The first UK survey and population estimate of breeding Snow Bunting Plectrophenax nivalis

Capsule: The first national survey for Snow Bunting Plectrophenax nivalis in the UK was carried out in 2011 and estimated the breeding population at 60 territories (95% confidence intervals?=?48–83).

Aims: To estimate breeding population size for Snow Buntings in the UK by surveying all sites with a history of breeding season occupation.

Methods: Surveys were carried out in June 2011 to detect males on territory at sites where Snow Bunting had been recorded during the breeding season since 1970. Each site was visited at least once during the survey period; suitable habitat was searched and vantage point watches were conducted in order to detect singing males. Repeated visits to a sample of sites allowed a correction factor to be calculated in order to account for birds undetected during surveys.

Results: In 2011, the number of Snow Bunting breeding in the UK (including adjusting for imperfect detection) is a minimum of 60 territories (95% CI?=?48–83) using confirmed and probable breeding records of males. A less conservative estimate of 99 territories (95% CI?=?88–114) results from including all records of males in suitable habitat. The vast majority of the population was found in the Cairngorm region, with isolated records in the north and west Highlands.

Conclusion: The results of the 2011 survey are consistent with well-informed estimates of the Snow Bunting population made previously. This work provides a baseline and repeatable fieldwork and analytical methods enabling future change in the population to be quantified more rigorously.     

Prioritising islands in the United Kingdom and crown dependencies for the eradication of invasive alien vertebrates and rodent biosecurity

Invasive alien vertebrates (IAVs) pose a significant threat to island biodiversity worldwide, and their removal is an important nature conservation management goal. As methods advance, eradications from larger islands and of multiple species simultaneously are increasingly undertaken. Effective targeting to maximise conservation gain is important given limited resources. We build on existing prioritisation methods and use the islands of the UK and Crown Dependencies (UK) as an example of how vertebrate eradications might be prioritised and invasive-free status maintained through biosecurity. For each of the 9688 UK islands, we assessed ecological importance for native vertebrates and the anticipated impacts of the IAVs present to estimate the benefit of restoration based on the feasibility and sustainability of IAV eradications in relation to island size, human population and risk of unassisted reinvasion by swimming. As reinvasion poses a threat to the long-term benefits of eradication, we incorporated species-specific swimming distances and explored the effects of varying reinvasion probability from risk-averse to higher-risk strategies. The 25 islands that would benefit most from eradications were in Scotland, Northern Ireland and the Channel Islands. Our prioritisation method should be seen as an initial guide to identify islands that might benefit from intervention when faced with a large list of potential sites. Feasibility studies taking account of factors such as interspecific interactions, anthropogenic reinvasion, views of residents or ‘social feasibility’ and cost need to be undertaken before planning any eradication. We prioritised biosecurity for rat-free islands to highlight where comprehensive measures might be most beneficial.     

Understanding species distribution in dynamic populations: a new approach using spatio‐temporal point process models

Understanding and predicting a species’ distribution across a landscape is of central importance in ecology, biogeography and conservation biology. However, it presents daunting challenges when populations are highly dynamic (i.e. increasing or decreasing their ranges), particularly for small populations where information about ecology and life history traits is lacking. Currently, many modelling approaches fail to distinguish whether a site is unoccupied because the available habitat is unsuitable or because a species expanding its range has not arrived at the site yet. As a result, habitat that is indeed suitable may appear unsuitable. To overcome some of these limitations, we use a statistical modelling approach based on spatio‐temporal log‐Gaussian Cox processes. These model the spatial distribution of the species across available habitat and how this distribution changes over time, relative to covariates. In addition, the model explicitly accounts for spatio‐temporal dynamics that are unaccounted for by covariates through a spatio‐temporal stochastic process. We illustrate the approach by predicting the distribution of a recently established population of Eurasian cranes Grus grus in England, UK, and estimate the effect of a reintroduction in the range expansion of the population. Our models show that wetland extent and perimeter‐to‐area ratio have a positive and negative effect, respectively, in crane colonisation probability. Moreover, we find that cranes are more likely to colonise areas near already occupied wetlands and that the colonisation process is progressing at a low rate. Finally, the reintroduction of cranes in SW England can be considered a human‐assisted long‐distance dispersal event that has increased the dispersal potential of the species along a longitudinal axis in S England. Spatio‐temporal log‐Gaussian Cox process models offer an excellent opportunity for the study of species where information on life history traits is lacking, since these are represented through the spatio‐temporal dynamics reflected in the model.