Scottish Marine and Freshwater Science Volume 6 Number 10: At-Sea Turnover of Breeding Seabirds - Final Report to Marine Scotland Science

2. Literature Review

2.1. Methodology

We conducted a review of the published literature relevant to estimating turnover in species included in the project but for which modelling was not carried out (red-throated diver, black guillemot, European shag, common eider, northern gannet and northern fulmar). We focused on studies (both UK and beyond) that provide estimates of parameters considered relevant to estimating turnover during the breeding season, such as time activity budgets, foraging trip characteristics and foraging site fidelity. The literature search was carried out in the Web of Science (all databases, 1950-2015) using the following search terms in combination with the species name: 'foraging range', 'foraging trip', 'foraging trip duration', 'site fidelity', 'foraging site fidelity' and 'foraging area fidelity', 'foraging and consistency', 'nest attendance', 'time activity budget' and 'activity budget'. Due to the limited time available and majority of the literature being focussed on the chick rearing period, the search was restricted to this stage of the breeding season.

Mean and standard deviation ( SD) were extracted for each parameter (where available), with the exception of foraging site fidelity where either various metrics or only qualitative information are reported in the literature. This parameter was, therefore, presented as a categorical variable, with two levels ('high'/'low') that directly reflect the interpretation of the authors of the original papers as to what constitutes a high or low measure of fidelity; details of the different fidelity metrics, however, are available within the cited references. In most cases parameter values were provided directly by the cited studies; in a few cases other relevant information was available which allowed us to derive the values of our parameters of interest. Derived values are presented in square brackets. Where data were available for more than one colony, estimates for each colony are presented separately; the only exceptions are two review studies (Langston 2010 and Thaxter et al. 2012) where estimates are averaged across multiple colonies and years. Where data were available for the same colony in multiple years, averaged values are presented; annual estimates, however, can be found within the cited references. Sample size of birds in each study is provided as an indication of reliability of the data; note also that estimates from recent studies are likely to be more accurate compared to those from older studies, as a result of the use of advanced bio-logging technologies in particular.

2.2. Results

Estimates of foraging trip characteristics (range, duration and frequency) were available for most species, and in many cases data for these parameters were available from multiple colonies (Table 1.2). In contrast, there was lack of information or only qualitative information available on foraging site fidelity for most species (Table 1.2). Data on daily activity budgets were of variable quality and often incomplete (Table 1.2). To fill these knowledge gaps, targeted field data collection involving the deployment of bio-logging devices and/or analysis of existing tracking datasets should be considered.

The most data-rich species was the Northern gannet, followed by the European shag. For these species parameter estimates from multiple colonies and years were typically available (Table 1.2). For the northern fulmar a reasonable amount of information was available regarding foraging trip characteristics but we found very little information on foraging site fidelity and daily activity budgets. Note also that in this species foraging behaviour of the adults changes substantially between the early (when chicks are brooded) and later (when chicks are not brooded) stages of offspring rearing which is why foraging trip characteristics are provided separately for these stages (Table 1.2). For the red-throated diver and black guillemot no recent data and very little older data were available for any of the parameters of interest (Table 1.2). Clearly, if turnover of individuals at sea is to be investigated in these species, new data collection would need to be prioritised as a first step. Due to the biology of the common eider, where females take their chicks to water soon after they hatch and do not return to the nest thereafter, the concept of a 'foraging trip' by a central-place foraging individual during chick rearing is not applicable. Linked to this, the cited estimates of foraging range indicate the general area used by the females and young once they have moved away from the nest site. Furthermore, male eiders take no part in offspring care and in the summer use different, generally more distant areas compared to females, where they initiate moult (Diéval et al. 2011). Therefore, to estimate turnover in this species, the approach to data collection would need to be sex-specific and may require (at least in females) relatively long-term deployments of the latest tracking technology (such as GPS- GSM tags, accelerometers) to obtain information of the birds' use of areas at sea at appropriate temporal and spatial scales.

Table 1.2

Parameters relevant to estimating turnover of individuals at sea during the breeding season (data from chick rearing period only; ' NA' = not available; '-' = not applicable; values in square brackets are derived based on information within the cited references - see Methods for details).

* from 5 days after hatching no brooding occurs (Gaston 1985)