Doctor Annabel Dorrestein


Graduate PhD 2023

Thesis Title

The social organisation of the Christmas Island flying-fox

Research Project

Social organisation within and between groups is driven by the conflicts that arise when individuals face different trade-offs concerning reproduction and survival (e.g. Clutton-Brock, 1989; Emlen & Oring, 1977). It is a topic of fundamental behavioural ecological interest because it explains what structures animal societies. Bats are of particular interest for studies of social organisation because they are highly social animals that form some of the largest known mammalian aggregations, and they exhibit a greater diversity in social organisation than any other mammalian order. However, little is known about social organisation of flying-foxes, mainly because their extreme mobility complicates studying individuals in the wild.

The Christmas Island flying-fox (CIFF; Pteropus natalis) is a medium-sized fruit bat confined to Christmas Island. The CIFF has been listed as Critically Endangered under the Commonwealth Environment Protection and Biodiversity Conservation (EPBC) Act 1999 (Threatened Species Scientific Committee, 2014), as it has been experiencing alarming population declines, with Christmas Island National Parks estimating the population at roughly 2000 flying-foxes, down from about 6,000 in the 1980s (Tidemann, 1985b). The CIFF is an important seed disperser and pollinator, and therefore considered a keystone species (Parks Australia, 2014). Its precipitous decline therefore poses an enormous threat to Christmas Island’s unique ecosystem (Beeton et al., 2010; Cox, Elmqvist, Pierson, & Rainey, 1991). Furthermore, with the recent extinction of the Christmas Island pipistrelle, the species is now the only indigenous mammal remaining on the island.

Recently, a lack of understanding of the social organisation was identified as a key knowledge gap preventing sound conservation management of the CIFF. Social organisation is important for the CIFFs conservation because of its effects on the size of the effective breeding population (Ne), patterns of seed/pollen disperser behaviours, and disease dynamics, issues that are particularly relevant in small populations of keystone species on islands. Therefore, by increasing our understanding of the social organisation of the CIFF, the research will contribute to the conservation of this Critically Endangered species.

The aims of this study are two-fold:

  1. To increase our fundamental understanding of social organisation in terms of underlying social and ecological pressures and individual selective benefits
  2. To provide management-relevant information to help secure the long-term persistence of the CIFF

Website: (opens in a new window)

Current  Projects / Grants

Nocturnal monitoring of the Christmas Island flying-fox
Co-Researcher: Justin Welbergen
Partner/funding body: Christmas Island National Park
Period: 2022


Lloyd-Jones LR, Bravington MV, Armstrong KN, Lawrence E, Feutry P, Todd CM, Dorrestein A, Welbergen JA, Martin JM, Rose K, Hall J, Phalen DN, Peters I, Baylis SM, Macgregor NA, Westcott DA, (2023) 'Close-kin mark-recapture informs critically endangered terrestrial mammal status', Scientific Reports, vol.13, no.1, Article no.12512

Pulscher LA, Peel AJ, Rose K, Welbergen JA, Baker ML, Boyd V, Low-Choy S, Edson D, Todd C, Dorrestein A, Hall J, Todd S, Broder CC, Yan LY, Xu K, Peck GR, Phalen DN, (2022) 'Serological evidence of a pararubulavirus and a betacoronavirus in the geographically isolated Christmas Island flying-fox (Pteropus natalis)', Transboundary and Emerging Diseases, vol.69, no.5, pp E2366-E2377

Dorrestein A, Todd CM, Westcott DA, Martin JM, Welbergen JA, (2019) 'Impacts of an invasive ant species on roosting behavior of an island endemic flying-fox', Biotropica, vol.51, no.1, pp 75-83

Walker MJ, Dorrestein A, Camacho JJ, Meckler LA, Silas KA, Hiller T, Haelewaters D, (2018) 'A tripartite survey of hyperparasitic fungi associated with ectoparasitic flies on bats (Mammalia: Chiroptera) in a neotropical cloud forest in Panama', Parasite, vol.25, p 19


Dr Justin Welbergen, Dr John Martin (Royal Bot Gardens & Domain Trust, Sydney), A/Professor David Phelan (USyd), Dr Karrie Rose (Taranga Zoo), Dr David Westcott (CSIRO)