Extinction and Its Prevention in ‘Island’ Species

Martin, Robert William (2018) Extinction and Its Prevention in ‘Island’ Species. Masters by Research thesis (MPhil), Manchester Metropolitan University In collaboration with BirdLife International, Cambridge.

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Abstract

The bird communities of the islands of Sangihe and Talaud in Indonesia provide an opportunity to examine two extinction paradigms; declining populations and small or restricted populations. On Talaud, species abundance responses to habitat modification informs relative extinction risk and future community impacts of habitat loss within an intact community with large populations. On Sangihe, identification and quantification of remnant suitable habitat for species with critically low population sizes allows the examination of options to extend their area of occupancy through targeted restoration. I constructed Distance-based density estimates for the bird community on Karakelang, Talaud Islands at eight locations along a habitat modification gradient and found species which increased, were stable, or declined in abundance along this gradient, and within those that declined individual responses occurred in both the rate of decline and the shape of the response. Forest-dependent and endemic species were far more abundant in primary forest, and as these species were large, total bird biomass declined dramatically with greater habitat modification. Several key bird species, including the Endangered Red-and-blue Lory, declined most severely where forest no longer contained primary elements. However, almost all were recorded at each step along the gradient. Currently, most species retain relatively large populations, but primary forest loss will cause substantial population reductions. For three Critically Endangered birds on Sangihe, I created habitat suitability models based on presence-absence data to identify those areas away from the current occupied range of the species with potential to support the species with minimal restoration effort. Three small areas are potential restoration sites for Cerulean Paradiseflycatcher away from the current occupied range and one area adjacent to these may be suitable for Sangihe Golden Bulbul, but more ‘nearly-suitable’ habitat exists for these species and Sangihe Whistler within the Sahendaruman crater. Restoration efforts should; focus on those areas that are most similar to currently occupied sites, enhance the abundance of lianas for Cerulean Paradise-flycatcher sites in valley habitat, and fill gaps within the ridgetop forest with native trees. Without restoration, the slow retreat of each species will continue, with Cerulean Paradise-flycatcher at greatest risk of global extinction.