Longterm study of the timing of breeding, breeding participation and reproductive success of four seabird species in the Houtman Abrolhos, Western Australia

Brief description

A comparative study of the timing of breeding, breeding participation and reproductive success over a 20-year period of four tropical pelagic seabird species in relation to the regional oceanographic conditions affecting the Leeuwin Current was conducted. Three tern species, the Lesser Noddy Anous tenuirostris, Brown Noddy A. stolidus and Sooty Tern Onychoprion fuscata (formerly Sterna fuscata), and the Wedge-tailed Shearwater Ardenna pacifica (formerly Puffinus pacificus) comprised our study species at the Houtman Abrolhos, eastern Indian Ocean, between 1991 and the current day. The diet of these species was also investigated between 1991 and 2000.

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Maintenance and Update Frequency: asNeeded

Statement: The study was conducted on Pelsaert Island (28°56′S, 113°58′30ʺE), the southernmost and third largest of an archipelago of 192 islands, islets and rocks (the Houtman Abrolhos), 60 km off the mid-western coast of Australia. Pelsaert Island (120 ha) is 12 km long, only 50–500 m wide and very low (<3 m Above High Water Springs), comprising coral rubble, limestone and sand. Nest sites of each species were selected at random and permanently marked. Nest contents were recorded weekly over the spring/summer period (September to May) between 1991 and 2001, and in more recent years (2002–2010) during several shorter visits between October and January of each year. There are some data gaps in these latter years, which were excluded from analyses. The burrow contents of the Wedge-tailed Shearwater were determined using an electronic burrowscope. Breeding participation was recorded as the percentage of all nest sites or burrows that contained an active breeding attempt during the breeding season. Laying chronology was determined using lay dates of known-age eggs; the laying dates of other eggs was estimated by backdating, using egg water-loss techniques (Wooller & Dunlop 1980, Surman & Wooller 1995). Eggs known to be re-laid were excluded from calculations of the mean date of laying for each species. Chick age was estimated from growth curves described in Surman (1997). As a measure of reproductive performance, we used breeding success or the proportion of all active breeding attempts that survived to produce a fledgling. We arbitrarily assigned those seasons when breeding success was less than 15% overall for each study species as “bad,” and those above 15% as “good.” In more recent years, we have noticed that the commencement of breeding was later for the three terns studied. Dietary samples Adult birds recently returned from a foraging trip were captured at the nest-site by hand or using a small net, whereupon most would spontaneously regurgitate. They were marked individually with leg bands to ensure that no individual was sampled more than once during any single breeding season. A minimum of 10–20 regurgitations were collected from each tern species in each sampling month, corresponding to the incubation, small nestling and large nestling stages in their breeding cycle. Regurgitations were collected from shearwaters during the nestling stages of their breeding cycle only, because earlier in the season, they were less likely to spontaneously regurgitate. Sampling was not undertaken in the period 2002–2007. Regurgitates were preserved in 70% ethanol, then rinsed and vacuum filtered to allow the percentage volumes of identifiable material to be estimated before obtaining the wet mass of each sample. We used a volumetric estimate that determined the surface area of a 14-cm diameter Petri dish covered by each prey type. Prey items were identified using keys (Last et al. 1983, Leis & Rennis 1983, Smith & Heemstra 1986, Leis & Trnski 1989, Gommon et al. 1994) and from reference specimens in the Western Australian Museum. The detailed methodology is described in Surman and Wooller (2003).

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WA Department of the Environment and Conservation

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Murdoch University Scholarship

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Fisheries Research and Development Corporation (FRDC)

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Natural Heritage Trust

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Northern Agricultural Catchments Council

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Santora, Jarrod A.