampling methodology was that it is labour-intensive. However it did ensure that human error and disturbance of the chicks was minimal. Chick growth comparisons could not be made between breeding periods or relative to food availability and weather conditions. Measurements were first recorded within the first 8 hours after the chick had hatched. This study does not compare growth of chicks relative to peak and replacement breeding periods or between subsequent months or years, but focuses on chick growth in relation to brood size at the nest during a two year period.

5.2.3 Growth models and data transformation For comparative purposes, three growth curves (i.e. the Logistic, Gompertz and von Bertalanffy growth curves) as discussed by Ricklefs (1967) were well-suited for the comparative purposes required in this study. Growth constants, correlation coefficients and data analyses were calculated according to Ricklefs (1967). The growth equations for the three plotted curves are as follows:

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1  the Logistic Curve: W = ; t 1+ be −kt

−bk − kt  the Gompertz Curve: Wt = e ;

−kt 3  the von Bertalanffy Curve: Wt = 1( − be ) .

Where:

Wt: is the weight of the organism expressed as a decimal fraction of its final or asymptotic weight; b: is a constant for the linear relationship of the growth equation (i.e. slope) where K = -b; t: is the time for a given interval in the growth curve; K: is the constant which is proportional to the overall growth rate.

In order for normality to be determined, growth data was linearly transformed. Asymptotic weights (i.e. weight infinity) of the growth curves for each chick were calculated using the solver application of Microsoft Excel on the transformed data. The asymptotic values that were determined for each individual chick were relative to its growth increment and therefore predicted the maximum possible weight that could be achieved. This is based on the improbable assumption that the growth rate remains linear until the chick fledges. Asymptotic values are thus higher than would usually be expected (i.e. when the data is not transformed).

The method used in determining the asymptotic weight is thus specific for each chick as compared to the more subjective method described by Volkman & Trivelpiece (1980). The growth constant (K) and correlation coefficient ratio of fit (r) of the transformed weight versus time were calculated for each growth model which was fitted to the recorded weights relative to time for each chick as described by Ricklefs (1967). The selection of the best fit growth curve for each individual chick was thus not subjectively determined but objectively selected based on the growth model that revealed the best fit to the data (i.e. the highest correlation coefficient). In order for comparisons to be made between chicks, a common growth curve would need to be selected for all chicks (Ricklefs 1967). Therefore, it was determined that the growth curve that best fitted the majority of chicks would be selected as the growth curve on which the statistical comparisons of growth between the three chick groups would be compared.

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5.2.4 Statistical treatment Comparisons testing for significant differences (i.e. 95% confidence intervals where p < .05) in growth (i.e. comparisons between the overall growth rate constants “K”), fledging day, fledging weight and maximum weight were undertaken between the three chick groups (i.e. A versus B versus C-chicks) using analysis of covariance (ANCOVA). Post-hoc Scheffé bivariate tests were used to distinguish where significant differences (if any) were recorded. This post-hoc test was utilised as a result of the chicks fledging on different days and with un-equal observational days. The degree of significance from a practical perspective was further quantified using the Cohen’s d test into small (> 0.2), moderate (> 0.5) or that of a large (> 0.8) significance.

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5.3 Results

5.3.1 Data analysis Forty seven chicks {10 from group A (i.e. A-chicks), 8 from group B (i.e. B-chicks) and 15 from group C (i.e. C-chicks)} were monitored from hatching till they either fledged or died. Of the 47 chicks monitored, 1 chick from group A, 3 from group B and 1 from group C died before fledging. The A-chick died on day 84 with a weight of 2 600 g. The three B-chicks died on days 89, 105 and 106 at the respective weights of 2 300 g, 1 400 g and 1 600 g. The C-chick died on day 123 with a weight of 2 600 g. Of the five chicks that died, one nest with 2 chicks failed to fledge both chicks and on two occasions only one of the two chicks fledged from a similar brood size. Due to the small sample size recorded for nests with 2- chick nests failing to fledge one of the two chicks, the two A-chicks were also omitted from further analysis. A further three chicks from group A and group B and five chicks from group C were identified as potential outliers (i.e. disadvantaged chicks with persistently low weights in comparison to the means). Due to the small number of chicks that successfully fledged in each group, outliers could not be dis-regarded from the statistical comparisons between the chick groups. Therefore, growth data (Table 3 to 6 of Appendix B) recorded for successfully fledged chicks comprised of twenty chicks from group C, eleven from both group A and group B. Although growth of the chicks that failed to fledge was not used in the statistical comparisons, they were represented for comparative purposes.

5.3.2 The best fit growth curve Growth constants (K) and correlation coefficient ratios of fit (r) for each growth equation (i.e. Logistic, Gompertz and von Bertalanffy) were plotted using transformed (linear transformation) weight data over the growth period for each chick using the methodology as described in Ricklefs (1967). Summaries are represented in Table 7 of Appendix B. In 90% of the cases (n = 38 of 42 chicks), the von Bertalanffy growth equation emerged as the best fit curve (i.e. highest r value) to the data. Consequently, this curve was used to compare growth between the chick groups.

5.3.3 Statistical treatment Mean descriptive statistics of the growth recorded for the three chick groups as well as for those that failed to fledge are summarised in Table 5.1. The standard error was calculated at the 95% confidence interval as represented in Tables 3 to 6 of Appendix B. The null hypothesis that chick growth is no different between the three chick groups that fledged was tested using a one-way ANCOVA. The weight recorded after hatching, the maximum weight achieved, fledging weight, fledging day and the rate of growth were then calculated.

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Table 5-1: Mean aspects of growth recorded per chick type.

Chicks that Aspects of Growth A chicks B chicks C chicks died Wt after hatching 98.64 84.18 91.30 86.60 Wt maximum 3006.82 2679.55 2960.00 2535.00 Wt at fledging 2740.91 2468.18 2640.25 2180.00 Wt loss % 8.84 7.89 10.80 14.00

grams) grams) Fledging day 84.64 89.00 89.05 94.40 Correlation coefficient (r) 0.98 0.95 0.96 0.95 Mean (Weight in (Weight Mean Growth constant (K) 0.0053 0.0046 0.0041 0.0036

Wt after hatching 2.86 6.91 11.14 12.02 Wt maximum 71.99 95.99 73.55 66.90 Wt at fledging 105.65 146.32 88.15 149.04 Day fledge 1.40 2.85 2.04 8.79

SE of Mean of Mean SE Correlation coefficient (r) 0.0054 0.0152 0.0068 0.0156

(Weight in grams) in grams) (Weight Growth constant (K) 0.0003 0.0005 0.0002 0.0006

a) Weight after hatching After the chicks had hatched and had fed for the first time, chicks from the A and C groups weighed approximately 98 g and 91 g respectively in comparison to the 84 g recorded for chicks from the B group and the 86 g for those chicks that died. Results from the one-way ANCOVA found no significant difference (F = 2.79; p = .072; df = 2; n = 42) in minimum weights recorded between the three different groups of successfully hatched chicks. Although, as a result of the test statistic p-value falling within the reportable interval (.05

b) Maximum weight achieved during growth With reference to Figure 5.2b, chicks from the A group recorded larger mean maximum weights (3 006 g) than either chicks from the B group (2 679 g) or single brood chicks from the C group (2 960 g). Results from the one-way ANCOVA revealed a highly significant difference in the maximum weights achieved between the three chick types (F = 4.66; p = .014; df = 2; n = 42). Post-hoc Scheffé tests were conducted to determine where the significant difference occurred and the associated practical significance (i.e. Cohen’s d)

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determined. A large practical significance for maximum weights achieved was found between chicks of group A in comparison to those chicks from group B (Scheffé p = .018; Cohen’s d = 1.00). No significant difference was recorded for the maximum weights achieved between chicks from the B and C groups (Scheffé p = .074) and to a less degree between chicks from the A and C groups (Scheffé p = .965).

c) Fledging weight With reference to Figure 5.2c, chicks from the A group (2 740 g) fledged with a weight higher than that of chicks from the B (2 468 g) and C groups (2 640 g). The one-way ANCOVA recorded no significant difference for fledging weights recorded between the three groups (F = 1.67; p = .19; df = 2; n = 42). The chicks that failed to fledge had the greatest variance in mean weight recorded at their death (2 180 g) as opposed to the fledging weights recorded for the chicks from group B. The latter recorded less weight with higher variance about the mean than that of chicks from the C group having the least variance in weight at fledging. In addition, chicks from single broods recorded the greatest weight loss (10.8%) between the maximum weight obtained during the growth curve and their weight with which they fledged with, whilst the B-chicks suffered the least weight loss (7.89%).

d) Fledging day With reference to Figure 5.2d, chicks from the A group fledged earlier (day 84) and with the least variance in fledging day (SE = 1.4 days) compared to chicks from the B (day 89, SE = 2.85) or C groups (day 89, SE = 2.04). Results from the one-way ANCOVA recorded no significant difference in fledging day between the three chick groups (F = 3.0; p = .059; df = 2; n = 42). The chicks that failed to fledge recorded a large variance about the calculated mean day of death (i.e. 94 days), in particular one chick remained at the nest site for 123 days and then died.

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a 110 b 3100

90 2750 Weight (g) (g) Weight Weight (g) Hatching Weight Weight Hatching Maximum Weight Weight Maximum

70 2400 Chick type A chicks B chicks C chicks Mortalities Chick type A chicks B chicks C chicks Mortalities

c 3200 d 110

2600 95 Weight (g) (g) Weight Fledgeday

Wt max WtFinal fledge Wt 2000 80 Chick type A chicks B chicks C chicks Mortalities Chick type A chicks B chicks C chicks Mortalities

Figure 5-2: Mean aspects of growth comparisons per chick type. Error bars denote 95% confidence interval.

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e) Growth rate comparisons using the von Bertalanffy growth equation The overall growth curve when fitted with the von Bertalanffy growth equation showed a gradual growth rate during the initial few days after the chicks had hatched. However, maximum growth rate was recorded from approximately day 4 to day 63. Following day 63 (chick type dependent) the growth rate continued to slow until the chicks fledged (Figure 5.3). Without the raw data being fitted to the von Bertalanffy equation, and in the ‘real life’ scenario, the growth rate of the chicks actually declines and a weight loss is recorded after maximum weights have been achieved up until they fledge (not illustrated in Figure 5.3).

For ease of interpretation of Figure 5.3 and for further comparison, the growth periods (i.e. day 1 - day 30 and day 31 to the mean fledging day) are represented on a larger scale in Figure 5.4. The graphical representation of the actual data to the von Bertalanffy growth equation has a strong goodness of fit (correlation coefficients represented in Table 5.1) that ranged between 95-98% and illustrates that a high confidence can be placed in the findings.

After the first feed, chicks from group B started with a lower initial weight and also experienced a slower rate of growth compared to chicks from the A and C groups. Hatching weights (i.e. following the first feed) between chicks from groups A and C were similar. Although growth rates of chicks from group C in comparison to chicks from group A was initially (day 1 - day 25) slightly quicker, the chicks from the latter group experienced a quicker growth rate after day 25 and obtained higher maximum weights and fledged sooner than any other chick group.

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3000 A chick growth curve B chick growth curve 2500 C chick growth curve Mortalities

2000

1500

Mean Weight (grams) 1000

500

0 0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105 Days

Figure 5-3: The plotted von Bertalanffy growth curve of the mean weights of chicks from groups A, B, C up until mean fledging day and/or mean day of death.

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3000 1250 A chick growth curve A chick growth curve B chick growth curve B chick growth curve C chick growth curve 2750 C chick growth curve Mortalities growth curve Mortalities growth curve

1000 2500

2250

750

2000 Mean Weight (grams) Weight Mean 500 1750

1500

250

1250

0 1000 Days 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Days30 31 35 39 43 47 51 55 59 63 67 71 75 79 83 87 91

Figure 5-4: Extrapolated growth periods from the overall growth curves of the three chick groups (Figure 5.3) illustrating day 1 - day 30 (left) and day 31 - mean fledging day (right).

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The overall growth rate of chicks from double broods was faster than that of chicks of single broods. With reference to Figure 5.5, the single brooded chicks (i.e. the chicks from the C group) record a lower growth rate (K = 0.0041) with the least variance (SE = 0.0002) over the entire growth period compared to the faster growth rates of chicks from group A (K = 0.0053, SE = 0.0003) and from group B (K = 0.0046, SE = 0.0005). However, the one-way ANCOVA recorded no significant difference between the growth rates of the three chick groups (F = 2.29; p = .11; df = 2; n = 42). Chicks from group A were able to maintain a high growth rate (i.e. low variance) until they fledged. Although single brooded chicks obtained higher weights than those of chicks from group B, overall C-chicks recorded a slower rate of growth and thus remained at the nest site for longer periods of time. This delay in fledging potentially increases the likelihood for weight loss prior to fledging. The chicks that failed to fledge recorded a very slow growth rate (K = 0.0036, SE = 0.0006) in comparison to those that fledged. The question that remains to be addressed is whether a critical weight exists during the growth cycle when it is determined whether a chick will continue to grow and successfully fledge or whether it will die?.

0.0065

0.0045 von Bertalanffy growth rate (K) rate growth Bertalanffy von

0.0025 A chicks B chicks C chicks Mortalities Chick type

Figure 5-5: Mean growth rate comparisons of the growth constants determined from the von Bertalanffy growth equation over the entire growth period for each chick type. Error bars denote 95% confidence interval.

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f) Determination of the critical weight and time period within the growth period With reference to Figure 5.6 and 5.7, the critical weight intersection point was determined by calculating the lower confidence interval of the weights for the successfully fledged B- chicks and correlating it with the upper confidence interval of the weights recorded for the chicks that died. From this it was determined that the minimum critical weight that a chick would need to have obtained in order to avoid death during the later stages of growth is about 1 060 g on or before day 30.5. Hence, if the growth rate of a chick prior to day 31 is not high enough, ensuring that a weight of about 1 075 g is obtained, the chick will most likely die. It is more important for chicks to be fed well during its initial growth stages affording it a high overall growth rate and an increased potential to successfully fledge.

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3000 A chick growth curve B chick growth curve C chick growth curve 2500 Mortalities growth curve

2000

1500 Mean Weight (grams) 1000

500

0 Days 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

Figure 5-6: The von Bertalanffy growth curve of the mean weights for chicks from groups A and C as well as the upper and lower 95% confidence intervals of the means for those chicks that died (i.e. mortalities) and the chicks from group B that fledged.

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1400 A chick growth curve B chick growth curve 1350 C chick growth curve Mortalities growth curve 1300

1250

1200

1150

1100 Mean Weight (grams) Weight Mean

1050

1000

950

900 Days 26 27 28 29 30 31 32 33

Figure 5-7: The critical time and weight that influences the survival of chicks.

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5.4 Discussion

5.4.1 Aspects of growth between the chick groups

a) Fledging day On average, chicks from groups A, B and C fledged on day 84, 89 and between 89-90 days respectively. These results are contrary to the findings for penguins from the Western Cape, where chicks from single broods usually fledged earlier (73 days) than chicks from double broods (80 days) (Cooper 1980). The results are however similar to penguins on St Croix Island where fledging occurred between 80-130 days (Randall 1983).

b) Fledging weight The chicks that were monitored in this study on Bird Island and the fledging weights obtained (i.e. 2 468 g – 2 740 g) were considered to be slightly below average. This conclusion follows the findings of Hockey (2001) where chicks receiving ample quotas (25- 30 kg) of food during their primary growth period fledged with a weight of approximately 4 000 g and those raised during un-favourable food stock conditions only fledged at approximately 2 000 g. Compared to the abundance of fish stocks associated with the Benguela region in the Western Cape (Randall 1983), food stocks in the Eastern Cape are unpredictable and can fluctuate seasonally (Ainley & Schlatter 1972, Randall 1983). The fledging weight results from this study found that chicks that hatched first from a double brood recorded a higher weight than their siblings and concur with the findings from other studies (Randall 1983, Seddon & van Heezik 1991a). Surprisingly, chicks from single broods recorded a lower fledging weight compared to first hatched chicks from double broods and also recorded no significant difference in fledging weight to the B-chicks. Prey availability, and the abundance thereof, can have a direct influence on the fledging weights of chicks (Duffy et al . 1984, Wilson 1985b), which is illustrated in the variance in weights of chicks at fledging (2 000 g - 3 900 g) (Randall 1983). Parental foraging experience and the type and quantity of prey fed to chicks can also influence final fledging weights (Adams et al. 1992).

c) Maximum weights and weight loss during chick growth Chicks from double broods are required to ‘share’ the feeding time and thus are expected to receive less quotas of food from the parents in respect to chicks from single broods. However, in this study the first hatched A-chicks attained a higher maximum weight than that of C-chicks during their time at the nest. Due to the un-predictability in the amount of feeding time, and thus the quota of food that the B-chick will receive whilst sharing with the

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A-chick (Randall 1983, Seddon & van Heezik 1991a), the B-chick recorded the greatest variance in maximum weights of the three chick groups.

After the chicks had achieved their maximum growth weights all the chicks in this study suffered a weight loss prior to fledging. Surprisingly, the C-chicks recorded the greatest loss (10.8%) with the B-chicks losing the least weight (7.89%). This suggests that Bird Island penguin chicks, regardless of body weight and clutch size, go through a starvation period prior to fledging. The loss in weight during the later stages of growth potentially explains why the greatest mortalities in chicks during the later growth stage is usually a result of starvation (Seddon & van Heezik 1991a).

The survival of chicks in a double brood that need to compete for food (more so for the B- chick than the A-chick) is determined by their ability to grow and fledge as quickly as possible. This ensures that when these chicks enter the starvation period (i.e. perhaps a strategy that induces chicks to fledge earlier), the remaining time spent at the nest is short and thus weight loss is kept to a minimum prior to fledging. Contrary to findings of Randall (1983), C-chicks on Bird Island delay fledging, recorded the lowest overall growth rates and experienced the greatest weight loss of all the chick groups. It is suggested that asynchronous breeding and the competition incurred between chicks of double broods increases their survivorship potential (i.e. a higher fledging weight) compared to that of solitary chicks.

5.4.2 Growth rate and survival of chicks African Penguin chicks generally experience a maximum growth period when they are aged between 15-30 days (Moreno et al. 1994). Slower growth rates are documented after day 30 (Ricklefs 1967) when chicks require an increased amount of food (Hockey 2001) and generally experience the greatest fluctuations in weight (Randall 1989). Similar results were found in this study where initially (day 1-24) the C-chicks recorded equally fast growth rates as the A-chicks. However, following day 24, the growth rate of the C-chick slowed whilst the A chicks continued to record fast growth rates and achieve higher fledging weights compared to the C-chicks (contrary to the findings of Randall 1983) and to their sibling B chicks (contrary to the findings of Williams & Cooper 1984).

Chick mortality during the later stages of growth is mainly caused from starvation as a result of parents not supplying sufficient food (Seddon & van Heezik 1991b). In this study the differences between the growth rates of the three types of chicks became less pronounced during the later stages of growth (i.e. crèche stage). This may have been the result of chicks being fed adequate quotas of food once both parents began foraging (Culik 1994). The

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discrepancies in growth recorded between the three chick types of this study occurred predominantly during the initial stages of growth and may have been the result of chicks not being fed adequate quotas of fish. However, if adults are able to supply chicks with sufficient food during the guard stage (up until day 30), the weight gained by chicks (entering into the crèche stage) and the rate of growth may influence whether chicks will survive or die during the later stages of growth. This is supported by the fact that the A- chicks were able to maintain a high growth rate until they fledged. Also, the chick from the single brood experienced the slowest overall growth rate, remained at the nest site for the longest, suffered the greatest weight loss prior to fledging, yet still fledged. This is because it initially obtained a similar weight to that of the A-chicks by day 30.

5.4.3 Growth rate used as an indicator of environmental conditions Chicks that are the last to hatch (i.e. B-chicks) have a greater chance of dying compared to the first hatched chicks (Seddon & van Heezik 1991a). In this study, the B-chick recorded the lowest weight of the successfully fledged chicks and up until day 30 recorded a similar weight to those chicks that failed to fledge. The likelihood that any chick will fledge can thus be determined using a once off weight measurement of the B-chick when it is 30.5 days old. The minimum critical weight that a chick would need to have obtained in order to avoid potential starvation and death during the later stages of growth is about 1 060 g on or before day 30.5. The quantity of food fed to chicks by adults prior to day 30.5 affects the growth rate and is thus critically important in determining whether a chick will successfully obtain a suitable weight to fledge.

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5.5 Conclusion It is clear from this study, and findings from similar studies (Randall 1983) on penguins in the Algoa Bay area, that penguins do not continuously reach similarly high fledging weights and thus do not fledge as soon as penguins from the Western Cape. The long growth period of penguin chicks from Algoa Bay allows the chicks to recover from weight loss if insufficient food was initially provided (Randall 1983). The findings from this study suggest otherwise. The fact that chicks from single broods as well as the B-chicks fledged on similar days, does not imply that the extended growth period of the C-chick is due to unfavourable food conditions. This is because these solitary chicks do not have to share or compete for food with another chick and should thus receive ample quotas of food in excess to what a B- chick would receive.

It is suggested that the reasons for the long growth period experienced by penguin chicks in Algoa Bay is a result of chicks not obtaining sufficient food during their initial stages of growth and thus it takes chicks longer periods of time to achieve a suitable fledging weight during the later stages of the growth cycle. More specifically, chicks may not recover from food deprivation experienced during their first 30 days of growth by remaining at the nest site for longer, as all chicks experience weight loss during the later stages of growth. For example, the chick from the single brood experienced the slowest overall growth rate, remained at the nest site for the longest, suffered the greatest weight loss prior to fledging, yet still fledged, because it initially obtained the critical weight. Quantity of food fed to chicks after hatching influences their overall growth rate and survival potential.

An alternative explanation is that certain un-fit or ill-adapted breeders that are marginal in their capabilities of raising offspring, already manifest itself in their chick weights which are usually below 1 060 g on day 30.5. Availability of prey stocks is considered to be the primary limiting factor which results in penguin chicks from Algoa Bay recording a slower growth and a poorer fledging weight to that of chicks raised in the Western Cape.

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6 GENERAL CONCLUSION African Penguins live in variable environments where large annual fluctuations in breeding conditions and prey abundance occur (Randall 1989). In evolutionary terms they may be in their last few moments of existence and could be extinct before 2040. Officially, the African Penguin population remains listed as vulnerable to extinction (BirdLife International 2005) but it seems that this conservation status could be revised to that of endangered to extinction. Population declines are presumed to be correlated with the over-fishing of the sardine and anchovy resources and possibly global climate change (Crawford et al . 1990, 2001b). Based on the present status of the South African fish stocks, and that every type of fishery in Algoa Bay is either under severe pressure or is in a state of collapse (Griffiths 1997a, b, 2000), it seems that an un-favourable environment for breeding exists for penguins at Bird Island. Efforts are underway to address the present shortages of fish and to ensure that favourable conditions of breeders exist however, the inadequate habitat available for breeding penguins also requires management and intervention. Although it seems sufficient area exists on Bird Island for penguin nests, it can hardly be considered as suitable to optimise breeding. Penguins do not select nest sites solely to avoid direct sunlight (i.e. those that are most sheltered) but ventilation of the nest site seems to be equally important. A concerted effort needs to be made to ensure that breeders from all colonies are provided with alternative nest sites that are cool, well-ventilated and protected. Breeders need to ensure that their own survival is not compromised whilst attempting to breed or raise offspring.

African Penguins will usually lay a 2-egg clutch (Randall 1983), however, during non- favourable conditions for breeding it is more likely that a higher frequency of 1-egg clutches are laid (Williams & Cooper 1984). This suggests that breeders that attempt to breed are already considered to be in healthy condition. Breeders in poorer condition may reduce their breeding efforts in order to avoid jeopardizing their own survival (Chastel et al. 1995, Erikstad et al. 1997, Olsson 1997) and hence may only lay a 1-egg clutch (Ankney & MacInnes 1978, Boutin 1990, Bolton et al. 1992). Breeders that are already under-nourished at the start of breeding would probably not have the expected nutritional reserves to sustain themselves during breeding (Yorio & Boersma 1994, Velando 2001) and are most likely to abort breeding sooner than those in a healthier condition (Dearborn 2001). This is supported by the fact that breeding failure was fairly similar to breeding success during the incubation stage for nests with a 2-egg clutch, however, breeding failure was substantially higher in nests with a 1-egg clutch. In addition, breeders are most likely to be in a poorer condition for breeding when prey resources are at their lowest (i.e. after the northward migration of sardines), which normally occurs after May in the Eastern Cape. This is why peak breeding

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attempts of the African Penguin in the Eastern Cape occurs from January – May coinciding with the abundance and availability of their prey resource (Crawford & Shelton 1978). Breeders raising chicks during a peak breeding attempt are able to optimise the favourable breeding conditions as opposed to replacement breeders that cannot (Crawford et al. 1995b, Crawford et al. 1999). This explains why a significant difference was recorded in the higher frequency of 2-egg clutches being laid during the peak breeding attempt as opposed to the replacement attempt where there was a higher frequency of inactive nests, and 1-egg clutches. Contrary to the above argument, penguins will usually lay two eggs (Randall 1983) regardless of whether adequate food stocks exist or not, simply because eggs are ‘cheap’ to produce.

The chick-rearing stage is a time when parental care involves substantial energy expenditure (Clutton-Brock 1991) and physiological stress on breeders peaks during this time (Bryant & Westerterp 1983). Breeders that attempt to raise chicks are inhibited from maintaining their own body condition because foraging excursions are restricted by time spent at the nest (Partridge & Harvey 1985, 1988). Due to additional food demands, it is more difficult for breeders attempting to raise chicks from a double brood and to maintain their own body condition. It is thus expected that failure within a double brood would occur more frequently than in a single one. On the contrary, no significant difference was found in the proportion of chick failures between single and double broods during the chick-rearing stage. It was found that, chicks from a nest with only a single chick failed to fledge more often than the single chicks from a 2-egg clutch. Even with the greater breeding demands placed on adults raising a double brood they are able to persist longer with breeding than those raising a single brood. In support of this argument, Williams & Croxall (1991) found that breeders that deserted nests weighed less than those that successfully completed breeding. Breeders that were well maintained (weight) were found to invest more energy into their offspring (i.e. heavier eggs not necessarily more clutches) than those that were not (Wright & Cuthill 1989, Chastel et al. 1995). Chick survival is thus greatly influenced by the breeding period in which they are raised (Randall 1983, 1989, Crawford et al. 1999) and by the body condition in which they fledge (Seddon & van Heezik 1991a).

The number of chicks that survive after fledging is important for the future recruitment of juveniles into the breeding population. Penguin chicks that are able to grow quickly and fledge with a higher weight have a better chance of survival. This ensures that when these chicks enter the starvation period (i.e. perhaps a strategy that induces chicks to fledge quickly), the remaining time spent at the nest is short and thus weight loss is kept to a minimum prior to fledging. Contrary to the findings of Randall (1983), chicks from single

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broods on Bird Island delayed fledging, recorded the lowest overall growth rates and experienced the greatest weight loss of all groups, yet fledged successfully. This is because they achieved in excess of the critical weight (i.e. 1 060 g) by day 30.5 of their growth cycle. To avoid starvation and possibly death in the later stages of growth, a critical weight of 1060 g is needed before day 30.5. The quantity of food fed to chicks by adults during the initial stages of growth is critical in determining whether a chick will successfully obtain a suitable weight in order to fledge.

Only if chicks adequately obtain a critical weight before day 30.5, does asynchronous breeding and the competition incurred between chicks of double broods increase their survivorship potential compared to that of chicks from single broods. Un-fit or ill-adapted breeders that are marginal in their capabilities of raising offspring, already manifest in a small clutch size and offspring that cannot obtain adequate weights during the initial stages of growth. The asynchronous breeding strategy also benefits the breeders when unfavourable breeding conditions occur because, the chicks that are last to hatch (i.e. B- chicks) have a greater chance of dying earlier on in the growth cycle compared to the first hatched chicks (Seddon & van Heezik 1991a). The death of one of the chicks during this initial stage of growth alleviates and prevents compounded rearing pressures on the breeding population, thus increasing the survival probability of the first hatched chick and ensuring that only the fittest birds breed. It is suggested that the asynchronous breeding strategy adopted by the African Penguin guarantees the fledging of at least one chick during unfavourable conditions and possibly two when conditions are favourable.

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APPENDICES

Appendix A: Nest Distribution CENSUS OF ACTIVE NESTS WITHIN THE IDENTIFIED HABITATS

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100

90

80

70

60

50

40

30

of Total HabitatTotal of CountNest 20

10 NestPercentage within each habitat locality 0 Mar May Aug Sep Dec Feb Mar May Aug Sep Dec Feb Feb Nov Feb Jun 1994 1994 1994 1994 1994 1995 2002 2002 2002 2002 2002 2003* 2003** 2003 2004 2004 Total Habitat Nest Count 1200 1075 525 275 400 1200 4359 1434 808 792 1266 1263 843 1232 712 783 Burrow 6.3 7.0 4.8 9.1 0.0 6.3 3.3 12.9 9.3 3.3 0.8 6.0 9.0 1.1 7.4 5.7 Houses 12.5 14.0 14.3 9.1 6.3 12.5 7.8 13.9 12.9 16.5 3.9 6.4 3.4 10.1 2.5 11.7 Surface 6 8.3 9.3 4.8 9.1 0.0 2.1 8.3 4.7 4.3 0.6 2.2 9.3 6.0 0.8 4.1 10.2 Surface 5 8.3 4.7 14.3 27.3 6.3 14.6 14.2 29.8 25.1 9.7 0.8 18.4 19.8 2.4 24.9 21.3 Surface 4 31.3 27.9 23.8 18.2 25.0 31.3 29.6 21.7 13.2 48.7 42.8 36.3 41.9 57.9 16.2 20.3 Surface 3 6.3 7.0 4.8 9.1 0.0 6.3 5.9 5.2 6.2 1.3 3.5 2.9 1.2 2.4 8.4 4.0 Surface 2 12.5 14.0 14.3 9.1 37.5 12.5 16.4 5.8 14.6 3.5 16.4 8.5 11.5 10.7 30.2 16.9 Surface 1 14.6 16.3 19.0 9.1 25.0 14.6 14.6 6.1 14.4 16.3 29.7 12.2 7.1 14.4 6.3 9.8

Figure 1: Nest count percentages of the total nest count for each habitat locality throughout the sampling period.

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Table 1: Nest count data recorded for each habitat locality. The abbreviations ‘S1-S6’ denote the ‘surface 1-surface 6’ localities.

Location S1 S2 S3 S4 S5 S6 Burrow Houses Count total Mar 1994 175 150 75 375 100 100 75 150 1200 May 1994 175 150 75 300 50 100 75 150 1075 Aug 1994 100 75 25 125 75 25 25 75 525 Sep 1994 25 25 25 50 75 25 25 25 275 Dec 1994 100 150 0 100 25 0 0 25 400 Feb 1995 175 150 75 375 175 25 75 150 1200 Mar 2002 636 714 256 1290 618 362 143 340 4359 May 2002 87 83 74 311 427 67 185 200 1434 Aug 2002 116 118 50 107 203 35 75 104 808 Sep 2002 129 28 10 386 77 5 26 131 792 Dec 2002 376 207 44 542 10 28 10 49 1266 Feb 2003* 154 107 36 459 232 118 76 81 1263 Feb 2003** 60 97 10 353 167 51 76 29 843 Nov 2003 178 132 30 713 30 10 14 125 1232 Feb 2004 45 215 60 115 177 29 53 18 712 Jun 2004 77 132 31 159 167 80 45 92 783

Table 2: Linear transformation of the nest density data. The abbreviations ‘S1-S6’ denotes the ‘surface 1-surface 6’ localities.

Date S1 S2 S3 S4 S5 S6 Burrow Houses Mar 1994 2.806 2.457 3.084 2.550 2.699 4.394 2.896 4.353 May 1994 2.806 2.457 3.084 2.327 2.006 4.394 2.896 4.353 Aug 1994 2.247 1.763 1.986 1.451 2.411 3.008 1.797 3.659 Sep 1994 0.861 0.665 1.986 0.535 2.411 3.008 1.797 2.561 Dec 1994 2.247 2.457 0 1.228 1.313 0 0 2.561 Feb 1995 2.806 2.457 3.084 2.550 3.259 3.008 2.896 4.353 Mar 2002 4.097 4.017 4.312 3.785 4.520 5.681 3.541 5.171 May 2002 2.108 1.865 3.071 2.363 4.151 3.994 3.799 4.640 Aug 2002 2.395 2.217 2.679 1.296 3.407 3.344 2.896 3.986 Sep 2002 2.502 0.778 1.069 2.579 2.438 1.399 1.836 4.217 Dec 2002 3.571 2.779 2.551 2.918 0.396 3.121 0.881 3.234 Feb 2003* 2.679 2.119 2.350 2.752 3.541 4.560 2.909 3.736 Feb 2003** 1.736 2.021 1.069 2.489 3.212 3.721 2.909 2.709 Nov 2003 2.823 2.329 2.168 3.192 1.495 2.092 1.217 4.170 Feb 2004 1.448 2.817 2.861 1.368 3.270 3.156 2.549 2.232 Jun 2004 1.985 2.329 2.201 1.692 3.212 4.171 2.385 3.864

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Aspects of the breeding biology of the African Penguin on Bird Island, Algoa Bay Page 109

7 6 Surface 1 Surface 2 6 5

5 4 4 3 3 2 2

1 1

0 0

* * 4 4 5 3 3 5 2 ** 3 4 9 94 02 02 04 94 94 94 02 02 02 3 0 99 9 0 0 03 * 00 0 9 9 9 0 0 0 0 00 0 1 19 0 2 2004 1 1 2 0 2 2 ar 1994 y g b 199 2 v n y g 1994 c g 2 c 2 v n a b u a u e u e b o u M M Au Sep 1994Dec 1 Fe Mar 2 May 2002Aug 2002Sep 2 Dec 2002Feb 200 e No Feb 2 J Mar 1994M A Sep 1 D Feb 199Mar 2 May 200A Sep 2002D e N Feb 2004J F Feb 2003F *

8 5 Surface 3 Surface 4 7 4 6

5 3 4 2 3

2 1 1

0 0

4 4 4 4 2 2 * * 3 4 4 4 5 * 4 4 9 9 0 0 * 0 0 9 94 94 02 02 02 03 0 99 0 002 0 9 9 9 0 002 0 0 3 * 0 1994 19 1 19 2 2 20 003 2 199 1 1 2 2 00 2 20 r c r y 2002 c 2 v 20 n r y c y c 2 v a e eb 1995 a a e o eb 2004 a a eb 199 a eb 200 M F Mar 2 b F Jun M May Aug 199Sep D F M M Aug 2002Sep D Feb 2003eb N F Ju M Aug 1 Sep 1994De M Aug 2 Sep 2002De Feb 2003e * No F F Figure 2a: Nest density (nests per 100 m²) for each locality throughout the study period.

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Aspects of the breeding biology of the African Penguin on Bird Island, Algoa Bay Page 110

10 35 Surface 5 9 Surface 6 30 8 7 25

6 20 5 15 4

3 10 2 5 1 0 0

4 4 2 2 2 3 4 4 4 4 2 2 3 4 9 9 0 0 0 3 * 0 0 9 9 9 95 02 0 0 0 0 9 994 9 0 0 002 0 0 0 0 9 9 9 0 002 0 03 ** 0 0 1 1994 1 2 2 0 2004 2 1994 1 2 2 2 2 r r 2 2 1 0 a y g a y 2003 ** b y b g p 2 v b a eb 1995 ep 2 b b ov 2 e a ec b o M M Au Sep 1994Dec 1 F M Ma Aug S Dec 2002 N F Jun Mar 1994M Aug 1 Sep 19 D Fe Mar 2 May 2002Au Se Dec 20 Feb 2003 * N Fe Jun 2004 Fe Fe Fe

5 20 Burrow Houses

4 15

3 10 2

5 1

0 0

4 * 3 4 4 5 4 4 9 2 3 * 0 0 9 9 02 0 9 9 0 0 3 * 0 0 994 9 9 002 0 994 9 1995 2002 002 0 0 0 2 1994 1 2002 2 1 1994 1 2 2 0 2 2004 r 1 1 r 2003 * p b 2 n a c b a ay g 1 e g b 2 eb e ec 2 b M Sep 1994D Fe M Sep 2002D Nov 2003Feb 2004Jun 20 Mar 1994M Au Se Dec F Mar May Au Sep 2002Dec 2002Fe Nov F Ju May 1994Aug May 2002Aug Feb Fe Feb 2003 ** Figure 2b: Nest density (nests per 100 m²) for each locality area throughout the study period.

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Appendix B: Chick Growth WEIGHT MEASUREMENTS OF CHICKS

Mark Shaun Ralph January 2008

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Table 3: Chick weight (grams) from initial nest observation day (day 0) to fledging day for C-chicks.

Day C017 C034 C042 C044 C055 C058 C060 C084 C113 C131 C132 C145 C152 C153 C154 C203 C240 C267 C289 C295 N 0 120 85 64 165 58 90 110 7 1 145 77 85 115 85 245 250 80 85 57 80 195 60 135 14 2 95 105 115 145 80 85 350 105 90 70 70 215 75 85 145 15 3 210 90 115 170 175 140 330 360 120 120 125 125 90 250 100 95 165 17 4 265 130 130 130 355 425 130 90 145 110 305 105 110 90 14 5 260 140 175 440 470 185 100 200 175 125 320 160 130 240 14 6 265 200 350 200 445 540 210 210 140 185 240 150 375 150 165 295 16 7 300 235 305 250 290 540 570 245 225 135 275 250 195 440 225 245 325 17 8 280 420 360 270 285 600 235 275 160 325 255 370 12 9 360 425 510 330 610 695 370 305 295 565 145 11 10 390 385 385 520 450 340 365 730 365 335 410 420 350 315 170 275 505 17 11 530 420 455 745 405 370 260 500 430 425 225 310 575 13 12 460 450 460 600 445 440 910 290 475 450 710 425 365 13 13 470 485 500 685 570 470 605 780 405 370 580 560 550 13 14 420 680 515 720 675 570 535 885 415 380 640 505 775 485 335 15 15 485 620 845 715 610 670 875 1060 500 480 435 625 715 590 765 695 430 570 645 19 16 495 715 685 830 680 735 885 580 490 820 740 685 865 570 760 15 17 750 785 890 860 765 750 925 985 560 745 720 475 505 13 18 615 700 925 880 855 885 1000 765 570 835 905 735 515 1075 14 19 675 810 815 800 1050 700 610 880 855 810 570 590 825 13 20 700 1075 925 720 650 840 850 920 550 855 1025 11 21 745 1075 880 1025 1125 790 750 900 890 860 925 905 750 730 975 15 22 810 925 1025 1150 925 950 1050 950 625 720 900 1050 890 950 620 1250 16 23 1050 890 1125 1175 1075 1125 1025 785 750 695 950 1100 900 1125 900 870 1025 17 24 1025 1100 1100 1025 1050 880 755 815 1000 915 845 880 975 13 25 895 1225 975 1150 1075 1225 880 800 755 1175 900 975 890 1000 975 15 26 1025 875 1275 835 815 865 1100 1275 1050 1125 10 27 975 1375 1025 1300 1150 1325 780 900 1200 1100 1225 1050 900 1100 1250 15 28 1150 1475 1100 1375 1300 1150 1100 900 875 895 1125 1275 1125 1075 1000 1300 16 29 1200 1500 1350 1050 1125 1250 1075 950 925 950 1150 1125 1250 1050 975 1050 1175 1375 18 30 1125 1350 1300 1025 1200 1250 1350 885 950 1375 1325 1275 1025 1175 1300 15 31 1350 1050 1400 1225 1275 1175 975 950 900 1325 1275 1300 1300 1150 1300 1275 16

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Day C017 C034 C042 C044 C055 C058 C060 C084 C113 C131 C132 C145 C152 C153 C154 C203 C240 C267 C289 C295 n 32 1325 1550 975 1575 1400 1150 1300 1400 1025 950 1200 1250 1100 1275 1150 1525 16 33 1425 1700 1200 1625 1450 1550 1175 950 1150 1275 1425 1525 1175 1575 14 34 1850 1450 1375 1475 1600 1150 1025 1475 1275 1550 1425 1100 1450 13 35 1375 1900 1100 1675 1525 1325 1375 1750 1100 1075 1050 1450 1400 1400 1500 1200 1025 1475 18 36 1425 2050 1000 1675 1550 1350 1275 1750 1125 1100 1025 1400 1475 1575 1650 1450 1300 1075 1375 19 37 1550 1475 1650 1600 1575 1350 1925 1325 1150 1650 1275 1725 1875 1600 1350 1525 16 38 1525 1950 1375 1775 1675 1225 1675 1300 1350 1575 1300 1900 1675 1375 1375 15 39 1700 2200 1175 1775 1625 1550 1400 1800 1525 1400 1250 1500 1800 1575 14 40 1600 2000 1200 1500 1475 1725 1725 1300 1325 1600 1225 1725 1725 1100 1350 15 41 1775 2195 1425 1775 1575 1350 1675 1625 1250 1350 1875 1525 1800 1925 950 1450 16 42 1750 2175 2025 1575 1550 1775 1225 1400 1450 1850 1300 1750 1825 1450 1225 1700 16 43 2025 2300 1250 1975 1850 1425 1250 1800 1925 1325 1500 1850 1525 1850 1875 1675 1475 1725 18 44 1725 2050 2200 1725 1200 1925 1950 1350 1975 1575 1875 2100 1725 1675 1750 15 45 2000 2050 1375 2050 1800 1975 1225 2025 1250 1575 1975 1650 1950 1975 2050 1900 16 46 1650 2175 2150 2000 1925 1475 1700 1475 1950 1675 2375 1925 1575 2175 14 47 2200 2450 1475 2325 1900 1350 2200 1675 1525 1450 2100 1725 2175 1950 2100 2075 16 48 2250 2375 1625 2325 2025 1375 2200 1850 1725 1725 1575 2000 1750 2225 1600 1550 2075 17 49 2500 1800 2375 2275 1450 2150 1975 1650 2400 2125 2025 2325 1700 13 50 2200 1600 2450 2325 1925 1525 2325 1725 1850 1575 2150 2300 1925 2175 1500 1675 1950 17 51 1725 2550 2000 1525 2275 1775 1825 2200 2425 2375 1525 1575 2125 13 52 2425 1900 1825 2400 1650 1975 1550 2225 1650 2525 2250 1875 1975 13 53 2325 2575 2475 2375 1700 2425 1775 2025 2325 1575 2275 11 54 2525 2725 2400 2075 1775 2175 1650 1525 2300 1650 2025 11 55 2375 2750 1700 2275 2400 1650 2350 2075 2000 1775 1825 2450 2525 1475 2175 15 56 2625 2725 1600 2325 2425 1650 2300 1850 1800 1575 2350 2675 1725 2275 14 57 1725 2300 2600 1850 2575 2450 2050 2300 2525 2525 2775 2550 1600 2000 2075 15 58 2875 1625 2550 2575 1900 1825 2700 2300 2000 2800 1975 2650 2550 2375 2000 2175 16 59 3175 1700 2450 2050 2050 2800 2350 2025 2550 2025 2750 2000 2650 1825 2275 2100 16 60 2450 3075 2575 2575 2400 2050 2650 2100 2150 2125 2025 2475 1850 2450 2225 15 61 2350 3075 1600 2575 2450 2475 2475 2200 2000 2575 2575 2250 2475 2825 14 62 2625 1800 2675 2775 2350 2375 2300 2750 2325 2025 2475 2525 12 63 2975 1800 2725 2550 2450 2475 2225 2325 2675 2250 2425 2300 2600 13 64 2400 3300 1925 2525 2400 2150 2350 2650 2675 2150 2225 2675 2250 2225 2225 2400 16 65 2675 2800 2300 2550 2900 2425 2525 2650 2200 2700 2975 2725 2425 2100 2875 15

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Day C017 C034 C042 C044 C055 C058 C060 C084 C113 C131 C132 C145 C152 C153 C154 C203 C240 C267 C289 C295 n 66 2725 2625 2725 2850 2400 2775 2475 2300 2725 2350 3225 2500 2375 2075 2525 15 67 2000 2150 3075 2625 2300 2650 2275 2950 2800 1900 2625 2500 12 68 2475 2925 2600 2750 2650 2250 2825 2475 2500 2675 10 69 2425 3200 1975 2550 2850 2125 2400 2550 8 70 2650 1975 2650 2425 2275 2500 2600 2600 2025 2250 2575 2675 2775 2550 14 71 3450 2025 2300 3125 2450 2775 2025 2900 2275 2800 2775 2200 2700 2525 14 72 3050 3125 2275 2125 2375 2625 2550 2725 2700 2950 2325 2650 2550 13 73 2750 3325 1825 2350 1975 2575 2400 2375 2725 2650 2350 2725 12 74 3200 3475 1850 2200 1875 2700 2875 2650 2425 2500 2775 1850 2750 2600 2675 15 75 3175 3275 1800 2550 2775 2750 2625 2550 2025 2600 1825 2675 2600 2900 2450 15 76 3000 3375 1700 2375 2075 2900 2900 2675 3075 2350 2725 2175 2400 2600 3150 2625 16 77 3200 3500 1625 2175 2125 2925 2575 2775 2150 2950 2700 2675 2825 2450 2700 15 78 3325 3225 1850 2725 2425 2775 3025 2550 2775 2675 2725 2550 2625 2700 2375 2500 16 79 3250 3250 2075 2425 2150 2850 2600 2775 2875 2750 2875 2750 2950 2700 2700 2525 16 80 3075 3075 2000 2375 1900 2500 2750 2800 2950 2675 2650 2725 2625 2675 2375 15 81 3650 3025 2900 2475 2825 2850 2550 2925 2750 2725 10 82 3200 3475 2525 1775 3075 2900 2775 2350 2725 2850 2650 2800 12 83 3425 3300 2075 2500 3175 2650 2400 2775 2500 2575 2850 11 84 3475 3300 2250 2475 3325 2625 2800 2325 2750 2700 2900 2475 2525 13 85 3550 3325 2025 3275 2500 2900 2450 2425 2775 2900 2675 2575 12 86 3300 2600 1775 3250 2725 3025 2400 2425 2725 2425 2525 11 87 1850 2775 1675 3300 2875 2850 2425 2550 2650 9 88 1875 2700 3250 2900 2725 2750 2425 2850 8 89 3375 1725 2175 2625 3000 2525 2475 2225 8 90 3450 2025 2175 3275 2725 2925 2700 2350 2605 9 91 3800 3400 2225 3 92 2175 2125 2 93 2000 3325 2075 2250 4 94 2075 2200 2 95 2375 2175 2050 3 96 2275 1975 2 97 3675 1925 2625 3 98 3425 2400 2350 3 99 3350 2150 2

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Day C017 C034 C042 C044 C055 C058 C060 C084 C113 C131 C132 C145 C152 C153 C154 C203 C240 C267 C289 C295 n 100 3250 2300 2475 3 101 2475 1 102 2300 1 103 2175 1 104 2275 1 105 2250 1 106 0 107 0 108 2125 1 109 2300 1

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Table 4: Chick weight (grams) from initial nest observation day (day 0) to fledging day for A-chicks.

Day A013 A022 A036 A041 A049 A093 A112 A134 A151 A195 A243 n 0 80 80 80 69 4 1 130 69 100 71 95 125 85 80 60 9 2 110 70 125 150 59 100 70 7 3 150 71 145 165 85 120 90 68 8 4 185 150 115 195 105 170 185 130 85 9 5 215 210 195 250 260 105 195 130 110 9 6 250 260 260 290 140 255 235 145 8 7 300 280 250 165 170 5 8 350 320 275 320 210 330 230 205 8 9 395 420 470 240 395 365 285 250 8 10 410 445 390 450 320 480 380 315 270 9 11 525 465 490 395 565 340 495 430 360 9 12 530 500 555 480 505 595 395 7 13 580 575 535 740 575 410 610 450 8 14 660 580 585 795 545 440 590 585 525 9 15 755 610 685 560 900 780 640 545 525 9 16 650 670 600 910 675 750 620 635 8 17 805 690 680 630 900 705 655 665 665 9 18 815 650 775 630 715 5 19 900 795 710 1100 810 895 700 7 20 950 900 810 765 1000 800 680 7 21 975 925 1200 950 860 900 725 795 8 22 950 975 815 850 830 950 785 875 8 23 855 875 1225 950 975 925 885 875 8 24 1125 810 925 1350 975 895 1025 950 925 9 25 1000 860 925 950 900 1025 885 925 1000 9 26 1100 1225 880 1375 1000 950 1000 7 27 1150 1200 1450 1100 1275 915 1000 7 28 1150 1025 1100 1500 1000 1300 1025 1125 8 29 1225 1100 1100 1475 1150 1400 1100 1025 1050 9 30 1375 975 1175 1625 1250 1425 950 1100 8 31 1400 1050 1225 1250 1150 1350 1050 1225 8 32 1325 1500 1225 1150 1175 1125 1150 7 33 1250 1500 1150 1600 1150 1250 1250 1150 1275 9 34 1425 1200 1200 1300 1700 1375 1150 7 35 1375 1325 1700 1250 1300 1725 1425 1075 1250 9 36 1525 1350 1775 1400 1775 1500 1075 1375 8 37 1625 1525 1600 2000 1825 1400 1100 1275 8 38 1625 1575 1500 1925 1500 1450 1850 1250 1100 1400 10 39 1775 1600 1450 1925 1525 1400 1625 1250 1425 9 40 1625 1650 1600 1400 1400 1225 6 41 1775 1650 1750 1725 2225 1625 1500 2150 1550 9 42 1775 2250 1625 1550 2350 1575 1600 7 43 1800 1600 2225 1575 1775 1550 6 44 2025 1800 1800 2350 1675 2300 1775 1375 1700 9 45 1925 1625 1750 1950 2625 2075 2400 1775 1575 1675 10 46 2175 1875 1750 2000 1775 2425 1950 1575 1600 9 47 2050 1975 1850 2100 2075 1775 2400 1675 8

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Day A013 A022 A036 A041 A049 A093 A112 A134 A151 A195 A243 n 48 2175 1725 2025 2600 2200 1825 2525 1725 8 49 2050 2200 2000 2625 2275 1950 2675 7 50 2075 2050 2250 2575 2050 2600 1925 1900 8 51 2275 2150 1900 2125 2800 2775 2275 1925 8 52 2275 2100 2075 2075 2725 2300 2700 2100 1725 1900 10 53 2425 2225 2100 2375 2175 1900 2025 7 54 2350 2275 2150 2375 2225 1950 2050 7 55 2300 2400 2050 2275 2650 2525 2250 2555 2025 9 56 2300 2525 2225 2775 2900 2375 2475 7 57 2425 2425 2250 2550 2525 2400 3075 2200 8 58 2325 2325 2675 2975 2550 3000 2200 2225 2275 9 59 2325 2275 2500 2925 2725 2225 2200 7 60 2450 2400 2500 2875 2900 2325 2325 2325 8 61 2375 2475 2325 2850 2925 2325 2925 2250 2175 2350 10 62 2475 2550 2500 2975 2875 3025 2300 7 63 2575 2925 3025 2300 2350 5 64 2550 2825 2900 2325 2925 2300 2475 2375 8 65 2925 2975 3075 2350 2725 2400 6 66 3000 2525 2875 3025 2375 2525 6 67 2800 2525 3150 2350 2450 2625 2475 7 68 2825 3000 3025 2425 2775 2450 2525 2475 8 69 2275 2425 3150 2400 2775 2650 2400 7 70 2150 3150 3025 2350 3025 2550 2425 2400 8 71 2275 3350 2375 2700 2375 2500 6 72 2225 2325 2875 3275 2825 2675 2600 7 73 2375 2775 3250 3125 2425 3000 2600 2650 8 74 2775 2350 2650 3175 2700 2625 2650 7 75 2175 2825 2725 2525 3100 2575 2525 2825 8 76 2775 3175 2975 2675 2550 5 77 2550 3425 2650 2675 2575 2650 6 78 2325 2625 3500 2550 3075 5 79 2200 2450 3200 3025 4 80 2275 2850 2425 3175 2875 5 81 2225 2525 2300 2975 2500 2425 6 82 2250 2575 3150 2500 2725 5 83 2200 2950 2425 2575 3275 2575 6 84 2125 2975 2625 3375 2950 2675 6 85 2675 2475 2650 3 86 2950 2475 2800 2750 4 87 2775 2325 2600 2700 4 88 2275 2475 2650 3 89 0 90 2350 1

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Table 5: Chick weight (grams) from initial nest observation day (day 0) to fledging day for B-chicks.

Day B013 B022 B036 B041 B049 B093 B112 B134 B151 B195 B243 n 0 50 125 2 1 59 71 67 63 110 70 6 2 77 63 66 80 77 120 105 58 8 3 120 88 69 85 90 100 175 105 64 9 4 135 115 140 110 120 105 105 215 90 9 5 80 165 130 135 120 145 250 105 8 6 215 105 160 215 300 185 135 7 7 250 255 245 210 360 235 170 7 8 285 285 230 250 220 255 190 7 9 305 215 340 305 230 290 280 490 380 245 10 10 410 345 265 355 225 315 285 7 11 415 350 285 435 295 360 620 320 8 12 450 370 360 485 350 415 645 370 8 13 515 445 385 560 590 300 415 635 470 465 10 14 620 520 570 670 385 455 795 555 445 9 15 500 545 595 755 410 555 500 590 8 16 615 620 550 810 445 475 565 7 17 650 580 640 800 505 495 900 625 620 9 18 705 695 520 710 875 5 19 835 580 650 1000 545 950 720 7 20 855 860 640 675 950 660 575 735 1100 9 21 845 725 1075 600 750 820 815 7 22 925 700 755 640 725 770 880 745 8 23 925 740 1150 640 850 900 780 7 24 900 1025 740 1225 670 710 880 950 845 9 25 975 975 745 925 675 825 975 1050 860 9 26 1025 1050 770 925 1175 780 975 1050 1025 9 27 1000 1075 975 1275 865 1025 1025 975 8 28 1125 1000 1275 850 1125 1100 1075 925 8 29 1100 900 1275 900 950 1225 1200 950 8 30 860 1600 975 925 1075 1200 1150 7 31 1250 900 875 950 975 5 32 1150 1075 1100 925 1175 1175 1150 7 33 1375 1275 1050 1100 1450 950 1375 1400 1225 9 34 1200 1050 1275 950 1075 1450 1285 1275 1075 9 35 1350 1200 1600 1075 1100 1400 1175 1225 8 36 1200 1575 1100 1450 1500 1200 1125 7 37 1450 1300 1275 1775 1100 1150 1450 1600 1200 1200 10 38 1250 1400 1700 1225 1150 1525 1425 1225 8 39 1525 1500 1325 1675 1400 1200 1500 1400 8 40 1600 1400 1400 1300 1250 1650 1650 7 41 1625 1575 1475 1425 1925 1300 1800 1625 1400 9 42 1575 1650 1975 1325 1775 1350 6 43 1825 1700 1800 1375 1825 1850 1550 1400 8 44 1675 1600 1800 1975 1675 1425 1875 1775 1600 1400 10 45 1875 1850 1525 1675 2200 1600 1525 1925 1725 1350 10 46 1900 1700 1625 1675 1650 1625 1875 1925 1425 9 47 1975 1950 1875 1875 1725 1875 1900 1550 8 48 1925 1975 1700 1850 2175 1800 2000 1925 8 49 1975 2075 1900 2225 1775 1975 2050 1625 8 50 2200 2100 1875 2275 1775 2175 1650 7

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Day B013 B022 B036 B041 B049 B093 B112 B134 B151 B195 B243 n 51 2100 2250 1900 2025 2500 1800 1875 1975 1725 1675 10 52 2350 2300 2075 1900 2375 1825 2075 1850 1750 9 53 2225 2250 2500 2000 2125 2175 1975 1750 8 54 2225 2025 2175 2675 2000 2500 2400 1900 8 55 2225 2025 2075 2350 2400 1850 2325 7 56 2275 2075 2200 2375 2700 1925 2150 2200 1725 9 57 2125 2350 2400 1975 2075 2100 1750 7 58 2275 2350 2700 2075 1650 5 59 2350 2675 2100 2150 1675 5 60 2375 2475 2675 2150 2125 2300 2075 1700 8 61 2450 2350 2500 2650 2175 2200 2400 2250 2300 9 62 2525 2475 2550 2650 2775 2250 2150 2400 2275 2325 10 63 2425 2575 2700 2150 2450 2175 2475 1575 8 64 2250 2575 2750 2350 2200 2125 2550 1625 8 65 2825 2250 2400 3 66 2325 2900 2125 2175 2525 1750 6 67 2500 2425 2275 2325 2375 2500 1800 7 68 2075 2900 2450 2450 1825 5 69 2050 2425 2600 2450 2225 2500 2325 1800 8 70 2075 1975 2400 3025 2175 2325 1800 7 71 2075 2075 2375 3150 2350 2275 1850 7 72 2025 2500 2375 3075 2550 2300 2550 1900 8 73 1875 2500 3075 2550 2400 2400 2575 1875 8 74 2150 2375 2625 2350 2225 2600 2075 7 75 2425 2275 2575 2250 2450 5 76 1800 3100 2525 2225 2425 2025 6 77 2175 3325 2200 2675 2250 5 78 2100 2050 3350 2325 4 79 2175 2100 2300 2225 3300 2725 2425 2025 2400 9 80 2200 2075 2200 2275 2525 2350 2025 2375 2250 9 81 2150 1900 2275 2325 2700 2550 6 82 2125 2200 2200 2100 2475 2225 6 83 2000 2075 2225 2225 3050 2525 2250 2575 8 84 1925 2025 2125 3275 4 85 2025 2550 2000 3425 2900 2550 2725 2275 8 86 1975 2525 2400 3 87 1950 3500 2675 2400 2275 5 88 1800 2375 2900 2300 4 89 1775 3525 2775 2350 4 90 2175 2225 2 91 1650 2275 3400 3 92 1600 2375 3425 2775 4 93 2375 2925 2 94 2450 1 98 2025 1 99 2100 1 100 2225 1 101 2350 1 103 2500 1 104 2525 1 105 2375 1 107 2675 1 110 2250 1 112 2450 1 113 2625 1

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Table 6: Chick weight (grams) from initial nest observation day (day 0) to mortality day for chicks that died.

Day C261 A146 B083 B146 B258 n 0 72 95 64 70 63 5 1 72 70 63 3 2 105 95 64 72 80 5 3 115 115 71 95 4 4 110 130 70 125 4 5 165 120 135 3 6 135 120 2 7 250 230 135 245 4 8 160 285 2 9 325 225 2 10 325 370 340 3 11 425 390 360 3 12 365 465 410 310 495 5 13 480 455 395 575 4 14 540 535 390 650 4 15 535 590 450 695 4 16 405 720 675 655 4 17 570 680 670 3 18 705 700 815 3 19 620 560 735 3 20 770 860 645 880 4 21 875 750 2 22 620 775 925 3 23 815 740 975 3 24 765 895 950 3 25 630 925 840 1025 4 26 805 865 900 1075 4 27 975 845 1100 3 28 950 1000 900 1200 4 29 900 1225 2 30 925 925 2 31 1075 1075 1200 950 4 32 1200 1100 1100 1000 1275 5 33 1150 1225 1100 3 34 1075 1225 1025 1425 4 35 1325 1075 1225 1025 1375 5 36 1400 1175 1300 1050 1525 5 37 1325 1125 1300 1075 1475 5 38 1125 1225 1450 3 39 1200 1150 1300 1250 4 40 1150 1225 1325 1725 4 41 1325 1100 1250 1700 4 42 1350 1300 1100 1375 1625 5 43 1450 1350 975 1250 1750 5 44 1300 1375 1900 3 45 1375 1 46 1400 1000 2 47 1450 925 1900 3 48 950 975 1375 1925 4

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Day C261 A146 B083 B146 B258 n 49 1000 1000 1500 2150 4 50 1000 1050 1475 1950 4 51 1425 1925 2 52 1025 1525 2 53 1550 1100 2 54 1075 1100 2150 3 55 2150 1 56 1125 1325 2 57 1050 1375 2150 3 58 1075 1175 1475 2250 4 59 975 1475 1100 1475 2275 5 60 1625 1075 2275 3 61 890 1850 1250 2350 4 62 925 1750 1275 1525 2500 5 63 1275 2375 2 64 1375 2375 2 65 925 1850 1625 2500 4 66 1400 1625 2 67 1125 1625 2475 3 68 1200 2000 1850 3 69 2025 1600 1900 2650 4 70 1225 2050 1525 1800 2525 5 71 1250 2300 1675 1975 2525 5 72 1450 2350 1625 1975 2500 5 73 2250 1 74 2375 1900 2 75 2425 1900 2025 3 76 2025 1 77 1550 2325 2025 1925 4 78 1625 2475 1925 2000 4 79 1900 1 80 2425 1800 2 81 2500 1750 2 82 1575 2375 2125 3 83 2375 2175 2 84 2250 2300 2 85 1525 1550 2 86 1600 2125 1675 3 87 1500 1575 2 88 1650 2025 1650 3 89 1375 1 90 1675 2000 2225 3 91 1600 2125 1850 3 92 2125 2050 2 94 1525 1750 2 95 2225 1 96 1975 1975 2 97 1775 2025 1775 3 98 2125 1750 2 99 1975 2175 1925 3 100 2075 2025 1725 3 101 2050 1625 2 102 1950 1950 2 103 2025 1925 1550 3 104 2000 1850 1475 3 105 1750 1425 2

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Day C261 A146 B083 B146 B258 n 106 2375 1675 2 107 2200 1 109 2200 1 112 2200 1 113 2250 1 114 2350 1 115 2375 1 116 2200 1 117 2175 1 118 2250 1 119 2450 1 121 2325 1 122 2600 1 123 2250 1

Mark Shaun Ralph January 2008

Aspects of the breeding biology of the African Penguin on Bird Island, Algoa Bay Page 123

Table 7: Summary of the best fit chick growth equation per chick with the determined growth constant (K) and correlation coefficient (r) for the fitted growth curves (Logistic, Gompertz, von Bertalanffy).

Best Fit curve Correlation coefficient (r) Growth constant (K) (i.e. highest Clutch correlation von von Day Wt Wt Wt W ID size Fledged value) Logistic Gompertz Bertalanffy Logistic Gompertz Bertalanffy n fledge fledge min max asymptote C261 single no von Bertalanffy 0.8877 0.9080 0.9115 0.0391 0.0233 0.0038 58 84 2125 130 2575 3678.85 A146 double no von Bertalanffy 0.9462 0.9821 0.9864 0.0576 0.0348 0.0058 55 75 2600 72 2700 3461.82 B083 double no von Bertalanffy 0.8949 0.9377 0.9450 0.0252 0.0139 0.0022 77 123 2250 72 2600 3765.03 B146 double no von Bertalanffy 0.9410 0.9786 0.9847 0.0414 0.0222 0.0035 59 84 2250 95 2500 4010.61 B258 double no von Bertalanffy 0.8619 0.9120 0.9211 0.0294 0.0167 0.0027 77 106 1675 64 2300 3336.28 C017 single yes von Bertalanffy 0.9540 0.9779 0.9811 0.0403 0.0227 0.0036 72 100 3250 120 3800 5308.17 C034 single yes von Bertalanffy 0.9356 0.9697 0.9736 0.0559 0.0351 0.0059 61 86 3300 77 3500 4117.13 C042 single yes von Bertalanffy 0.8623 0.9034 0.9132 0.0313 0.0167 0.0026 72 90 2025 85 2625 3928.34 C044 single yes von Bertalanffy 0.9546 0.9778 0.9801 0.0573 0.0368 0.0062 49 70 2650 115 2725 3463.35 C055 single yes von Bertalanffy 0.8949 0.9268 0.9319 0.0399 0.0238 0.0039 72 88 2700 85 2850 3941.96 C058 single yes von Bertalanffy 0.8440 0.8694 0.8745 0.0307 0.0168 0.0027 68 105 2250 80 2550 4033.61 C060 single yes von Bertalanffy 0.9249 0.9725 0.9806 0.0383 0.0185 0.0028 66 93 3325 64 3400 6276.62 C084 single yes Gompertz 0.9680 0.9800 0.9792 0.0445 0.0275 0.0046 56 79 2850 165 3125 4182.65 C113 single yes von Bertalanffy 0.9493 0.9667 0.9693 0.0363 0.0232 0.0039 58 82 2900 250 2900 3910.05 C131 single yes von Bertalanffy 0.9441 0.9789 0.9829 0.0442 0.0241 0.0038 76 90 2725 58 2875 4415.91 C132 single yes von Bertalanffy 0.9624 0.9873 0.9887 0.0483 0.0274 0.0044 68 90 2925 85 3075 4182.65 C145 single yes von Bertalanffy 0.9015 0.9352 0.9405 0.0424 0.0239 0.0039 68 97 1925 57 2525 3450.55 C152 single yes von Bertalanffy 0.9513 0.9775 0.9800 0.0542 0.0345 0.0058 59 84 2750 80 2950 3551.50 C153 single yes von Bertalanffy 0.9094 0.9421 0.9488 0.0384 0.0211 0.0033 60 76 2175 125 2700 4168.14 C154 single yes von Bertalanffy 0.8788 0.9136 0.9207 0.0415 0.0217 0.0034 63 89 2475 70 3225 4746.99 C203 single yes von Bertalanffy 0.9382 0.9535 0.9550 0.0429 0.0283 0.0048 62 87 2550 195 2800 3541.53 C240 single yes von Bertalanffy 0.9353 0.9695 0.9744 0.0487 0.0300 0.0050 73 90 2700 75 3150 3808.53 C267 single yes von Bertalanffy 0.8728 0.9113 0.9189 0.0331 0.0185 0.0030 74 109 2300 60 2750 3928.85 C289 single yes von Bertalanffy 0.9259 0.9570 0.9608 0.0449 0.0249 0.0040 56 86 2425 90 2800 4285.48 C295 single yes von Bertalanffy 0.9256 0.9578 0.9629 0.0422 0.0261 0.0044 76 90 2605 110 2875 3710.22

Mark Shaun Ralph January 2008

Aspects of the breeding biology of the African Penguin on Bird Island, Algoa Bay Page 124

Best Fit curve Correlation coefficient (r) Growth constant (K) (i.e. highest Clutch correlation von von Day Wt Wt Wt W ID size Fledged value) Logistic Gompertz Bertalanffy Logistic Gompertz Bertalanffy n fledge fledge min max asymptote A036 double yes von Bertalanffy 0.8847 0.9217 0.9282 0.0419 0.0217 0.0034 62 88 2275 70 2925 4780.03 A041 double yes von Bertalanffy 0.9499 0.9837 0.9875 0.0582 0.0370 0.0063 62 84 3375 80 3500 3987.03 A049 double yes Gompertz 0.9655 0.9825 0.9808 0.0541 0.0331 0.0055 62 84 2950 80 3175 4109.62 A093 double yes von Bertalanffy 0.9563 0.9847 0.9870 0.0621 0.0384 0.0064 60 81 2500 59 2650 3134.27 A112 double yes Gompertz 0.9512 0.9698 0.9681 0.0684 0.0441 0.0075 50 78 3075 69 3075 3558.89 A134 double yes von Bertalanffy 0.9506 0.9831 0.9873 0.0504 0.0280 0.0045 53 77 2675 80 3000 4149.89 A151 double yes von Bertalanffy 0.9311 0.9637 0.9677 0.0447 0.0260 0.0042 60 90 2350 70 2800 3867.59 A195 double yes von Bertalanffy 0.9439 0.9827 0.9884 0.0513 0.0297 0.0048 67 88 2650 60 3025 3782.98 A243 double yes von Bertalanffy 0.9551 0.9888 0.9926 0.0479 0.0304 0.0051 65 91 3100 90 3200 3818.50 A013 double yes von Bertalanffy 0.9452 0.9752 0.9788 0.0492 0.0314 0.0053 61 87 2775 69 3000 3670.44 A022 double yes von Bertalanffy 0.9460 0.9748 0.9780 0.0509 0.0307 0.0051 61 83 2425 80 2725 3455.48 B013 double yes von Bertalanffy 0.8713 0.8935 0.8980 0.0365 0.0195 0.0031 58 84 1925 120 2525 4274.69 B022 double yes von Bertalanffy 0.8051 0.8401 0.8485 0.0329 0.0147 0.0021 66 92 1600 50 2475 5402.33 B036 double yes von Bertalanffy 0.9248 0.9574 0.9613 0.0505 0.0279 0.0044 60 85 2550 63 2575 3866.80 B041 double yes von Bertalanffy 0.8435 0.8702 0.8753 0.0275 0.0152 0.0024 77 113 2625 71 2675 4301.91 B049 double yes von Bertalanffy 0.9430 0.9855 0.9907 0.0522 0.0328 0.0055 65 92 3425 66 3525 4132.62 B093 double yes von Bertalanffy 0.9628 0.9891 0.9910 0.0499 0.0298 0.0049 66 93 2925 67 2925 3701.98 B112 double yes Gompertz 0.9730 0.9879 0.9851 0.0656 0.0422 0.0072 59 80 2350 63 2425 2751.47 B134 double yes von Bertalanffy 0.9596 0.9828 0.9845 0.0628 0.0402 0.0068 49 77 2675 100 2675 3109.42 B151 double yes von Bertalanffy 0.9146 0.9430 0.9474 0.0464 0.0297 0.0050 60 85 2550 110 2550 3015.39 B195 double yes von Bertalanffy 0.9285 0.9615 0.9659 0.0450 0.0275 0.0046 61 90 2225 70 2725 3495.54 B243 double yes von Bertalanffy 0.9293 0.9719 0.9794 0.0475 0.0278 0.0045 66 88 2300 58 2400 3030.02

Mark Shaun Ralph January 2008

Aspects of the breeding biology of the African Penguin on Bird Island, Algoa Bay Page 125

Mark Shaun Ralph January 2008