CSIRO PUBLISHING Emu, 2007, 107, 300–307 www.publish.csiro.au/journals/emu

Reproductive activity in the Osprey (Pandion haliaetus) on Kangaroo Island, South Australia

T. E. Dennis

5 Bell Court, Encounter Bay, SA 5211, Australia. Email: [email protected]

Abstract. This study reports on aspects of the breeding biology of Ospreys (Pandion haliaetus) on Kangaroo Island from data collected over 18 breeding seasons between 1985 and 2004. Over this period an average of nine pairs were located each year, and a total of 145 occupied territory years were monitored for breeding activity and outcomes. Of these, active breeding occurred in 103 (71%), with 60% of these successfully fledging young. Productivity was found to average 0.66 young fledged per year per occupied territory, and 0.92 young fledged per year per active nest. This level of productivity, while similar to that of other studies in Australia, is below the minimum recruitment levels needed to maintain migratory Osprey populations in the northern hemisphere. However, such high rates may not be needed in the non-migratory population of Australia. Although some early dispersal was recorded among marked Osprey young, strong philopatric recruitment was also evident, with 22% of survivors either remaining on the island, or returning at maturity to join the breeding population. Through the re-identification of individuals, Osprey pairs were found to remain together over many seasons and to use the same primary nesting site. The breeding season began later than reported elsewhere in Australia, extending from August to February, with most laying occurring in September. Undetected nest predation and human disturbance was suspected at accessible nests as contributing to the high level of nest failures recorded. The apparent elongated nestling development period found is comparable to that determined in other studies where fluctuating prey availability directly influenced nestling growth and survival. These factors, plus geographical isolation, suggest the Osprey may be precariously balanced ecologically at the southern extent of its breeding range in Australia.

Additional keywords: disturbance, eye character recognition, low productivity, nest failure, nest predation, pair fidelity, reproductive outcomes.

Introduction The Osprey (Pandion haliaetus) is a fish-eating raptor with an with former coastal and estuarine habitats being re-occupied almost cosmopolitan distribution and four geographically dis- (Clancy 2006). crete subspecies (Prevost 1983; Poole 1989). The Australasian In South Australia, concentrated human settlement in subspecies (P. h. cristatus) is found mainly in tropical to warm coastal regions has resulted in broad-scale clearance of indige- temperate zones and differs physically from northern hemi- nous vegetation and a profound loss of biodiversity, with most sphere subspecies in size, with both sexes 12–14% smaller. coastal areas now being regarded as disturbed or degraded They vary slightly in plumage, and P. h. cristatus is non-migra- (Nance and Speight 1986). In contrast, Kangaroo Island is a tory (Poole 1989). large and biologically diverse island, 4350 km2 in area with The Osprey is classified as Endangered in South Australia 480 km of coastline, lying 15 km off the South Australian main- under state wildlife protection legislation (National Parks and land, ~110 km south-west of Adelaide. The island has several Wildlife Act 1972; amended, 2007. By definition this classifica- minor river estuaries, which retain a body of open water tion recognises a species ‘in danger of extinction if the causal through summer and where eucalypt woodland extends to the factors continue to operate’ (Robinson et al. 2000). As top-order sea, particularly along the island’s sheltered northern coast. predators in coastal and estuarine habitats, Ospreys can be Large tracts of the island are protected in national parks and regarded as indicators of environmental health and stability in a wilderness protection areas but, particularly near the coast, region, with population trends a useful indicator of ecological land-use is changing, with many of the large holdings, tradi- change (Poole 1989). tionally involved with low-intensity agriculture and grazing, While the Osprey population appears stable in remote north- being subdivided, which has resulted in denser human habita- ern and tropical areas of Australia, there is evidence of a decline tion and increased human activity. This process appears to be in historical times at the southern extent of its range (Marchant threatening the habitat of Osprey and other coastal raptors and Higgins 1993; Olsen 1998; Dennis 2007). However, in (Dennis and Baxter 2006). northern New South Wales, on the eastern coast of Australia, The aims of this study were to measure breeding productiv- some population recovery has been evident in recent decades, ity over time among the Kangaroo Island Osprey population,

© Royal Australasian Ornithologists Union 2007 10.1071/MU07010 0158-4197/07/040300 Osprey productivity on Kangaroo Island Emu 301 determine the seasonality and duration of the breeding season, the hide found to be minimal, with the female settling back on and to examine pair- and site-fidelity. the nest within minutes. In all cases, the male continued to deliver fish to the nest, taking little notice of the hide. These Methods behaviours varied little between pairs and enabled periods of Population survey and nest monitoring protocol extended observation from the hide with minimal disturbance. Beginning in 1983, opportunistic surveys on land, at sea and in Placement of hides was only attempted when the nest contained aircraft were conducted to locate nesting sites of Ospreys (and well-developed young, >35 days old (by which time the adults other coastal raptors). In 1984, a network of observers was were settled into strongly established roles of foraging and nest- established to report observations of Ospreys and their activity protection), or if a nest had failed or was inactive, when adults at nest sites in particular. Subsequently, between 1985 and 2001 used the nest-platform to eat prey or to roost. and in 2004, known territories and newly discovered nesting In addition to ABBBS bands, a method of re-identifying sites were surveyed each year to determine occupancy, and most individual adults from natural markings was trialed and adopted were then systematically monitored to record outcomes. during this study. This involved the visual recognition of indi- Following a protocol adapted from Poole (1989), this involved vidual eye characteristics. From within the hide, using the spot- 2–4 visits to each territory during the spring–summer breeding ting scope, simple sketches were made of both eyes for each season: the initial visit to determine if the territory was occupied adult at the nest. Each eye sketch detailed the ‘clock face’ loca- or active; subsequent visits were timed to coincide with young tion of obvious darker flecks or flecking patterns, which con- being sufficiently advanced to enable an estimate of age from trasted markedly against the bright yellow iris of the Osprey the stage of plumage development at time of banding (hide (Fig. 1). Comparison with original sketches over subsequent placement occurred on this visit and the hide occupied there- years revealed a level of consistency enabling an Eye Character after for varying lengths of time); and a final visit 2–4 weeks Recognition (ECR) method to be used with confidence on a few after a calculated fledging date to determine the number of individuals. However, there was evidence of the iris darkening young that fledged. with age in two individuals >18 years old, with fleck characters Early observations were typically made from a distance of no longer distinguishable. >500 m to avoid interruption to normal behaviour. This was pos- The individual re-identification technique using characteris- sible as, typical of those elsewhere in South Australia, most tics of the crown plumage, described by Bretagnolle et al. nests were found below the level of the adjacent cliff-line and (1994) was also trialed, but discarded early on as unreliable in constructed on collapsed or eroding sections that have formed the windy conditions which prevail during early summer. near-shore rock-stacks, or on the wave-cut platform, and so could be viewed from above (Dennis 2007). Determining age of nestlings and start of incubation The age of nestlings was determined at the time of banding Individual marking and re-identification based on a comparison of feather development with a photo- Nestlings graphic index of Osprey young of known age. The index was Between 1984 and 2001 Osprey nestlings were banded when 35–45 days old, on the right tarsus, with Australian Bird and Bat Banding Scheme (ABBBS) stainless steel bands. From 1986 to 1991 nestlings were also banded on the left tarsus with PVC wrap-around colour-bands, following a prescribed ABBBS sequence. This enabled others to report sightings, thereby con- tributing data on post-fledging survival and dispersal behaviours. However, the use of colour-bands was discontinued in 1992 when it was concluded that PVC bands were prone to early loss or removal.

Adults In 1991, banded adults were observed among the breeding pairs. Four of these were subsequently individually identified from ABBBS band numbers using a tripod-mounted high-reso- lution spotting telescope at 40× or 60× magnification (Kowa Prominar TSN-4, Japan), used from within a camouflage netting ‘hide’ draped over rocks or bushes 20–40 m from the nest-platform. In Ospreys, incubation is shared by both adults (Dennis 1987; Clancy 2006), with the female assuming sole responsibil- ity for brooding and guarding small young and rarely leaving the nest over the first 45 days of the nestling period (Poole 1989; T. Fig. 1. Adult Osprey showing typical iris characteristics used to re-iden- Dennis, unpubl. data). Therefore each nest was only approached tify individuals in this study (photograph © Nicholas Birks, May 2004, Red when the male was absent and disturbance from placement of Banks, Kangaroo Island). 302 Emu T. E. Dennis based on a series of photographs taken at 7-day intervals from year, ranging from eight (in 1993 and between 1998 and 2004) hatching to fledging (A. F. C. Lashmar, pers. comm.). This to 10 (in 1988, 1990, 1991 and 1995). Among these, five were visual comparison provided an approximate hatching date, continuously occupied and used the same primary nest-site. which was likely to be accurate to within 5 days (expressed as Between 1985 and 2004, 145 occupied territory years were ±5 days). monitored to determine breeding outcomes, of which 103 (71%) The incubation period for the Osprey is reported to be became active, with 62 (60%) of these successfully fledging ~36 days, and incubation begins with laying of the first egg, young. A total of 95 young fledged from the 103 active territo- resulting in asynchronous hatching over 3–5 days (Holsworth ries, producing an average of 0.66 fledged young per year for 1965; Poole 1989). The incubation period was subtracted from occupied territories, 0.92 fledged young per year in active terri- the calculated hatching date to provide an estimate of the dates tories, and 1.53 fledged young per year at successful territories. of laying and start of incubation (±5 days) for each active nest. Breeding season and frequency Terminology Breeding seasons were found to be elongated and varied from The universally accepted raptor survey and research terminol- year to year, with no fixed or discernable pattern between terri- ogy was adapted to this study (Postupalsky 1974; Poole 1989): tories. At most (72%) nest-sites, laying and start of incubation Occupied territory – where a pair of adult birds appear together occurred in September, but ranged from mid-August to early in the breeding season in the vicinity of the nest(s) and terri- October, which is later than reported elsewhere in Australia torial defence is observed. (Holsworth 1965; Surman 1994; Clancy 1989, 2006) and later Active nest or territory – a site where eggs are laid (may be than reported for South Australia by Marchant and Higgins determined from prolonged incubation behaviour only) or (1993). Correspondingly, most hatching occurred from mid- young are recorded. October to mid-November, with some hatching in mid- to late Successful nest or territory – a nesting site from which young September (n = 2) and late November to early December (n = 5) fledge. (Fig. 2). The hatchings, in late November and early December, Failed nest or territory – where eggs fail to hatch, or where eggs may have resulted from an undetected loss of the first clutch, as or young are lost, e.g. to predation or severe weather. Osprey elsewhere are likely to re-lay about 3 weeks after loss of Primary nest – the most frequently used nest within a territory. eggs providing that loss occurred early in incubation (Poole Alternate nest – one of sometimes several nesting structures 1989). within the home-range of one pair. The number of days between first and last hatching in the population over 15 seasons averaged 24 days (±5 days), though Results hatching spanned >60 days in three seasons (1985, 1991 and Population and nest-productivity 1995). The period from hatching to fledging at a small number Over 18 breeding seasons between 1985 and 2004 an average of of sites (n = 8) was estimated to average 69 days (±5 days) and nine occupied Osprey territories were identified each survey ranged from 62 to 74 days. Young continued to be fed at or near

Year n August September October November December January February 1985 4 ↔ ↔ ↔ ↔ 1986 3 ↔ ↔ ↔ 1987 4 ↔ ↔ ↔ 1988 1 ↔ 1989 4 ↔ ↔ ↔ 1990 3 ↔ ↔ ↔ 1991 5 ↔ ↔ ↔ ↔ Fig. 2. Diagrammatical representation of the 1992 3 ↔ temporal span of the Osprey breeding season (laying to fledging) between 1985 and 2004. 1993 6 ↔ ↔ ↔ ↔ ↔ The symbol ‘↔’ represents one or more 1994 2 ↔ ↔ 3–5 day hatching periods (±5 days) and ‘n’is 1995 3 ↔ ↔ ↔ the number of successful territories recorded 1996 2 ↔ ↔ for each year. 1997 4 ↔ ↔ 1998 4 ↔ ↔ ↔ 1999 3 ↔ ↔ 2000 3 ↔ 2001 3 ↔ 2004 5 ↔ ↔ ↔ ↔ Osprey productivity on Kangaroo Island Emu 303 the nest for several weeks after fledging, and begging and unknown, prior to the breeding season in 1993 an unbanded attempted piracy behaviours were recorded 10 and 11 weeks mature female, presumed to be the resident female of that terri- after fledging. tory, was found dead nearby, negating the likelihood of surro- In some territories, long-term pairs were found to be active gate incubation by the young female. In another territory in in most breeding seasons for several years. For example, at one 1994, a young banded female was recorded as breeding suc- site (DB) a newly established pair in 1993 were active in eight cessfully aged 3 years. out of 10 subsequent seasons (not 1994, 2001). Other pairs Age of first breeding was known for six males. In 1993 two appeared to breed in alternate years, e.g. at site BB, the pair bred banded males, aged 4 and 5 years, were recorded at an active successfully in 1993, 1995, 1997 and 1999, and nested unsuc- nest with a female in an apparently successful polyandrous rela- cessfully in 2000 and 2001. In other territories, there were two tionship that continued for at least four breeding seasons. In four and sometimes three years between breeding attempts. other territories, two males were aged 6 years, one 7 years and another 8 years when first recorded as paired and defending a Re-sighting individually identified birds territory or at an active nest. In the case of the 7 year old, it was Of the 95 young fledged from monitored nests over the study strongly suspected that this male was already in the territory in period, 73 were banded with ABBBS stainless steel bands, and the previous year when a new nest was constructed. From this 26 of these also had PVC colour-bands. Among those banded, limited data, the average age at first breeding for young male 10 were found as post-fledging mortalities aged <12 months, Ospreys was 6 years (n = 6) and two females first bred at <2 and and 12 were later re-identified among the territorial pairs. Nine 3 years old. of these were male and three were female. In addition, there The oldest individuals identified in this study were a male were two banded males at active nests in 2004 that remained aged 22 years (banded as a nestling in 1978) and recorded at an unidentified. active nest in 2000, and a female, also aged 22 years (banded as Before this study 12 nestlings had been banded between a nestling in 1982) when recorded at an active nest in 2004. Two 1973 and 1982 on Kangaroo Island. Of these, two were found other males were 17 and 19 years old in 2004. Although there is dead, one in 1984 on Kangaroo Island aged 11 years, and a dearth of longevity data for the Osprey in Australia, individu- another in 1991 on southern Yorke Peninsula aged 12 years als aged 24 and 25 years have been recorded among active (D. Drynan, ABBBS, unpubl. data). Two others, one male and breeding pairs in North America (Poole 1989). one female, were identified in this study among breeding pairs. Over the duration of the project a total of 18 adult Ospreys Polyandry (including the two banded before 1985) were identified among Between 1993 and 1996, two males were present in one territory the territorial pairs by either ABBBS band number (n = 14 birds, and bred successfully over at least four breeding seasons. These a total of 51 times) or by ECR (n = 4, a total of 19 times). Among were re-identified each year from ABBBS bands, and although the latter, two were female and provided pair- and site-fidelity data spanning 4 and 8 years respectively.

Pair-fidelity and nest-site attachment Among individuals re-identified from year to year, three pairs and one trio (polyandry), remained together over many succes- sive seasons and bred at the same primary nesting site. The fol- lowing pairs demonstrate this: (1) male 02 + female 43, at least five consecutive breeding seasons, 1994–98; (2) male L1 + female E1, at least eight consecutive breeding seasons, 1993–2000; (3) male 13 + female 41, at least 12 consecutive breeding seasons, 1993–2004; (4) males 19 and 28 in polyan- drous relationship with female E2, at least four consecutive breeding seasons, 1993–96. Although mortality and subsequent new pairs were recorded over the course of the study, none of the known individuals, of either sex, was found to re-locate from the territory where first identified, or to desert an established pair-bond.

Age at first breeding and longevity Age of first breeding was known for two females. Between 1985 and 1992, at a regularly monitored nest site in territory DB, an unbanded pair had continuously failed to produce young. Early Fig. 3. Photograph of two adult males (identified from ABBBS bands) and in the 1993 breeding season in this territory, courtship the resident female (centre, identified by ECR), with one young aged ~20 behaviour was observed between a colour-banded female aged days in the nest. These three adults, in an apparent polyandrous relationship, <2 years and a banded male aged six years and, using the long- co-operatively fledged five young over four seasons between 1993 and 1996 established primary nest, this new pair successfully reared two (photograph © T. Dennis, October 1997, Dudley Peninsula, Kangaroo young. While the fate of the former territorial male was Island). 304 Emu T. E. Dennis the female was unbanded she was identifiable using ECR. Both Among migratory Osprey populations, productivity is sig- males were observed to bring fish to the nest and all three adults nificantly higher. For example, in the United Kingdom, average were occasionally on the nest-platform with young present productivity of 1.57 young per pair per year at active nests was (Fig. 3), when behaviours appeared passive. Both males, one 4 recorded from >1500 breeding attempts, and elsewhere in years old and the other 5 years old when first observed in 1993, Europe, productivity was 1.52 young per year per active nest were from the same natal site (and parent pair), ~15 km distant. (R. Dennis, pers. comm.). These results are comparable to There were four other instances, between 1997 and 2000, several long-term studies in North America (Poole 1989). where the territorial male (identified from ABBBS band) and Poole (1989) provides a formula to calculate a minimum the brooding female appeared to tolerate visits to the nest-plat- reproductive rate for population stability among migratory form containing advanced young, or to nearby roosting sites, by Ospreys. When this formula is applied to the data presented an unmarked male. However, these observations did not include here, productivity, and therefore recruitment, would need to be bonding interactions with the female, or the delivery of fish. around 1.25 young per year per active nest to maintain the popu- lation, well above the level of 0.92 young per year per active nest Discussion found in this study. However, the level of recruitment required Productivity and population stability to maintain migratory populations is likely to be higher than for Other studies of Ospreys in Australia report similar levels of non-migratory populations owing to the exposure to risk and productivity (1.53 young per pair per year) at successful nests, higher mortality inherently associated with migration (Poole e.g. on Rottnest Island, in Western Australia, productivity was 1989). 1.4 young per pair per year from nine nesting attempts (Holsworth 1965); and in northern New South Wales, produc- Rates of breeding inactivity tivity was 1.6 young per pair per year from eight nests in the late An average of 29% of occupied territories were found to be 1980s (Clancy 1989) and 1.36 young per pair per year a decade inactive each year. This is double the frequency determined over later from 57 successful breeding attempts (Bischoff 2001). 50 years of monitoring migratory Ospreys in the United However, of more significance to population stability is pro- Kingdom where the average is 14% (R. Dennis, pers. comm.). ductivity from all active nests, inclusive of nesting failures. In Because the timing of the first nest monitoring visit at most sites this study, overall productivity was found to be 0.92 young per during this study was usually a few weeks after incubation was pair per year from 103 active nests (Table 1), which is almost expected to have begun, some early egg losses may have gone identical to that recorded in a similar study in northern New undetected, particularly if a second clutch was not produced. South Wales (0.91 young per pair per year from 86 active nests; Therefore the high level of inactivity among pairs given here Bischoff 2001). may be negatively biased.

Table 1. Reproductive activity among the Osprey population of Kangaroo Island over 18 breeding seasons between 1985 and 2004

Year Number of territories Number of No. of young fledged per year per: OccupiedA Active Successful young fledged Occupied Active Successful territory territory territory 1985 7 (9) 6 4 5 0.71 0.83 1.25 1986 8 (9) 7 3 6 0.75 1.0 1.5 1987 9 9 4 7 0.77 0.77 1.75 1988 9 (10) 6 1 1 0.11 0.2 1.0 1989 7 (9) 6 4 7 1.0 1.17 1.75 1990 9 (10) 6 3 5 0.55 0.83 1.66 1991 10 8 5 7 0.7 0.87 1.4 1992 8 (9) 3 3 5 0.62 1.66 1.66 1993 7 (8) 6 6 8 1.14 1.33 1.33 1994 8 (9) 5 2 3 0.37 0.6 1.5 1995 9 (10) 4 3 4 0.44 1.0 1.33 1996 7 (9) 4 2 3 0.43 0.75 1.5 1997 7 (9) 5 4 6 0.86 1.2 1.5 1998 8 6 4 4 0.5 0.66 1.0 1999 8 6 3 6 0.75 1.0 2.0 2000 8 6 3 5 0.62 0.83 1.66 2001 8 5 3 4 0.5 0.8 1.33 2004 8 5 5 9 1.12 1.8 1.8 Total 145 (160) 103 62 95 Mean 8.05 (8.89) 5.7 3.6 5.3 0.66 0.92 1.53

ANumbers in parentheses include additional occupied territories that were not monitored to determine reproductive outcomes. Osprey productivity on Kangaroo Island Emu 305

Nestling development sible nests, though the difference is not statistically significant χ2 The nestling period, between hatching and fledging, for Ospreys ( = 1.74, d.f. = 1, P > 0.05). in Australia is reported as: ~50 days (Holsworth 1965), 55 days Potential avian nest predators include ravens (Corvus), gulls (Cupper and Cupper 1981), and 49–56 days (Olsen 1995), all of (Larus) and other raptors, such as the White-bellied Sea-Eagle which are similar to those for migratory populations elsewhere (Haliaeetus leucogaster) and the Wedge-tailed Eagle (Aquila in the world (Poole 1989). In this study, the mean nestling period audax). In the Canary Islands, the Yellow-legged Gull (Larus was 69 days (with potential variation in estimates of ±5 days, cachinnans), which is similar in size and habit to the Pacific giving a range of 62–74 days), ~14 days longer than the results Gull (Larus pacificus), was identified as a likely predator of of other studies. Clancy (2006) also reports an elongated Osprey nestlings and eggs, particularly during instances of dis- turbance, when adults may be distracted and drawn away from nestling period at two nests in north-eastern New South Wales, the nest (Siverio and Rodriguez 2005). From the frequency and of 71 and 76 days. These long nestling periods are closer to intensity of nest defence, the White-bellied Sea-Eagle was iden- those reported from a study of the non-migratory Caribbean tified as a possible predator of Osprey young in northern New population of Ospreys (P. h. ridgewayi) in Mexico, where the South Wales (Clancy 2006). With the average distance from fledging period at 10 nests averaged 63 days and ranged from each Osprey nest to the nearest Sea-Eagle nest on Kangaroo 55 to 76 days (Judge 1983). Island being 6.8 km, and even closer along the north coast In reference to the Caribbean study, Poole (1989) suggested (Dennis and Baxter 2006), similar overt interactions were that young from regions with a poor or fluctuating food supply observed during this study. develop more slowly and fledge later than young at ‘well-fed nests’. He also suggests that without the temporal pressures of Human disturbance migration, non-migratory subspecies may have evolved slower Although fairly tolerant of people and able to habituate to growth rates. Of likely significance to this present study, Poole human activity, Ospreys do not readily accept novel intrusions (1989) also suggests that the incidence of persecution of runt- or events near the nest during the breeding season and especially chicks and of fighting among siblings, which was observed fre- among pairs at more remote sites (Van Daele and Van Daele quently among nestlings during this present study, is also more 1982; Poole 1989). Disturbance causing adults to leave the nest prevalent at nests when availability of prey is limited. during critical periods of incubation and early brooding can be Nesting failure fatal to embryos and small nestlings through cooling and expo- sure to predation (Poole 1989). Productivity is significantly The 40% failure rate among active nests is higher than reported higher at Osprey nests remote from human activities (Levenson for migratory populations, but comparable to a recent study in and Koplin 1984) and the most productive nests are those where northern New South Wales, where a 34% failure rate was incubation is continuous (99.5–100%) during daylight hours recorded from 86 nesting attempts over three breeding seasons (Van Daele and Van Daele 1982). (Bischoff 2001). In a study of non-migratory Ospreys on the Cape Verde Although it was beyond the scope of this study to determine Islands, Palma et al. (2004) found that increasing tourism and the actual causes of nesting failure, some early nest predation consequent disturbance at or near active nests caused failures is suspected. Studies in North America show that Ospreys and desertion, particularly at exposed and accessible nests breed at their highest densities and raise significantly more ‘placed on the ground’. Over the last decade, instances of dis- young on islands free of mammalian predators or where preda- turbance causing frequent interruptions to incubation have tor-proof artificial nesting platforms have been provided occurred at remote nesting sites in the study area and also on the (Poole 1989). Although Ospreys will vigorously defend their Eyre Peninsula, resulting in nesting failures and desertion of nests, nocturnal predators can be successful in raiding accessi- territories (Dennis 2004; Dennis and Baxter 2006). Coincident ble nests (Poole 1989). The nocturnal and omnivorous with increasing tourism activity has been the decline in the Common Brushtail Possum (Trichosurus vulpecula)is number of occupied nests on the sheltered northern coastline of extremely abundant on Kangaroo Island and has been identi- Kangaroo Island, where between 1984 and 1991 there were five fied as a significant predator of eggs and young in another nests dispersed over 68 km of coastline, but which declined to threatened bird species studied there (Garnett et al. 1999) and two by 1993 and since. similarly in New Zealand (Brown et al. 1993). These possums Environmental contamination may also effect the breeding are larger (3–4.5 kg) than the mainland form and spend con- success of the species on Kangaroo Island. The irregular breed- siderable time foraging on the ground owing to the absence of ing activity and low productivity levels found in this study are predators (Inns 2002). In addition, feral Cats (Felis catus) and consistent with raptor populations affected by accumulated pes- Sand Goannas (Varanus rosenbergi) have both been observed ticide residue found in their prey (Newton 1979; Poole 1989) climbing onto and scavenging around active Osprey nests and low to moderate levels of organochlorines have been found during this study. in Osprey eggs and in some prey species from Kangaroo Island Of the 13 primary Osprey nesting sites monitored during the and nearby (Falkenberg et al. 1994). Similarly, DDE and other course of this study, five are surrounded by deep water and con- organochlorines were found in Ospreys from northern New sidered inaccessible to Possums and other terrestrial predators South Wales during the 1980s (Clancy 2005). These compounds (and people). When productivity data from nesting attempts are are known to take decades to break down and even at very low classed as accessible (n = 72) or inaccessible (n = 31), failure concentrations (of only a few parts per million wet weight) can rate of accessible nests is 46% compared with 26% at inacces- reduce egg viability (Poole 1989). There has been no recent 306 Emu T. E. Dennis investigation to determine if these, or similar contaminants, are breeding sites has been an accepted practice for decades, with still prevalent in coastal or marine environments in South restrictions on physical modification of the landscape and limits Australia. to increased human activity within a prescribed radius of a nest (Poole 1989; Richardson and Miller 1997). Pair-fidelity and attachment to nest-sites Some research and management directions that could be of Pairs in three territories maintained pair-bonds for many years benefit to Osprey conservation in South Australia include: (average duration of pair-bond 8.3 years, range seven to ten (1) development of a species management plan; (2) greater years), continued to use the same primary nesting site within awareness of the need to protect habitat and reduce disturbance their territories, and remained together in their territory of nesting sites in planning and coastal land management agen- throughout the year. Strong pair- and site-fidelity has also been cies; (3) monitoring the population for stability and productiv- observed in migratory Ospreys in Scotland and North America ity; (4) to trial predator-proof artificial nesting platforms in key (Dennis 1983; Poole 1989). habitats and to monitor subsequent productivity outcomes; and In northern New South Wales, adult Ospreys were found to (5) to investigate the level of organochlorine residues and other stay in the territory and attend nesting sites to some extent in all contaminants likely to affect breeding and the population. months of the year (Bischoff 2001; Clancy 2006). Similar Recognition of the need for protection of habitat and nesting behaviour was observed in this study, with adult pairs continu- sites of sensitive coastal species, such as the Osprey, is particu- ing to use the nesting platform throughout the year as a vantage larly pertinent on Kangaroo Island where the population appears point while hunting, to eat prey, or to roost. to be precariously balanced ecologically at the extreme south- eastern edge of its breeding range in Australia. Post-fledging dispersal and philopatric recruitment Among the 85 young Ospreys banded on Kangaroo Island since Acknowledgements 1973, only three are known to have dispersed to the mainland: This project was conducted under an annual Scientific Permit from the one aged 6 months was found dead on a cliff near Maslins Beach South Australian Department for Environment and Heritage (E13678-05 (~20 km south of Adelaide) in 1987, ~100 km NE from the natal and Y13688-05), and a Banding Licence and Colour Banding Authority site; another aged 3 months was found alive near Peebinga (~290 (A1154) from the Australian Bird and Bat Banding Scheme (Department of km inland in the Murray Mallee region) in 1989, ~400 km ENE the Environment and Heritage, Canberra). from the natal site; and one aged 12 years was found dead near I thank the many people who have contributed to this project over the Edithburgh on Yorke Peninsula in 1991, ~80 km N from its natal years, particularly: D. Drynan for access to ABBBS data; and C. Baxter, site (ABBBS data). All other movements recorded during this C. Bald, D. Ball, L. Bebbington, M. Schulz, N. Birks, A. Walker, M. Berris, L. Pedler, M. Munday, S. Goldsworthy, R. Ashendon, B. MacIntosh and study were of adults banded as nestlings and of colour-banded A. Bayliss. young aged <6 months, and all <70 km from their natal site. I also particularly thank: Jerry Olsen and the late Allen Lashmar whose Elsewhere in Australia greater dispersal distances have been collective advice and encouragement initiated the project in 1984; the South recorded. In Western Australia, two banded Osprey young aged Australian Department for Environment and Heritage for logistical support; <6 months dispersed ~400 km to the south-east from their natal The International Osprey Foundation, Sanibel, FL, USA; Nicholas Birks for territory on Rottnest Island (Holsworth 1965); and in north- use of his Osprey portrait; Kangaroo Island Sealink Pty Ltd; Roy Dennis eastern New South Wales banded subadult Ospreys have been (Scotland) and Peter Shaughnessy for encouragement and constructive com- recorded 504 km (Clancy 2006) and 714 km (G. Clancy pers. ments on early drafts, and the anonymous reviewers who considerably comm.) from their natal territories. improved the final manuscript; and to Helen Dennis for editing skills and Philopatry is common among male birds of many species tireless support. (Greenwood 1980) and among migratory Ospreys where most surviving subadult males return to near their natal area to estab- References lish breeding territories at maturity (Dennis 1983; Poole 1989). Bischoff, T. (2001). Aspects of breeding of the Osprey Pandion haliaetus on Poole (1989) concluded that ‘familiarity with a locale would the Mid-north Coast of New South Wales. Australian Bird Watcher 19, help males find nest sites and foraging resources’, whereas 88–93. Bretagnolle, V., Thibault, J. C., and Dominici, J. M. (1994). Field identifi- ‘females might be expected to disperse further because their cation of individual ospreys using head marking pattern. Journal of main imperative is to locate a free male with a nest and wander- Wildlife Management 58, 175–178. doi:10.2307/3809565 ing would enhance that search’. These fundamental strategies Brown, K., Innes, J., and Shorten, R. (1993). Evidence that possums prey on may be underlying the philopatric recruitment level evident in and scavenge bird’s eggs, birds and mammals. Notornis 40, 169–177. this study, where 14 (22%) of the 63 surviving young (including Clancy, G. P. (1989). A survey of breeding Osprey Pandion haliaetus in two unidentified males in 2004) banded since 1985 entered the northeastern New South Wales 1980 to 1982. Corella 13(1), 9–14. breeding population. Alternatively, this level of ‘internal’ Clancy, G. P. (2005). Feeding behaviour of the Osprey Pandion haliaetus on recruitment may also reflect the isolation of the population in the north coast of New South Wales. Corella 29(4), 91–96. South Australia, which is >1000 km from other Osprey popu- Clancy, G. P. (2006). The breeding biology of the Osprey Pandion haliaetus lations in Australia (Dennis 2007). on the north coast of New South Wales. Corella 30(1), 1–8. Cupper, J., and Cupper, L. (1981). ‘Hawks in Focus.’ (Jaclin Enterprises: Management and conservation issues Mildura, Vic.) Dennis, R. H. (1983). Population Studies and Conservation of Ospreys in Conservation issues facing the Osprey appear to revolve around Scotland. In ‘Biology and Management of Bald Eagles and Ospreys’. the need for greater protection of nesting sites. In many parts of (Ed. D. M. Bird.) pp. 207–214. (Harpell Press: Ste Anne de Bellevue, North America and Europe protection of threatened Osprey Quebec.) Osprey productivity on Kangaroo Island Emu 307

Dennis, T. E. (1987). Behaviour of southern Osprey. Australasian Raptor Olsen, P. (1998). Birds Australia Conservation Statement No. 2. Australia’s Association News 8, 44. raptors: diurnal birds of prey and owls. Wingspan 8(Supplement), i–xvi. Dennis, T. E. (2004). Conservation status of the White-bellied Sea-Eagle, Olsen, P. D. (1995). ‘Australian Birds of Prey.’ (University of New South Osprey and Peregrine Falcon on western Eyre Peninsula and adjacent Wales Press: Sydney.) offshore islands in South Australia. South Australian Ornithologist 34, Palma, L., Ferreira, J., Cangarato, R., and Vaz Pinto, P. (2004). Current 222–228. status of the Osprey in the Cape Verde Archipelago. Journal of Raptor Dennis, T. E. (2007). Distribution and status of the Osprey (Pandion Research 38(2), 141–147. haliaetus) in South Australia. Emu 107, 294–299. doi:10.1071/ Poole, A. F. (1989). ‘Ospreys – A Natural and Unnatural History.’ MU07009 (Cambridge University Press: Musselburgh, UK) Dennis, T. E., and Baxter, C. I. (2006). The status of the White-bellied Sea- Postupalsky, S. (1974). Raptor reproductive success: some problems with Eagle and Osprey on Kangaroo Island in 2005. South Australian methods, criteria and terminology. In ‘Management of raptors. Ornithologist 35(1–2), 47–51. Proceedings of Conference on Raptor Conservation Techniques’. Raptor Falkenberg, I. D., Dennis, T. E., and Williams, B. D. (1994). Organochlorine Research Report No. 2. Fort Collins, CO. (Eds F. N. Hamerstrom, pesticide contamination in three species of raptor and their prey in South B. E. Harrell, and R. R. Olendorff.) pp. 21–31. (Raptor Research Australia. Wildlife Research 21, 163–173. doi:10.1071/WR9940163 Foundation: Vermillion, SD, USA.) Garnett, S. T., Pedler, L. P., and Crowley, G. M. (1999). The nesting biology Prevost, Y. A. (1983). Osprey distribution and sub-species taxonomy. In of the Glossy Black-Cockatoo Calyptorynchus lathami on Kangaroo ‘Biology and Management of Bald Eagles and Ospreys’. (Ed. Island. Emu 99, 262–279. doi:10.1071/MU99032 D. M. Bird.) pp. 157–174. (Harpell Press: SteAnne de Bellevue, Quebec.) Greenwood, P. J. (1980). Mating systems, philopatry and dispersal in birds Richardson, C. T., and Miller, C. K. (1997). Recommendation for protecting and mammals. Animal Behaviour 28, 1140–1162. doi:10.1016/S0003- raptors from human disturbance: a review. Wildlife Society Bulletin 25, 3472(80)80103-5 634–638. Holsworth, W. N. (1965). Nesting success of the Osprey on Rottnest Island, Robinson, A. C., Kasperson, K. D., and Hutchinson, M. N. (Eds) (2000). Western Australia. Western Australian Naturalist 10, 13–15. ‘A List of the Vertebrates of South Australia.’ (Department for Environ- Inns, R. W. (2002). Terrestrial mammals. In ‘Natural History of Kangaroo ment and Heritage: Adelaide.) Island’. 2nd edn. (Eds M. Davies, C. R. Twidale and M. J. Tyler.) Siverio, M., and Rodriguez, B. (2005). Population status, reproduction and pp. 74–79. (Royal Society of South Australia: Adelaide.) conservation of Osprey Pandion haliaetus in La Gomera and El Hierro, Judge, D. S. (1983). Productivity of Ospreys in the Gulf of California. Canary Islands (2003–2004). Airo 15, 85–90. Wilson Bulletin 9, 243–255. Surman, C. A. (1994). Some observations on the timing of breeding of Levenson, H., and Koplin, J. R. (1984). Effects of human activity on pro- seabirds on Pelsart Island, Western Australia. Corella 18, 41–43. ductivity of nesting Osprey. Journal of Wildlife Management 48, Van Daele, L. J., and Van Daele, H. A. (1982). Factors affecting the produc- 1374–1377. doi:10.2307/3801800 tivity of Ospreys nesting in west-central Idaho. Condor 84, 292–299. Marchant, S., and Higgins, P. J. (Eds) (1993). ‘Handbook of Australian, New doi:10.2307/1367371 Zealand and Antarctic Birds. Vol. 2: Raptors to Lapwings.’ (Oxford University Press: Melbourne.) Nance, C., and Speight, D. L. (Eds) (1986). ‘A Land Transformed – Environmental Change in South Australia.’ (Longman Cheshire: Melbourne.) Newton, I. (1979). ‘Population Ecology of Raptors.’ (T. and A. D. Poyser: Berkhamsted, UK.) Manuscript received 25 January 2007, accepted 3 October 2007

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