Life history, ecology, and population dynamics of the Australian Fairy Tern and implications for their conservation

Claire Greenwell

Developing effective wildlife conservation strategies requires an understanding of animal behaviour, their life history strategy, population demographics, resource use, and the processes threatening survival. Despite being classified as Vulnerable to extinction and in urgent need of conservation action, there have been no major studies on the Australian Fairy Tern (hereafter Fairy Tern) Sternula nereis nereis. This thesis investigated various aspects of Fairy Tern behaviour, life history, population movements, and ecology with a view to help inform future conservation actions. First, I used a mark-recapture study and coordinated community-based resighting’s of marked birds to understand the seasonal movements, meta-population structure and site use of Fairy Terns across their breeding range in Western Australia (Chapter 2). Two distinct populations were identified: a widely distributed, partially migratory spring/summer-breeding population; and a smaller, sedentary, winter-breeding population in the Pilbara. Based on the likely spatial extent of exchange among breeding adults and natal recruits, seven management units were proposed. Second, a bird banding study, supported by extensive field observations, photographic recapture of marked birds and sunrise to sunset video observation was used to understand mating systems, colony formation processes, egg-laying and incubation periods, time to fledging and post-hatching care (Chapter 3). The median distance from the nearest neighbour, at a colony in North Fremantle, was 0.71 m, which increased with time. Birds laying earlier in the season selected nest sites with higher beach shell cover compared to those that laid later. The mean incubation period (n = 86) was 21 days, with both pairs contributing, almost equally, to incubation. On average, chicks fledged 22 days after hatching (n = 10), leaving the colony with their parents within 8 days of fledging. Third, I used a novel bird banding method and photographic recapture to describe plumage development and age-related behaviour of juvenile Fairy Terns up to 100 days of age (Chapter 4). This information may be used for the development of a field ageing guide, enabling the collection of standardised information on colony demographics and juvenile development. Fourth, I investigated prey composition among colonies, between years, times of day and feeding stages, i.e. courtship vs chick feeding, using non-invasive digital photography (Chapter 5). Significant differences were identified for each factor, likely driven by differences in environmental conditions and fish species assemblages at each site, diurnal patterns in prey behaviour, Fairy Tern behaviour, and differing prey handling capabilities and nutritional requirements between adult females and chicks. Overall, the diet of Fairy Terns was dominated by three main taxa: Blue Sprat Spratelloides robustus; hardyheads (Atherinidae); and garfishes Hyporhamphus spp., which contributed ≥ 75% of all prey at each site. This feeding study demonstrated that colony site selection is likely associated with habitats that support a large biomass of small, pelagic schooling fishes. However, the strong reliance on Blue Sprat, a short lived (< 1 year) schooling clupeid, highlights a potential vulnerability of Fairy Terns to changes in prey biomass during the breeding season. Finally, I assessed whether simulated conspecific cues, i.e. call playbacks and decoys, increased the likelihood of attracting Fairy Terns to potentially suitable nesting habitats. To understand the influence of playbacks compared to decoys, I measured the behavioural response of terns to the different cues using a full cross-over design (Chapter 6). While settling decisions varied between sites, call playbacks were the primary cues needed to attract terns but may be required over several seasons before colonies are established.

Life history, ecology, and population dynamics of the Australian Fairy Tern and implications for their conservation

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