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ECOLOGY AND BEHAVIOR OF THE BLACK-AND-NHITE CASQUED HORNBILL (WWW) IN KIBALE FOREST, UGANDA

Jan Kalina

A DISSERTATION

Submitted to - Michigan State University in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Department of Fisheries and Wildlife

1988 5".

ABSTRACT

ECOLOGY AND BEHAVIOR OF THE BLACK-AND-NHITE CASOUED HORNBILL BXQANLSIES SUBQILINDRIQQS SQBQQADBAIQS) IN KIBALE FOREST, UGANDA

Jan Kalina

The ecology and behavior of the black-and-white casqued

hornbill (Bycanistgs subgyliggricus subguagggtgs) was studied in

logged and unlogged areas of Kibale Forest, Uganda (June l981-June

l984; l986 and 1987 breeding seasons). Hornbill (family

Bucerotidae) breeding behavior differs from that of other birds in

that the nest cavity entrance is sealed, with the female and young

imprisoned inside. This was the first long-term, intensive study of

an African forest hornbill species.

Hornbill movements, spatial dispersion, and habitat use varied

seasonally. Hornbills were present in selectively logged areas but

in lower numbers than in primary forest in the core of the Reserve. Hornbill movements were closely related to their diet.

Particularly during the dry seasons, hornbills traveled long

distances (> 6 km) in search of fruiting trees. These birds fed on

at least 67 fruit species. Fruits comprised 90% of the diet by

volume, with Eigus spp. comprising 57% of the volume of all fruits.

Seeds from most species of fruits were either regurgitated or Jan Kalina defecated and dispersed intact. Hornbills, therefore, mediated seed dispersal of rainforest trees.

Hornbills required very large trees (> 3 m circumference; n =

45) for nesting. Trees had large (> 25 cm depth), naturally formed cavities at a minimum height of 8 m above ground. Hornbill nest densities were highest in primary forest in .the center’ of the

Reserve, where the density of trees > 3 m circumference was greater and where the trees were, on average, much larger.

The number of young fledged per unit area was also highest in primary forest in the core of the Reserve. Reasons for nest failures were varied, but intrusions at nests by conspecifics often caused resident birds to abandon their nests. Competition for nest sites by hornbills was high. In this study, the nest-seal appeared to function primarily to prevent intra-specific competitors from entering the nest. Three other hypotheses concerning the function of nest-sealing are discussed.

Based on findings in this study, general lrecomnendations are made concerning timber-management practices which seem likely to affect the conservation of forest hornbills in Uganda and elsewhere in the tropics. Copyright by

JAN KALINA

1988 Dedicated to my family

and the memory of

Rebekah D. Fischer.

iv ACKNOWLEDGMENTS

I wish to acknowledge the President’s office, Uganda National

Research Council, and the Uganda Forest Department for permission to work in Kibale Forest. The New York Zoological Society, Sigma Xi, and the American Museum of Natural History’s Frank M. Chapman

Memorial Fund provided financial support. Much of this thesis was written at the U.S. Forest Service’s Institute of Tropical Forestry in Puerto Rico. A return research trip to Uganda was also funded by the U.S. Forest Service.

My husband, Tom Butynski, contributed to every phase of this study through his advice, encouragement, and field assistance. His companionship and knowledge of the forest helped make completion of this work possible.

My research and dissertation benefited from suggestions by nw' doctoral committee members: Professors George Petrides (chairman),

Don Beaver, Niles Kevern, John King, and Peter Murphy. I am thankful to them for their guidance, accessibility, and support.

I am grateful to Dr. Petrides for providing the opportunity for students of diverse backgrounds and nationalities to pursue their interests in wildlife ecology and conservation tn1 an international' scale. Perhaps more important than the structured education at

Michigan State University was the inspiration gained from these other graduate students. I am especially thankful for the

friendships of fellow students: Stan Koster, Heidi Grether, and

John and Terese Hart.

In Kibale Forest, Tom Struhsaker and Lysa Leland provided

logistical support and made available their observations and

comments. Joseph Skorupa, Lynne Isbell, Matti Nummelin, and

Isabirye Basuta also shared information from 'their own studies.

Everyone at Kibale helped locate hornbill nests. Steven Yongili,

John Kyalimpa, Nyakairu Godfrey, John Rwagara, and Lawrence Rusoke were particularly successful nest-finders and were enthusiastic

assistants in the field. This work would not'have been possible without their cooperation. Senior Game Guard Alfred Otim and his

family also offered help freely.

During trips to Kampala, Oscar and Linda Rothen kindly welcomed

us into their home. Anthony Katende, curator of the Makerere

University Herbarium, identified many plants. Identifications of

hornbill foods were made by John Njoroge (National Museum of Kenya),

John Corner, and Johnathan Baranga. Alan Kemp, Steve Martindale, and Mike Underwood offered valuable coments on observations and

manuscripts. Betsy Anderson drew hornbill Figure 5.1. Mark Ritchie

provided information on insects. Dr. Peter G. Waterman of the

University of Strathclyde analyzed fruit samples.

My sister, brother, and parents were the first to teach me how

to find and observe wild animals. My greatest appreciation goes to

family and friends who encouraged me to continue in graduate studies

and who have reliably provided moral support and warm welcomes after

vi long absences. My parents, Joseph and Celeste Kalina, handled financial and other obligations at home while I was in Uganda.

Margie, Bob, and Rob Blake; Joe and Kim Kalina; Rebekah D. Fischer;

JoAnne Fischer; Patty Cohen; Teresa Dorn; Jill Keilblock; Joyce

Manko; and Barbara Rowe also sent much-needed mail and packages to us in Uganda.

vii TABLE OF CONTENTS

LIST OF TABLES ......

LIST OF FIGURES ......

Chapter

I. INTRODUCTION ......

Reasons for Study ...... Study Animals ...... Study Areas ...... Methods ...... REFERENCES ......

II. BLACK-AND-HHITE CASOUED HORNBILL DENSITIES IN KIBALE FOREST, UGANDA: SEASONAL AND HABITAT VARIATIONS

Introduction ...... Study Area ...... Methods ...... Resident Hornbill Densities ...... Development of the Census Method ...... Line-Transect Censuses ...... Calling-Rate Index (CRI) ...... Relative Abundances Based on a Total Detection Index ...... Results/Discussion ...... Confidence in Census Results ...... Relative Abundance of Hornbills in Different Habitats ...... Seasonal Trends in Habitat Use ...... Overall Hornbill Numbers in Kibale ...... Conclusions ...... REFERENCES ...... APPENDICES Z-A. Calling Rate Index (CRI) Data Collected During lS-Second Scans at S-Minute Inter- vals During Transects Censusing Bycanistgs Hornbills in Ngogo, Kibale Forest, Uganda (1983-84) ...... 43

viii Page

2-8 Calling Rate Index (CRI) Data Collected During 15-Second Scans at S-Minute Inter- vals During Transects Censusing Byganistgs n ' Hornbills in K-30, Kibale Forest, Uganda (1983-84) ...... 44

Z-C Calling Rate Index (CRI) Data Collected During lS-Second Scans at 5-Minute Inter- vals During Transects Censusing Bygagistgs subgylingriggs Hornbills in K-15, Kibale Forest, Uganda (1983—84) ...... III. DIET OF BYCANISIES SQBCILINQBIQUS, HITH EMPHASIS ON THE NESTING SEASON ......

Introduction ...... Methods ...... Opportunistic Observations ...... Nest-Hatches ...... Nest-Trap Data ...... Nutritional Analysis ...... Fruit Morphology ...... Results and Discussion ...... Foods and Foraging ...... ‘ ...... Nest-Hatch Data ...... Nest-Hatch Size Categories ...... Nest-Trap Data ...... Nutrition ...... Conclusions ...... REFERENCES ...... APPENDICES 3-A A Systematic List of All Food Items Recorded in the Diet of Byganistgs subgylindrjggs ...... 7O

3-B Description of Fruits in the Diet of Byganistgs subcylindriggs Hornbills in Uganda ...... 75

3-C Chemical Analysis of Some Byganistes 5gb_ cylindnigus Food Items (Analysis by P. Haterman) ...... 77

3-D Chemical Analysis of Some Byganjstgs sub- ;yljndrjggs Food Items (Analysis by Colo- rado State Univ.) ...... 78

ix IV. BREEDING BIOLOGY OF THE BLACK-AND-HHITE CASOUED HORNBILL (BIQANISTES SUBQILINDBLQUS) IN KIBALE FOREST, UGANDA ...... 79

Introduction ...... 79 Methods ...... 80 Results ...... 83 Timing of Nesting ...... 83 Courtship and Nesting Behavior ...... 83 Nest-Site Characteristics ...... 89 Density of Nests ...... 90 Nesting Success ...... 90 Sex-Ratio Bias in Fledglings ...... 96 Discussion/Recommendations for Further Study . . . 98 REFERENCES ...... 101 APPENDICES 4-A Characteristics of Byganjstgs subcyljndzi- cg; Nest Sites in Kibale Forest, Uganda . . 103

4-8 Characteristics of Bycanistgs sgbcylindri- cu; Display Cavity Sites in Kibale Forest, Uganda ...... 104 4-C Dimensions of 31m subsxljpdcisus Nest Cavities in Kibale Forest, Uganda . . 105

4-0 Bycagistgs subgylindgigus Nest Occupancy and Nesting Success Over Five Years (1981- 1986) in Kibale Forest, Uganda ...... 106

V. NEST INTRUDERS, NEST DEFENSE, AND FORAGING BEHAVIOR IN THE BLACK-AND-HHITE CASOUED HORNBILL ...... 110

Introduction ...... 110 Methods ...... 113 Results ...... 115 Discussion ...... 121 REFERENCES ...... 124 VI. FUNCTION OF NEST-SEALING: HITH SPECIAL REFERENCE TO THE BLACK-AND-HHITE CASOUED HORNBILL (BIQANISIES SUBCYLINDRICUS) ...... 125

Introduction ...... 125 Predation Hypothesis: Nest- -Sea1ing Protects Against Predation ...... 127 Interspecific- Competition Hypothesis: Nest- Sealing Protects Against Interspecific Competition ...... 129 Page

Intraspecifie-Competition Hypothesis: Nest- Sealing Protects Against Intraspecific Competition ...... 132 Microclimate Hypothesis: Nest-Sealing Protects Against Adverse Heather ...... 135 Discussion ...... 139 Convergent Evolution Among Unrelated Bird Species ...... 140 Natural History Studies of Hoopoes ...... 140 Comparative Field Studies of Hornbills ..... 141 Summary ...... 143 REFERENCES ...... 145 APPENDICES 6-A Descriptions of Bygagistgs subgyljndrjgus Behaviors, Sounds, and Vocalizations Mentioned in Appendices 6-8 and 6-C . . . . 150

6-B Example of Intruding Byganjstes subgylin- drjgus Supplanting Residents Early in the Nest-Cycle (Kibale Forest, Uganda) 153

6-C Example of Intruding Byganistes subgylindricus Supplanting Residents Late in the Nesting Cycle (Infanticide) ...... 156

VII. SUMMARY AND RECOMMENDATIONS ...... 163

REFERENCES ...... 168 REFERENCES ...... 169

xi LIST OF TABLES

Table Page

2.1 Summary of Kibale Forest Study-Area Characteristics 13

2.2 Numbers of Byganjstgs sgpgylindriggs Hornbills Detected at Ngogo During Transect Censuses in Kibale Forest, Uganda (1983-84) ...... 20

Numbers of Byganistes subcylingriggs Hornbills Detected at K-30 During Transect Censuses in Kibale Forest, Uganda (1983-84) ...... 21

Numbers of Bygagistes subgylindrjggs Hornbills Detected at K- 15 During Transect Censuses in Kibale Forest, Uganda (1983- 84) ...... 22

Census-Route Characteristics, Kibale Forest, Uganda 23

Bycagjstgs subgylindriggs Density, Biomass, and Ratio of Transients to Residents in Kibale Forest, Uganda (1983-84) ...... 33

Bycanistes subcylindricus Nest-Hatch and Nest-Trap Locations and Collection Regimens in Kibale Forest, Uganda (1983-84) ...... SO

Rank Order for Fruits and Invertebrates Fed at an subgylingrjggs Nests During Nest- Hatches in Kibale Forest, Uganda (1983-84) ..... 58

Fruits and Invertebrates Fed Into Bycanjstgs Sghgxlingzigus Nests During Nest-Hatches (1983-84), by Size Category ...... 59

subgylindriggs Food Remains Collected From Nest- -Traps, Ranked in Order of Percentage of All Remains Found in Traps ...... 62

Rank Order by Percentage for Frequency of Presence or Absence of Particular Invertebrates in Byganistes subgyljndrjgus Nest-Traps, Kibale Forest, Uganda (1983-84) ...... 63

xii Page

4.1 Density of Byggnistgs subgylingriggs Nest Cavities, Display Cavities, and Breeding Individuals in Kibale Forest, Uganda ...... 85

4.2 Total Rainfall (mm) During Byganistgs Pre- -breeding and Breeding Months (July- March) in Kibale Forest, Uganda (1981- 1984) ...... 99

5.1 Changes in Four Measurements of Foraging Behavior of Nesting Male Byganistes subcyljndrigus in Kibale Forest, Uganda (1983-84) Before, During, and After Intrusions by Conspecifics at the Nest Site ...... 116

5.2 Composition of Fruit Loads Brought to the Nests by Male Byganistgs subcylindriggs Hornbills in Kibale Forest, Uganda (1983-84) Before, During, and After Intruder Attacks ...... 118

xiii LIST OF FIGURES

Figure Page

1.1 Distinguishing Characteristics of Several Individual Byganistgs subgylindniggs Hornbills in the Kibale Forest, Uganda ......

Location of Kibale Forest in H Uganda, East Africa . .

Location of Study Areas in Kibale Forest Reserve, Uganda ...... 12

Locations of Census Route (5.34 km) at Ngogo, Kibale Forest, Uganda ...... 17

Locations of Census Route (4.7 km) at K-30, Kibale Forest, Uganda ...... 18

Locations of Census Route (5.28 km) at K-15, Kibale Forest, Uganda ...... 19

Byganistg; subgylingrjcus Calling Rate Indexes on Three Study Areas in Kibale Forest, Uganda (1983-84) ...... 27

Relative Abundance of Bygaﬂistgs subcyljndrigus Hornbills in Three Study Areas During Different Stages of the Breeding Cycle (1983-84; Kibale Forest, Uganda) ...... 29

Percentages of Bygagistes subgyliggrjgus Hornbills Detected at Various Distances During Censuses in Three Study Areas of Kibale Forest, Uganda (1983-84) ...... 30

Relative Abundance of Bycanistes sybgyljngriggs in Kibale Forest, Uganda, Showing Seasonal and Among- Habitat Variation ...... 32

2.9 Byganistes subgylindrjggs Hornbills Recorded in K-15 During August 2, 1983, Census ...... 37

2.10 Byggnjstgs subcyljndrjgus Hornbills Recorded in K-15 During February 10, 1983, Census ...... 38

xiv Page

Relationship Between Percentage Annual Rainfall, Fruit Abundance (Measured by the I'Surplus Fruit Index”), and the Period Over Hhich Byganistgs subgylingrjggs Start Nesting in Kibale Forest, Uganda (January 1982-1984) ...... 84

Courtship Feeding by Bygagistgs sybgyljndrigus . . . . 86 Locations of Misses subsxundnisus Nests (n - 30) and Display Cavities (n - 10) at Ngogo (Unlogged Forest) in Kibale Forest, Uganda (1981-1987) . . . . 91

Locations of Bygaﬂistgs subcyljndrjgus Nests (n - 7) and Display Cavities (n - 4) at Kanyawara (K-30 Unlogged Forest) in Kibale Forest, Uganda (1981- 1987) ...... 92

Locations of Byganistes subcyligdrigus Nests (n - 4) at Kanyawara (K-l4 Light-Moderately Logged Forest) in Kibale Forest, Uganda (1981-1987) ...... 93

Locations of Byganistgs subcyljngrjgus Nests (n - 3) at Kanyawara (K-lS Heavily Logged Forest) in Kibale Forest, Uganda (1981-1987) ...... 94

Difference Between Casque Development on Fledgling Male and Fledgling Female Byganistes subgylin-

SLDLCJLS OOOOOOOOOOOOOOOOOOOOOOO 97

During the Nesting Period, the Male Byggnistes subgylindrjggs Is Solely Responsible for Feeding Himself, His Mate, and His Offspring in the Nest. At the Same Time, His Foraging Behavior Hill Be Influenced by Risks of Predation and Demands of Protecting the Young ...... 111

Compass Direction by Bxganistgs subcylingrigus Nest Entrances in Kibale Forest, Uganda (n - 44) 138

Hypothetical Relationship Between Byganjstes sub- gyljndrigus Nest Success and Number of Trees Removed Per Unit Area ......

XV CHAPTER I

INTRODUCTION

Hornbills (family Bucerotidae), with their unique nest-sealing behavior and ornate casques, have interested scientists and laymen alike. Although approximately 10 species have been the subject of detailed study (Kemp 1976; Kemp & Kemp 1980; Leighton 1982), little is known about most of the 53 species in this group of birds (Kemp

1979). Practical constraints probably account for the lack of data, since most of the species inhabit remote rainforests of Africa and

SE Asia (Kemp 1979, 1988).

Today, as rainforest destruction escalates (Sommer 1976; Bolin

1977; IUCN 1980; Myers 1984), it is timely to focus attention on hornbills which depend on that habitat to survive. Hornbills mediate seed-dispersal for rainforest trees (Leighton 1982; Kalina &

Butynski in prep) and, therefore, facilitate regeneration of these threatened ecosystems. Previous studies of the behavior and ecology of' hornbills have focused on species inhabiting either African savannahs (Kemp 1976; Kemp & Kemp 1978) or SE Asian rainforests

(Leighton 1982). Little is known about the 12 hornbill species, including the black-and-white casqued hornbill (Bycanistgs subgylingrjcus subguadratus), which occur' in African rainforests (Kemp 1979). This is the first long-term, intensive study of an

African forest hornbill. Objectives of this research are to: (1) determine. hornbill densities, movements, spatial dispersion, and habitat use in areas of disturbed and undisturbed forest; (2) describe food habits; (3) investigate hornbill reproductive ecology and reasons for nesting failure; (4) develop suitable methods for collecting this information; and (5) make recommendations concerning timber-management practices which are pertinent to the conservation of forest hornbills in Uganda and elsewhere in the tropics. It is planned that results from this study will be relevant to the formulation of scientifically based policies for the protection of wildlife and the utilization of tropical rainforest by humans.

Study Anjmals

Black-and-white casqued hornbills (B. subcylindricus) are found in forests of Cameroon, N and E Zaire, S Sudan, Uganda, H Kenya, NH

Tanzania, and N Angola. They are large (1.3 kg; Kemp 1979), black birds with gleaming white secondary feathers, abdomens, rumps, and outer tail feathers. During their distinctive glide-flapping flight, B. subgylindricus wings produce a loud whooshing sound which can be heard 100 m away. They are extremely vocal birds and produce a great variety of sounds, the loudest of which can be heard up to

2 km away. Males are larger than females, with deeper voices and. more developed casques. B. suchlindrigus are easily habituated and make excellent research subjects. They can also be recognized individually' by the unique patterns of white on the bicolored casque. The angle of the forward projection of the casque, the number of vertical and horizontal ridges, and variations in size or shape of the casque also help in the identification of individual birds (Fig. 1.1). The age of a hornbill can be determined by noting the color and development of the casque and by Observing the birds’ behavior and interactions with other individuals. Hornbills less than one year old have brown feathers on the forehead and make squeaky vocalizations. Subadults travel in flocks of approximately

5 to 12 individuals. Adults are most often seen in pairs.

u as

A Data were collected in moist, evergreen rainforest in Kibale Forest Reserve (560 kmz; elevation 1590-1110 m), H Uganda (O°13'-0°

41'N and 30°19'-30°32'E; Fig. 1.2). Kibale is one of the few forest patches left in Uganda, a country with less than 3% of its land surface now covered in closed forest, of which an estimated 2% (110 kmz) is being lost each year (Hamilton 1984; Struhsaker 1987).

Kibale has been subjected to logging in its northern third

(Struhsaker 1972) and has been the focus of much comparative ecological research in logged and unlogged areas for the past 15 years (Struhsaker 1975; Ghiglieri 1984; Skorupa 1988; Butynski in prep). The Reserve includes 560 km2 of land, but because of historical, edaphic, and altitudinal factors, only about 60% to 70% of any given area is covered by high forest (Hing 81 Buss 1970).

Hith the northern third selectively logged (Struhsaker 1972) and much of the southern third deforested by agricultural encroachment

Fig. l.l.--Distinguishing characteristics of several individual Byganjstes subcylindrjggs hornbills in the Kibale Forest, Uganda. -

, (Al-’— \ 111141111011 p J 1 (V ( nunuun;,'

TANZANIA

Fig. 1.2.--Location of Kibale Forest in H Uganda, East Africa. Inset: Location of Ngogo and Kanyawara (K-30, K-l4, K-15) study areas in Kibale Forest Reserve, H Uganda. (Adapted from Ghiglieri 1984 and Skorupa 1988.)

(Struhsaker 1981), only an estimated 185 km2 remains as primary forest (Kingston 1967; Collar & Stuart 1985).

Four study areas in Kibale were used for this research, three at Kanyawara in the northwest (K-30, K-14, K-15) and one in the center of the Reserve (Ngogo) (Fig. 1.2 inset). Ngogo is part of a

60 km2 nature reserve and is protected from all human use other than that of nonintrusive scientific research (Kingston 1967; Struhsaker

1972). Kanyawara is divided into adjacent timber compartments, which were subjected to various levels of selective timber harvesting in 1968-69 (see Skorupa 1988 for detailed description of management history of Kanyawara). Since 1970, all legal exploitation of timber has stopped at Kanyawara. Although some poaching of animals occurs in the Reserve, hornbills are not hunted.

Two hornbill species occur sympatrically with B. subgyljngrjggs in Kibale Forest (Hilliams 1967). The crowned hornbill (IQCLNS alboterminatgs) (0.3 kg; Kemp 1979) was commonly observed, primarily along forest edge. The African pied hornbill (Loggus fasciatus)

(0.3 kg; Kemp 1979) was not seen but possibly can be found locally in other parts of Kibale Forest.

Methods

A series of separate papers has been prepared, each of which relates to a different aspect of B. subgylindrjcus behavior and ecology. Methodology for data collection pertaining to each subject is presented at the beginning of each chapter. REFERENCES

Bolin, B. 1977. Changes of land biota and their importance for the carbon cycle. Science 196:613-615.

Butynski, T. M. in prep. Comparative ecology of blue monkeys (Cercopithecus mitis) in high and low density subpopulations.

Collar, N. J. and S. N. Stuart. 1985. r n ir fri and Related Islands. IUCN, Cambridge, UK.

Ghiglieri, M. P. 1984. T e im n ' 1 F re . Columbia Univ. Press, N.Y.

Hamilton, A. C. 1984. Deforestation in Uganda. Oxford Univ. Press. Nairobi, Kenya.

IUCN. 1980. Save the rainforests. IUCN Bgllgtin: 11(5). Gland, Switzerland.

Kalina, J. and T. M. Butynski in prep. Seed dispersal ecology of Trichilia splendida in Kibale, Forest, Uganda.

Kemp, A. C. 1976. A study of the ecology. behaviour and systematics of Tockus hornbills (Aves: Bucerotidae). Transv. Mus. Mom. 29.

Kemp, A. C. 1979. A review of the hornbills: Biology and radiation. Living Birg 17:105-136. _

Kemp, A. C. 1988. Bucerotidae--In Urban, E., S. Keith and H. Fry (eds.), The Birds ofsAfrjca Vol. 3. Academic Press, London.

Kemp, A. C. and M. I. Kemp. 1978. nggrygs and Sagittarius: Two modes of terrestrial predation. Proc. Svmp. Afr. Predatory Birds: 13-16.

Kemp, A. C. and M. I. Kemp. 1980. The biology of the Southern ground hornbill, Bucorvgs Igadbeatgri (Vigors), (Aves: Bucerotidae). Ann. Iransvaal Mus. 32:65-100.

Kingston, 8. 1967. Horking Plan for Kibale and Itwara Central fg£g§1_ﬁg§gnvg§. Uganda Forests Department, Entebbe, Uganda.

Leighton, M. 1982. Fruit resources and patterns of feeding, spacing and grouping among sympatric Bornean hornbills. Ph.D. dissertation, Univ. Calif., Davis. Myers, N. 1984. The Primar ur Tr i r and r Future. H. H. Norton, N.Y.

Skorupa, J. P. 1988. The effects of selective timber harvesting on rainforest primates in Kibale Forest, Uganda. Ph.D. dissertation, Univ. Calif., Davis.

Sommer, A. 1976. Attempt at an assessment of the world’s tropical moist forests. Unasylve 28:5-24.

Struhsaker, T. T. 1972. Rainforest conservation in Africa. Erimetes 13:103-109.

Struhsaker, T. T. 1975. 1he_3eg_§eleBe§_ﬂenkey. Univ. of Chicago Press, Chicago, Illinois.

Struhsaker, T. T. 1981. Forest and primate conservation in East Africa. Afr. J. Ecgl. 19:99-114.

Struhsaker, T. T. 1987. Forestry issues and conservation in Uganda. ngl. genserv. 39:209-235.

Hilliams, J. G. 1967. A Field Guide to the National Parks ef E, Afrjee. Collins, London.

Hing, L. D. and I. O. Buss. 1970. Elephants and forests. Hildlife Monographs: No. 19. The Hildlife Society, Hashington, D.C. CHAPTER II

BLACK-AND-HHITE CASOUED HORNBILL DENSITIES IN KIBALE FOREST, UGANDA: SEASONAL AND HABITAT VARIATIONS

Introduction

Today, as rainforest destruction escalates (Sommer 1976; Bolin

1977; IUCN 1980; Myers 1984), it is timely to focus attention on hornbills (family Bucerotidae) which depend on that habitat to

survive. The majority of hornbill species require large, hollow trees for nesting and vast areas of tr0pical forest for foraging

(Kemp 1979). These large birds disperse tree seeds, thereby

facilitating regeneration of the ecosystems they inhabit (Leighton

1982; Kalina & Butynski in prep).

As selective timber harvesting continues to convert

primary forests to agricultural land or to secondary forest, conservationists have begun to examine the capacity of disturbed

forest to support wildlife (Johns 1983, 1985; Skorupa 1988).

Results from surveys of SE Asian forests indicate that most hornbill

species studied can persist in selectively logged forest, provided

the area is large enough (Kemp & Kemp 1975; Hilson & Johns 1982;

Johns 1987) and has sufficient numbers of large trees (Kemp & Kemp

1975). On the other hand, hornbills in primary forest have

abandoned territories after even neighboring areas were disturbed lO

(Leighton in Kemp 1985). Little is known about the effects of logging on African forest hornbill species since, prior to this research, they have not been the focus of detailed study.

Because so many hornbill species are nomadic, or seasonally so, censuses designed to compare populations in' different habitats should be conducted at least several times of year. Descriptions of seasonal movements are needed to improve the interpretation of census data. Also needed are quantitative data concerning breeding activities and reproductive success in various habitats.

Seasonal fluctuations of black-and-white casqued hornbill

(Bycanistes subcylindrieus eubguadratus) densities in logged and unlogged areas were investigated in Kibale Forest, Uganda. Results of population censuses and breeding activity in various habitats are the focus of this report. This paper is the first in a series of reports comparing the socioecology of black-and-white casqued hornbills (hereafter referred to simply as "hornbills”) in logged and unlogged forest. Recomendations are made concerning timber- management practices which seem likely to affect the conservation of forest hornbills wherever they occur in the tropics.

Stgdy Aree

Data were collected in the moist, evergreen rainforest of the

Kibale Forest Reserve (560 kmz; elevation 1590-1110 m), western

Uganda (0°13'-O°41' N and 30°l9'-30°32' E). Kibale is one of the few forest patches left in Uganda, a country with less than 3% of its land surface now covered in closed forest and an estimated 2% of 11 in closed forest and an estimated 2% of that remnant (110 kmz) being lost each year (Hamilton 1984; Struhsaker 1987). Kibale has been subjected to logging in its northern third (Struhsaker 1972) and has been the focus of comparative ecological research in logged and unlogged areas for the past 15 years (Struhsaker 1975; Ghiglieri

1984; Skorupa 1988; Butynski in prep). The Reserve includes 560 km2 of land, but because of historical, edaphic, and altitudinal factors, only about 60-70% of any given area is covered by primary forest (Hing 81 Buss 1970). Hith the northern third selectively logged (Struhsaker 1972) and much of the southern third deforested by agricultural encroachment (Struhsaker 1981), an estimated 185 km2 remains as undisturbed forest (Kingston 1967; Collar & Stuart 1985).

Four study areas in Kibale were used for this research, three at Kanyawara in the northwest (K-30, K-14, K-15) and one in the center of the Reserve (Ngogo) (Fig. 2.1). Ngogo is part of a 60 km2 nature reserve and is protected from all human use other than that of nonintrusive scientific research (Kingston 1967; Struhsaker

1972). Kanyawara is divided into adjacent compartments, which were subjected to various levels of selective timber harvesting in 1968-

1969 (Table 2.1; see Skorupa 1988 for description of management history of Kanyawara). Since 1970, all legal exploitation of timber has stopped at Kanyawara. Illegal timber harvesting has continued at a low level outside of the study areas. Although some poaching of animals occurs in the Reserve, hornbills are not hunted. 12

‘ 01115 K14 Kanyawara .1130

NATURE RESERVE KIBALE FOREST RESERVE D ‘ PD

Fig. 2.1.--Location of study areas in Kibale Forest Reserve, Uganda. (Adapted from Skorupa 1988.) I3

Ha at (180

Commer-

Stems 5.1 7.4

No. Removed higher Ngogo

cial (5%) than

9 cm 8 year

gg per was

Degreenof

Undisturbed

Light- Heavy

moderate days rainy (1977-1984)

Nature reserve

compartment

Magzgiﬁgnt compartment compartment

Timber Timber Timber more ears 8 (16%1

(kmz) for

3.0

3.9 3.6 28

60.0

Forest

characteristics.

Size

Compartment avg. rainfall on

Size

study-area

1.7

1.1 1.2

6.6

(km?)

Study annual

Area received

Forest

Annual

149 157

157 157 prep-Mean

(cm)a

Kibale Kanyawara in

Rainfall

1988.

Mean

of Ngogo.

Butynski Skorupa

1350 1590

1590 1590 than

AIE;§Udé .

2.1.-Summary

”a. aT.‘M. 152

K-BO

Ngogo K-l4 K-15 Kanyawara vs.

iﬁggy

Table

A system of trails l m wide is maintained in each study area.

The grid system includes c. 140 km of trails mostly 50 m apart at

Kanyawara and c. 140 km of trails mostly 100- m apart at Ngogo.

Since only stems < 4 cm dbh are cut for these paths, there seems to be little effect on the wildlife. Yet these trails are highly beneficial to research, permitting easy movement through the forest without disturbing animals. They also served as spatial references during censuses.

Ngogo and Kanyawara study areas have been sites of comprehensive habitat analysis. Detailed descriptions of habitat and primate communities in these areas have been completed by

Ghiglieri (1984) and Butynski (in prep) for Ngogo and by Struhsaker

(1975), Skorupa (1988), and Butynski (in prep) for Kanyawara. Ngogo was found to have a higher tree density and .basal cover plus a greater tree-species richness and diversity than Kanyawara

(Butynski in prep). Butynski (in prep) compared his results with those of Skorupa (1985) and concluded that the habitat and primate communities of the undisturbed Ngogo and the unlogged K-30 were more similar than that of the unlogged K-30 and logged areas (K-l4, K-15) at Kanyawara. Study-area descriptions are summarized in Table 2.1.

Methods i t rn 1 iti

In June 1981, I began a long-term study of black-and-white. casqued hornbills in Kibale Forest. Intensive research ended in

June 1984, but nest monitoring continued every year (except 1985) 15 through 1987. This research has focused on hornbill behavior and on reproductive and feeding ecology. From the start, every effort was made to locate all hornbill nests in the four study areas of Ngogo, K-30, K-l4, and K-15. By the 1983-84 breeding season, all nesting territories in these study areas had been found. ”Resident hornbills" are defined here as those with nesting territories. In this paper, resident hornbill densities for 1983-84 are presented for comparison with hornbill density estimates from 1983—84 line- transect census results.

Beveloumeut uf the Census Methog

Although nests provided information about the densities of breeding birds, it was impossible to determine seasonal changes in abundance and habitat use of hornbills without making regular population censuses“ 'The objectives of these censuses were to describe seasonal changes in abundances of hornbills within and between logged and unlogged habitats and to estimate overall numbers and biomass of hornbills in Kibale Forest. In developing a technique suitable for censusing hornbills, it was first necessary to determine if calling rates changed seasonally and whether hornbills were easier to detect in logged forest than in unlogged forest.

From April 1982 to February 1983, I walked 107.4 km of censuses

(37.4 km at Ngogo, 70.0 km at Kanyawara) before developing a method that seemed adequate to address potential census problems. Data collected during the April 1982-February 1983 censuses are not 16 reported here, but experience and information gained in that preliminary work were essential for accuracy in the later data collection. During this period I (l) learned to detect, identify, and record the hornbill’s sex, age, and type of call quickly; and

(2) developed skills for recording distances accurately in different forest types.

i - n n

Due to time constraints, population censuses were limited to

Ngogo (unlogged), K-3O (unlogged), and K-15 (heavily logged) study areas. Hornbill abundance in these study areas was measured using a modified version of line-transect techniques used for sampling bird communities (Emlen 1984) and for estimating primate densities in

Kibale (Struhsaker 1975; Ghiglieri 1984; Skorupa 1988; Butynski in prep). As a means of comparison with prior studies in Kibale, my census routes were nearly identical to those used previously by these other researchers.

I conducted replicate censuses along three_routes, one each in

Ngogo, K-30, and K-15 study areas (Figs. 2.2, 2.3, 2.4). These were conducted each month from February 1983 through May 1984 (Tables

2.2, 2.3, 2.4). Every effort was made to conduct one census per month along each route. Sometimes, however, two census were conducted in one month to make up for previous months when no census was run. Biannually, I conducted a series of five replicate

censuses on consecutive days, or nearly so, in each study area.

These "census-series" were undertaken immediately after the hornbill

CENSUS ROUTE [5.34 km) a

Fig. 2.2.--Locations of census route (5.34 km) at Ngogo, Kibale

Forest, Uganda. Shaded areas are grassland, is trail grid, ----- is elephant trail, and ==-== is motorable track. (Adapted from Ghiglieri 1984.) 18

BUTANZI

FOOTPATN

£00

0..

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00%

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M‘

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It" "’4'.

Census route (4.70 km) 4’

Fig. 2.3.-- Locations of census route (4.7 km) at K-30, Kibale Forest,

Uganda. is trail grid. l9

K-15

1 \

1NBRD’ 1 1 1 41 Q‘ss‘ﬁ o 100 200 zoom

CENSUS ROUTE (5.28 km)

Fig. 2.4.--Locations of census route (5.28 km) at K-15, Kibale

Forest, Uganda. is trail grid. 20

Table 2. 2. --Numbers of Byeeu_stes suueylinguieus hornbills detected at Ngogo during transect censuses in Kibale Forest, Uganda (1983- 84). Route length - 5. 34 km. Means are + standard error.

Total No. No. Detected Total No. No. Detected No. per km2 Detected per km Detected' per km Min. Density Census Strip Hidth (m): (400) (400) (50) (50) (Based on 50 m)

Date (1983)

Feb. 11 21 3.9 20 3.8 74.0 Feb. 24 10 1.9 5 0.9 18.5 Feb. 25 2 0.4 -, 2 0.4 _ 7.4 Feb. 26 7 1.3 X-1.0+0.7 6 1.1 X-O.7+O.5 22.2 Feb. 27 7 1.3 " 6 1.1 ' 22.2 Feb. 28 1 0.2 O 0 0 Mar. 25 l 0.2 O O 0 Apr. 30 O O 0 O 0 May 25 9 1.7 2 0.4 7.4 June 26 20 3.8 9 1.7 33.3 July 22 34 6.4 9 1.7 33.3 Aug.16 16 3.0 5 0.9 18.? Aug. 17 42 7.9 __ 23 4.3 _ 85. - Aug. 19 24 4.5 x-4.s+2.1 9 1.1 x-z.3+1.s 33.3 3'49-0129-0 Aug. 21 30 5.6 ’ 18 3.4 ' 66.6 Aug. 23 15 2.8 6 1.1 22.2 Sept. 30 44 8.2 23 4.3 85.1 Nov. 9 14 2.6 7 1.3 25.9 Nov. 30 22 4.1 9 1.7 33.3 Dec. 31 43 8.1 7 1.3 25.9

(1984)

Jan. 25 26 4.9 7 1.3 25.9 Feb. 19 5 0.9 3 0.6 11.1 Mar. 24 8 1.5 7 1.3 25.9 Apr. 30 7 1.3 3 0.6 11.1 May 14 10 1.9 2 0.4 7.4

Total 78.3 188.0 35.2 695.6 7+ SE 3.1:2.5 1.51.5.7 1.411.: 27.8+24.8

Table 2.3.--Numbers of WW ' hornbills detected at K-3O during transect censuses in Kibale Forest, Uganda (1983-84). Route length - 4.7 km. Means are 1 standard error.

Total No. No. Detected Total No. No. Detected No. per km2 Detected per km Detected per km Min. Density Census Strip Hidth (m): (400) (400) (50) (Based on 50 m)

1211: (1983)

Mar. 5 0 0 O 0 0 Mar. 7 O 0 O 0 . 0 Mar. 10 5 1.1 X-O.6+1.0 2 0.4 Y-O.21-0.2 8.3 Mar.11 10 2.1 ' 2 0.4 8.3 Mar. 12 0 0 0 0 0 Mar. 30 5 1.1 2 0.4 8.3 May 3. 9 1.9 2 0.4 8.3 May 31 O O O O 0 July 3 22 4.7 8 1.7 33.4 July 26 12 2.6 2 0.4 8.3 July 27 22 4.7 7 1.5 29.2 __ July 28 24 5.1 I-a.3+1.6 a 1.7 li-o.9+o.7 33.4 xa16.0+12.7 July 29 13 2.8 ' 5 1.1 ' 20.9 T Aug. 1 6 1.3 O 0 0 Sept. 12 8 1.7 4 0.9 16.7 Oct. 3 14 3.0 7 1.5 29.2 Nov. 3 11 2.3 4 0.9 16.7 Dec. 10 20 4.3 9 1.9 37.5

(1984)

Feb. 11 19 4.0 5 1.1 20.9 Feb. 27 5 1.1 0 0 0 Mar. 11 0 0 0 0 0 Apr. 2 2 0.4 0 0 0 May 2 10 2.1 4 0.9 16.7

Total 46.2 71.0 15.1 296.1 X'+ SE 2.0:1.7 3.1:3.1 0.7:0.7 12.9112.8

Table 2. 4. --Numbers of Byeenistes suheylingrieus hornbills detected at K-15 during transect censuses in Kibale Forest, Uganda (1983- 84). Route length - 5.28 km. Means are + standard error.

Total No. No. Detected Total No. No. Detected No. per km2 Detected per km Detected per km Min. Density Census Strip Hidth (m): (400) (400) (50) (50) (Based on 50 m)

Date

(1983)

Mar. 2 0 N '0 Mar. 3 Mar. 6 {-03:02 Y-o.o:o.1 Mar. 8 Mar. 9

Apr. 2 d May 7 June 1 NNO 404004 July 7 Aug.

Aug. O

230.8104 i-o.3:o.2 O 114.2353 6.." Aug. GNND d o

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Oct. 5 o Nov. 5 o

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(1984)

Feb. 10 45 21 I 80.9 13 50.1 Feb. 22 29 O

Mar. 14 14 N090! 5 19.3

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May 3 3 0! 2 7.7

Total 37.1 77.0 14.6 296.5 Y+ SE 1.15:2.0 3.4:s.o 0.611.0' 12.91192

23 nesting season (Feb./Mar. 1983) and then again immediately before the next nesting season (August 1983). Biannual census-series were conducted in order to obtain larger samples for comparing changes in hornbill abundance during different seasons. 'Daily censuses also helped identify variations in hornbill densities on a daily rather than monthly basis.

The total number of censuses conducted per study area varied from 23 to 25 (Tables 2.2, 2.3, 2.4). This sample size coincides with previous analyses recommending that 20-30 repetitions would be optimal for censusing primates in Kibale (Struhsaker 1981). Route lengths ranged from 4.7 km to 5.3 km (Table 2.5). The total number of km censused per route ranged from 108.1 to 133.5. Including all study areas, a total of 363.0 km of censuses were walked (Table

2.5).

Table 2.5.--Census-route characteristics, Kibale Forest, Uganda.

Total Study Area Route Type Route Census Length (km) Route (km)

Ngogo Trail grid 5.34 133.50

K-3O Trail grid 4.70 108.10

K-15 Trail grid and 5.28 21.44 logging road

Total for all study areas 363'04

Two censuses (Ngogo and K-30) were conducted entirely along the

1 m wide trails which were part of the study-area grid system. The

K-lS census route was located along trails, with the final 1 km along an old logging road (Figs. 2.2, 2.3, 2.4; Table 2.5).

Vegetation on this road was periodically cut, but it was my opinion that visibility there was no better than along the usual trails.

Logging roads have been incorporated into census routes by other researchers in Kibale, and according to analysis by Skorupa (1988), for five of seven primate species studied there was no bias to results. The trail system in Kibale was extremely beneficial during censuses. Hith undergrowth removed, I walked quietly at a steady pace (c. 1 km/h) and therefore avoided startling animals. I conducted all censuses alone and timed my progress along the route by noting the time I reached each trail intersection. Trails also provided the spatial references necessary for precise estimates of the locations of hornbills detected.

Routes were designed as rectangular circuits, returning to the starting point. Censuses were started between 0730 and 0800, weather permitting. Censuses were postponed for up to l h or canceled on rainy days.

Two separate data-collection techniques were used simultaneously during censuses, one for determining cue production rates (for the “calling-rate index” [CR1]) and one for determining the relative abundance of hornbills. 25

Callin -R e Inde R

Data for* calculating the calling-rate index: were collected during regular periods when I stopped along the census route to listen and record the number of individual hornbills heard calling.

Throughout the length of each census, I listened for 15 sec. at 5 min. intervals, recorded the number of different individual hornbills heard calling, the number and types of calls, and whether or not the hornbill(s) heard was a hornbill not previously recorded that day during the 15 sec. listening scans. I decided whether or not the hornbill had already been recorded on the census based on its location, direction of travel, and sometimes visual identification. The calling-rate index (CRI) was then calculated for each census route by dividing the mean number of new individuals heard calling/scan by the mean number of all hornbills heard calling/scan - 1.

Relative Abundances Based on a Total Detection Index

Hhile traversing the census route, I plotted the location of each hornbill seen or heard directly on prepared maps and also onto a tally sheet. The combination of map and tally-sheet records facilitated the cross-checking and summary of information gathered at the end of the day’s census. Hornbills were represented as dots on the map, and arrows were drawn to indicate their direction of travel. Plots of hornbill locations were extremely useful for (1) identifying and keeping track of individuals during a census, (2) tracing changes in spatial distribution of hornbills over time and 26

between censuses, and (3) confirming the attachment of particular birds to particular parts of the study area.

For each hornbill detected, I recorded the time, my location, estimated "perpendicular distance” from the census route to the hornbill, mode of detection, and direction of travel of the hornbill. This information was used to describe the relative abundance of hornbills. Additional information was gathered during censuses concerning age, sex, activities, and behaviors of hornbills observed and will be presented in other reports.

Perpendicular-distance data were both visual and auditory estimates. 1 consider precision of these estimates to be good, based on experience gained before these censuses during the longitudinal studies and practice censuses mentioned earlier.

During practice sessions and when possible during censuses, I actually paced out distances to hornbills after making original estimates. Estimates and paced distances were usually within 5%.

Results Disc ssion

Cunfigence in Census Results

In all study areas censused, auditory cue detection represented by the calling-rate index (CRI) varied about as much on a daily basis as seasonally or among study areas (Fig. 2.5, Appendices 2-A,

2-B, 2-C). Data recorded during line-transect censuses evidently — reflected actual changes in hornbill numbers rather than a change in detectability of birds at different times of year. This is suggested by the absence of a relationship between the CRI (Fig.

(lOGGED) N-IS

(UNLOGGED) K-30

INDEX

RATE

(UNLDGGED)

CALLING NSOGO

counmen

anus

111111

1983 1 984

Fig. 2.5.--Bycanistes subcyljuduicus calling rate indexes on three study areas 1n K1bale Forest, Uganda (1983-84)

2.5) and the relative abundance of hornbills (Fig. 2.6; Tables 2.2,

2.3, 2.4) censused. In fact, the CRI can be low when the relative abundance of hornbills is high. For example, during October- December 1983, the CRIs were low, while the number of hornbills contacted was high.

Several authors (Kemp & Kemp 1975; Struhsaker 1975; Dates 1977;

Marsh & Hilson 1981) have suggested that animals are generally more visible in logged than in unlogged forest. Results of censuses may, therefore, be biased in favor of logged areas when comparing relative abundance of hornbills between logged and unlogged fbrest types. Results of line-transect counts for hornbills in Kibale showed, however, that overall detection (auditory and visual combined) was roughly comparable among study areas (Fig. 2.7). There was one noticeable difference in cue detection between habitats. A higher percentage of detections at perpendicular distances greater than 250 m was made in the logged than in unlogged study areas (Fig. 2.7). This is probably because there were fewer hornbills to census in K-15 during most months, so I had more time to listen and look for individuals that were very far away.

Since hornbills are such conspicuous, noisy birds, I am confident that few individuals went undetected within the 25 m perpendicular' distance to ‘the census trail (50 m strip width).

Hornbill densities as determined from these data are likely close to albeit slightly less than the absolute densities because of 29

_ E 5 5 GB 4— E a. 5 E 3' "‘

13 ° 2- . 2 1— E u 11 E El 5' 5 4- e a a V u E E s 2- g H ‘ 4'5 .3 1- i ID a 3 o

E 3' “I? O =. 5- ; E 1:: 4' 8 s 3- .3. 2- g a 2

4;, 4555 o .é‘ *Q

Fig. 2.6.--Relative abundance of Bycanistes subcylindricus hornbills in three study areas during different stages of the breeding cycle (1983-84; Kibale Forest, Uganda). Census lengths are 5.34 km at Ngogo, 4.7 km at K-30, and 5.28 km at K-15. Data are based on the total detection index.

N45 30

20 lDGGED

uuuuuuu IO 0000000000000000

...... """""""""" ...... In. ‘

......

(“/o]

4D n = 236 K-30

20 UNLOGGED Detentions 10

30 NGOGO

UNLOGGED

10 nnnnnnnnnnnnnn...... nnnnnnnnnnnnnn

no. I ...... nnnnnnnnnn ooooooooooo ...... a o oooooo ooooooooooooooo oooooooooooooooooooooooooooo ......

50 150 Perpendicular Distance (m)

Fig. 2.7.--Percentages of Bygeuistes subeyljndrjeus hornbills detected at various distances during censuses in three study areas of Kibale Forest, Uganda (1983-84).

individuals I may have missed. Most detections based on sight and

sound (92% for Ngogo, 83% for K-30, 78% for K-15) were made,

however, within a perpendicular distance of 200 m of the trail (400

m strip width) (Fig. 2.7). A comparison between relative abundance

of hornbills using data from the 50 m strip width and 400 m strip width revealed similar trends (Fig. 2.8; Tables 2.2, 2.3, 2.4).

Since the 400 m strip appeared to be representative of actual

trends, I used this perpendicular strip width for most analyses

involving relative hornbill densities since this allowed me to

utilize more of the data. I believe that these data reflect actual

differences in population density among study areas since patterns

of abundance were consistent whether I used data based on a 50 m,

200 m, or 400 m census strip width.

Relative Abundance of Hornbills in Different Habitats

From detailed studies of nesting hornbills (Table 2.6), I

estimated that in the 1983-84 breeding season there was a resident hornbill density of 11.2/km2 at Ngogo, 10.5/km2 at K-30, 5.5/km2 in

the lightly to moderately logged K-14 study area, and 3.3/ka in

heavily logged K-15. Independently, these results showed that

undisturbed forest in Kibale provides better habitat for hornbills

than heavily logged forest” Habitat use by. hornbills is more

complicated, however, since these birds travel long distances

between areas and habitats and become nomadic when not nesting. A

clearer' picture of’ hornbill habitat use and spatial dispersion

lull/P9193190

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MONTH (1983) FEB/ MAR AUGUST All. CENSUSES . . . All MONTHS

II = 5,5,5,15 5,5,5,15 25,23,211,"

Fig. 2.8.-Relative abundance of B canistes subcylindricus in Kibale Forest, Uganda, showing seasonal and among-habitat varia on. atbhédiareas represent mean relative abundance within a

50 m wide census strip. Black areas represent mean relative abundance within a 400 m

wide census strip (1983-84). 33

of .

1.2:1

0.5:1 Res1dents 3.4:1

Rat1o

Transients to

- residents

km2

3.9

5.5

38.0 Per

Mean Tra"519"t5 J01y-Sept.

No. transients

km 7.2

16.0

49.2 of

Per

Mean territories.

Hornbil

July-Sept.

2.4).

1979).

ratio 2.3,

11:9)

and

(Kemp breeding

km 7.1)

4.3) ( (

(13.6)

(14.6) 2.2,

Per

Resident with

Biomass

biomass,

(Tables

g/hornbill

of km2c

5.5 3.4

hornbills

10.5

1300

No.

density, Per

Residents

transect

(1983-84).

no.

strip

weight

Uganda

(16.8)

(16.7)

(36.2)

Biomass

(kg%zger

50 based

subcylindricus mean

Forest,

No.

censuses.

kma

12.9

density 12.9

27.8

based

Per

Hornbitls

Mean

Kibale

no.

2.6.-Bycanistes

Area bBiomass

23)

cResident

aDensity 23) 25)d

= =

(n (n (n=

K-14 K-15 logged

K-3O ‘°gged

Heavily Light/mod.

Unlogged

Unlogged Ngogo Study

Table

became evident upon analysis of line-transect census results from different study areas.

Based on a 400 m strip width, the number of hornbills per km of

census was higher at Ngogo than at K-30. The heavily logged forest

(K-lS) had fewest hornbills during most months (Tables 2.2, 2.3,

2.4; Fig. 2.8). Hhen minimum densities of hornbills were calculated

using the 50 m wide strip, unlogged Ngogo supported more than twice

as many individuals (27.8/km2) than either unlogged K-30 (12.9/km2) or logged K-15 (12.9/km2) (Tables 2.2, 2.3, 2.4, 2.6; Fig. 2.3).

Ngogo, located near the center of the Forest Reserve, is not

adjacent to logged areas. The K-30 study area, although itself

undisturbed, is contiguous with logged forest and is only 2.5 km

from the heavily logged K-15 study area. Hornbills move freely

between unlogged and logged forest at Kanyawara. They probably did

not travel the 11 km between Ngogo and Kanyawara often. It is not

known whether the lower density of hornbills at Kanyawara was a

result of the effects of logging or natural differences in

vegetation type, or both. Seasonal use of logged versus unlogged

habitats at Kanyawara does indicate, however, that although

hornbills persisted in logged areas, they preferred not to breed

there or could not breed there because of fewer nest sites.

Seasunal Trends insHebitet_use

Seasonal fluctuations in hornbill densities in different study

areas were dramatic. So also was the pattern of habitat use in

relation to the breeding cycle (Figs. 2.6 and 2.8). During "pre and 35 early breeding" months (July, Aug., Sept.), hornbills arrived at nest sites and claimed their territories. Once all nest sites were occupied by breeding pairs, hornbills which were unsuccessful at obtaining nest sites continued to traverse the area searching for nest cavities. These nonbreeding birds were "transients.” The ratio of transients to breeding pairs in a particular habitat may be

an indication of the preference of that habitat for breeding. From

July through Sept. 1983-84, the ratio of 3.4:1 for Ngogo (Table 2.6)

indicated that unlogged Ngogo was the study area most preferred by hornbills for breeding. Kanyawara study areas had ratios of 0.5:1

(K-30) and 1.2:1 (K-15), which were considerably less (Table 2.6).

An estimate of' the density' of resident hornbills in each area

indicated that unlogged habitats were several-fold higher than

logged (Table 2.6). Although unlogged forest attracted more

hornbills for breeding, a better indicator of habitat quality for

breeding was to measure the nesting success of hornbills among

habitats. Nesting success, which was consistently highest at Ngogo,

is discussed in detail in Chapter III.

Although logged habitat (K-lS) was not preferred for nesting,

it did temporarily attract many hornbills during some other times of

the year, as shown by the influx of birds in Feb. 1984 (Fig. 2.6).

Large numbers of adult, subadult, and fledgling hornbills flocked to

K-15 immediately following the breeding season in Feb. 1984 to

forage in mass-fruiting Ejeus geuei and Eieus uetalensjs trees.

Hornbills flocked and became nomadic during the nonbreeding

season, causing the reduction in numbers of hornbills detected on 36

censuses in all study areas during the months of March through May

(Fig. 2.6). Hornbill pairs, which were somewhat homogeneously spaced at nest sites during prebreeding (July-Aug.) and breeding months (Sept.-Feb.), congregated at super-abundant fruit resources during the dry, nonbreeding season. Since fruiting trees were patchily distributed, hornbills became scarce in some parts of the forest and common in others. A good example of the seasonal change

in spatial distribution is illustrated in Figs. 2.9 and 2.10.

During an August 1983 census in K-15, only three hornbill pairs were detected. These birds were active around potential nest sites.

During a Feb. 1984 census in K-15, 45 hornbills (including adults,

subadults, and fledglings) were observed flying around and foraging

in fruiting trees.

QueuelltHornbill Numbers in Kibele

Using the mean overall density of 12.9 hornbills per km2 at

Kanyawara (Table 2.6), and approximately 336 km2 (60% of 560 kmz;

Hing 8 Buss 1970) of forested land (disturbed or undisturbed) in

Kibale, there are an estimated 4,300 black-and-white casqued

hornbills in Kibale Forest Reserve (Table 2.6). At a mean body weight of 1300 g (Kemp 1979), the estimated hornbill biomass is

5,630 kg.

0 i 11

Data from monthly line-transect censuses in Kibale show that

hornbill movements, spatial dispersion, and habitat-use vary 37

K-15

100m

Fig. 2.9.--Bycanistes subcylindricus hornbills recorded in K-15 during August 2, 1983, census. Dots indicate where individuals were encountered. All were active near

potential nest sites. is trail grid. 38

100m

Fig. 2.10.--Bycanistes subeylinguicus hornbills recorded in K-15 during February 10, 1984, census. Dots indicate where individuals were encountered. They were concentrated at mass-fruiting fig trees (Fjeus deuei at NB/GS; Eieus neteleusjs at 2E/lS). is trail grid. ' 39 seasonally. Because of this temporal variability in hornbill numbers, surveys meant to estimate hornbill densities should be repeated in the same area several times per year or should be based on nesting birds.

Results from this first detailed survey of an African forest hornbill population are similar to findings from surveys of hornbills in logged versus unlogged forests of SE Asia (Kemp 8 Kemp

1975; Hilson 81 Johns 1982; Johns 1987). Like hornbills in Asia, black-and-white casqued hornbills were present in selectively logged areas, but in lower numbers than in primary forest in the core of the Reserve. Although long-term ecological studies are necessary to determine what factors limit hornbill numbers (Chapters II, III, and

IV), census results alone indicate that primary forest is the most suitable habitat for these birds.

Hith an estimated mean density of 12.9 birds/km2 at Kanyawara and 27.8 birds/km2 at Ngogo, black-and-white casqued hornbills in

Kibale are at greater densities than any other forest hornbill species on record (i.e., Kemp & Kemp 1975; see Johns 1987 for 8 species). The ‘total population estimate of 4,300 hornbills in

Kibale Reserve is, however, lower than the minimum viable population size of 10,000 recommended by Johns (1987) from his studies on eight hornbill species in Malaysia.

Hornbill densities seem to be determined by the extent of logging in and around forest tracts. Therefore, they might be an indicator species to measure the level of disturbance in a tropical forest. The two-fold difference in hornbill densities in logged 40

versus unlogged areas of Kibale Forest suggests that this is true.

Additional studies are needed, however, to determine habitat types and minimum forest patch size necessary for preventing local extinctions of hornbill populations. 41

REFERENCES

Butynski, T. M. in prep. Comparative ecology of blue monkeys (Ceueopitheeus mitts) in high and low density subpopulations.

Bolin, B. 1977. Changes of land biota and their importance for the carbon cycle. Beieuee 196:613-615.

Collar, N. J. and S. N. Stuart. 1985. Threatened Bjuds uf Afrjea and Relateu Islauus. IUCN. Cambridge, U.K.

Emlen, J. T. 1984. An observer-specific, full-season, strip-map method for censusing songbird communities. The Auk 101:730- 740.

Ghiglieri, M. P. 1984. The Chimpanzees uf Kibale Eorest. Columbia . Univ. Press. N.Y.

Hamilton, A. C. 1984. Deforestation in Dgauda. Oxford Univ. Press. Nairobi, Kenya.

IUCN. 1980. Save the rainforests. IDDN Bulletin 11(5). Gland, Switzerland.

Johns, A. D. 1983. Ecological effects of selective logging in a Hest Malaysian rain forest. Ph.D. dissertation, Cambridge Univ. Cambridge, U.K.

Johns, A. D. 1985. Selective logging and wildlife conservation in tropical rainforest: Problems and recommendations. Bju), Donserv. 31:355-375.

Johns, A. D. 1987. The use of primary and selectively logged rainforest by Malaysian hornbills (Bucerotidae) and implications for their conservation. Bjol, Dunserv. 40:179-190.

Kalina, J. and T. M. Butynski in prep. Seed dispersal ecology of Injehilja selenuiga in Kibale Forest, Uganda.

Kemp, A. C. 1979. A review of the hornbills: Biology and radiation. Ljviug Bird 17:105-136.

Kemp, A. C. 1985. IDBP Bornujl! Sues. Ga, Baum. 5.

Kemp, A. C. and M. I. Kemp. 1975. Report on a study of hornbills in Sarawak, with comments on their conservation. Kuala Lumpur, Horld Hildlife Fund Malaysia. (unpublished report.) 42

Kingston, B. 1967. H k n P n or b wara r Eurest Reseuues. Uganda Forests Department, Entebbe, Uganda.

Leighton, M. 1982. Fruit resources and patterns of feeding, spacing, and grouping among sympatric Bornean hornbills. Ph.D. dissertation. Univ. Calif., Davis.

Marsh, C. H. and H. L. Hilson. 1981. A survey of primates in peninsular Malaysian forest. Final report for the Malaysian primate research programme. Univ. Kebangsaan, Malaysia and Cambridge Univ., Cambridge, U.K. ‘

Myers. N. 1984. WWW Eutuue. H. H. Norton, N.Y.

Oates, J. F. 1977. The guereza and man: How man has affected the distribution and abundance of Dolubus guereza and other black colobus monkeys. pp. 419-467 in Prince Rainer and G. H. Bourne (eds.), Eujmate Donservatjan. Academic Press. London and N.Y.

Skorupa, J. P. 1985. Responses of rainforest primates to selective logging in Kibale Forest, Uganda: A summary report.

Skorupa, J. P. 1988. The effects of selective timber harvesting on rainforest primates in Kibale Forest, Uganda. Ph.D. dissertation, Univ. Calif., Davis.

Sommer, A. 1976. Attempt at an assessment of the world’s tropical moist forests. Dnasylua 28:5-24.

Struhsaker, T. T. 1972. Rainforest conservation in Africa. Erimates 13:103-109.

Struhsaker, T. T. 1975. h e bus n . Univ. of Chicago Press. Chicago, Illinois.

Struhsaker, T. T. 1981. Forest and primate conservation in East Africa. Afr, J, Eeul. 19:99-114.

Struhsaker, T. T. 1987. Forestry issues and conservation in Uganda. Bjul, Buusery. 39:209-235.

Hilson, H. L. and A. D. Johns. 1982. Diversity and abundance of selected animal species in undisturbed forest, selectively logged forest and plantations in East Kalimantan, Indonesia. B191. Bunserx. 24:205-218.

Hing, L. D. and I. O. Buss. 1970. Elephants and forests. Bilglife Buuuguauhs: No. 19. The Hildlife Society, Hashington, D.C. 43

APPENDIX 2-A CALLING RATE INDEX (CRI) DATA COLLECTED DURING lS-SECOND SCANS AT 5-MINUTE INTERVALS DURING TRANSECTS CENSUSING HORNBILLS IN NGOGO, KIBALE FOREST, UGANDA (1983-84)

Mean No. Mean No. New Census Date Hornbills Individuals CRI No. Recorded/Scan Recorded/Scan

(1983)

1 Feb. 11 0.3 0.2 0.3 2 Feb. 24 0.4 0.3 0.3 3 Feb. 25 O O O 4 Feb. 26 0.1 0.1 0.5 5 Feb. 27 0.1 0.1 0.2 6 Feb. 28 O O O 7 Mar. 25 0 O O 8 Apr. 30 0 0 O 9 May 25 0.2 0.2 0.2 10 June 26 0.6 0.4 0.4 11 July 22 0.6 0.4 0.3 12 Aug. 16 0.3 0.3 0.2 13 Aug. 17 0.7 0.6 0.1 14 Aug. 19 0.6 0.3 0.5 15 Aug. 21 0.6 ? ? 16 Aug. 23 0.2 0.2 0 17 Sept. 30 0.6 0.5 0.1 18 Nov. 9 0.1 0.1 O 19 Nov. 30 0.2 0.2 O 20 Dec. 31 0.6 0.5 0.2

(1984)

21 Jan. 25 0.5 0.3 0.3 22 Feb. 19 O O O 23 Mar. 24 0 l 0.1 0 2 24 Apr. 30 0 O O 25 May 24 0.1 0.1 0

Total 3.6 'i_+_ SE 0.23.0.2

APPENDIX 2-B CALLING RATE INDEX (CRI) DATA COLLECTED DURING lS—SECOND SCANS AT 5-MINUTE INTERVALS DURING TRANSECTS CENSUSING T BDBBILINDBLBDB HORNBILLS IN K-30, KIBALE FOREST, UGANDA (1983-84)

Mean No. Mean No. New Census Date Hornbills Individuals CRI No. Recorded/Scan Recorded/Scan

(1983)

.1 Mar. 5 0 0 0 2 Mar. 7 O 0 0 3 Mar. 10 0.1 0.1 0.6 4 Mar. 11 0.1 0.1 0.5 5 Mar. 12 0 O 0 6 Mar. 30 0 O 0 7 May 3 0.1 0.1 0.4 8 May 31 0 O 0 9 July 3 0.6 0.4 0.3 10 July 26 0.2 0.2 0.3 11 July 27 0.5 0.4 0.2 12 July 28 0.4 0.4 0.1 13 July 29 0.3 0.2 0.3 14 Aug. 1 0.1 0.1 O 15 Sept. 12 0.3 0.2 0.4 16 Oct. 3 0.1 0.1 0.2 17 Nov. 3 0.1 0.1 0.1 18 Dec. 10 0.2 0.2 0

(1984)

19 Feb. 11 0.4 0.2 0.5 20 Feb. 27 0.1 0.1 0 21 Mar. 11 0 O O 22 Apr. 2 0 0 0 23 May 2 0.2 0.1 0.3

Total 4 1 1T: SE 0.2102

APPENDIX 2-C

CALLING RATE INDEX (CRI) DATA COLLECTED DURING lS-SECOND SCANS AT S-MINUTE INTERVALS DURING TRANSECTS CENSUSING BDBBXLLNDBLBBB HORNBILLS IN K-15, KIBALE FOREST, UGANDA (1983-84)

Mean No. Mean No. New Census Date Hornbills Individuals CRI No. Recorded/Scan Recorded/Scan

(1983)

1 Mar. 2 O 0 O 2 Mar. 3 0 O O 3 Mar. 6 O O 0 4 Mar. 8 O 0 O 5 Mar. 9 O 0 0 6 Apr. 2 0.1 0.1 0 7 May 7 0.2 0.2 O 8 June 1 0.1 0.1 0 9 July 7 0.2 0.2 0 10 Aug. 2 0.1 0.1 O 11 Aug. 3 0.1 0.1 0 12 Aug. 4 0 0 O 13 Aug. 5 0.3 0.1 0.5 14 Aug. 8 0.2 0.1 0.3 15 Sept. 11 0.1 0.1 0.3 16 Oct. 5 0.2 0.2 0.2 17 Nov. 5 0.1 0.1 O 18 Dec. 11 0.2 0.2 0.1

(1984) 19 Feb. 10 0.5 0.4a 0.33 20 Feb. 22 0.4 0.4 O 21 Mar. 14 0.4 0.3 O 2 22 Apr. 3 0 0 0 23 May 3 0 O 0

Total 1.8

X 1 SE 0.1:0.1

aApproximate value. CHAPTER III

DIET 0F mm W. WITH ENPHASIS ON THE NESTING SEASON

1113mm

Previous studies on the food habits of hornbills, family

Bucerotidae, have focused on species inhabiting an African savannah

(Kemp 1976a; Kemp 81 Kemp 1978) and SE Asian rainforest (Leighton

1982). There has been no detailed account of the diet for any of the 12 hornbill species which occur in African rainforests (Kemp

1979). This paper describes the diet of the black-and-white casqued hornbill (Byeanistes subcylindrieus) in Kibale Forest, Uganda.

Knowledge of the diet is a prerequisite for understanding the relationship between hornbills and ‘their‘ environment. “The availability of food has a strong influence. on the timing of hornbill breeding (Kemp 1976b; Chapter IV), reproductive success

(Chapters IV & V), ranging patterns, and social organization

(Leighton 1986). Since hornbills mediate seed-dispersal for rainforest trees (Leighton 1982; Kalina in prep; Kalina 8 Butynski

(b) in prep), particular attention to dietary needs of these birds and their influences on the regeneration of this fragile and. threatened ecosystem is needed.

46 47

Methods In 1981, I began a long-term study of the black-and-white casqued hornbill in Kibale Forest, western Uganda. The study area consists of both primary forest and selectively logged tropical rain forest (Chapter I). Data used in this paper were collected during over 4000 h of field work in Kibale Forest from 1981-1984 and during yearly working-visits since 1986.

Methods used to identify foods in the diet of B. suDeylindrieus included:

1. opportunistic observations, inspections of the ground below nests,.

”nest-watches,” wa "nest-trap” collections.

Dpuortunistic Observations

Opportunistic observations on food habits were recorded while I was following hornbills, watching fruiting trees, or conducting censuses, tree phenology, and other work in the forest. Some food items were first found during sporadic inspections of the ground below active nests.

NeSL-Hatshﬂ

Since 1981, 45 B. Wen nests have been found. All were located in natural cavities of large trees 8-27 m above ground.

Much information on the diet of B. subcylinuujeus was gained by quietly sitting and watching these nests. "Nest-watch" data used in this paper were collected over the 1983-1984 nesting season during 4 48 h (n - 28) and 12 h (n - 28) sampling periods (700-1100 h and 700-

1900 h). Observations were made from locations 20-60 m from the base of the nest tree using a telescope or 10 x 408 Leitz binoculars. Only information at sealed, occupied nests was analyzed. Thirteen nests were observed for a total of 447 h (Table 3.1).

I only watched nests with clearly visible entrances so that birds landing on the nest could be identified and the food items fed into the nest distinguished. The male hornbill’s arrival and departure times at the nest, and the kinds and numbers of items fed into the nest, were recorded. Hornbills are multiple-prey loaders; i.e., more than one food item may be collected before a load is delivered to the nest.

Male hornbills regurgitate food items into their bill tips just before they feed them to the female in the nest. These food items are usually easy to see and identify. Each species of fruit was identified and given a rating of 1-4 based on size, with 1 being the smallest and 4 the largest. Examples of species (with approximate mean diameter of the fruit) in each category are: Deltis Durandii

(0.5 cm) . l, Djosuyras abyssiujea (1.0 cm) - 2, Mimusous bagshawej

(2.0 cm) - 3, Eieus gauei (3.0 cm) - 4. Size ranges (diameter) of fruits for each category are as follows: 1 - (0.3-0.7 cm), 2 -

(0.8-1.5 cm), 3 - (1.6-2.5 cm), 4 - 2.6-3.5 .cm). Volumes were calculated for each category, based on the medians: 1 - 0.07 cm3, 2 - 0.52 cm3, 3 -= 4.19 cm3, 4 . 14.14 cm3. These values were derived from the diameters and volumes of samples of fruits. 49

Invertebrates were identified or described and also rated into these same four size categories.

Traps were placed below nests to catch fruits, seeds, insect remains, and other materials dropped by hornbills. These “nest- traps” consisted of burlap fabric suspended l m above the ground on a square frame. Each trap had a collecting area of 1 square metre.

Rainwater was able to drain well through the small holes in the cloth, while all fruits and debris which fell into the trap remained there. The burlap was replaced as needed. Trap contents were collected, labeled, and sun-dried about every 6th day (Table 3.1).

Traps were usually set in place before the hornbill entered the nest cavity. In most cases, the entire nest period was sampled in this way. Nesting hornbills eject their feces and throw debris out the nest hole, so that the cavity remains clean. The percentage of the discarded nest debris caught in the trap varied between nests. The amount of debris falling in the trap depended on foliage cover, nest height, and angle of the nest opening. Because of these variables, the purpose of setting nest-traps was to: (1) identify rare food items and those items usually difficult to see, (2) see how specific food items were "processed” (e.g., defecated or regurgitated), (3) get relative indexes of quantities of various food items fed throughout the nest-cycle, and (4) collect "processed" seeds for germination experiments. Table 3.1.-Byeanistes subcxljnurjgus nest-watch and nest-trap locations and collection regimens in Kibale Forest, Uganda (1983-84).

No. of Hours Hours No. of No. of Days Between Study Forest Nests of Nest- Per Nest Nests Hith Collec- Collections Area Type Hatched Hatches Mean1SD Traps tions MeaniSD

Ngogo Unlogged 8 294.4 36.8:41.0 10 150 6.6:l.8

K-3O Unlogged 1 4.0 4.0: 0 3 , 49 6.0:2.0 50

K-l4' Light- 2 40.3 20.2122.5 1 15 5.7:l.2 moderately logged

K-15 Heavily 2 108.0 34.4:34.8 2 27 6.0:1.0 logged

Total 13 446.7 15 241

Once trap contents. were dried, the materials were sorted, counted, weighed, identified, and recorded. Volumes of fruits, seeds, and insect parts were measured by displacement in a graduated cylinder, or were calculated from shape and measures of length and diameters. All insect remains were taken to the National Museums of

Kenya for identification by John Njoroge.

Nutritional Analysis

Sun-dried samples of fruits eaten by hornbills were sent to the

Range Science Laboratory at Colorado State University, or to Dr.

Peter Haterman at the University of Strathelyde, for chemical analysis in order to determine nutritional content. Analyses were carried out on a variety of fruit parts, but only results concerning ripe, fleshy food parts are presented here. Fruits were analyzed for calories per gram, percentage total available carbohydrates (or nonstructural carbohydrates), percentage lipids cn' fat, percentage protein, and total phenolics, including the presence of condensed tannins.

Fruit Burpholugy

The color, shape, numbers of seeds/fruit, and characteristics of the fleshy fruit parts were recorded for all fruit species.

Length, maximum and minimum cross-sectional diameters of seeds, and of seeds plus surrounding flesh, were measured for a sample of fruits of each species. Fruits were grouped into the four morphological types (capsular, drupaceous, husked, and fig) as described by Leighton (1982). "Capsular fruits" are dry, dehiscent, 52

and many-seeded. They are often conspicuously colored and contain oily, arillate seeds. 'Drupaceous fruits" are more or less fleshy, one-celled fruits with one or more seeds. Most of these fruits may be plucked by hornbills and swallowed whole. 'Husked fruits" have a thick, woody pericarp that requires extensive processing. "Figs”

(Ejeus spp.) are soft, fleshy fruits with many small seeds. Figs lack a hard covering.

R 5 1t nd i '

Eouds and Furaging

Fruits and other items were observed to be eaten by B_. subeyljndrjeus in Kibale Forest, Uganda (Appendix 3-A). Foods recorded for this species in south-central Uganda by Kilham (1956) and others are also included in order to make a complete listing of known foods for this species. B. subgyljnuujeus eat a minimum of 67 fruit species from 26 plant families, plus lichens, fungi, mosses, mammals, birds, reptiles, mollusks, and arthropods. Unlike the SE

Asian forest hornbills described by Leighton (1982), B. subeyliudrjeus select fruits which are diverse in color and morphological type, with sizes ranging in diameter from the 5 111m

Deltis afrieaua to 60 mm Ejeus uaeusu. Also, Be subeylinarjeus eat the same species of fruits consumed by sympatric primates

(Struhsaker 1978; Kalina & Butynski (a) in prep). Fruits may have. single large stones, or they may be many-seeded (Appendix 3-B).

Like the SE Asian hornbills, B. suBeylingrjeus apparently takes almost any animal prey which it can find, catch, and swallow. 53

Proportions of fruit in the diet varied from year to year and from season to season. During the 1987-88 breeding season, for example, Rauvolfia uyyuhylla fruits comprised most of the diet at some nests. Yet this species accounted for less than 1% of the fruits fed into nests during 1983-84. Also, fruits of [:jehjlja splengjua were not available during the 1983-84 breeding season, although they were highly preferred during the prebreeding months of

August and September.

B. suBeylindrieus are most frequently observed foraging in the rainforest canopy, hopping or fluttering from branch to branch, leaning forward to pluck a fruit with the tip of the bill. Then, with a backward flick of the head, the bird swallows the fruit.

The hornbill’s long, laterally flattened bill is well adapted for frugivory. The long bill extends the bird’s reach, so that a greater number of fruits are available within the radius of the perched bird. Unlike the sympatric crowned hornbills (leekus

l t rmi us), which hover above trees and sally in to pluck fruits while remaining in flight, B. subcylindricus generally pick fruits while perched. Hornbills are particularly adept at manipulating capsulate fruits. These fruits are often conspicuous, colorful, and attractive to hornbills, which are able to peck and pry them apart at the seams. In this way they get at the edible part of the fruit before less-agile competitors, which must wait for the tough capsules to dehisce. Unlike barbets, starlings, and other small birds which sometimes act as ”fruit-robbers” that tear off 54 fruit pieces and leave seeds to drop below the parent tree, hornbills are high-quality seed dispersers for most trees they forage in (Kalina in prep; Kalina & Butynski (b) in prep).

Hornbills swallow large seeds that other birds and mamals cannot handle, ”process" them in the crop, and then regurgitate them cleaned, but intact and viable. Small seeds (< 0.8 cm) pass through the gut and are usually defecated intact (Appendix 3-B). Insects swallowed whole are sometimes alive when they are later regurgitated into the nest, as was the case of one katydid (Euryeuryuha sp.) which I found that had been dropped below a nest.

The hornbill beak is strong enough to open thick, leathery fruit capsules, but it is also a sensitive organ used to test the ripeness and quality of fruit before ingestion. Hornbills visually examine fruits, then squeeze and toss them in their bill tips before swallowing good ones or dropping those they reject. Hornbills prefer ripe, insect-free fruits.

B. subcylindrieus sometimes forages in lianas (e.g.,

Phytolaceaceae) or bushy, forest-edge tree's (e.g., Bridelia mierautha). Hornbills also cling vertically to branches and peel lichens from the bark of trees. Mosses and lichens are sometimes passed out in feces. Fungus is fed into nests by male hornbills, and presumably is also ingested by the imprisoned female.

Hith repeated, downward thrusts of the bill, hornbills cleave pieces of bark from wood and then use the bill as a lever to remove the bark. Bark and wood strips collected in this way are carried and tossed about by males during displays (Chapters IV, V, 8 VI) and 55

are used for nest lining. Bark peeling and the pecking of rotten wood also expose grubs and other insect prey, which are then crushed and eaten. Hornbills similarly sort through rotting seeds in old, dehisced ﬂeuuguta mﬂBLaegjl capsules, apparently in search of prey. I have never observed hornbills foraging for mantid oothecae, but these items are often delivered to nests. These well- camouflaged oothecae must be highly sought after despite the gall- like appearance and tough exterior.

B. subeyliadrjeus hunts for a wide variety of vertebrate and invertebrate prey (Appendix 3-A). Eggs ranging in size from those of the small mousebird (Kilham 1956) to large chicken-sized eggs like that. of' a guinea fowl (pers. obs.) are sought after and devoured. Lizard eggs are removed from the ground. I observed six of them being fed into a nest, along with the adult red and black skink (3j_Qp_a fernandj). Nestling and adult sunbirds were once regurgitated by a male hornbill into a nest. Hornbills, traveling alone or in flocks, raid weaver bird colonies and eat the eggs, nestlings, and any adults they can catch (J. Corner, pers. comm.; pers. obs.). Egyptian rousette bats (Buusettus_ egyutteus) are sometimes caught in flight (J. Baranga. pers. comm.). I suspected that a roost was raided when one male hornbill delivered several

Eutesjgus gauensls bats to a nest. I identified one that it dropped. Captive hornbills feed on rodents (Kilham 1956; pers. obs.), swallowing them whole. Most mammal fur which was dropped by hornbills into traps below nests probably came from rodents. 56

The remains of a lesser galago (Galagu senegaleusis) were found in one nest-trap. The location of this trap was such that the animal could only have fallen into it from the edge of the hornbill nest. The skull bones were crushed in the characteristic way that

B. subeyljnurjeus kill their prey. The contents of the skull were gone, but the body was intact. I suspect that the animal was too large to fit into the narrow entrance to the nest. It was certainly too large to swallow whole.

The kinds of invertebrates eaten by hornbills are varied, with prey items ranging in size from the fly or bee to the goliath beetle or 6-inch-long millipede. Foraging for. invertebrates is accomplished in many different ways. Hornbills perform aerial hawking and swooping maneuvers to catch alate termites. Flies and bees are snapped from the air as the insects fly by the hornbill’s head. The presence of millipedes, lizard eggs, and other food items suggests that they regularly forage on or near the ground. B. SUD; eylinuuieus hunts for terrestrial prey by scanning the ground from the perch of a low limb.

B. subeyljudrieus is omnivorous, but feeds primarily on fruit.

Ninety-one percent of the volume of the 13,235 edible items delivered by males at nests (during 1983-84 nest-watches) were fruits; 9% were invertebrates. The remainder was comprised of 16 birds or mamals, 17 eggs, 28 pieces of lichen, and 3 pieces of moss. In addition, 61 pieces of bark were delivered for nesting material. 57

Nest-Hatgh Data

Information collected during nest-watches (Tables 3.2 and 3.3) was preferable to nest-trap data for examining relative proportions of the diet. During nest-watches, the exact number and sequence of all items fed into the nest could be recorded. Soft food items such as fungi, papaya (CaLtea uauaya), insect larvae, and grubs were accounted for in nest-watch data, whereas these items were absent from nest-traps.

On the basis of volume, invertebrates made up 9% of the B. 520; eyliuuuieus diet. They comprised a greater percentage of the diet for hornbills in the heavily logged study area (15% in K-15) than in unlogged forest (9% in Ngogo) or light-moderately logged forest (5% in K-14).

The largest number of insects fed upon were in size categories

1 (509 items) and 2 (272 cases). The greatest total volume of insects was, however, in size category 4, which represented 72% of the total volume of all invertebrates delivered to nests (Table 3.2).

Figs (fieus spp.) were the most prominent fruit in the diet, comprising 58% by volume of all fruits fed. A greater volume of figs was eaten in light-moderately logged forest (80% of all fruits in K-l4) than in heavily logged forest (54% in K-15) or unlogged forest (52% in Ngogo). Eteus spp. fruits were sometimes difficult to identify during nest-watches and were, therefore, counted, desdribed, and recorded according to size. Eleus spp. were represented in all size 58

AAAAAA

5‘ IN 05 N N m 2) 2)

8) vvvvvv

( ( (15) (

(

(n)

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1,874)

3,714)

(n)

(1983-84). abyssiniea

(n (n

items

papaya

durandjj gurapdjj

insects spp. welwitschij

welwitsehjj

Uganda

K-15

K-lS

Byeanistes

1 and

Invertebrates

insect Invertebrates Eieus

at Dipspyros

Celtis Cariea Others Olea

Others

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fed Forest,

and

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(27) (24) vvv (

( (7 (1

fruit

Kibale

(cm3)

1,755)

2,753)

- -

invertebrates

abxssjuisa.(46) abxssinisa

number

volume

guranuii

duranuij

999913

spp. sop.

and

K-14 K-14

total

nest-watches total

Invertebrates

Eicus

Beltis

Others Celtis

Diesexros

% Qiosnxros Carlee Eicus

fruits

for 1)

7) 2) 1) 3) 8) 9)

during

(57) (18) (13) ( ( ( (47) ( ( ( (

order

nests

9,751)

8,477)

Rank

eus

abyssiniga

bagshauei

durandii

spp. son.

3.2.-Rank

Ngogo Ngogo

Invertebrates

Ejeus

Others

Table Others

Celtis Uiuusons,bagshauei

Diosnxros .Eicus Minusons Celtis

59 4

91 14 19 71

68 48 35 198

141 494 4 14.14 2.6-3.5 9 2 identified 16 67 3 4.19

nest-watches 1.6-2.5 Category 18 32 128 247 2

during mantids 0.52

Invertebrates Size necessarily 0.8-1.5 not

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0 5 6

19 26 29

34 32

434

beetles beetles,

0.07 natalensis were

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dung and

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1 3

2 microcagpa

39 56 30

551 grasshoppers,

204 792 4

..35

invertebrates 2884

14.14 Goliath 2.6-3.5

and

termites

welwitschii,'Ficus 2

22 dawei 51 18

14 82

Bycanistes

344 africana 316 267 3 1119 1324

4.19 Olea 1.6-2.5

Fruits Pseudospondias

into

caterpillars,

Ficus millipedes,

Category

Celtis

wasps

33 28 17 50

Fruits 78 47

fed

525 were: 447

859 1010 7010 3645

0.52

. caterpillars, Size

0.8-1.5

. abyssinTca,

category.

katydids,

bagshawei, mantids, 1

bees,

termites,

durandii, 69 29 35

braEhylepis,

176 503 category 104

A 2511 1488 0.07 size 0.3-0.7

invertebrates

size

Flies, Flies,

Roaches, Roaches,

Celtis

Ficus

Mlmusops Diospyros

and each

species.

Size

Size Size

Size

Size Size

Size Size 31 (1983-84), 3) to

(cm) (cm3)

(cm

(cm3)

species

items

items items

3.3.-Fruits

range

. Fruits:

. volume items

items

volume

items

volume

o Inverts:

Volume No.

Volume % N

% %

Volume %

K-15

K-14 Major N Volume Size

Table

categories of fruits. The following analysis of the relative

importance of the various fieus spp. in the diet of B. supeylindri- eus is incomplete, therefore, since it only accounts for those

species that could readily be identified. It does, however, give

some indication of variation in number and volume of ﬁteus spp.

being delivered to the nest. Overall, for all study areas combined,

Ejeus uatalensis ranked first with 44% of all the fieus fruits fed.

Ejeus dauei ranked first for volume (14% of all figs fed). [Lotus

Brachylepis ranked first (13% of all figs fed) in K-15, but was

ranked third (1% of all figs fed; 5% by volume) in the analysis of

all study areas combined.

Papaya (B. papaya) was the only cultivated fruit observed fed

into nests. It was only recorded at nests in the selectively logged

areas (K-14 and K-15). This fruit, which comprised 2-3% of the

fruit fed at nests in these study areas, was delivered as large,

amorphous chunks. Papaya accounted for 1% of the total volume of

fruits fed for all study areas combined. Hornbills in the logged

forest flew to nearby cultivated areas where this fruit could be

found. Hornbills at Ngogo would have to fly 11 km for such access.

Diaspyuus abyssiniea fruits ranked first in the number of fruit

items fed into nests at Ngogo and K-14, and second for K-15 (Table

3.2). D. apyssiuiea fruits ranked second to fieus spp. by volume

for all nests in all study areas. D. atyssiuiea is among the four

most. common tree species in all study' areas .(Butynski in prep.

Skorupa 1988), and it produces fruits throughout the nesting season

(unpubl. data). 61

Celtis durandii fruits comprised 57% of the fruit items fed into nests in K-15, but this was only 9% of the volume of all fruits fed. D. durandji ranked in the top five fruit species fed by item, or by volume, in all study areas. It was less significant, however, in the diet of hornbills at Ngogo and K-l4 (1% by volume) than it was in K-15.

Nest-Hateh Biae Categories (Table 3.3)

For Ngogo and K-l4, the greatest number of fruit items was in size category 2, a reflection of the large number of D. abyssinica fruits fed into nests. The greatest number of fruits were in size category 1 for K-15, a reflection of the large quantities of

B. gurandii fed into nests. fjeus spp., which made up most of the

B. subcylindricus diet, occurred in all sizes.

The number of invertebrate items per size category varied between study areas. The greatest volume was always in size category 4. Lepidoptera larvae constituted many of the items in the smaller categories, whereas larger mantids, beetles, and millipedes made up much of categories 3 and 4.

W Figs and soft foods such as larvae, flies, and fungus were often fed during nest-watches, but were under-represented in nest- traps (Tables 3.4 and 3.5). Although fig seeds were part of the fecal debris in traps, a relative estimate of the number of ficus

2 7 2)

6 6

17 36

10 16

62%)

67%)

(44%)

the

by “fecal

seeds

fruits fruits: fruits

seeds

found

ca of

Combined intact

15,044

9,711 3,344

ssinica ssinica

I ssinica ssinica

ssinica

part I

I All

debris

debris yss1n

uran n n

remains

a ab ab

ab ab

dropped

Invertebrates

Fecal

D. D. Fecal

D. D.

“683

I'n‘verte

ﬁve—Ema all

C—

sometimes

were

3 5

\DQMNN 9

32 ll 10 58%)

27% 22

(37%)

{6%) (

but

were

seeds seeds

seeds

percentage seeds

seeds seeds

seeds

consumed

logged)

383.5

2,156 1,029

x-15

rates

Ficus

I I not I

seeds

fruits

seeds

ssinica shawei

ssinica ssinica

debris debris

n n n

uran

order

durandii ba

durandii ab ab

were

(Heavily

Invertebrates

Invertebrates Fecal

41683 41683 Fecal

0. D.

0. C.

7T magma- 72883

'TGWs C.— I'tTverte

_C_._

(g) (c1113)

items

volume. iculata

of or

ranked

QNNNN 2

gsﬁawel

"fruits"

13 12;

67%) 73%) (33

(34%)

volune weight

number

weight

ueria

seeds seeds seeds

fruits fruits

seeds total by

seeds

ruits total

whereas

musops

logged) seeds

seeds

Van ca

total 132

361 513

of nest-traps,

rates % than I

I I % K-14 iI

of ssinica

shawei ssln1ca ssinica

ssinica n

n debris

debris

by by from p1eces yss

urandii urand1

ba Egshawei

a5 durandii ab

a ab ab

0 hornbills,

rather

Type)

(Light-mod.

Invertebrates

Fecal

C. 0. Fecal

O D. C.- M. L; M.

mails—— I'11verte Hc—iod

0— __

aiculata

order order listed.

order H—Sggsfﬁwe

collected WVNNN

5 Rank

m 04001") 2 Rank (Forest

53%)

27 17

53%) are

l6 71%)

Rank

defecated

Area/ remains

seeds

seeds or

fruits

seeds

seeds seeds

seeds presence/absence

seeds

Study

food 538.5

2,927

1,740 by n1ca

rates

K—3O

ﬁawel

I ssinica I

ssinlca spp.

ssinica

debris

iculata 1culata

(Unlogged)

apiculata

a representing-

durandii

durandii abyss a5 abyssinica ab

asb

regurgitated

Invertebrates

Fecal

D. Fecal

D. D.

C. duranﬁll RT_g___{__5‘aEs»

IRverte E FTcus measured

liverte T

"V.

items

been

subcylindricus

were

3) 7

6 6 0105

77%) 14)

42%) 41;

(12

(67%)

had

I ICeltgs

Only spp.

hornbill.

seeds seeds seeds

fruits

"Seeds'I

Ficus

seeds ssinica

aeEris.' Faps.

male

-Bycanistes

uran

9,600 2,290

nica

6,429 ab

2. rates 1.

I e I I

ssinica

ssinica 3. Ngogo ss1n1ca

ssinica

debris

n 11

(Unlogged)

ab ab

abyss abyssinicafruits

Invertebrates

Fecal Key:

O. D D.

Table Notes:

Ufa

hdurandii Ivaerte 15.1-vertebrates FEca D;

Table 3.5.-Rank order by percentage for frequency of resence or absence of particular invertebrates in Bycanistes subcylindricus nest-traps, Kibale Forest, Uganda (1983-84 . Only categories representing 2 2% are listed.

Study Area Ngogo K-3O K-14 K-15

Dates covered Oct. 8-Feb. 13 Oct. l6-Feb. 14 Oct. 23-Jan. 17 Oct. 23-Feb. 6 Total No. of nest days 982 296 92 215 covered Total no. of invertebrates 550 ‘35 46 98 No. 2“l 13:) Millipede 23:) 110. 2 231) . 2 281) Mantidae "" MONO‘D‘DWQMMMNNNNN No. 2 24) No 1 1 l9 No. 1 No. 1 16 No. 25 (13 ”NWMMMQNNN Pachnoda arrowi Cetoniinae 7 Millipede 11 G511atﬁus sp. Pedinorrhina subaenae 6 Cetoniinae 7 Mesoto us sp. Pa1norrﬁina subaenae Widae ( 5; Mesoto us sp. 4 EudIcella sp. 63 Cetoniinae No. 25 2 Rintiaae 4 Cetoniiaae Pachnoda spp. MAAMAMA Proso coelus sp. 2 Carabidae N5. 25 tun es sp. 2 'Homoderus mellyi Eudicella ralli G o 1' 1at R us sp. 2 Galiathus sp. MR CaraEi aae am. ndet. . [ami lnae 2 R'a'ntidae Isopod No. 21 ( 2 No. 25 Metopodontus savagei Metopodontus savagei 2 1 ElateFTHae Millipede No. 21 No. 13 A v 'Total % O N (36) (100) (92)

aCategories of invertebrates include several species: No. 1: Metopodontus savagei, Mesotopus sp., Homoderus mellyi, or Carabidae family indet. No. 2: DTCrarorrhina, Eccoptocnemis babaulti, Ecoptocnemis sp., or Chelorrhina No. 13: Eudicella ralli or Carabidaellndet. No. 21: Peainorrhina, ethodesma No. 25: Metopodontus savagej_or Cetoniinae indet. 64 fruits fed into the nest. was difficult to determine from such samples.

The nest-trap method compares favorably with the nest-watch method for other fruit species, particularly ones with large, hard seeds. For example, as is the case for nest-watch results,

D. abyssjnjea, B. Mum, and invertebrates represent the top- ranking items in the diet based on nest-trap analysis.

Traps are preferable to nest-watches in that less effort must be extended by the researcher for the collection of a large amount of information. Also, foods unknown to the observer during nest- watches can often be collected and identified from traps. During this study, seeds of 20 species were collected in traps and remain unidentified. The seeds are catalogued, however, for possible future reference. They must have come from rare trees or lianas.

The nest-trap method is particularly good for the

identification of invertebrate remains. Most invertebrate species

(Appendix 3-A) were taken from traps. Invertebrates from traps had been defecated, regurgitated, or crushed and dropped by hornbills.

Records of the presence or absence of invertebrate categories during trap collections (samples of the diet throughout the 6-month nesting

season) can be used to map seasonal changes in abundance of

particular species in the diet. It must be remembered, however, that large-bodied, keratinacious Species such as the scarabs are_

perhaps over-represented Since their body parts are more difficult

to digest than other species. Scarabeidae are, nevertheless,

frequent prey items. These insects are probably very obvious 65 because of their large size and the noisy, buzzing sound of their flight. This family of insects is also extremely diverse and numerous in the Ugandan forests (M. Ritchie, pers. comm.).

From the presence or absence data collected, differences between study areas were evident in relative amounts of various invertebrates in the diet of hornbills (Table 3.5). Beetles and mantids, for example, ranked highest at the Ngogo study area, and millipedes were represented in only 2% of the trap collections there. Yet in all the Kanyawara study areas, millipedes comprised

26% of the collections for K-30, 11% for K-l4, and 7% for K-15.

Nutrition

Based on chemical analysis of selected fruit species

(Appendices 3-C, 3-D), hornbills primarily ate ripe fruit items that were relatively low in toxins (phenolics). The chemical composition of fruits in the diet was variable. Arils from capsular Bljgm unijugata and Trichilia splendida fruits were very high in lipids compared to the pulp of D. abyssjniea and Pseudosppndias mierpearpa drupes. 1D. abyssinica. was high in nonstructural carbohydrates.

_i;'_i_c_us spp. were, for a fruit, relatively high in protein (Janzen

1979). The nutritional breakdown of these wild fruits should be informative for aviculturists attempting to breed in captivity birds that are primarily frugivorous in the wild. Hild fruit species have a relatively high protein content for which there is no domestic fruit substitute (M. Underwood, pers. comm.; Hatt & Merrill 1977). 66

Invertebrates were not analyzed nutritionally, since prior research has shown that various insect tissues are similar in terms of caloric value (Slobodkin 1961). Insects and other animals were undoubtedly' important in their' contribution of protein. Other dietary components, such as lichen, may have had minerals that, in addition to calories, were significant to the diet.

Fruit species differing in nutritional composition may have been of varying degrees of significance at different stages of the hornbill breeding cycle. ,1. splendiga fruits, for example, comprised much or most of the hornbill diet during prebreeding months. A diet of I. splendiga fruits alone would be too low in protein to sustain hornbill nestlings (M. Underwood, pers. comm.). but the high energy content in these fruits could help bring hornbills into breeding condition. 1. spleugiga is higher in energy than other fruits, and that energy may be more readily digestible because it is in the form of lipids (M. Underwood, pers. comm.).

Perhaps a diet of I. splendiga fruits allows hornbills to store fat on their bodies, helping them to meet energetic demands during the long breeding season.

Eieus spp. fruits (figs) comprised much of the diet during the breeding season. Figs, unlike I. splengjga fruits, are high in protein (Appendix 3-C). At 21% crude protein, figs would provide close to the 25% protein diet that is probably necessary for raising hornbill young (M. Underwood, pers. comm.): Frugivorous, tropical cavity-nesting toucans (family Ramphastidae) need 25% protein in the diet for their nestlings to thrive in captivity (Iwinski & 67

Iwinski 1984; Svoboda 1988). Since ﬁgs spp. and D. aByssjnjea fruits comprised approximately 80% of the hornbill diet during the nesting period, further analyses of D. abyssinica should be conducted to determine if these fruits are also high in protein. If total caloric intake is to be determined, the energy content of

Eieus spp. must also be ascertained.

mansions

Four methods were used to study the diet of B. subcyljudrieus, an African rainforest hornbill. Most quantitative data were collected at nests during one breeding season. Although B. s_u_b_- cylinduieus ate a wide variety of fruits, fieus spp. and D. apys; sluiea fruits accounted for most of the diet. Proportions of fruits represented in the diet were found to vary from year to year, and from season to season.

The differences in nutritional values of foods, the energy expended in obtaining the foods, and the degree of assimilation of various nutrients have not been addressed in this study. Volumes, weights, and frequencies of food items are given, however, as approximations of their significance in the diet. Further nutritional analyses of fruits eaten by hornbills are recommended. 68

REFERENCES

Butynski, T. M. in prep. Comparative ecology of the blue monkey (Bereppithecus mutis) in high and low density subpopulations.

Eggeling, H. J. and I. R. Dale. 1952. Iue_1pg1geuuus_1uees_ef_the Dgauga_£uuteetuuate. 2nd edition. Government Printer, Entebbe. Hamilton, A. C. 1981. A field Guide tp Dganda Fprest luees. Makerere University Printery, Kampala.

Hubbard, C. E., E. Milne-Redhead, R. M. Polhill and H. B. Turrill, eds. 1952. Flor of Tr 'cal st r' . Crown Agents, London.

Iwinski, D. and B. Iwinski. 1984. Too many toucans. The A.F.A. Hat hbi X6:18-20.

Janzen, D. H. 1979. How to be a fig. Ann. Rev. Ecol. Syst. 10:13-52.

Kalina, J. in prep. Effects of animal dispersers on germination success of five tree species in Kibale Forest, Uganda.

Kalina, J. and T. M. Butynski (a) in prep. Comparative feeding ecology of sympatric hornbills and primates in Kibale Forest, Uganda.

Kalina, J. and T. M. Butynski (b) in prep. Seed dispersal ecology of lrichilia splendida in Kibale Forest, Uganda.

Kemp, A. C. 1976a. A study of the ecology. behaviour and systematics of Tockus hornbills (Aves: Bucerotidae). Iransv. Bus. Mem. ZD.

Kemp, A. C. 1976b. Factors affecting the onset of breeding in African hornbills. Dupe, 15th Int, Drn. Cpng[., pp. 248-257.

Kemp, A. C. 1979. A review of the hornbills: Biology and radiation. Ljying Bjud 17:105-136.

Kemp, A. C. and M. I. Kemp. 1978. Bucorvus and Sagittarius: Two modes of terrestrial predation. Pr S . fr. tor HEELS, pp° 13'16' 69

Kilham, L. 1956. Breeding and other habits of casqued hornbills (8154.519; W) W 131(9):

Leighton, M. 1982. Fruit resources and patterns of feeding, spacing, and grouping among sympatric Bornean hornbills. Ph.D. dissertation, Univ. Calif, Davis.

Leighton, M. 1986. Hornbill social dispersion: Variations on a monogamous theme, pp. 108-130. In Eeplpgieal Aspects pf Boeial Evolution, eds. D. I. Rubenstein and R. H. Hrangham. Princeton Univ. Press.

Skorupa, J. P. 1988. The effects of selective timber harvesting on rainforest primates in Kibale Forest, Uganda. Ph.D. dissertation, Univ. Calif., Davis.

Slobodkin, L. B. 1961. Preliminary ideas for a predictive theory of zoology. Am. Nat. 45:147-153.

Struhsaker, T. T. 1978. Food habits of five monkey species in Kibale Forest, Uganda. In Recent Agvances in Primatplggy, eds. D. C. Chivers and J. Herbert. 1:225-248. Academic Press, London.

Svoboda, F. J. 1988. Toucan tending. [he A.F.A, Hatehpirg XV3:36- 38.

Hatt, B. K. and A. L. Merrill. 1977. C m osi F 0d Bay. ProcessedssPrepaueg. Agriculture Handbook #8, U. S. Dept. of Agriculture, Hashington, D.C. 70

APPENDIX 3-A

A SYSTEMATIC LIST OF ALL FOOD ITEMS RECORDED IN THE DIET OF BYBANISTES SDBBXLLNDBLQDB

Observations were made in Kibale Forest, Uganda, by the author unless noted otherwise (a or b). The following symbols indicate where the food was recorded: B - below nest, N - nest-watch, F - foraging observation.

Food Item

Family Species

PLANT FOODS (FRUITS)

Agavaceae Dracaena steudneri

Anacardiaceae Eseudosppugias uieupeaupa Annonaceae Monodoua myristica We 'smgeusis Apocynaceae Aauyelfia pxyphylla Voacanga thouarsii

Boraginaceae Dguuia abyssinica

Burseraceae Danarium sehweinfurthii

Butaceae Eagarppsis angolepsis

Caricaceae Dauiea papaya

Ebenaceae Diospyrps apyssipiea

Euphorbiaceae Brigelia migrantua Bapium elliptieum

Lauraceae Beilseuuiegia ugangeusis

Meliaceae Triehilia splengiua Melianthaceae Beusama abyssiniea

Moraceae Antiaris tpuicaria 593999.13 L9__sn bero 71

Food Item

Family Species

Bhlprpphpua excelsa Eieus braehylepis

XX Eieus prachypoda X Eieus eongensis Ficus eyanthistipula Eisus_u_dwi EiSUS exaseetata EIQUS DASHSQ Fieus natalensis XXXXXX XXXX Ficus polita U—usor lastea Musauga rc 101 XX Myristicaceae Eycanthus angolensis

Myrtaceae Magnum Oleaceae Dlea welwitsehii

Phytolaccaceae Phytplacea dodicandra

Rhamnaceae Naesoesis eminii Rubiaceae Vangueria apieulata

Rutaceae Isslee 3991119

Sapindaceae Blighia unijugata Lychnpdiseus ro mus

Sapotaceae Beguaertiodendron.oblanceolatum 111—mono bagshauea

Simaroubaceae mm

Sterculiaceae mm Stepeulia dawei

Ulmaceae Celtis africana Calm duLL—ndii

Verbenaceae Euemna augplensis

Unidentified 20 spp. 72

Food Item

Family Species

Moss

Fungus

Lichen

ANIMAL FOODS

Mammalia

Chiroptera Eptesicus capensis Rousettus egyptieus

Primate Balago senegalensis

Ayes

Colliidae Com. sp.

Nectariniidae Anthreptes epllaris

Ploceidae Plpeeus nigerrimus Ploceus nigricollis

Re i ia

Scinsidae Mabuya sp. Rippa fernandi

Chamaeleontidae Chamaelep sp.

Mollusea unident. ”snail"

Arthrppoda

Diplopoda unident. "millipede"

Insecta

Coleoptera

Lucanidae ﬁpmoderus mellyi Homoderus sp. 73

Food Item

Family Species

Metopodpntus sayagel Besptopus taua ngus Nigidi ius sp

WM XXXX

Scarabeidae X

Subfam. unident.

Cetoniinae Detpniinae unident. spp. Chelorrhina sp. Coelorrhina loricata Dicranorrhina mieans Eccoptocnemis bapaulti W89- M91931 Eudicella spp. Goliathus spp. Neptunides stauleyi Eachnoda arrowi Pachnoda sp. Eedinorrhina subaenae Stephanorrhina sp.

Mm SP- XXXXXXXXXXXXXXX

Hybosorinae genus and spp. unident. X

Coccinellidae genus unident.

Anthribidae genera unident. (3 spp.)

Elateridae ietralobus s

Meloidae genus unident.

Hydrophilidae §phaeridium,pietum

Cerambycidae §L§£DQLQmiS SP- Lamiinae genus unident.

Prioninae Acanthpphozus sp. 74

Food Item

Family Species B N F

Carabidae

Harpalinae Ietflus Sp. x

Fam. unident. (several spp.) x

Diptera x x x

Anthomyiidae Anthomyia sp. x

Fam. unident. (puparium) x

Lepidoptera

Pyralidae genus unident. x

Fam. unident. larvae (several spp.) x x x

Dictyoptera . x x x

Mantidae genus unident. x x x

(oothecae) genus unident. x x

Blattidae genus unident. x x x

Orthoptera x x x

Tettigoniidae genus unident. x

Hemiptera-Homoptera x x x

Cicadidae genus unident. x x x

Hymenoptera x x x

Apoidea Apis mellifeua agauseni x x x

Insect order indetermined for 9 specimens

aObservations in Kampala-Entebbe, Uganda, by J. Baranga, Isabirye Basuta (pers. comm.) and/or L. Kilham (1956).

bObservations in Kibale Forest by T. M. Butynski (pers. comm.); M. Ghiglieri (1985). 75

APPENDIX 3-B

DESCRIPTION OF FRUITS IN THE DIET OF BYCANISTES SUBCYLINDRICUS HORNBILLS IN UGANDA

j Fruit Fruit Fruit No. Part “12:3" 51:3“ "'32: °f 5235 Fruit Species Type Size Color Seeds Eaten Eaten 'Eaten Dispersal Damaged? (unl' (II!)

Antiaris toxicara Orupe 7-13 Red 1 Orupe Red ’7;13 Regurgitation No

Beilschmiedia Orupe 25 Purple- 1 Orupe Purple- 25 Regurgitation No uganaensis brown brown

Beguaertiodendron Orupe Red Orupe Red 7 oblanceolatum

Bersama abyssinica Capsule Red 4-5 Aril Red + No yellow Blighia unijugata Capsule 32-51 Red 3-4 Aril Yellow + 19 Regurgitation No black Defecation Bosqueia phoberos Orupe 17 Green Orupe Green 11 No

Bridelia micrantha Orupe 5-8 Blue- 1 Orupe Blue- 5-8 No black black

Canarium Orupe 25 Purple 1 Orupe Purple 25 7 scﬁiElnfurthii

Carica papaya 100-230 Green Many Pulp Orange Varies Regurgitation No Celtis africana Orupe 5 Brown 1 Orupe Brown 5 R urgitation Some- De ecation times

Celtis durandii Orupe 9 Yellow 1 Orupe Yellow 9 Regurgitation Some- Defecation times Chlorophora excelsa Achene 35 Green Many Achene Green 35. Defecation 7 Cola gigantea Capsule 105 Brown- 7 Aril Red 33 Regurgitation No red Cordia agyssinica Orupe 9 Purple 1 Orupe Purple 9 Regurgitation No

Defecation

Diospyros abyssinica Orupe 9-13 Red 1 Orupe Red 9-13 Regurgitation No

Defectation

Dracaena steudneri Orupe 9-13 Black Orupe Black 9-13 7 Eugenia iambolana 7 Fagaroasis Orupe 6-8 Purple 1 Orupe Purple 6-8 Regurgitation No angg ensis

Ficus brachylepis Fig 25-38 Green + Many Fig Green + 25-38 Defecation .No purple purple Ficus bracuypgga Fig 25 Many Fig 25 Defecation No 76

Col r f 1 Fruit Species T;:;t Slglt 5510: 52:3: EEEEn 23::Z SEEE::f ::§EE§S:: 0:£E§:d7 (no) (on)

flags cougensis Fig 25 Reddish Many Fig Reddish 25 Defecation No flags cyanthistupula Fig 19 Green Many Fig Green 19 Defecation No [1225.92221 Fig 27-50 Yellow Many Fig Yellow 27-50 Defecation No

Ficus egasperata . Fig 9-13 Red Many Fig Red 9-13 Defecation No E1£!§.!££!§2. Fig 30-55 Orange Many Fig Orange 30-55 Defecation No Ficus natalensis Fig 9-13 Yellow Many Fig Yellow 9-13 Defecation No [1225.221121 Fig 39-55 Purple- Many Fig Purple- 39-55 Defecation No green green '

Hagrisgn'i‘aca Orupe 9 Red Orupe Red 9 7

Lychnodiscus Capsule 24-39 Red 3 Aril Red + 18-24 Regurgitation No cercospermus white . Maesopsis £51311 Orupe 22-30 Yellow 1 Orupe Yellow 22-30 Regurgitation No Mimusops gagshawei Orupe 25 Orange 1 Orupe Orange 25 Regurgitation No Monodora nyristica Husk 100-225 Green 125-750 Pulp Hhite 20-30 Regurgitation No

Magus_1agtea Orupe 10 Green 3 Orupe Green 10 7 Musagga_cercopioides Achene 50 Green Many Achene Green 50 Defecation 7 Dlea_welwitschii Orupe 6-9 Purple 1 Orupe Purple 6-9 Regurgitation No Defectation

Phygolaggara Orupe 5-8 2::; 5 Orupe Red- 5-8 Regurgitation 7 ge orange Defecation frauga_angolensis Orupe 9 Green Orupe Green 9 Regurgitation 7

Pseudos ndias Orupe 18-27 Purple 1 Orupe Purple 15-25 Regurgitation No microcarpa

Pyganthus angolensis Capsule 25-44 :r::;; 1 Aril Pink Regurgitation 7

Rauvolfia oxyphylla Orupe 25 Green >3 ' Orupe Green 25 Regurgitation No Defecation Sapiug ellipticum Capsule 5 Aril 7 Sterculia gayei Capsule 75-100 Red 3 Aril Black 19 Regurgitation No 125122.2221113. Orupe 6-8 Red 1 Orupe Red 6-8 Regurgitation 7

Trichilia splendida Capsule 23-39 Red 3-4 Aril Black + 17-25 Regurgitation No

Uvariogsis congensis Orupe 17-45 Red 3-10 Orupe Red 17-45 Regurgitation No

Vangueria apiculata Orupe 25 Green Orupe Green 25 Ne

Voacanga thouarsii Orupe 50 Green Orupe Green 50 7

Sources: Eggling (1952), Milne-Redhead and Polbill (1952), Hamilton (1981), and personal observation.

1982 1982

1979

1982

1977 1976 1977 1977 1982

Sample Date

Dec.

Collection Aug.

Aug. Aug. Aug.

Mar.

Aug. Waterman)a

- -

- - - -

% P.

Lipids by 9.19 9.46 9.39 9.40 9.40 9.19 9.46 7.45 7.45

Crude 8.40

8.40

15.22 -1.00 19.83

28.45

21.10

(Ana1ysis

Protein

ITEMS 0.23

0.50 9.20

0.00 9.20

4.65 4.30

-1.00

11.45

13.90 10.77

11.45

FOOD 12.12 13.90

10.77 12.12 Con- densed

Tannins

3-C

gNMI—mNPwNMF-m PNNOMNMPNNO O O O O

Phe- 2.01 2.19 2.15 mochmtocnooooccnxmso "'1000

nolics

Total APPENDIX

SUBCYLINDRICUS basis. Part

fruits

fruits arils arils

BYCANISTES

Plant Ripe

Ripe Ripe Ripe weight

SOME

dry a

l 2 1 r—NMQ'LOWNQOI

ANALYSIS

11 12

analysis

splendida

unijugata

no: durandii

Species

exasperata aAll

CHEMICAL

Ficus

Sample Blighia

Celtis Trichilia

1983 1983 1982

1983 1984 1984 1982 1983

Sample

Univ.)3 Date

Collection Jan. June July July

of Aug. Aug.

April

State

6.81 6.70 ‘2.92

29.60 55.09 36.43 35.03

34.70 24.90 39.10 29.30 43.69

Lipids 40.00

Co1orado

5.13 5.42 7.46

Total

13.32 12.09 14.15 14.20

(Ana1ysis

Available

Carbohydrate

ITEMS

3-D

FOOD

Per

Gram

5783 6084 6184 6514 6789 6761 4228 4296

Calories

APPENDIX

Part

SUBCYLINDRICUS

fruits) fruits

fruits

arils arils

fruits)

arils)

basis.

Plant

(38

(100

(70

Ripe

Ripe Ripe

Ripe

BYCANISTES

weight

dry

SOME

on microcarpa l

1 1

ANALYSIS abyssinica spjendida

analysis

unijugata no:

Species

aAll

CHEMICAL Pseudospondias

Lichen

Sample

Diospyros Blighia

Trichilia

CHAPTER IV

BREEDING BIOLOGY OF THE BLACK-AND-HHITE CASOUED HORNBILL

(BYCANISTES SUBCYLINQRICQS) IN KIBALE FOREST, UGANDA

Introduction

Hornbills (family Bucerotidae) are best known for their unusual breeding habits. In most species, the nest entrance is sealed with mud with the female inside the tree cavity for much or all of the nesting period (Kemp 1979). The male feeds his mate through a narrow slit in the wall that barricades the nest. Observations of the breeding activity of hornbills in captivity have been published for many species, including the black-and-white casqued hornbill

(ﬁyganistes subcylindricus) (Harvey 1973; Porritt & Riley 1976;

Bourne & Chessell 1982). Very little information is available, however, for hornbills nesting under natural conditions in the wild.

This is particularly true for those species living in forests.

Moreau and Moreau (1941) and Kilham (1956) were among the first to describe the breeding activities of wild Bycanistes species“

The present study expands on their work with results from the first long-term, quantitative study of an African forest hornbill. As a broad overview, this report is meant to emphasize the many facets and complexities involved in 5. subcylindrjggs reproduction.

79 80

Objectives of this study were to (1) determine timing of nesting and its relationship to rainfall and food availability, (2) describe courtship and nesting behavior, (3) assess nest-site characteristics, (4) determine nest density and reproductive success in logged and unlogged areas, and (5) identify factors influencing breeding success. Information presented here on breeding behavior and nesting requirements for B. subcylindricus provides the basis for further appraisal of data concerning the socioecology and conservation of African rainforest hornbills.

Methods

In June 1981, I began a long-term study of the black-and-white casqued hornbill in Kibale Forest Reserve, western Uganda (0 13 -

0 41 N and 30 19 -30 32 E). Intensive research ended in June 1984, but nest monitoring continued every year (except 1985) through 1987.

Observations on hornbill activity and behavior were made opportunistically, or while systematically watching nests and fruiting trees. From the start, every effort was made to locate all hornbill nests in the four study areas: 6.6 km2 of Ngogo, and 4 km2 of Kanyawara (1.7 km2 of K-30, 1.1 km2 of K-l4, and 1.2 km2 of

K-15).

Ngogo is a nature reserve, consisting of primary, unlogged forest. Kanyawara is located 11 km north of Ngogo and consists of unlogged forest (K-30), lightly logged forest (K-l4), and heavily logged forest (K-15). These areas are described in Struhsaker

(1975), Ghiglieri (1984), Skorupa (1988), and Butynski (in prep). 81

Over 300 km of trail system permitted all parts of the study areas

to be searched for birds and nests. By the 1983-84 breeding season,

all regularly used nests in survey areas had been found.

Hornbill nests, which are located in natural cavities of large

trees, were usually found by following the sounds of the birds

displaying, building, or feeding at the sites. Each year, old nests were checked for occupancy and new nests were located. I made a

distinction between proven nests and other tree cavities where

hornbills displayed but never, to my knowledge, sealed the entrance with mud. These I called "display cavities." Cavities that were

occupied and at least partially sealed with mud at one time or

another I considered "nest cavities.”

During the 1983-84 breeding season, each nest was checked every

1-3 days until the nest entrance was sealed. After that, the nest

was checked every 1-6 days until the 100th day of confinement for

the female hornbill. At that time, the nest was checked every 1-3

days until the chick fledged. In this way, I was able to record

exact, or nearly exact, entrance and exit dates for birds in the

nest. For each breeding season other than 1983-84, nests were

checked every 3-7 days or as often as possible to record hornbill

activity and occupancy of the nest.

An assessment of fruit availability in different study areas

was made each month from February 1983 to June 1984. Since

hornbills only eat fruits still attached to plants, fruits that fell

to the ground unconsumed could be considered "surplus.” The

quantity of ”surplus” fruits on the ground was assessed in Ngogo, 82

K-30, and K-15 during regular bird census walks (Chapter II).

Lengths of census routes were 5.34 km at Ngogo, 4.7 km at K-30, and

5.28 km at K-lS.

Only fresh, ripe fruits known to be eaten by B. subcylindricus were recorded. For each 100 m of census route walked, the relative abundance of each fruit species was assessed along a 1 m wide strip

(0.5 m on each side of the middle of the trail). The amount of fruit was scored on a relative scale of 0-4, with 4 being the maximum quantity possible. The relative abundance of each fruit species was noted in this way.

For each monthly census, scores obtained for all fruits were added and this total divided by the number of kilometers walked during the census. This value is called the "surplus fruit index."

This fruit index has been used by other researchers (Lwanga 1987;

Butynski in prep) in Kibale and is believed to be a good indicator of fruit availability.

Habitat analyses at nest sites were conducted to measure factors that characterize nest location. .Most habitat data collected were from April-June 1984, after hornbills had left their nesting areas.

Unless a tree had fallen, measurements of tree height, circumference at the nest cavity, height of nest hole, percentage of live wood in the.tree, nest hole dimensions, amount of foliage (or shade) covering the nest, and distance between forest canopy and nest tree top were estimated visually. Detailed descriptions of 83 methods for estimating these measurements and their accuracy are available (Kalina in prep). Exact measurements of tree height, circumference at the nest cavity, height of nest hole, and nest hole dimensions were taken on fallen trees. Percentage slope was measured using a D. H. Brunton pocket transit.

Resglts

Timing of Nesting

In Kibale, B. subcyligdricus individuals started nesting at the beginning of September, in the early part of the most pronounced of the two yearly wet seasons (Fig. 4.1; Appendix 4-O). The Kibale nesting season resembles that found in eastern Uganda, which spans

September through January (Kilham 1956). This long period contrasts with the breeding records for April and July at Mt. Elgon, N Kenya, as recorded by Mackworth-Praed and Grant (1957).

As is the case for other African hornbill species studied (Kemp

1973), the onset of B. subcylindricus breeding activity corresponds with the onset of the rains. During this rainy season, there is a relative abundance of arthropods (Nummelin 1986) and fruits

(Butynski 1988; Table 4.1) in Kibale Forest.

Courtship and Nesting Behavigr

The avian breeding season is divided into five phases: (1) song and display, (2) nest-building or repair, (3) incubation, (4). fledgling, and (5) post-fledgling when young are out of the nest but still dependent on their parents. Although a general account of g. subgyljndricus breeding behavior is available in Kilham (1956), I 84

Ii==2 45" —- AnnualRalniall(°/o) . H 12 Surplus Fruit Index ,‘\\ - ,5 35- - --- _ 1 g g " “—2 E.’ :2

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Fig. 4.l.--Relationship between percentage annual rainfall, fruit abundance (measured by the "surplus fruit index"), and the period over which Bygagistes subcylindricus start nesting ( L———|) in Kibale Forest, Uganda (January 1982-1984). Nesting season lasts from September through March. 85

Table 4.l.--Density of Bycanistes subcylindrjgus nest cavities, display cavities, and breeding individuals in Kibale Forest, Uganda.

Study B d' Nest Display Total No. individuals Area gee ‘"9 Cavities Cavitigs Cavitiss Displaying-Nesting (km ) 935°" per km per km per km per km

Ngogo 1983-84 2.9 2.7 5 6 11.2 (6.6) 1984-85 3.5 l l 4.6 9.1 1986-873 1.8 -- -- 3.6

K-30 1983-84 3.5 1.8 5.3 10.5 (1.7) 1984-85 3.5 2.9 6.5 12.9 19236-87a 0.6 -- 0.6 1.2

K-l4 1983-84 1.8 0.9 2.7 5.5 (1.1) 1984-85 0 l 8 1.8 3.6 1986-87a 0.9 -- 0.9 1.3

K-15 1983-84 1.7 0 1.7 3.3 (1.2) 1984-85 2.5 0 2.5 5.0 1986-87a 2.5 -- 2.5 5.0

a1986-87 figures represent minimum numbers since the study areas could be checked for nest activity only during December 1986.

determined detailed courtship and display behaviors that had been incompletely described in previous works. These behaviors indicated when the breeding season had begun. Observations of interactions between males and females also provided important clues for locating

ﬂ. subcylindricus nests.

During courtship and display, a. subcylindricus spent considerable time preening themselves and their mates. The male fed fruits to his mate (Fig. 4.2) while 'chuttering" softly (Chapter VI,

Appendix 6-A). The female 'purred" in acceptance of the food, which 86

Fig. 4.2.--Courtship feeding by Bygagistes subcylindriggs. 87

was often a red fruit (Kilham 1956; pers. obs). The male sometimes separated a piece of bark off a tree with a downward thrust of his beak, then manipulated the bark by flipping it about in his bill several times before giving it to the female or dropping it. This behavior was repeated during the incubation period when the male broke nest-lining materials to the proper dimensions for fitting through the narrow opening of the nest.

In July and August, the hornbill pair chose a tree cavity--or returned to a nest site which they had used in previous years-~and advertised their territory (which was only the nest tree itself) with loud, repetitive ”long-calls" (“ka-waaack”) that grew into

”repeated hi-pitched screams" (Chapter VI, Appendix 6-A). Daily activities centered around the nest site, which they visited regularly. Other hornbills who approached the nest tree were chased away.

The fleshy eye—rings of female hornbills may swell and fﬁush pink or red. Male and female took turns clinging to the tree cavity entrance and calling into the hole. Sometimes, while vocalizing into the cavity, either bird weuld “head-shake” (i.e., shake its head in a vibrating motion like that of the female when she plasters mud) (Chapter VI, Appendix 6-A). One bird perched atop the entrance

(if possible) while the other clung vertical1y to the rﬁnn Then, facing each other, they "chuttered" or "groaned" softly, and would head-shake and clack their bills together, producing an additional rhythmic sound. The male lowered his voice and groaned into the 88 cavity. The deep, hollow sound he produced carried a distance of

200 m or more. In this way, the male hornbill used the tree as an instrument to resonate his own vocal sounds. .

The duration of the courtship and display stage was variable.

Some pairs vigorously displayed at their tree cavity throughout the

6-month breeding season without ever proceeding to the nest-building stage. Although the female entered the tree cavity and removed debris from its interior during this first breeding phase, the nest- building phase began when she plastered mud to the walls of the cavity entrance.

Nest-sealing followed a brief copulation, which sometimes occurred immediately before the female entered the nest cavity. A typical mating sequence was recorded as follows:

September 15, 1983, at Ngogo:

18:20 N and F feeding in Trichilia splendida tree; N regurgitates 2 shiny red and black fruits to F; M and F spar with bills and then peck at each other’s bills;

18:23 N and F fly 20 m to a Pterxgota milbraegii limb (7.5 cm diameter; 33 m above ground); M perches on F’s right, they spar; M mounts F and they copulate for 17 sec.; during copulation, both wag tails and F’s neck is bent back as she nips at M’s face.

18:25 Pair perches 5 cm apart while self-preening.

Most avian biologists consider that a definite breeding attempt has not been made until an egg has been laid (Brown a Britton 1980).

Since it was impossible to tell when an egg had been laid (without disturbing the nest), I considered the hornbill pairs to have made a breeding attempt when nest-sealing had begun. There appeared to be some instances when the female sealed herself in and then broke out 89

of the nest again before laying an egg. On the other hand, one female at Ngogo seemed to have laid eggs in an unsealed nest. I observed this female seated inside the cavity, with her bill in the opening, for over a week before she finally plastered the walls with mud. I could see her head clearly as she refused the offerings of food from her mate and remained quiet and still in the nest. The nest was eventually sealed, and, though without proof, it is believed that she laid eggs before the nest was sealed.

Nest-Site Characteristics

5. subcylindricus hornbills in Kibale Forest compete for nest cavities (Chapters V and VI) and return to the same trees for breeding year after year. Some pairs nested in the same cavity for

7 consecutive years (pers. obs.). Heavily worn cavity entrances suggested that some cavities had possibly been used for decades.

3. subcylindricus used large trees with relatively large cavities for nesting (Appendices 4-A, 4-8, 4-C). Circumferences of nest trees in Kibale Forest ranged from 3.15 m-11.02 m (mean - 5.22,

SE = 1.8, n =~44). Circumferences of display cavity trees ranged from 2.82 m-9.90 m (mean - 5.40, SE - 4.16, n - 12). Nest trees were 25.0 m-48.0 m tall (mean - 34.76, SE - 6.75, n - 44).

Entrances to nest cavities were at heights of 8.0 m-30.0 m (mean -

18.06, SE a 5.0 m, n - 44). These holes were a minimum width of 9.0_ cm. The entrances of three nests in trees that fell intact measured

9x9 cm, 9x13 cm, and 15x26 cm (Appendix 4-A). Dimensions of nest cavities were variable (Appendix 4-A). A 30 cm cross-section (i.e., 90

J/O.5 nest, Appendix 4-C) cavity was probably the smallest used.

Cavity depths smaller than 30 cm probably would not be suitable for a female hornbill and her offspring to remain inside for 4.5 months.

Oensjtx gf Nests

A total of 45 nests and 15 display cavities were found in

Kibale Forest (Figs. 4.3, 4.4, 4.5, 4.6). One nest was located on the edge of the forest in Bigodi Village. Although the same nest and display cavities were often used year after year, tree falls and other factors (Appendix 4-O) contributed to annual variation in nest density (Table 14.1). During the 1983-84 and 1984-85 breeding seasons, the greatest density of nest cavities and display cavities was in unlogged study areas (Ngogo and K-30; Table 4.1). Since hornbills require large trees for nesting, it is not surprising that nest density is high at Ngogo. The density of trees > 3 m circumference is higher at Ngogo than at Kanyawara, and these trees are, on average, much larger (T. Butynski, unpubl. data).

Nestin ccess

Female hornbills emerged with fledglings after being confined between 115 and 142 days in the nest (n - 56) (Appendix 4-O). Mid-

March was the latest date for fledging. Although two eggs were laid, one chick was usually raised (Kilham 1956). Only one nest

(n = 56) at Kibale contained twins that were ready to fledge. Fledglings emerged from nests located in both logged and unlogged areas (Appendix 4-O). Nesting success was assessed as percentages of nests from which young hornbills fledged. Values 91

------G .\ NGOGO I H A 7‘ f ‘ f e HORNBILL NEST (n-30)

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Fig. 4.3.--Locations of Byganistes 5gbgyliggrigg§ nests (n - 30) and display cavities (n -'10) at Ngogo (unlogged forest) in

Kibale Forest, Uganda (1981-1987). is trail grid, ----- is elephant trail, and ----- is motorable track. BUTANZI FOOT PATH

NIIIV

O HORNBILL NEST (n-7l A HORNBILL DISPLAY (n84) CAVITY I CROWNED EAGLE (n- I) NEST

Fig. 4.4.-- Locations of ﬁyganistgs subcylindricus nests (n = 7) and display cavities (n . 4) at Kanyawara (K-30 unlogged forest) in Kibale Forest, Uganda (1981-1987). is trail grid. 93

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Fig. 4.5.--Locations of Byganistes subcylindricus nests (n = 4) at Kanyawara (K—l4 light-moderately logged forest) in Kibale

Forest, Uganda (1981-1987). is trail grid. 94

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Fig. 4.6.--Locations of Bxcanjstes subcylindriggs nests (n - 3) at Kanyawara (K-15 heavily logged forest) in Kibale Forest,

Uganda (1981-1987). is trail grid. 95 ranged from minimum to maximum percentages of successful nests.

Minimum percentages were determined by counting the number of total nests from which young definitely fledged. Maximum percentages were determined by counting the number of total nests from which young may have, but did not certainly, fledge. Maximum percentages resulted from lack of precision in data collection; i.e., the date on which the nest was first sealed was not determined, or the date and sighting of the chick leaving the nest was not verified. Nesting success was at least 40% (n = 5) in 1982,

36-55% (h = 22) in 1983, and 62-66% (n - 29) in 1984 (Appendix 4-O).

Birds attempting to breed had a nesting success of 36-66% or more

(i.e., 1982). g. subcylindricus nesting success in Kibale Forest was considerably lower than that of Tockus spp. hornbills in a South

African savannah. Of 249 nesting attempts by Tockus there, more

than 90% were successful in fledging young (Kemp 1976).

During 1983-84, the only year when all nests apparently had been found and monitored in all study areas, more young were fledged from unlogged than from logged forest. Ngogo had the highest density of chicks fledged (1.82-1.97/km2),followed by K-30 (1.76/km2), K-15 (1.67/km2), and K-l4 (0.9l/km2).

Reasons for nest failure were varied. Several nests had entrance holes. that. were too large or faced upward, subjecting them to flooding. One female abandoned her nest on a horizontal limb after Red Colobus (Cglgbus gagigs) monkeys walked across the nest entrance. 96

Crowned eagles (Stephanoaetus cgronatgs) also threatened nesting hornbills. One male hornbill was apparently killed by an eagle while he was trying to feed his mate. His remains were found below his nest half-way through the nesting season (Appendix 4-O).

After the male hornbill’s death, the female hornbill abandoned the nest and any chicks in the cavity. Hithin weeks, the crowned eagle pair moved their nest into the dead hornbill’s nest tree (JJ/47 in

K-30) from its prior location 200 m away. As of October 1987, crowned eagles continued to nest in the JJ/47 tree. A pair of hornbills displayed at the old nest cavity but did not nest.

Intraspecific intruders were the suspected cause for 20% of the nest failures in 1983 and 80% of the nest failures in 1984 (Appendix

4-O). Harassment by intruding 8. subcylindricus males and females caused nesting birds to abandon their nests during incubation, nestling, and fledging stages of breeding (Appendix 4—D; Chapters V

and VI).

Percentage of nest failure was higher in the 1982-83 than in the 1983-84 breeding season. In 1982-83, 20% of the failures (n =

10) were attributable to the starvation of chicks that were very

near to fledging (Appendix 4-O). In these cases, females broke out

of the nest cavity prematurely. Abandoned chicks were heard crying

from their nests, but the parents did not feed them. One hungry

nestling squeezed out of the nest and fell to her death.

Sex-Ratio Bias in Fledglings

Sexual dimorphism in casque size (Fig. 4-7) allowed for

identification of each chick’s sex upon fledging. Sex ratios were 97

Fledgling Female Fledgling Male

Fig. 4.7.-—Difference between casque development on fledgling male and fledgling female Bycanistes subc lindricus.

skewed, favoring different sexes in different study areas. Sex

ratios of' 22 fledglings in unlogged forest (Ngogo, K-30) and 5 fledglings in logged forest (K-l4, K-lS) over 3 years (1981-1984)

were used for analysis (Appendix 4-O).

The sex ratio of 18 males/(18 males + 4 females) in unlogged

forest is significantly different from 50:50 (X2 a 7.68, df - l, p <

.001). The sample size for logged study areas is small. It

appears, however, that the sex ratio of 1 male/(l male + 4 females)

is not significantly different from unity (X2 - 0.80, df - l, g) >

.20), although females were in a majority. Fledgling sex ratios in

Kibale Forest were skewed toward males in unlogged forest and were

50:50 or skewed toward females in logged forest. This is the first

account of a skewed sex ratio in young of any species of hornbill.

Hypotheses for cause and effect of this phenomenon will be presented

elsewhere.

OisgussionZRecommendations for Further Study

From observations of B. subcylindricus breeding biology in

Kibale Forest, it is apparent that rainfall and habitat are factors

influencing reproduction of this African hornbill species. Not only

does nesting begin with the onset of ‘the rains, but there is

evidence that nesting success is also related to rainfall.

Starvation of nearly fledged chicks was observed during a drought

year. The relatively low percentage of nest success during the

1982-83 breeding season may, therefore, be related to rainfall and

food supply. Rainfall during pre-breeding and breeding months of 99

July 1982-March 1983 was less than half as much as in other years

(Table 4.2). The 1982-83 drought appears to have been particularly unusual and severe when compared to the relatively regular rainfall patterns typical for Kibale Forest over the past 20 years (Butynski

1988). Relationships between rainfall and food supply will be investigated in a planned analysis of my 1981.-1984 Kibale Forest tree-fruiting phenology data. Activity and feeding data collected at hornbill nests will also be assessed to reveal differences in quantity and quality of foods supplied to nest inmates during the

1982-83 drought year.

Table 4.2.—-Total rainfall (mm) during Byganistes subcylindricus pre-breeding and breeding months (July-March) in Kibale Forest, Uganda (1981-1984).

Study Area Year Rainfall (mm)

Ngogo 1981-82 1339.9 1982-83 644.6 1983-84 1368.1 Kanyawara 1981-82 ' 1229.9 1982-83 710.6 1983-84 1608.5

B. subcylindricus nesting requirements are specific in that the birds only nest in large, natural cavities of very large trees.

Nest-site characteristics will be appraised through multivariate analysis to distinguish other important parameters possibly affecting habitat choice. Primary forest is apparently the preferred habitat for breeding, since nest and display cavity 100

density is higher there. The number of young fledged per unit area was also greater in unlogged forest. A more detailed analysis of macro- and micro-habitat at (B. ,sgbgylindrjcg§_ display-sites and nest-sites, and of the success or failure of breeding at those sites, will also be undertaken to estimate the effects of logging and other forestry practices on hornbill reproduction. 101

REFERENCES

Bourne, O. and O. Chessell. 1982. Breeding the black-and-white casqued hornbill (Bycggjstes subgylindrjsus subggadratgs) at the Metro Toronto 200, Canada. Avicglt. Mgg. 88:15-23.

Brown, L. H. and P. L. Britton. 1980. eedin eas s f ast Afrisan Birds. The East African Natural History Society, Nairobi.

Butynski, T. M. 1988. Guenon birth seasons and correlates with rainfall and food. pp. 284-322 in A. Gautier-Hion, F. Bourliere, J. P. Gautier, J. Kingdon and R. M. Martin, eds. Primate Radiation: Evolutionary Biology and the Afrigan Guenons. Cambridge Univ. Press, Cambridge.

Butynski, T. M. in prep. Comparative ecology of blue monkeys (Cer- cogithecus mitis) in high and low density subpopulations.

Ghiglieri, M. P. 1984. The Chimpanzees of Kibale Fgrest. Columbia Univ. Press, N.Y.

Harvey, P. M. 1973. Breeding the casqued hornbill at "Birdworld." ijgult. Mag. 79:23-25.

Kemp, A. C. 1973. Factors affecting the onset of breeding in African hornbills. Proc. 16th Int. an. Cong.: 248-257.

Kemp, A. C. 1976. A Stgdy of the Ecology, Behavior and Systematics

of Tockus Mar '11 Aves: Bucero ' . Transvaal Mus. Memoir No. 20. Pretoria, South Africa.

Kemp, A. C. 1979. A review of the hornbills: Biology and radiation. Livinq Bird 17:105-136.

Kilham, L. 1956. Breeding and other habits of casqued hornbills (Byganistes subcylindrigus). Smithson. Misc. Collns. 131: 1-45.

Lwanga, J. S. 1987. Group fission in blue monkeys (Cercopithecus mjtjs stuhlmanni): Effects on the socioecology in Kibale Forest, Uganda. M.Sc. thesis. Makerere Univ., Kampala, Uganda.

Mackworth-Praed, C. N. and C. H. 8. Grant. 1957. Birds of Eastern and North Eastern Africa. Longman, Green and Co., London.

Moreau, R. E. and Moreau, H. M. 1941. Breeding biology of the silvery-cheeked hornbill. Auk 58:13-27. 102

Nummelin, M. 1986. The seasonal fluctuations of forest floor insect densities on the areas of different forestry practices in Kibale Forest, Western Uganda. t nt. Conf. n Tr ical Entgmology, Nairobi.

Porritt, R. and M. Riley. 1976. Breeding the black-and-white casqued hornbill (Byganistes subcylindrisgs) at Birdworld, Farnham. Int. log ka. 16:104-105.

Skorupa, J. P. 1988. The effects of selective timber harvesting on rainforest primates in Kibale Forest, Uganda. Ph.D. dissertation. Univ. of Calif., Davis.

Struhsaker, T. T. 1975. T R l s k . Univ. of Chicago Press. Chicago, Illinois. 103

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CHARACTERISTICS

APPENDIX 4-B CHARACTERISTICS OF BYCANISTES SUBCYLINDRICUS DISPLAY CAVITY SITES IN KIBALE FOREST, UGANDA

T Circumf. . Nest Dir. X Hest Distance From Folia g e Dir . Loggglon Tree Species CirEE§f _ at 0113:: Hole Hole . Live Hole Hole to Nearest Cover Down- ' Cavity Height Faces Hood Oimen. Climbable Loc. (O-IO)c slope (111) (In) (111) (m (cm) (111)

A/ll no data ------

C.75I7.5 ‘ Pterygota Illdbraedii 6.00. 2.5 39.0 18.0 NH 0 10x10 - 0 E

0/5.5 Lovoa sgygnertonli 5.51 2.5 ‘ 45.0 27.0 UP+N 95 13x13 1.6c 3 M 0.5/8.5 no data ------E-“

r.5/3 Antiaris toxlcara 0.50' 3.01 40.0 24.0 ‘0 95 - WWWOWNN 0

F.5/9 - 9.90 2.5 37.5 10.0 at 95 0 1.2 0.5/11 - ~’ 3.40 2.0 . 30.0 10.0 E 05 13x13 0.0c 1(14

0/4 -. ‘ " 4.00 2.0 20.5 12.0 ME 0 -. -- 83H!”

J.5/4 Pi tadeniastium africanum 2.82 1.3 21.0 15.0 UP+H 80 10x10 0

K/2(ll) Parlnari excelsa 5.88 1.5 39.0 16.5 M 80 b 0c __

L.5I9.5 -" -- 2.5 48.0 5500 SE 95 b 0

Kan aware 4124 - 0.00 1.0 45.0 12.0 ME 00 18x10 -- 2 00/0 - 4.00 ' 1.7 27.0 12.0 ' u 0 - -- 0 NE Krd/K Mimusops bagshawei 4.90 2.5 30.0 21.0 50 00 66x26 -- 4 5 L10 Mlmusops bagshawei 3.07 1.5 24.0 10.0 50 90 31x31 -- 3

aCircumference measured above buttress.

bHole out of view.

cO - no shade; 10 - always shaded. 105

APPENDIX 4-C DIMENSIONS OF BYCANISTES SUBCYLINDRICUS NEST CAVITIES IN KIBALE FOREST, UGANDA

1.5/2 nest cavity in tree bole (Ngogo). 77

\ dimensions 1 01 1101- 1ch . ’I/ ’2 “2 "' 4% é%

//'/‘/°/°/“

lertlcal on" union oi tree at cavity.

J/0.5 nest cavity In tree limb (Ngogo). 00711:“ cm! 8.911.. II III. II "'1". 1.0 I CIR-I1. at 00le 106

APPENDIX 4-D BYCANISTES SUBCYLINDRICUS NEST OCCUPANCY AND NESTING SUCCESS OVER FIVE YEARS (I981-l986) IN KIBALE FOREST, UGANDA

Breeding Season:' September 1901th 1982 Nest Date Nest Stage Location Found Probable - :::: ":;ﬂ£:{s :301t Success- Sex of Reason Sealed in Nest Female f"]7 51°d911"9 FaIYEPe Exits

ﬁgggo (unlogged forest) A/l3 10/17/82 -A.5/8.5 9/18/83 -B/ll 10/3/83 C/10.S 9/25/83 C.25/ll 9/25/83 0/10.5 9/25/83 5.5/6 1/29/81 7 >5 Fledgling Yes M 5.5/7.5 12/21/81 <12/21 7 7 7 5.5/10 7/10/82 F/2.S 10/14/84 F/5.5 9/12/82 F/9.5 7/22/82 F/lZ 9/26/82 F.5/0 9/19/83 F.5/3.5 9/16/82 G/7 12/21/81 <12/21 7 Fledgling Yes M H/O 9/21/83 H/3.5 9/29/83 H.5/10 9/30/83 1.5/2 12/19/81 <12/l9 7 7 7 J/-O.5 8/22/83 J/0.5 10/1/82 K/Z 9/13/83 K/4.5 9/14/83 K/7.5 9/12/82 L/9 9/9/83 L/lO 9/7/83 L.5/7.9 9/14/83 M/lO 9/27/83 H/9 9/26/83

Bigodi Village (forest edge)

Kanyawara (K-30 unlogged forest)

HH/S 9/30/82 J/39 10/1/82 JJ/46 10/15/81 <10/15 7 7 JJ/47 10/14/82 5/40 9/12/83 J/4 10/1/82 J/O 10/1/82

Kan awara K-l4 li ht-moderatel ed forest F/Q 10/1/82 M/24 10/5/82 Y/l7 10/6/82 Y/17A 12/22/86

Kanyawara (K-ls heavily logged forest)

3E/ZS 10/21/82 3E/3S 10/21/82 2E/7S 9/30/84

107

Breeding Season:a September 1%2-March 1983

ocat on Found Date "°' Days "he" Success- Sex of Reason "“1 Fm“ Adm ful7 r120 lin for Sealed in Nest Female 9 9 Failure Exits

Ngogo (inlogged forest)

A/l3 10/17/82 10/17 107+ 7 -A.5/8.5 9/18/83 -B/ll 10/3/83 C/lO.5 9/25/83 0.25/11 9/25/83 0/10.5 9/25/83 E.5/6 1/29/81 9/11 129 Fledgling Yes M E.5/7.5 12/21/81 9/24-10/14 101-113 Nestling No Chick starved E.5/10 7/10/82 9/26-10/6 126-136 Fledging Yes F F/2.5 lO/l4/84 F/5.5 9/12/82 9/17 1-7 -- Ho Hole faces up; old birds F/9.5 7/22/82 9/26 129 Fledging Yes M F/12 9/26/82 9-10/6 14- Incub. No 7 F.5/O 9/19/83 F.5/3.5 9/16/82 9/7%25 12-7 Incub. No Mgnkeys frighten ema e G/7 12/21/81 9/24-10/6 114-7 7 7 Intruders H/O 9/21/83 H/3.5 o9/29/83 H.5/10 9/30/83 1.5/2 12/19/81 10/2 112-? Fledgling Yes M J/-O.5 8/22/83 J/O.5 10/1/82 lO/l 38-128 7 7 K/Z 9/13/83 K/4.5 9/14/83 K/7.5 9/12/82 9/12-16 11-15 Incub. No Intruder enters nest L/9 9/9/83 L/lO 9/7/83 L.5/7.9 9/14/83 M/lO 9/27/83 "[9 9/26/83 Bigodi Yillgggs(forest edge)

Kanyawara (K-30 unlogged forest)

HH/S 9/30/82 <9/3O 116 Fledgling Yes 7 .1/39 10/1/02 <10/1 0100911119 Yes 14 JJ/46 10/15/81 lO/lO-23 82-95 Nestling Mo 7 JJ/47 10/14/82 110/14-23 7-16 Incub. No 7 S/40 9/12/83 J/4 10/1/82 510/1 7 7 J/O 10/1/82 10/1-7 38-71 7 No 7 Kanyawara (K-14 light-moderately logged forest)

F/O lO/l/82 'lO/l-6 22-31 Incub. Ho Hole too large M/24 10/5/82 <10/5 2110 Nestling No F Chick starved Y/l7 10/6/82 DISPLAY ONLY Y/17A 12/22/86

Kan awara K-lS heavil 10 ed forest 35125 10/21/02 510/21 2110 Yes 2 3E/35 10/21/82 510/21 2142 Yes F 2E/7S 9/30/84

11313

Breeding Season:a September 1983-March 1984 Nest Date Nest Sta e Location Found DateNest No. Female Days AdultHheigi Su ccess- Sex of Probable Reason 500100 in Nest Female 1°17 “°‘9“"9 ‘°' Exits Failure

Ngogo (unlogged forest) A/l3 lO/l7/82 10/13-22 73-86 Nestling No Intruders -A-5/8.5 9/18/83 9/18-25 116-123 Fledgling Yes M -B/ll 10/3/83 10/14-22 114-122 Fledgling Yes M C/10.5 9/25/83 9/25 27-40 Incub. No 7 C.25/ll 9/25/83 DISPLAY ONLY D/lO.5 9/25/83 9/25 133 Fledgling Yes M E.5/6 1/29/81 9/12 130 Fledgling Yes M E.5/7.5 12/21/81 9/22-25 133-133 Fledgling Yes M E.5/10 7/10/82 9/16-18 126-127 Fledgling Yes M F/2.5 10/14/84 F/5.5 9/12/82 DISPLAY ONLY 7 F/9.5 7/22/82 9/20-22 132-134 Fledgling Yes M F/12 9/26/82 9/23 116 Fledgling Yes 7 F.5/0 9/19/83 9/19 117 Fledgling Yes M F.5/3.5 9/16/82 DISPLAY ONLY G/7 12/21/81 lO/l7-27 22-44 Incub. No Intruders H/O 9/21/83 DISPLAY ONLY H/3.5 9/29/83 DISPLAY ONLY H.5/10 9/30/83 9/30 126 Fledgling Yes M 1.5/2 12/19/81 DISPLAY AT STUMP Nest fell 6/83 J/-O.5 8/22/83 9/2-8 118-124 Fledgling Yes F J/O.5 10/1/82 DISPLAY AT STUMP Mest fell 8/83 K12 9/13/83 DISPLAY ONLY (HOLE ll) too large K/4.5 9/14/83 SEALING NOT COMPLETED Hole K/7.5 9/12/82 SEALING NOT COMPLETED Intruders L/9 9/12/83 9/22 114 Fledgling Yes 7 L/10 9/7/83 9/14-17 10-13 Incub. No Intruders L.5/7.9 9/14/83 9/20-23 80-87 Nestling No Hole faces up M/lO 9/27/83 59/27 93-7 7 Intruders present N/9 9/26/83 £9/26 92-? Nestling Mo H-F Intruders

Bigodi Village (forest edge)

9/83 7 7 7 No

Kanyawara (K-3O unlogged forest) Intruders took over nest HH/S 9/30/82 10/1 1-4 Incub. No J/39 10/1/82 9/23-25 122-124 Fledgling Yes M Eagle kills male JJ/46 10/15/81 10 88-94 Nestling No Eagle nearby? JJ/47 10/14/82 9/21-23 73-76 Nestling No S/4O 9/12/83 DISPLAY ONLY J/4 10/1/82 9/19 124 Fledgling Yes M F J/D 10/1/82 lO/l2-16 121-124 Fledgling Yes

Kanyawara (K.l4 light-moderately logged forest)

F/Q 10/1/82 DISPLAY ONLY M/24 10/5/82 9/13-18 122-126 Fledgling Yes M Mest rim worn; intruders Y/l 7 10/6/82 11/4-7 22-34 Incub. No Y/l7A 12/22/86 Kanyawara (K-15 heavily logged forest) F One chick died 5 70d 3E/25 10/21/82 10/1-5 121-124 Fledgling Yes F 3E/3S 10/21/82 10/1-5 113-116 Fledgling Yes 2E/7S 9/30/84

109

Breeding Seasonz' September 1984-November 28. 1984 December 1986

Nest Date Nest Stage Has Is Nest Location Found Date No. Days Hhen Suc Sex f Pg?” Nest Sealed mum Reason Adult f‘fgs' Fl :1 fson Sealed During 54-100 Nest in Female Nest Female “ “9 "9 r °" m. o... 1’" Exits “1“" Year? Check? “11“"

l_igggo (unlggged forest) 3 lO/l7/82 lO/lO-l4 345 7 7 No data -A.5/8.5 9/18/83 9/19-23 :66 7 Yes Yes -B/ll 10/3/83 10/5 249 7 7 No data C/10.5 9/25/83 DISPLAY ONLY 7 No C.25/ll 9/25/83 10/10-14 :45 7 7 No 0/10.5 9/25/83 9/19-23 :66 7 Yes No 7 E.5/6 1/29/81 9/5-11 276 7 No No 7 E.5/7.5 12/21/81 9/24-26 :61 7 Yes Yes E.5/10 7/10/82 9/11-18 >69 7 Yes No 7 r/2.s 10/14/04 10114-10 15-17 No 7 2 No data F/5.5 9/12/82 DISPLAY ONLY 7 No F/9.5 7/22/82 10/5-10 247 Yes No Nesting hornbill ‘ killed F/12 9/26/82 lO/26-3O 252 7 7 F.5/0 9/19/83 9/6-12 276 7 No, tree fell in 1985 F.5/3.5 9/16/82 9/30-10/6 252 7 Yes Yes G/7 12/21/81 9/11-18 :71 7 Yes Yes H/O 9/21/83 9/30-10/6 252 7 7 No data Hl3.5 9/29/83 9/30-10/6 252 7 7 No data H.5/10 9/30/83 9/24-29 :58 7 Yes Yes 1.5/2 12/19/81 ------J/-0.5 8/22/83 DISPLAY ONLY 7 No J/0.5 10/1/82 ------K12 9/13/83 9/30-10/6 252 7 (HOLE 42) Yes Yes (HOLE 43) data 104.5 9/14/83 SEALING NOT METED Hole toolarge 7 No DISPLAY ONLY Intruders 7 No KI7.5 9/12/82 7 L/9 9/9/83 9/23-29 :59 7 Yes No L/lO 9/7/83 9/29-10/6 252 7 Yes Yes L.5/7.9 9/14/83 9/11-18 :70 7 7 No broke at nest 9/27/83 9/5-11 277 7 No. tree M/lO Yes N/9 9/26/83 9/5-11 277 7 Yes

Bigodi Village (forest edge)

Kanyawara (K-30 unlogged forest) Yes HH/S 9/30/82 9/22-26 :32 7 Yes 9/22-29 :29 7 No. nest limb broke off J/39 lO/l/GZ eagles DISPLAY ONLY No No Crowned JJ/46 10/15/81 nest in tree No No Eagles nearby JJ/47 10/14/82 DISPLAY ONLY S/4O 9/12/83 10/20-24 2 l 7 7 NO on 10/1/02 10/3-7 219 1 Yes No .1/0 10/1/02 10112-19 a l 7' Cavity a bee hive in 4/04 110. trunk broke near mt Nan awara K-l4 li ht-moderatel 1 ed forest No data F/O 10/1/82 DISPLAY ONLY Tree fell before 8/84 -- -- '- M/24 1015/82 H0?" Y/l7 10/6/82 DISPLAY ONLY N0 "0 RIO Y/17A 12/22/86 YES Yes Kan awara K-15 heavil 1 ed forest :30 7 Yes Yes 3E/25 10/21/82 9/28 Yes 9/23-28 :30 7 Yes 3E/3S 10/21/82 Yes Yes ZE/7S 9/30/84 9/30-10/4 2 8 7

'Dates covered. CHAPTER V

NEST INTRUDERS, NEST DEFENSE, AND FORAGING BEHAVIOR IN THE BLACK-AND-HHITE CASOUED HORNBILL

During the 4.5 month nesting period, the male black-and-white

casqued hornbill (Bycanistes subcylindricus) is soler responsible

for feeding himself, his mate, and his offspring in the nest.

According to optimal foraging theory, he should accumulate food in

the minimum amount of foraging time in order to maximize the

delivery rate of food to the nest (Andersson 1978; Orians & Pearson

1979; Schoener 1979). This prediction is based on models which

assume that there is need only to maximize the net rate of energy

intake. The foraging behavior of the male hornbill will, however,

be influenced by riskSof predation at the nest (Fig. 5.1) and

demands of feeding and protecting the young. In order to account

for these additional demands, several authors have investigated time

budget conflicts between feeding and other activities such as maintaining vigilance (Caraco et al. 1980; Lendrem 1983), minimizing

predation risk (Sih 1980), and defending territories (Kacelnik et a1. 1901). ’

Martindale (1982) incorporated nest defense and central place

foraging into a model which makes different predictions about

110 111

Fig. 5.1.--During the nesting period, the male Bygsnistes subgylin- gyigys is solely responsible for feeding himself, his mate, and his offspring in the nest. At the same time, his foraging behavior will be influenced by risks of predation and demands of protecting the young. 112

foraging behavior. Martindale’s logical assumption for development of' his "nest defense model" is that ”natural selection Should produce animals which behave to maximize their net fitness, not just their delivery rate." His nest-defense model predicts that, as predation risks increase, the defending bird will forage closer to its nest, and bring smaller food loads and smaller food items than predicted by models based on delivery-rate maximization. Although not tested under conditions of actual intrusion, Martindale (1982) found that male Gila woodpeckers (Mglanerges urogygislis) did indeed forage closer to the nest and deliver reduced food loads and smaller food items after attacks from an artificial "intruding" woodpecker.

Although Martindale’s experiment was valuable, two factors may have compromised his test of the model: (1) the "intruding" woodpecker at the nest was artificial, and (2) both male and female woodpeckers provisioned and defended the young. Results of his study were difficult to interpret when both male and female woodpeckers joined in foraging and defense. In contrast, the black- and-white casqued hornbill serves as an ideal species f0r testing the nest-defense model. The female uses mud to seal herself inside the nest cavity. She remains in the cavity until the nesting attempt ends. The male is solely responsible f0r food provisioning and external defense of the nest. Nest defense is crucial for hornbills since inadequate nest protection against intruding 113 conspecifics may result in the eviction of the resident pair and/or death of the resident pair’s young (Kalina in prep).

093002;

In 1981, I began a long-term study of’ the black-and-white casqued hornbill in Kibale Forest, western Uganda.’ The study area consisted of both primary and selectively logged tropical rainforest. This area has been described in detail by Struhsaker

(1975) and Ghiglieri (1984). Since 1981, 45 nests have been found.

All are located in the natural cavities of large trees. Except for

1985, nests were monitored each breeding season from 1981 through

1987. Observations were made from locations 20-60 m from the base of the nest tree using a telescope or 10 x 408 Leitz binoculars.

The data used in this paper were collected over the 1983-84 nesting season during 4 h (n = 28) and 12 h (n - 28) sampling periods (700-1100 h and 700-1900 h). Only information collected at sealed, occupied nests was analyzed. Thirteen nests were observed for a total of 448 h. Data meeting the requirements necessary for testing Martindale’s nest-defense: model were obtained during 10 sampling periods from six nests. To reduce sampling error caused by between-day variation in foraging activity, I only utilized data collected on the same day before, during, and after the visit of one or two intruding hornbills. Therefore, these data describe foraging activity during short-term intrusions. An ”intruding hornbill" is~ defined here as one that approaches to within 50 m of the nest and evokes an agonistic response by the resident male and/or female. 114

I only watched nests with clearly visible entrances so that

birds landing on the nest could be identified and food items fed

into the nest distinguished. The male hornbill’s arrival and

departure times at the nest, and the kinds and numbers of items fed

into the nest, were recorded. Hornbills are multiple-prey loaders;

i.e., more than one food item may be collected before a load is

delivered to the nest. ‘

Male hornbills regurgitate food items into their bill tips just

before they feed them to the female in the nest. These food items

were usually easy to see and identify. The species of fruit was

identified to Species and given a rating of 1-4 based on size, with

1 being the smallest and 4 the largest. Examples of species (with

approximate mean diameter of the fruit) in each category are:

Celtis durandij (0.5 cm) - l, D_i_Qsp_yLo_s abyssiniga (1.0 cm) . 2,

Mimgsgps bagshawsi (2.0 cm) a 3, and Eigys ggygi (3.0 cm) - 4. Size

ranges (diameter) of fruits for each category are as follows: 1 =

(0.3-0.7 cm), 2 - (0.8-1.5 cm), 3 - (1.6-2.5 cm), and 4_- 2.6-3.5

cm). Volumes were calculated for each category, based on the means:

1 . 0.07 cm3, 2 = 0.52 cm3, 3 = 4.19 cm3, and 4 - 14.14 cm3. These

values (were derived from the volumes and diameters of samples of

fruits. For each visit, the number of fruits in each size category

was totaled and multiplied by the volume for that category, then

, added together to determine the "load volume.” For example, 4 Eiggs

ggygi fruits fed during one visit would be multiplied by 14.14 cm3

to get a "load volume" of 56.6 cm3. 115

Data were combined for all 10 sampling periods for the two visits to the nest by the resident male "before the intrusion," for the two visits "after the intrusion," and for all visits ”during the intrusion." Sample sizes vary from table to table because of incomplete observations. For example, on three occasions, data are available for only one (not two) visit to the nest by the resident male prior to the intrusions. For one sample, no data are available concerning visits by the resident male before the intrusion. For each intrusion, the following were determined: (1) total time (min) that intruders remained within 50 m of the nest, (2) mean time the resident male spent perched on the nest entrance, (3) mean time since the resident male’s last visit to the nest, (4) mean "load volume” fed by the resident male into the nest, and (5) mean volume of food brought/min to the nest (Table 5.1).

Results

Intruding hornbills stay in the nest area for a few seconds to several days or weeks. The "short intrusions” considered in this paper lasted for 1-51 min (n = 10, mean = 20.9, SD = 16.7).

Once intruders were detected by the resident male, he remained within the vicinity of the nest, going only short distances (up to

100 m) to forage. Before or after intrusions, males often flew to fruit patches 1 km or more away (pers. obs.). Agonistic responses by resident hornbills to intruding hornbills of either sex included calling and drumming by the imprisoned resident female, and chases and vocalizations by the resident male. The male sometimes

116 of

After

(cm3) (n.s.) O.4:1.4 0.9:l.8 0.7il.3 vs.

conspe-

Volume

.001

.001 .20 .0005 .01

subcylindri- Food

Brought/min

< >

< <

p p

p p p

During

(n=19)

(n=25) (n=16)

Bycanistes

Insects)

intrusions

Volume

(cm3) 5.7

male

Load

after

2.8: After

(Fruit

23.8227.5 22.4i40.7

(n.s.) (n.s.)

(n.s.)

(n.s.) (n.s.)

and

error. vs.

nesting

.20 .20

.02

.10 .10

of A A A A A Q. Q

during, Q. D.

(n=25)

(n=19)

(n=16) Before

(Student's

) level.

standard

Only)

Vglume 3.7 .05 (cm

behavior

before,

means

(Fruit

Load

the 1.5:

means

23.1:27.5 22.4i4l.2

are

foraging below

between During

(1983-84)

m (n.s.)

C or

(n=25) (n=19)

(n=16) o 1.0 N vs. Values Spent C C

O at

O .20

e . O .02

Nest

V V V <

Uganda

Q. D. D. p p

Difference

site.

Before

1.6i0.3

3.210.6

2.7iO.4 Minutes

measurements

Forest,

nest significant

four

the

(n=19)

(n=20) (n=16)

Visit

Kibale

Since

4.4il.7 cus c1f1cs —I_e insects) statistically

Previous 37.416.3

48.8:7.9

Minutes food

only) nest not

visit of

5.1.-Changes

Since

volume volume

on (fruit

(fruit brought/min

last

During Load n.s.

Before Load Volume Table Time

Time

After

117

"chuttered" loudly and tapped his bill against the nest entrance while rapidly shaking his head in a ritualistic ”nest-sealing display." The intensity of these behaviors varied with the severity of’ the attack. Resident females "bill-grappled” with intruding hornbills that perched at the nest entrance. During bill-grappling, birds jabbed at each other’s bills, sometimes cutting the other bird’s head or knocking the opponent off balance. Males were observed to bill-grapple only with males, except on rare occasions.

Once, an intruding male perched at a nest entrance and grappled with the resident female, who was inside the nest.

During the period covered by this analysis, a total of 960 fruits and 11 insects were fed. Insects comprised only 1% of all food items (8% by volume). Load volumes were calculated, both including and excluding insects (Table 5.2). Items fed and not tallied were two pieces of lichen and one piece of bark.

Hornbills bring mud to the nest during initial nest-sealing.

Later in the nesting period, the male brings mud when the seal is in need of repair. I saw 10 pieces of mud brought to a nest by the male during one sampling period. In this case, all mud was presented to the female by the resident male during and after the

intrusion, but not before. Mud was delivered only after the

intruders had remained 4-100 m from the nest for 1.4 h. The female hornbill did not accept most pieces of mud offered to her, presumably because the opening into the nest was already very narrow. Mud plastering had ceased two days earlier, when the nest-

seal was completed. Table 5.2.-Composition of fruit loads brought to the nests by male Bycanistes subcylindricus hornbills in Kibale Forest, Uganda (1983-84) before, durThg, andiafter intruder attacks. Fruits were given a rating of 1-4 based on size, with 1 being the smallest and 4 being the largest. Insects are not included since they represent only 1% (8% by volume) of total loads.

Number of Fruits 1 (small) 2 (med-5m) 3 (med-lg) 4 (large) Total No. of g No. of

X'diam. (cm) = 0.50 1.00 2.00 3°00 Fru1ts Loads Fruits/Load 1 SE Xvol. (cm3) = 0.07 0.52 4.19 14.14

118

Before 89 (32)a 154 (56) 21 (8) 13 (5) 277 16 17.3 _ + 16.6

During 22 (26) 63 (73) 1 (1) O (0) 86 25 3.4 +1 7.7

After 17 ( 3) 543 (91) 37 (6) O (O) 597 19 31.4 +1 33.4

aFigures in parentheses are percentages. 2 Before vs. during intrusions - X 12.3, df 3, p < .01. 2 Before vs. after intrusions - X 73.7, df 3, p < .001. 2 During vs. after intrusions - X 191.9, df = 3, p < .001. 119

As predicted by Martindale’s nest-defense model, nest guarding by the resident male during intrusions altered foraging patterns

(Table 5.1):

a. Male hornbills had a significantly higher rate of visita- tion to the nest when intruders were in the vicinity of the nest site than when intruders were absent. A greater proportion of these visits was without food (binomial test, 2 - -9.65, p < .0005). All

(n = 16) of the visits before, 36% (n = 25) of the visits during, and 84%. (n = 19) of the visits after intrusions by hornbills resulted in food delivery to the nest. Often the male visited the nest only to perform his nest-sealing display. Such activities indicate that much of the defense against conspecifics is focused on the mud barrier at the nest entrance.

b. The mean time the resident male spent perched at the nest entrance was significantly less during an attack by intruders than either before or after the attack.

c. The volume of food brought to the nest per visit decreased significantly during the intrusion and increased to about pre- intrusion level again after foreign hornbills left the nest area.

Delivery of smaller loads during attacks by intruders was as predicted by the nest-defense model.

d. There was no significant change in the delivery rate of food (mean volume brought to the nest/min) before, during, or after‘ intrusions.

In short, the presence of intruders resulted in more frequent but shorter visits to the nest by the resident male, with smaller 120 food loads being delivered. Hhen intruders remained in the nest area for a short time (5 51 min), the volume of food delivered per unit time did not change with the presente of intruders.

There was a significant change in the composition of the fruit load brought to the nest before, during, and after attacks by intruders (Table 5.2). During the intrusions, resident males delivered a greater proportion of small (size 1) and small-medium

(size 2) fruits to the nest than any other size category. They brought more large (size 4) fruits before than during or after intrusions. Greater proportions of small-medium (size 2) and medium-large (size 3) fruits were brought after the intrusions.

During intrusions, rather than traveling long distances to collect the larger Ficus or Mimusops fruits, males gathered the smaller,

more common, ggltis and Diospyros fruits that were available nearer the) nest. In summary, during short intrusions, male hornbills foraged closer to the nest and delivered smaller food items in smaller loads. These observations are as predicted by Martindale’s model.

During long, severe intrusions, however, food-delivery rates declined as the resident male hornbill Spent. most of' his time defending the nest. At least 4, and probably 6, out of the 10 nest failures in 1984 can be attributed to disturbance of this kind.

Imprisoned females were forced to abandon the nest when their mates could not provide enough food. At one such nest, I saw the resident male chase an intruding female 52 times in 8 h. Hhen food was 121

delivered, fruits were rapidly dumped directly into the nest, rather than fed to the female one at a time.

In a second case, I found an intrusion already in progress, with the resident female breaking out of her nest. Although most

nests contained only one young, this one housed two nestlings that would have fledged in about 10 days. The female flew fEeny from the nest after her 4 mos of confinement, but re-entered the

cavity within 24 h. She remained there and defended the nest

entrance from repeated attacks during the next 4 days. During this

5-day period, the resident male was visibly tired, often chased away

from the nest, and frequently driven to the ground by the intruding

pair. This harassment led to reduced food-delivery rates to

the nest. The nest was watched for 5-7 h each day during the 5 days

of intrusion. The volume of food (cm3) brought/min was as follows:

Day 1 - 0.5, Days 2 and 3 - 0, Day 4 = 0.3. On Day 5, the intruding

female broke into the nest cavity, drove the nesting female out, and

attacked the two nestlings. At least one, probably both, chicks

died as a result of the attack.

Discussjgn

Evidently, the male hornbill changes his foraging behavior

markedly as the threat to the nest increases. Changes in foraging

activity in response to an intruder may be particularly dramatic in

hornbill males because only that member of the pair is responsible

for food provisioning and external defense of the nest. Even when

the nest is sealed with hard, brick-like mud, the cost of leaving 122 the nest unprotected can be great. It was not unusual to find intruders perched on a nest, chipping the mud-seal away with their bills, while the resident male, unaware of their presence, foraged far away.

Most changes in foraging behavior were as predicted by the model. During the short-term presence of intruding hornbills, the resident male altered his foraging pattern so as to maintain surveillance and food delivery to the nest.

Throughout this study, competition for nest sites by hornbills was high. In areas where the ratio of hornbill pairs to nest sites was highest, the proportion of unsuccessful nests was greater

(Kalina, unpubl. data). Hornbills that did not acquire a nest at the beginning of the breeding season sometimes attacked nests that were already occupied. Some intruders successfully drove off nesting hornbills, then took over the nest site.

In this study, the nest-seal appeared to be used more often in defense against conspecifics than against other potential predators.

Kemp (1970), whose studies focused on savannah hornbills (lcycﬂs species in particular), hypothesized that the mud barricade at the nest entrance served primarily to keep interspecific predators out of the nest. Unlike the black-and-white casqued hornbill, individuals of Iggtgs spp. appear not to compete for nest cavities

(Kemp 1976). Located in small trees, the nest cavities of Igttgs spp. are usually 3-4 m above ground and are relatively vulnerable to predation (Kemp 1976). In contrast, black-and-white casqued hornbill nests, located high in boles of large forest trees (8-30 m 123

above ground), are inaccessible to most predators (Kalina, unpubl. data). It seems, therefore, that, for this species, the nest-seal

functions primarily to keep other hornbills out of the nest. 124

REFERENCES

Andersson, M. 1978. Optimal foraging area: Size and allocation of search effort. Theor. nggl. ngl 13:397-409.

Caraco, T., S. Martindale and H. R. Pulliam. 1980. Avian flocking in the presence of a predator. Netgre 285:400-401.

Ghiglieri, M. P. 1984. Ihe_thimgen;ees_gf_§ihele_ﬁerest. Columbia University Press, N.Y.

Kacelnik, A., A. 1. Houston and J. R. Krebs. 1981. Optimal foraging and territorial defense in the great tit (Pergs major). Behav. Ecol. Sociobjol. 8:35-40.

Kemp, A. C. 1970. Some observations on the sealed-in nesting method of hornbills (family Bucerotidae). Ostrich (suppl.) 8:149-155.

Kemp, A. C. 1976. A study of the ecology, behaviour and systematics of Tockus hornbills (Aves: Bucerotidae). Transvaal Mus.

Memoir 20.

Lendrem, D. 1983. Predation risk and vigilance in the blue tit. Behav. Ecol. Sociobiol. 14:9-13.

Martindale, S. 1982. Nest defense and central place foraging: A model and experiment. Behav. Ecol. Sgsigbiol. 10:85-90.

Orians, G. and N. Pearson. 1979. On the theory of central place foraging. In D. J. Horn, G. R. Staris, and R. 0. Mitchell, eds., Analysis of Ecological Systems. Ohio State University Press, Columbus.

Schoener, H. 1979. Generality of the size-distance relation in models of optimal foraging. Am= Net. 114:902-914.

Sih, A. 1980. Optimal behavior: Can foragers balance two con- flicting demands? Seience 210:1041-1043.

Struhsaker, T. T. 1975. lhe Reg tglgtgs. University of Chicago Press, Chicago, Illinois. CHAPTER VI

FUNCTION OF NEST-SEALING: WITH SPECIAL REFERENCE

TO THE BLACK-AND-HHITE CASOUED HORNBILL (W W)

Most of the 53 species of hornbills, family Bucerotidae, live in forests (Kemp 1979, 1988; Kemp & Crowe 1985). Only 12 species inhabit savannahs. Hornbills vary in body size from the dwarf

Tockus species (83-gram female) to the turkey-sized Bueorvus Species

(up to 6180-gram male) (Kemp in 1itt.). Their behavior is also diverse; a Species may be sedentary or nomadic, territorial or nonterritorial, strictly monogamous or a cooperative breeder (Kemp

1979).

Hornbills nest in natural cavities in trees, rock faces, or earth banks. With the possible exception of two species (genus

Bucorvus), hornbills seem incapable of excavating their own nest cavities (Penny 1975; Kemp & Kemp 1980). They are, however, able to seal their nest entrances with mud and/or feces, a behavior unique among birds (Kemp 1970). Nest—sealing is accomplished as the hornbill moves its laterally flattened bill side to side in the nest entrance; sealing material is held in the bill tip and is plastered onto the wall of the entrance as it is squeezed out the sides of the

125 126 bill. The material is applied in thin layers until on1y a narrow vertical slit leads into the nest, and the female is imprisoned inside. She remains in the nest throughout incubation and all, or most, of the nesting period, which, depending on the species, lasts

1.7-4.7 months (Kilham 1956; Kemp 1979; Chapter IV). Confined females and nestlings eject or throw their feces out the nest entrance, keeping the cavity clean.

Kemp (1970) has discussed some advantages and disadvantages of the sealed-nest for hornbills, as well as how this behavior may have evolved. It is generally implied, when not stated, that nest- sealing evolved in response to predation at the nest (Kemp 1970;

Hatchtel 1982; Nelty 1982; Collias & Collias 1984; Leighton 1986).

Much evidence supports this assumption. Intuitively, authors argue that selection favors those birds able to shield themselves and young from predators (Kemp 1970). Alternative hypotheses for the evolution of nest-sealing have not been considered. The hypothesis that nest-sealing evolved in response to predation has been repeated so frequently that it has begun to be accepted without question. In this case, it is important to make the distinction of whether protecting the nest from predators is the specific function of nest- sealing or merely an incidental consequence.

In this paper, I discuss evidence supporting the predation hypothesis and introduce three alternative hypotheses concerning the origin of nest-sealing behavior. These alternative hypotheses involve inter- and intraspecific competition for the nest and increased protection from weather. Information is presented that 127

demonstrates how, for black-and-white casqued hornbills (Bycanjstes sgbcylindrjegs), the nest-seal most often functions to guard against conspecifics.

Eredatigg ﬁypgthesjs: Nest-Sealing Prgteets A inst Pr dati n

Predation has probably been a major evolutionary force determining the form and structure of nests (Collias & Collias

1984). Lack (1954) suggested that predation is responsible for over

75% of the losses of eggs and young of open-nesting birds. Bird species with enclosed nests tend to have greater nesting success than those with open nests (Nice 1957; Skutch 1966; von Haartman

1971; Oniki 1979). For example, in a study of 16 cavity-nesting bird species in a Central American forest, 60% of the nests produced at least one fledgling. Cavity-nesting species were almost three times as successful as species with open nests in the same forest

(Skutch 1966). Among cavity-nesting species, those which seal the entrance may experience the lowest predation rates. Of 249 nesting attempts by Igckgs hornbills in South Africa, more than 90% were

successful in fledging young (Kemp 1976), and predation was not a

factor in most of the failures. In addition, other bird species

nesting in open holes in the same area during Kemp’s study had a

lower nesting success than did hornbills.

Nest concealment, inaccessibility, and impregnability have been

cited as anti-predator adaptations in avian nest-building (Jackson

1974; Skutch 1976). Hornbill nests have all of these 128

characteristics. Often situated high above ground in the bole of a

large tree, the sealed entrances are visually camouflaged and

difficult to reach. The sealing material dries brick hard. This makes the nest nearly impregnable, especially as the narrow entrance

is guarded from inside by the Sharp, snugly fitting beak of the

female hornbill. The funk hole, or chimney-like escape tunnel,

inside many hornbill nests also works in conjunction with the sealed

entrance to help in avoiding predators.

Carnivores, apes, monkeys, snakes, and raptors are potential

hornbill predators. Yet elephants (Kemp 1976), humans (Hannenburgh

1980), and other hornbills (Poonswad et al. 1983; Kalina in press)

are the only species known to break open hornbill nests. Only the

bushmen open the nests. with the intention of' eating the birds,

although nest damage usually leads to the death of the nestlings

anyway. Elephants inadvertently split the walls of one leetgs nest

when they bent the branch where it was located. Despite attempts by

the nesting hornbill to seal up the cracks in the walls, the nest

was presumed to have been robbed when Kemp (1976) found it empty a

week later. Perhaps it was an accident of this sort that permitted

access to a naked black-wattled hornbill (Ceyetggymne etyete) chick

by a crowned eagle (Stephanoaetgs egrgnatgs). Keith (1970) saw the

eagle carrying an unfledged chick which should certainly have been

confined to its cavity. It is unlikely that the eagle could have

broken the nest-seal, but it may have reached into a cavity after

the female broke out for any of several reasons. 129

Concerning his study’ of three Ipekps species, Kemp (1970) remarked that the "most striking aspect of the study was the lack of predation occurring at the nest." During my 3-year study (65 nest years; 1981-1984) of B. sppeyljpgyiegs ‘Hl Kibale Forest, Uganda, interspecific predation on nestlings was not observed. In short, studies of hornbills have indicated that interspecific predation at the nest is unusually low when compared to that for birds in general. It seems probable that the primary reason for this is that the nests are sealed.

Interspecific-Competition Hypothesis: Nest-Sealing

Protects Against Interspeeific Competition

Competition for nest sites has been noted among birds (Lawrence

1966; Burger & Shishler 1978; Burger 1979; Newton 1979; Trivelpiece

& Volkman 1979; Short 1979, 1982) and between birds and other animals (Dennis 1971; Kemp 1976; Short 1982). Competition for nests has probably had a strong influence on the evolution of nest diversity and nest-building behavior (Collias a Collias 1984).

Since suitable nest cavities can be limited in supply, competition for breeding sites may be magnified by cavity-nesting species. For example, populations of the house wren (Trpglpdytes eegpp) (Kendeigh 1934) and the pied flycatcher (Fieedula hyppleuca)

(von Haartman 1971) increase in response to provisions of nest boxes.

Interspecific aggressive encounters at cavities are often intense (Sielmann 1959; Lawrence ‘1966; Kilham '1968, 1969, 1972;

Short 1979, 1982). Such competition is likely a factor in the 130

evolution of size-class divergence among different species of birds.

Short (1979) suggested that different-sized entrance holes typical for each woodpecker species act to minimize loss of nests to competitors.

Hhen competition for nest sites occurs among open-nesting birds, there is a general precedence of larger species over smaller ones. For instance, on certain cliffs in Britain, kestrels (Eelepp tinnuneulus) are usurped by peregrine falcons. (meg peregpjnps) that are in turn supplanted by golden eagles (Mm shrysaetos)

(Collias & Collias 1984). Similarly, Chinstrap penguins (Pygpseelis antartica) take nest sites from Adele penguins (Pygpsceljs egeliee)

(Trivelpiece & Volkman 1979), and herring gulls (Lepgs ergentatus) displace the smaller laughing gulls (Legs etricille) (Burger &

Shishler 1978; Burger 1979).

If entrance holes are large enough, large birds dominate smaller birds in cavity-nests as well. Hairy woodpeckers (Pjgpjdes villosus) replace downy woodpeckers (Pieoides pubescens) (Short

1979), and starlings (Steppes, vulgarjs) usurp eastern bluebirds

(Sim; siaiis) (Zeleny 1977). Small body size is advantageous, however, when it permits a bird to fit into a hole small enough to keep larger competitors out. Biologists have used this concept to help increase bluebird populations across the United States. Artificial nest boxes with exact entrance-hole dimensions effectively prevent the larger starlings from taking over the nests. 131

European nuthatches (Sitte,.eppppeee) prevent intrusions at their nests when they reduce the entrance-hole dimensions with mud.

The small nuthatch would be unable to prevent the European starling from taking over its nest were it not for this barrier (Sielmann

1959). The wall is built so that the entrance is just large enough for the nuthatch to slip through and small enough that the starling cannot. Sielmann (1959) described the interaction between representatives of these two Species at a nuthatch’s nest as a

"battle." As the nuthatch furiously plastered the nest entrance, a starling pecked away at the barrier. The starling was only able to break away pieces of mud that were still damp, and after several days it abandoned the attempt to take over the cavity. The nuthatch had successfully protected its nest by reducing the size of the entrance hole. At least one other nuthatch (Sitte pegmeyep), the Hallcreeper (Tricodroma murarje), and two swallows

(Petrpehelidon nigpjeens and Eypgpe ehelybea) also reduce the entrances to nest cavities with mud (Rowley 1970).

Hornbills also» experience interspecific interference at the nest. Unsealed Toekps spp. nests in South Africa may be occupied by the pearl-spotted owl (ﬁleucigium perlatum), purple roller (gpracius peeyie), lilac-breasted roller (Coregjus eeggete), greater starling

(Lemprptppnis eustraljs), monitor lizard (Varanus elbpgglaris),

python (Pytppp sebae), and bees (Kemp 1976). Bees also occupy unsealed B. subcylindrjggs nests in Uganda, as do red-legged sun squirrels (Helipsejgrgs :ufpbraehigm) and scaly-tailed flying squirrels (Anomelurgs degpiepgs) (Chapter IV). Because of the 132

prolonged hornbill nesting period, and the protracted season in

Kibale Forest when many of the larger animals breed (Butynski 1988;

Chapter IV), arboreal carnivores, prosimians, parrots, and many other species are also potential competitors for hornbill nest cavities. Grey parrots (Psittaeus exjtpeegs), for example, nested simultaneously with B. sgbcylindriegs, occupying a nest cavity below that of the hornbills’ in the same tree (pers. obs.).

The most serious competition might be expected between sympatric hornbill species with similar nest-cavity requirements.

This was suggested in Kemp’s (1976) study of three Ipetps species when it was found that species interchanged nest holes.

Interspecific competition did not occur, however, since there was no shortage of appropriate nest sites (Kemp 1976). During a study of four forest hornbill species (Bucerps bieprpjs, prtjserps pndulatgs, Anthreepcerps elbirpstris, and Etjlplgemgs tittelli) in

Thailand, however, competition for nests did occur among the same or different species (Poonswad et al. 1983). By attacking the nest and breaking the seal with their bills, intruding hornbills caused nesting birds to abandon the site.

WWW Prote ain t tr i om eti i n

Because of the similarity of their requirements, the most

intense competition often occurs between birds of the same species.

Agonistic interactions between individuals. ore pairs of“ the same

species are COITITIOll at nest sites early in the breeding season. 133

Possession of preferred nest Sites by Canada geese (mm senedepsis) is attained according to dominance after successive replacements of' different individuals or pairs (Collias a Jahn 1959).

Intraspecific competition is undoubtedly magnified for birds with highly specialized requirements, such as those nesting in tree cavities or on cliff edges. Intraspecific competition for nest sites has contributed to the decline of at least one endangered species: the Puerto Rican parrot (Amegppe yittete). One instance of combat between pairs of this tropical rainforest cavity-nesting bird over a single nest site resulted in neither pair producing eggs and injury to the adult birds (Wiley 1980).

Nest sites are apparently limiting for B. subeylindriegs in

Kibale Forest, Uganda, since competition between conspecifics for traditional sites is evident and often severe (Kalina in press; see

Appendix 6-A for descriptions of interactions at nests). Suitable nest cavities seem rare, as the ratio of nonbreeding hornbill pairs to breeding pairs can be as high as 3.4:1 during the pre- and early breeding period (July, Aug., Sept.; Chapter II). Nonbreeding pairs that do not find suitable cavities sometimes guard and display at unsuitable tree holes that may have entrances that are too large, too small, face Skyward, or offer no perch at the entrance. The ratio of sealed hornbill nests to these unsealed "display cavities" is as high as 1.06:1 in some areas (Chapter IV). E. sgpeyljppyiegs are large birds (1.3 kg; Kemp 1979) which, like most other hornbills

(Moreau & Moreau 1941; Kemp 1976), cannot excavate their nests and 134

which depend upon traditional sites. The same 8. sgbcylingricus

pair may occupy the same nest cavity each consecutive breeding

season (Chapter IV). At least one pair in Kibale used the same nest

for 7 years. Heavily worn rims at entrance holes suggest that some

8. subcylindricus nests have been used for decades (pers. obs.).

To maintain ownership at such l'preferred" nest sites, resident

B. sgbeylindrjegs must often defend the nest against conspecifics.

Fights between pairs at nests occur before and/or after the nest is

sealed. At a sealed nest the intruding hornbill(s) will cling to

the rim and attempt to knock out the mud wall that blocks access to

the nest (Kilham 1956; Appendix 6-A). Such attacks are particularly

prominent when the resident male is foraging away from the nest, an

activity that can take 1 h or more (Kalina in press; Chapter IV).

The nest-seal serves to reduce the impact of such attacks until

the male returns to drive off the intruders and help guard the nest.

The advantage of the mud barricade is obvious at such times. Since

8. subeylindrieps forage in widely spaced fruit patches (Chapters 11

and III), the nest-seal protects the nest and allows the resident

(male to forage further away for longer periods of time (Kalina in

press).

Kilham (1956) described intraspecific interference at 6 of 16

B. subeylindriegs nests he observed in south-central Uganda. It

seems reasonable to assume that every hornbill nest in Kibale would

be visited by intruders (intending to supplant the resident pair) at

least once during each 4.5 month nesting period.1 In the 1983-84 135 breeding season, at least 4, and probably 6, of the 10 nest failures were caused by intraspecific intrusions at the nest. Attacks at these nests were severe, repeated, and directed. The nest-seal was either removed by intruders or, eventually, by the resident female before she abandoned the nest. At one nest, an intruding female hornbill broke into the cavity and attacked the two young inside.

This action led to the death of at least one of the two nestlings

(pers. obs.). That the goal of intruding hornbills, even those committing infanticide, is nest occupation rather than some other cause (Mock 1984) was shown by the behavior of successful

"intruding" birds. On at least three occasions in Kibale, intruding hornbills took over the nest site and guarded it after evicting the resident pair (Appendices 6-A, 6-B, 6-C).

Micrpclimate Hypothesis: Nest-Sealing Protects Against Adverse Heether

Nests often protect birds from the physical environment, as well as from other animals (Collias a Collias 1984). Inside tree cavities, birds are sheltered from extreme changes in temperature

(Kendeigh 1961). The 10 C temperature range inside a sealed Ipetps hornbill nest is, for example, relatively stable compared to the

29 C temperature range on the outside surface of the nest tree

(White et a1. unpubl. report). Most of the temperature stability inside the nest chamber can be attributed to the insulation provided- by thick tree walls. The vertical opening to the sealed hornbill nest also helps to regulate the microclimate inside the cavity. The design of the entrance slit allows for good ventilation since warm 136

air escapes at the top part of the opening, while cool air enters at

the bottom. White et al. (unpubl. report) recorded a 0.5 C

temperature gradient between top and bottom parts of the opening.

They also noted that 02 and C02 levels inside the nest chamber

remained within safe limits because of the ventilation system.

The sealed entrance also helps protect birds inside the cavity

from wind, rain, and hail. Dampness in the nest is a limiting

factor for the endangered Puerto Rican parrot (Wiley 1980), which

is, like the hornbill, a tropical cavity-nesting bird. During his

study of the red-cockaded woodpecker (Dendrocopus borealis), Dennis

(1971) noted the advantages that a small nest entrance provides during heavy rains. After 15 red-cockaded woodpecker nests were

enlarged by pileated woodpeckers (Dyypeppgs pjleetus), about half of

them were rendered useless by flooding with rainwater. Hornbill

nesting behavior is influenced by the effects of wetness in the

nest. At least one nest hole was probably abandoned as a result of

flooding in the previous season (Kemp 1976).

Many bird species select cavities with openings that face away

from the direction of approaching storms (Ricklefs 81 Hainsworth

1968; Balgooyen 1973; Conner 1975; McEllin 1979). Cactus wrens

(tampylorhynehus brunneieapillgs) favor nests with openings facing

away from cold winds (Ricklefs & Hainsworth 1968), and Austin (1974)

found that nest orientation was directly related to fledging success

for this species. Parents and young probably conserve energy by

avoiding the chilling effects of prevailing winds and rain. 137

Nesting hornbills are faced with adverse weather conditions since the onset of breeding corresponds with the onset of the rains

(Kemp 1973; Chapters III and IV). There is a potential conflict here since the rains also correspond with a relative abundance of arthropods (Kemp 1973; Nummelin 1986) and fruit (Butynski 1988).

Ground hornbills (Bumps spp.) nest during the rainy season in South Africa, and yet most nests open skywards in broken-off tree trunks (Kemp in 1itt.). Birds in this genus do not seal their nest entrances, but they do have another nest-building behavior that helps to prevent flooding of the nest. Ground hornbills load heaps of dry leaves into the nest as "lining." This serves to level out the uneven nest floors and provides either a drainage or sump for rainwater. There are no records of ground hornbill nests flooding, but there are some where the whole floor apparently collapsed (Kemp in 1itt.).

Hornbill species that seal the nest entrances have not been found to select nests with entrances facing in any particular compass direction (Kemp 1976; Poonswad et al. 1983). In Kibale

Forest, Uganda, 8. subsylindrisus nest-cavity openings faced in all directions (X2 . 5.62, df . 7, p > .25; Fig. 6.1). It is likely, however, that the sealing of nest entrances permits occupation of nests that would be unsuitable were it not for the mud barricade which keeps out wind and rain. Hhere cavities are limited,

selection should favor hornbills with this capability.

The fact that some pairs selected cavities with entrances

facing Skyward indicates that nest holes for B. subcylindpiegs in 138

O O O 0 NW : NE 0 0

W 0.00 eeeeee E

SVY e SE e e e e e Predominant Direction S oi

Fig. 6.l.--Compass direction of B. spbcylipdrjegs nest entrances in Kibale Forest, Uganda (n = 44). (If a nest hole was located midway between any of these eight compass bearings, it was recorded as the next clockwise compass direction.)

139

Kibale Forest are limiting and that the nest-seal permits occupation of otherwise unsuitable cavities. Although a significantly higher proportion of "Skyward facing” nests failed (n . 10, 90%) compared to nests with "outward facing” entrances (n - 39, 31%; X2 - 24.62, df = l, p < .001), it is notable that, at least once, a nest with a

Skyward-facing entrance did not fail. The angle to this successful nest was the least severe of all Skyward-facing openings.

Nevertheless, without the additional protection provided by the nest-seal, it is likely that even this nest would have succumbed to driving rain.

Discussion

Nest-sealing by hornbills could function to protect nest occupants against predators, prevent inter- and intraspecific competition for nest cavities, or protect nesting birds against bad weather. Each of the possible advantages of sealed nests might be of various degrees of importance to individuals of different hornbill lineages (Kemp pers. comm.). Insight into the advantages and evolution of nest-sealing to various hornbill taxa may best be accomplished by taking diverse approaches to investigation. Future studies might focus on convergent evolution among unrelated bird species which reduce nest entrances with mud. Much information could also be gained from comparative field studies, particularly of hornbills and their relatives the hoopoes (families Phoeniculidae and Upupidae), diverse hornbill taxa, or a single hornbill species in different environments. 140

Convergent Evolution Ampng Unrelated Bjrd Speeies

Further studies of the function of nest-sealing behavior might focus on the context and extent to which nuthatches, wallcreepers, and swallows perform the nest-entrance-reduction activity. Convergent evolution among such unrelated species as swallows and hornbills could give insight into the nature of relevant selection pressures. Accounts of intruding female tree swallows (Tachycineta pieplpy; Shelly 1934) and purple martins

(m subis; Loftin & Roberson 1983) entering cavities to kill

conspecific young are surprisingly similar to intrusions by conspecific B. subcylindricus (Appendices 6-A, 6-8, 6-C). Might infanticide be a selection pressure acting on those other Progne species (e.g., E. shalybea; Rowley 1970) which reduce nest-cavity entrances with mud?

Natural History Studies pf Hopppes

Although the green woodhoopoe (Phoenieulus purpureus) has been the subject of much investigation (Ligon a Ligon 1978a, 1978b, 1983;

Ligon 1981), little is known about the behavior and ecology of most species of hoopoes. Hoopoes are considered the closest relatives of hornbills (Sibley & Ahlquist 1972; Kemp 1979). Although hoopoes do not seal their nests like hornbills do, they have developed effective methods of nest defense by means of odorous secretions and aggressive behavior. A. comparison of environmental and social factors influencing nest defense in these two families of birds may 141

have bearing on understanding those selection pressures to which

ancestral hornbills were subjected (Kemp 1979).

m ar tiv ' d St di f H r '1

It may be significant that all observations of intraspecific

interference at hornbill nests have been described for two species

(B. supeylipdricus and B. undulatus) with a similar social system

and feeding ecology (Chapter III; Poonswad et a1. 1983; Leighton

1986). One species is African and the other SE Asian, yet both live

in tropical rainforests and are monogamous, nonterritorial, semi-

nomadic omnivores that feed mainly on fruit. Nesting birds of these

species apparently benefit from protection the nest-seal provides while foraging males are collecting fruit far away from the nest.

8. subcylindricus and 3. undulatus socioecology seems to

predispose their nests to threats of attacks by intruders since the males leave the nests unguarded and vulnerable for long intervals (1

visit/60 min). Ipetus socioecology may tend to prevent threats of

intrusions because male Ipetus spp. return to their nests frequently

to deliver single items of animal prey (1 visit/8 min; Kemp 1976).

Their nests are not, therefore, left unguarded for long (Kemp pers.

comm.). In addition, Ms spp. maintain exclusive territories which are established before breeding. These territories, which are

maintained intra- but not interspecifically, probably also serve to

repel any potential enemies (Kemp pers. comm.) A

Selection pressures acting on nesting ancestral hornbills would

certainly be different depending on similarity of habits to either 142 of the two foraging patterns just described. Leighton (1986) suggested that foraging constraints are the most important ecological factor for Bornean hornbills and are responsible for the evolution of the varied hornbill social systems described in his study. He argued that cooperative breeding by two species and the maintenance of year-round territories by five of seven sympatric hornbill species function to protect fruit resources for these primarily frugivorous birds. Leighton (1986) assumed that suitable cavities were not in limited supply. He presented little data,

however, on nesting birds.

Although cooperative breeding and territoriality may be social

behaviors developed for protecting limited food resources, they may

also help prevent competition for nest cavities. Territories meant

to protect food resources will also protect encircled nests.

Perhaps the availability of fruit is the most important factor

influencing the development of hornbill social systems, but it is

equally reasonable to suggest that nesting constraints were

evolutionarily significant as well. Analysis of the distribution,

abundance, suitability, and use of nest cavities in the Bornean

study site is necessary to continue the argument either way.

Unfortunately, these data are not available at this time.

Contrary observations concerning reproductive success of

3. unduletus on Bornean and Thai study sites should prompt a new

study' of ‘this species--with emphasis on the comparison of

3. unduletus nesting behavior in two different natural communities.

Poonswad et a1. (1983), as mentioned previously, observed 143

B. undulatus abandoning their nests after disturbance by conspecific intruders. Leighton (1986) observed nothing similar for this species in Borneo. In fact, several 3. unduletus pairs were able to nest successfully within territories of other Bornean hornbill species to which they were subordinate. Hhat environmental factors differ' between habitats ‘that are altering the behavior of this species? The identification of factors influencing reproductive strategies should be relevant to the testing of nest-seal hypotheses.

ummar

Most hornbills seal the entrance to their nest cavity so that the female and young are imprisoned inside. Previous Speculations about this curious behavior focused on selective advantages obtained against interspecific predation of the nest occupants. Evidence presented here supports the predation hypothesis. Additional information was provided, however, which attempted to qualify three new hypotheses for nest-sealing (inter- land intraspecific competition for nests, and protection against the weather). Any of several possible benefits could result from chance rather than natural selection. Nest-sealing behavior might be attributable to selection for any one, or a combination of some or all, of these benefits.

The last three hypotheses, unlike the predation hypothesis, are based on the assumption that nest cavities for hornbills are limited in supply. Evidence .was provided that supported this 144

assumption in Kibale Forest, Uganda, and perhaps in Thailand

(Poonswad et a1. 1983) but not for hornbills studied in some other areas (Kemp 1976; Leighton 1986). If nest cavities are limited for hornbills, there should be selection for mechanisms that reduce intra- and interspecific competition for nests, or that make more cavities suitable as nest sites. The nest-sealing specialization could be attributed to a long period of selection in this regard. 145

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APPENDIX 6-A DESCRIPTIONS OF BYCANISIES §UBCILINQRI§U§ BEHAVIORS, SOUNDS, AND VOCALIZATIONS MENTIONED IN APPENDICES 6-B AND 6-C

ehaviors

Bedd;skeke--The rapid movement of the bill side to side as is done during nest-sealing, only the head-shake is a display performed without mud. The head-shake is executed by males and females as a component of courtship displays (directed at each other) and during intrusions at the nest by conspecifics (defending residents directing display at intruder). Head-shake is often observed near or on the nest, but is also performed away from the nest. Sometimes combined with chutter or purr vocalizations. Feathers above the eyes may be erected during head-shakes performed for courtship, but they are flattened against the head during agonistic encounters. During intrusions by conspecifics, the male often will strike his bill against a branch, break off a 4-9 inch long piece of bark or wood, and head-shake while holding the bark or wood in his bill.

Spunds and Vocalizations

Sounds and vocalizations have been tape-recorded and will be spectrographically analyzed. The hornbill’s vocal repertoire is extensive and is not fully represented here.

Brumming--Rapid drumming sound made by female from inside the nest as she head-shakes so that her bill hits against one wall of the nest entrance and then the other. If the sound resonates in the cavity, it can be heard 300 m away. Usually heard during nest- sealing, but also during agonistic encounters with conspecific hornbills intruding at the nest.

Ehutter--A soothing "chuckle" (re: Kilham 1956) usually made by a male while transferring food to his mate.

Flying long-caI|--The long-call (described below) given during flight, which causes a change in the rhythm as it is timed with the beats of the wings. Can be heard 2 km away.

Bunk--Commonly heard, brief calls which may be soft (quiet contact calls between mates), moderate or loud, depending (Hi the context. Soft honks often made by males before they approach the nest to ‘feed. Honks may be given singly or in very rapid succession.

Buh-huh--An "ugh" sound given in twos. 151

Lung-eel --The drawn-out 'ka-waaack" most characteristic of this species. A call that descends and then ascends in succession. Used often and in many circumstances (e.g., pairs advertising their territory at the nest and hornbills at fruiting trees). Can be heard for 2 km. Long-calls give the listener the location and activity of the bird (whether it is stationary or moving). The intensity, timing, and duration of the call, and whether or not it is combined with repeated hi-pitched screams, indicate whether the caller(s) are foraging or are at the nest site.

Bonkey-hoo--This monotone, muffled call sounds like it could be made by a monkey. It is an alarm call made by hornbills as other hornbills approach or as a human approaches. The first note (hoo) is longer than the hoos that follow in rapid succession.

Purr--A soft sound made by females most often while accepting food or during courtship displays.

Repeeted hi-oitched scred_--Shrill rapid screams most often given by males and females during territorial counter-calling bouts. Often following long-calls and rapidly repeated loud-honks. Because females have higher-pitched voices than males, this call is most expressive among females.

Ruah--Ascending scream of panic and pain heard only once, from resident male during a physical attack by an intruding pair of hornbills.

Bumbling--Low, guttural sound. kdpf--Soft, full sound made with bill closed.

Vocalizations Made N tlin s

Buy--Squeaky whimpers.

Hiss--As the hiss of a snake. The chick flattens the head feathers, opens the bill wide in defensive posture, exposing the red spiny tongue, and hisses. Given to humans when approached while on the ground. Since chicks on the ground are totally vulnerable to predators, this is the only form of defense.

Rhythmjc sgueak--Given by nestlings and females while inside the nest. Sounds like the squeaking of a wooden sawhorse as it is being rhythmically rocked under the movement of a saw. Associated with feeding, and lack of feeding, by the male. 152

--Ascending and then descending distinct notes given by females and nestlings during periods of great excitement. Females often make this call loudly if intruders arrive while the resident ma)? is far away from the nest. Apparently a long-distance contact ca . kee--Immature version of the long-call.

Bee-Hi-pitched call which is given repeatedly by chicks when the male parent approaches or lands on the nest. ”Begging” call which continues throughout feeding and often for a short time afterward. 153

APPENDIX 6-B EXAMPLE OF INTRUDING BYCANISTES SUBCYLINDRICUS SUPPLANTING RESIDENTS EARLY IN THE NEST-CYCLE (KIBALE FOREST, UGANDA)

Nest location: HH/S; Undisturbed forest in K-30, Kanyawara Date female sealed inside nest: Oct. 1, 1983 Number of days female sealed in before nest failure: 1-4 Time is read: hours: minutes(seconds)

Oct. 2, 1983

The resident pair (RP) at nest is the same one that nested here successfully in 1982-83.

7:50 RP male is long-calling in the nest tree. RP female is inside the cavity, where she spent her first night last night. She is tapping the remainder of the mud-seal in place with her bill.

8:OO(45)-8:Ol(58) RP male lands on nest, clings vertically to the nest rim, and head-shakes with bill pointed-into the nest hole, while making a low rumbling sound. No food is delivered to the nest.

Male flies off nest, into the nest tree crown. He woofs and counter long-calls to hornbills which are long-calling 250 m away.

8:05(58)-8:09(27) RP male lands on nest, head-shakes, puts his bill deep into nest hole, then repositions his head as he apparently tries to see inside cavity. 8:O9(26) RP male makes a low rumbling sound and flies to 15 m from nest and long-calls.

8:15 All is calm when I leave the area. RP female is still tapping mud from her position inside the tree.

10:40 I check the nest again and the situation is the same as at 8:15. The female is still tapping from inside the nest.

Oct. 4, 1983

I return to the nest site after a technician has informed me that there is a conflict at the nest. -

15:59 I arrive at the site to find that the RP female has broken out of the nest and the RP is confronting an intrusion by conspecifics. One hornbill pair long-calls 5 m from the nest, and a second hornbill pair is 50 m from the nest tree. Unfortunately, neither pair was seen clearly enough to identify at the time. Dried 154 mud is smeared on outside of nest entrance. Both pairs flutter back and forth, flying toward and away from each other. Vigorous vocal exchanges include mbnkey-hoos, long-calls, and repeated hi-pitched screams.

16:19 I get my first good look at the intruding pair (IP) when they fly (long-calling in flight) from approximately 70 m away into the nest tree. The IP hornbills are easily distinguished from the RP hornbills, as the male has unique casque markings and the female’s casque and bill are unusually long with a wide gape (even when her mouth is closed). The female also has a black spot on her white abdomen. He fleshy eye rings are bright red and very swollen, an indication of her excited state. She has mud on the top of her bill at the top, suggesting that she may have knocked out the RP nest- sea .

16:19-16:57 IP and RPS continue to counter long-call. RP moves farther away from the nest.

16:57(28) IP male 1ands on nest rim.

16:57(43) IP female lands on nest and wildly head-shakes into the nest hole, tapping her bill on its edges. IP male self-preens while watching the female, then makes soft huh, huh sounds.

17:00 IP flies to 1.5 m from nest. They purr, perform the head- shake display with bills tapping together, then make huh, huh vocalizations. 17:02(22) The IP female lands on the outside rim of the nest and head-shakes 10 times. The IP male makes huh, huh sounds and the female head-shakes, tapping her bill in the hole as if she had mud in her bill. l7:03(l3) Hhile the IP female flies off the nest and lands 0.5 m away, the IP males makes huh, huh sounds. l7:O4(OO) IP female makes four low, drawn-out long-calls and IP male huh, huhs.

17:05(OO) IP continues to call and remains within 50 m of the nest. RP has flown to > 100 m from the nest and they occasionally counter long-call with the IP from distances of up to 250 m from the nest.

18:18 I leave the area with IP in the nest tree and RP still away. 155

Oct. 5, 1983

17:36 I arrive at the nest site to find the IP long-calling from in the nest tree. IP female’s eye rings are now tan-grey and have lost their swelling, an indication that she is less excited than yesterday. Red mud stains her back and is smeared on her body where she was spotless yesterday. She has obviously been inside the nest cavity. The IP males is breaking off bits of bark from the branch where he is perched, and he is manipulating it about in his bill before drgpping it and breaking off another piece. RP hornbills are not aroun .

17:40-17:59 IP male and female quietly preen themselves and then each other. IP male occasionally utters soft woofs.

17:59 I leave, having been convinced that they are the new residents at that site. -

Oct. 10, 1983

15:53-17:00 IP male fed IP female while she was inside the nest cavity. They attempted to seal the nest with mud, but the female later joined her mate outside the cavity. Both were long-calling from their perch on a limb of the nest tree when I left.

Nov. 2, 1983

IP still resident, guarding the nest site, but the female is not sealed inside the nest cavity.

Nov. 21, 1983

18:11-18:39 Five individuals in a sub-adult hornbill group are perched in the nest tree. I? is not seen in area.

§uma_rx

The RP attempted to nest in the HH/S cavity as they had done successfully the year before. On Oct. 2, 1983, the RP female was sealed into the nest. The RP was supplanted at the nest site by IP 4 days after RP female had initially entered the nest. The RP abandoned the site to IP, which then occupied the site for at least 1 month. IP attempted to, but did not successfully, seal the nest. 156

APPENDIX 6-C EXAMPLE OF INTRUDING BYCANISTES SUBCYLINDRICU§ SUPPLANTING RESIDENTS LATE IN THE NESTING CYCLE (INFANTICIDE)

Nest location: N/9.5; Undisturbed forest, Ngogo Date female was sealed inside nest: < Sept. 26, 1983 Number of days female sealed in before failure: 92+

Jan. 3, 1984

Observations made from: 10:30-12:05: 14:40-18:05

This nest is the only one observed in the wild to contain two nestlings. A male and female chick could be seen inside the cavity. At the time of this intrusion by conspecifics, the nestlings were approximately 1-2 weeks from fledging.

10:33 The male of the resident pair (RP) is found clinging to the nest hole, pecking away the mud of the nest-seal when an intruding pair (IP) of hornbills chases him off the nest. The IP lands on the nest, begins pecking at the seal, and then the RP male chases them away.

10:44 RP male lands on the nest and resumes opening it by pecking at the mud. (Note: When nesting females and young are ready to leave the nest, they typically break the seal themselves.) At 10:45, RP male finishes opening the seal and RP female comes out of the nest. Both RP male and female long-call loudly and fly around the immediate area of the nest site together. 'The chicks remain inside the tree cavity, peck at the nest rim, waa-call, and occasionally stick their bills out the hole.

Although the RP lattempts to approach the nest, IP aggressively guards the nest tree. IP male and/or female lands on the nest rim, attempt to feed the chicks inside, and then peck and jab at the nest rim and at the chicks. IP can be distinguished from RP based on appearance and sound. IP female has a raspy voice. Her tail is frayed, an indication that she has also been sealed into a nest this season. when IP is on or near the nest, the chicks are quiet. Nhen RP long-calls or honks, the chicks respond immediately with a waa call or 6-note call. RP keep their distance when IP is in the immediate vicinity of the nest. RP male "sneaks" in to feed the chicks in the nest when IP is away from the nest site, presumably on foraging trips.

During the hours of observation, intruders (IP male, female, or both together) land on the nest rim on 9 separate occasions, for a total of 19 min., 22 sec. IP male drops 2 dark unidentified items and 4 157

Ficus sp. fruits into the nest. RP male lands on the nest 9 times, for a total of 12 min., 22 sec. and feeds 128 Diospyrgs abyssinica and 5 Mimgsops bagshawgi fruits into the nest.

Jan. 4, 1984

Observations made from: 7:30-13:02

7:30 I arrive to find IP calling in the crown of the nest. The male chick is pecking on the inside rim of the nest hole. RP female has re-entered the nest cavity, and the three hornbills are moving inside.

7:35(56)-7:40(58) IP female lands on nest. RP female head-shakes in hole with bill parted, even before IP female lands. IP female and RP female clack bills and head-shake. IP male perches 4 m away, monkey hoos, woofs, and long-calls. IP female jabs RP female, head- shakes, and pecks hard on the nest rim. Chicks and RP female 6-note ca .

7:40(36)-7:44(35) IP male lands on nest four times, once joined by IP female. All birds head-shake and counter-call to RP male, who is loud-honking 100 m away.

Vigorous and excited vocal exchanges follow between IP and RP. The chicks are active in the nest hole. One throws a wood chip out the hole and the other chick then does the same. One nibbles on the other chick’s bill tip. Chicks wee, 6-note call, and then make repeated hi-pitched screams as IP and RP male jockey for positions around the nest. The intensity of vocal exchanges increases to a high level.

8:21(00)-9:25(20) and 8:46(29)-8:53(10) IP female is on the nest, head-shaking, pecking at nest rim, and attacking the RP female by jabbing with her bill. IP male and RP are screaming at a high level from their positions. Finally, the RP female pecks so hard at the IP female that IP female loses her balance. She pecks back with much force and flies off the nest. - 8:59(27) Hale chick in nest is holding a long wood chip in bill tip and is manipulating it back and forth in his bill as hornbills do to crush their prey. This behavior is the same as used by adult males during displays against intruders, and also during courtship displays. 9:02 The male chick drops that piece and picks up another 3-inch piece of wood to do the same thing.

9:O6(38)-9:07(00) IP male is on the nest, holding an insect in his bill tip. He head-shakes but does not feed the chicks. He flies to 5 m. RP male lands at 10 m and IP chases him. 158

Chicks appear agitated and active in nest with much wood flipping. IP female lands on nest and RP female and both chicks face her in defense posture with bills parted. All head-shake and peck at each other. RP male dives low through the trees, swooping near the nest. Much vigorous counter-calling follows. RP male is no match for the IP, and the fighting at the nest continues. RP female knocks IP female so hard that IP female screams and falls off nest rim. IP female does the vigorous fighting. IP male head-shakes and backs her up by remaining near her, but he does not jab the RP female as viciously as IP female does.

9:47 RP male is fluttering about 70 m from the nest when IP fly long-calling to him, perch, huh, huh, and then chase him to a spot 15 m from me, low (about 3 m up) in the vegetation. They attack him together and he tumbles to the ground. RP male cries a ruah ruah ascending scream, a sound of panic and pain. I have never heard this vocalization on any other occasion. '

11:02 RP male is self-preening 50 m from the nest. His tail is frayed and feathers are in disarray. IP chases him and RP female drums her bill on the walls of the nest entrance. Chicks wee.

Today, one or both intruding hornbills are on the nest on 21 separate occasions, for a total of 46 min., 42 sec. RP male does not land on the nest, and no food is fed in to RP female and chicks.

Jan. 5, 1984

Observations made from: 8:00-12:05

RP female is still inside the nest guarding her chicks against frequent attacks by IP. RP male is able to feed the chicks a small amount (approximately 5 small items) of food on one brief occasion.

Jan. 6, 1984

Observations made from: 7:59-15:05

7:59 I arrive at the nest site to find RP female 6-note calling and repeatedly screaming inside the nest cavity. I can see the chicks as they waa call. IP are 4 m from the nest, woofing and long- calling. RP male is fluttering about 100 m away. .

8:02(25)-8:02(55), 9:00(20)-(40) IP male is on the nest jabbing at RP female.

9:27(50)-9:28(20) RP male lands on nest and dumps about 10 Q. abyssinica fruits very quickly into nest. IP male approaches and RP male dives off the nest, only to be chased by IP female. 159

9:38(59)-9:49(38) IP female is on nest fighting with RP female. RP female’s bill is wide open in defense posture while IP female jabs aggressively with bill closed. 9:48(48) IP male also lands on nest. 9:49(08) RP male lands in tree crown and IP flies off nest. 9:50 RP male flies out of nest tree.

10:01(47)-10:02(30) RP male lands on nest and feeds 12 ﬂ. bagshawei fruits very quickly. He dives off nest as IP approaches him. Vigorous counter-calling by all hornbills continues off and on throughout.

10:05(29)-10:08(54) IP female is on nest fighting with RP female. RP female knocks IP female off nest.

10:10(29)-10:11(33) IP female fighting with RP female at nest. RP male is fluttering about 80 m away.

10:30 All three hornbills in nest are tapping their bills on the nest rim very quietly. RP male loud-honks from 70 m away and chicks immediately waa loudly in response. Much counter-calling between all hornbills follows.

11:38(44)-11:4l(44) IP on nest. IP female vigorously head-shakes and purrs coarsely while tapping her bill against the tip of IP male. Then IP female jabs at RP female. RP male is quietly approaching closer and closer to nest.

11:57(20)-11:59(11), 11:59(42)-12:01(52) IP male is on the nest jabbing at the RP female. 12:00(06) RP male flies into nest tree and loud-honks with fig in bill tip. Chicks answer RP calls with waas and 6-note call. RP female long-calls and 6-note calls. IP female chases RP male down through the canopy and IP male follows in the chase. RP male’s bold approach to the nest attracts the IP’s attention away from the nest and toward himself.

12:36 Chicks wee and cry rhythmic squeak.

12:44(52)-12:45(50) IP male chutters and feeds 1 ﬂ. bagshawei fruit. RP male dives at IP male but is chased away by IP female.

14:03 RP male is inching quietly toward the nest with a Q. abyssinica fruit in his bill tip. Hhen he is 20 m from the nest, IP dives down very quickly and chases him away. Loud vocal exchanges between hornbills continue. .

During hours of observation today, one or both intruders are on the nest on 12 separate occasions, for a total of 30 min., 34 sec. RP male lands on the nest 3 times for a total of 2 min., 37 sec. He rapidly dumps several fruits at a time into the nest. He remains very alert and dives down off the nest quickly as soon as the wings 160 of approaching IP are heard. RP male feeds approximately 37 Q. ab ssinic , 20 n. bagshawei, and l insect into the nest.

Jan. 7, 1984

Observations made from: 8:20-10:05, 15:08-17:40

8:20 IP is in the nest tree long-calling. A chick is wee calling in the nest. The RP female has again left the nest. She may have left in order to obtain food, since the RP male has been unable to provide adequate quantities during the intrusion.

8:30-8:32 IP female lands on nest rim, puts her head deep into the hole, and fights with a chick in the nest.

8:37 A chick pecks on the side of the hole, places his beak outside the hole, and cries softly.

8:39 IP female enters the hole. The chicks waa loudly, crying continuously. There is much movement and circling inside the cavity as the IP female is chasing and jabbing the chicks. The IP male is quietly perched in the nest tree crown. RP is long-calling from approximately 150 m away the entire time IP female is inside the nest.

8:48 IP female comes out of the nest hole and chicks stop vocalizing.

8:50 IP female lands on nest and pecks on rim, but does not enter.

9:03 1P male lands on the nest, looks inside, and soft-honks. Chicks do not vocalize in response.

9:04 IP male flies to the north. 9:15 IP female follows him.

9:19 Hhile IP is still away, the female chick sticks her head outside the nest hole, but she pulls it back in again. The male chick is not seen or heard.

9:20 RP male and female fly while long-calling to 20 m from the nest. RP calls to the chicks, and the female chick responds with waa calls.

9:33 Female chick squirms her way out of the nest and quietly lands 5 m below the nest on a Celtis durandii branch.

9:40 The chick waa calls from her perch. The IP suddenly appears and flies at her, knocking her off the branch. At this time, RP flies away to approximately 100 m. The IP female attacks the chick with her claws, and the chick falls to the ground approximately 30 m 161 from the nest. As she falls, IP female follows close behind her. The chick waa cries as she hits the ground. The IP female lands atop her, biting and pecking at her. During this attack, all adults are quiet and only the screams of the chick can be heard. IP male remains 2 m away.

9:45 My technician rushes over to rescue the chick. As he approaches, IP monkey hoos, then flies quietly away to the north. Chick hisses, snaps, and waa calls as he picks her up. Then she immediately calms down and becomes very weak and docile. Chick has bloody puncture wounds on her back from the claws of IP female. She also has a large swelling on her right side and a superficial wound on the right leg. There are no broken bones. She weighs 750 grams and she accepts food readily. She is wounded and too weak to fly, and would surely fall victim to predators (intra- or interspecific). Judging from the immature condition of her feathers, I suspect that shed should have remained in the nest for one more week before e ging.

There is no sign of the male chick, and I suspect he was badly injured or killed inside the nest by the IP female. He was not heard calling, and there is no indication that he is with the RP. Ne take the chick back to camp for treatment. '

15:08 There is no activity at the nest site.

15:30 RP male lands on nest with fruit in bill tip. There are no vocalizations from the male and no sounds from the nest.

Ne search the area for a dead male chick on the ground, but find nothing.

16:53 IP lands in nest tree, but not on the nest.

17:05 IP flies from area.

17:40 He leave nest area with no activity at the site.

Jan. 8, 1984

Observations made from: 8:45-14:40

IP long-calls from the nest tree and remains around the nest site. No chicks are seen or heard. RP is not seen, but there are hornbills counter long-calling at 100-200 m from the nest which may be them. On two occasions, IP female lands on the nest and looks inside. Once she holds a fruit in her bill tip, and once she only pecks at the nest rim. IP male also lands on the nest twice. Once, he soft-honks and looks inside, and once he counter long-calls to the hornbill pair at 100 m. 162

Jan. 9, 1984

Observations made from: 16:09-17:00

IP remains at the nest-site long-calling. RP and chicks are not seen or heard. IP male lands on the nest once, with a fruit in his bill tip. There is no activity inside the nest. CHAPTER VII

SUMMARY AND RECOMMENDATIONS

Byganjstes subcylindricus habitat is restricted to forested areas, which in Uganda are experiencing rapid destruction and conversion. Basic information provided here on the ecology and behavior of black-and-white casqued hornbills birds permits recommendations to be made concerning the conservation of this species and of its rainforest habitat.

In Kibale Forest, 8. subcylindricus movements, spatial dispersion, and habitat use vary seasonally. Hornbills are present in selectively logged areas, but in lower numbers than in primary forest in the core of the Reserve. Primary forest is the most suitable habitat for these birds. Hith an estimated mean density of

12.9 birds/km2 at Kanyawara and 27.8 birds/km2 at Ngogo, hornbills in Kibale are at greater densities than any other forest hornbill species on record.

Hornbill movements are closely related to their diet.

Particularly during dry seasons, 8. subcylindricus travel long distances (probably > 10 km) in search of fruiting trees. Because they exploit fruit resources that are widely dispersed,

B. sgbgyligdrjcgs require very large areas of forest for survival.

These birds are primarily frugivorous and feed on a wide variety of

163 164 fruit species. Since seeds of most plant species consumed are passed out in feces or are regurgitated intact, these birds mediate seed-dispersal of tropical rainforest trees. The conservation and regeneration of this threatened ecosystem are certainly influenced and possibly maintained by these birds.

8. subcylindricus have a complex reproductive ecology. Data indicate that rainfall, intra-specific competition for nest-sites, predation, and food supply influence nesting success. Hornbill reproduction is dependent on the availability of large, over-mature trees for nesting. Primary forest is apparently the preferred habitat for breeding, since nest and display-cavity density is highest there. The number of young fledged per unit area is also highest in unlogged forest.

Logging alters the forest habitat for hornbills by reducing the number of large, over-mature trees available for nest sites.

Therefore, it might be expected that, for each large nest tree removed, one less breeding pair is able to produce young (Fig. 7.1).

Observations during this study indicated, however, that in forest tracts subjected to intensive logging of nest trees, far more than one breeding pair would be affected for each nest tree removed.

8. subcylindricus are long-lived (probably > 20 yrs.) and compete for nest-sites with fervor. As nest trees are removed, the severe competition for remaining sites would likely decrease nesting success exponentially (Fig. 7.1, line b), rather than linearly (Fig.

7.1, line a). Today, it is important to note age distributions of

8. subcylindricus when determining the population status of this 165

AREA)

SUCCESS

NEST

FLEDGED/UNIT

CHICKS

HORNBILL (N°

a N° NEST TREES REMOVED/UNIT AREA

Fig. 7.l.--Hypothetical relationship between ﬁyganistgs sybgyljndri; 9g; nest success and number of trees removed per unit area. Line "a" represents the linear response that might be expected if, for each nest tree removed, one hornbill pair was prevented from breeding. Line "b" represents the exponential reduction in nest success that is predicted based on expected increase in competition for remaining nest-sites. 166

species in degraded forested areas. Although birds may seem abundant, the population may be aged due to limited nest sites and low recruitment of young. Numbers of individuals would make a precipitous decline as aging birds die.

More data analyses are needed for the effects of logging on the reproductive ecology of B. SW5 to be better understood.

Based on the findings of this study, general recommendations can be made to reduce the negative effects of logging on this species.

Recommendations made here for the conservation of 8. subcylindricus in Africa agree with those of Johns (1987) and Kemp and Kemp (1974) for the conservation of hornbills in SE Asian rainforests.

1. Degradation of primary forest correlates with reduction in hornbill numbers. Large tracts of primary forest should, ideally, be left intact and undisturbed.

2. Should timber trees be removed, forestry practices should be as follows:

a. Leave as many large trees standing as possible.

b. Prevent incidental damage to the forest during timber

extraction.

c. Leave snags, hollow trees, and large or over-mature

trees likely to produce nest cavities for hornbills. Often

these trees are of no commercial value anyway.

d. Leave trees known to contain hornbill nest or display

cavities. These sites are used by hornbills year after year. 167

e. Leave large fruit trees (especially figs, Ficus spp.) standing, which are known to produce mass crops for hornbills.

Fig trees are an extremely important food source for hornbills and many other animals, and they are of little or no commercial value. Fig trees fruit aseasonally and may be a key factor in hornbill survival.

f. The collection or hunting of hornbills must continue to be prohibited. 168

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