Energetic synchrony throughout the non‐breeding season in common guillemots from four colonies

Abstract

The non‐breeding season presents significant energetic challenges to birds that breed in temperate or polar regions, with clear implications for population dynamics. In seabirds, the environmental conditions at non‐breeding sites drive food availability and the energetic cost of regulatory processes, resulting in variation in diet, behaviour and energetics; however, very few studies have attempted to understand if and how these aspects vary between populations. We investigated whether non‐breeding location influenced diet, behaviour and energetics in the common guillemot Uria aalge. We studied guillemots from four UK breeding colonies, two located on the west coast of Scotland and two on the east. We quantified non‐breeding distribution, foraging behaviour and activity budgets of 39 individuals from July to March, using geolocation–immersion loggers and time‐depth recorders, and used feather stable isotope signatures to infer diet during the post‐breeding moult. We calculated energy expenditure and investigated whether the peak (an indicator of the potential vulnerability to marine threats) varied between colonies. Individuals were spatially segregated according to the coastline they breed on, with west coast guillemots distributed off the west coast of the UK and east coast guillemots distributed off the east coast. Diet and behaviour were more similar in guillemots that shared a breeding coastline than those that did not, as west coast guillemots foraged at a lower trophic level, spent less time diving and engaged in more pelagic foraging than east coast guillemots. However, energy expenditure was remarkably similar between colonies, peaking during late February/early March, indicating that, during our study period, there was high synchrony between colonies in the timing of potential vulnerability to marine threats. Therefore, any anthropogenic changes that result in decreased food availability or increased energy expenditure during late winter may have greater impacts on energy balance, with consequences for population dynamics.

Temporal and spatial variability in availability bias has consequences for marine bird abundance estimates during the non-breeding season

“…In this study, the proportion of daylight hours that all four species spent submerged below the water’s surface varied across the non-breeding season, generally demonstrating an increase over this time (Fig 2-4). This temporal variation is likely to be representative of fluctuations in climatic conditions, and the birds’ subsequent energy requirements and activity budgets (Buckingham et al, 2023; Clairbaux et al, 2021; Fort et al, 2009). Differences in dive behaviour can also be compounded by variation in daylight availability impacting the ability of these visual foragers to gain the energy needed to meet their energetic demands, therefore driving changes in their time activity budgets (Duckworth et al, 2021; Dunn et al, 2020).…”

“…Schematic map illustrating the locations of the breeding sites (shown as blue points and labelled with blue text) where time-depth-recorder loggers were deployed on and retrieved from Atlantic puffins, common guillemots, razorbills, and red-throated divers. Wintering areas are shaded in grey and labelled with black text and are adapted from (Buckingham et al, 2023; Duckworth et al, 2022; Harris et al, 2010). …”

“…Dive incidences were classified as occasions where time-depth-recorder depth values exceeded 1 m. To categorise dive incidences as occurring during either daylight, twilight, or nighttime, we extracted time- and population-specific area estimates. To do this, we obtained centroids of each population’s monthly non-breeding distribution from previous work using light-based geolocator devices (Buckingham et al, 2022, 2023; Duckworth et al, 2022; Harris et al, 2010) (Supporting Information S1). We used the ‘ oce ’ R package to extract sun elevation angles at these areas and categorised each dive incidence as occurring during daylight (sun was >0 degrees above the horizon), twilight (sun was 0–15 degrees below the horizon), or nighttime (sun was >15 degrees below the horizon) accordingly.…”

“…Birds were recaptured during subsequent breeding seasons and the devices were removed. For more details on the puffin and razorbill deployments see Dunn et al (2019), for guillemot deployments see Buckingham et al (2023), and for red-throated diver deployments see Duckworth et al (2021). Sampling periods varied (Table 1) due to some TDRs failing during the autumn and winter.…”

A framework to unlock marine bird energetics

“…Similarly, estimations of the field metabolic rate (FMR; the sum of energy that a wild animal metabolises over a specified period of time) of breeding seabird species are now increasingly common, thereby allowing inferences into the energetic expenditure and requirements of this group of predators ( Dunn et al, 2018 ). To extrapolate beyond the confines of the breeding seasons of marine birds, year-round biologging devices have been used to determine behavioural time–activity budgets and increasingly also year-round energy budgets, in recognition of the major role of behaviour-specific energetic costs in driving energy budgets ( Brown et al, 2023 ; Buckingham et al, 2023 ; Burke et al, 2015 ; Dunn et al, 2020 ; Elliott and Gaston, 2014 ). Currently, however, these inferences remain difficult for species where accelerometery, doubly labelled water and heart rate data from the breeding season are not available to aid the interpretation of year-round data.…”