Foraging ecology of great black-backed gulls and their impact on Atlantic puffin populations

Populations of many species of seabirds have declined significantly over the past 30 years, with climate change identified as a primary cause. One species undergoing large declines is the Atlantic puffin, a species of high conservation concern that has recently been re-classified as 'vulnerable' by BirdLife International. The reduction in availability of prey (sandeels) has been proposed as a principal cause for declines, however, predation by predatory seabirds such as the great black-backed gull and great skua may also play a role, especially as these species are showing marked increases in many locations. Since both seabird predator and prey are legally protected, this may lead to wildlife conflicts, especially if management measures such as culling are proposed. Furthermore, conflicts will be shaped by the effects of other pressures on both species e.g. great black-backed gulls and puffins are potentially at risk from the development of offshore renewable energy installations such as wind farms and from the ingestion of [micro]plastics. It is therefore vital that detailed information is available on the interactions between the species involved in order to ascertain the population dynamic consequences of this predator-prey relationship, and to devise effective management strategies to alleviate this wildlife conflict.

The PhD would examine the consequences of the significant increase in the great black-backed gull population on the Isle of May, south-east Scotland, on the Atlantic puffin populations. Atlantic puffins on the Isle of May have declined by more than a third in the last decade, while the great black-backed gulls have more than doubled over the same period. Past work at this colony has demonstrated that the majority of predation is undertaken by a subset of specialist gulls that generally target juvenile puffins [1, 2]. However, the extent to which this predation has population-level effects on puffins, and whether this is predicted to change in the future, has not been tested. Further, it is not clear whether potential effects on puffins are apparent more widely, because of limited knowledge of the population trends of great black-backed gull and the extent of interactions with local puffin populations. Therefore the project would involve focussed research on the Isle of May and analyses at the national scale to address the following key questions: a) What is the degree of foraging specialism among individual gulls? b) What is the age structure of predated puffins? c) What are the population-level consequences of predation by gulls on the puffin population? d) What are the predicted changes in puffin and gull population sizes associated with future changes in predator-prey interactions on the Isle of May and at the UK scale? e) What are the predicted changes in populations of both species caused by multiple drivers including offshore renewable effects and ingestion of marine plastics? Addressing these questions would provide conservation managers with the evidence they need to select the best options for alleviating this wildlife conflict.