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Scottish Marine and Freshwater Science Reports

Formal report series, containing results of research and monitoring carried out by Marine Scotland Science


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Improving estimates of seabird body mass survival relationships

Scottish Marine and Freshwater Science Vol 11 No 13
The Scottish Government has set a target of 100% of Scottish demand for electricity to be met by renewable sources by 2020. Offshore renewables have the potential to make a significant contribution to achieving this target. However, the Scottish Government has a duty to ensure that offshore renewable developments (ORDs) are achieved in a sustainable manner, by protecting habitats and species from adverse impacts.

ORDs may negatively affect seabirds, in particular due to collisions with turbine blades, displacement to less favourable habitats and barrier effects to movement. Displacement and barrier effects are 'sub-lethal effects', whereby individuals birds are not killed instantaneously by an interaction with the wind farm, but their behaviour is affected in the short term, which may have knock on effects on energetic budgets and, in turn, demographic rates such as survival and productivity.

A key potential process linking sub-lethal effects of ORDs and demography is the relationship between adult body condition at the end of the breeding season and survival probability over the following winter. However, our understanding of this relationship is limited.

This project, led by UK Centre for Ecology & Hydrology (UKCEH) and funded by the Scottish Government and Scottish Natural Heritage, used data on mass, body size, timing of breeding and recapture/resighting histories to estimate the relationship between mass at the end of breeding season and over-wintering survival probability for four key species in the Forth and Tay region: kittiwake, puffin, common guillemot and razorbill.

There was evidence for a positive relationship between end-of-breeding season body mass and the survival of puffins with less evidence of an effect in kittiwakes, guillemots and razorbills. This information will help reduce uncertainty in how the impacts of offshore renewables on seabirds are assessed.

This research is part of the Scottish Marine Energy Research Programme (ScotMER).

F Daunt, Z Fang, R Howells, M Harris, S Wanless, K Searle and D Elston. 2020. Improving estimates of seabird body mass survival relationships. Scottish Marine and Freshwater Science Vol 11 No 13, 54pp. DOI: 10.7489/12329-1
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UK Open Government Licence (OGL)
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We formatted and pre-processed five data sets for survival analysis, two obtained using a capture-recapture protocol (puffins and kittiwakes) and three using capture-resightings (guillemots, razorbills and a subset of kittiwakes). Data were collected as part of the UK Centre for Ecology & Hydrology’s (hereafter “UKCEH”) long-term study of seabird populations on the Isle of May National Nature Reserve in the Forth Islands SPA, a Key Site in the Seabird Monitoring Programme.

For each species, we developed linked statistical models for mass and body size, and used these to predict body mass at the end of the breeding season each year, taking account of varying breeding phenologies of species across years by using data on median laying dates. We then developed statistical models for the recapture/resighting histories of each bird, making allowance for variation in recapture/resighting rates to estimate the probabilities of birds in the breeding population surviving from the end of one breeding season to the start of the next. These survival probabilities were modelled as a function of individual-specific body mass at the end of the preceding breeding season, the latter being imputed from the model of mass.

Our models were contingent on a number of assumptions of the type usually adopted in analyses of similar data sets. Estimates of survival probabilities of kittiwakes based on recaptures were markedly lower than those derived from mark/resighting data suggesting that they were unreliable. Accordingly, we used the latter data set that enabled us to obtain more biologically plausible estimates of survival rates.

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Marine Scotland
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