Effects of displacement from marine renewable developments on seabirds breeding at the Isle of May

1. Introduction

1.1. Background

Offshore renewable developments may have an effect on the daily energy and time budgets of seabirds by displacing birds from favoured foraging habitats, potentially forcing them to forage at greater densities in sub-optimal habitats (Larsen & Guillemette 2007). The current worst case scenario is that displacement causes 100% mortality, so there is a need to model more realistic consequences of displacement.

The impact of displacement is predicted to be particularly important for breeding seabirds that, as central place foragers, are constrained to obtain food within a certain distance from the breeding colony (Daunt et al. 2002; Enstipp et al 2006). Changes in time and energy budgets resulting from displacement from a renewable development have the potential to impact on the body condition, and hence survival prospects, of breeding adults and also reduce breeding success because of changes in provisioning rates. Both these outcomes could have population consequences and thus need to be quantified, particularly where renewable developments are proposed within the foraging range of breeding individuals from SPAs.

1.2. Aims & Objectives

The aim of this project is to develop a displacement model for adult common guillemots Uria aalge rearing chicks on the Isle of May (part of Forth Islands SPA) in relation to the proposed offshore wind farm at Neart na Gaoithe. This site is one of a suite proposed in the Forth/Tay region that currently also include Inch Cape and Firth of Forth Zone 2. The model compares the time/energy budgets of breeding guillemots in the absence of a wind farm, utilising available data on distribution and activity budgets, with time/energy budgets in the presence of the wind farm, based on plausible behavioural responses to the development.

Our novel approach represents a significant advancement in our understanding of the potential effects of displacement based on a step change in the degree of realism captured by the model in terms of incorporating both:

• how guillemots use their foraging landscape, both in the absence and presence of a wind farm, and
• how their fish prey are distributed within it.

Thus, our model compares the effects of displacement when prey is dispersed or patchy, and under elevated levels of interference competition among guillemots feeding in the same patch (individuals may interfere with one another at higher densities, resulting in lower prey capture rates, Hassell & Varley 1969).

In addition to presenting outputs from the model, this report discusses how the model can be adapted to other species or locations and expanded in complexity to parameterise population models that estimate the population consequences of displacement.