Quantifying the impact of offshore wind farms on gannet populations: a strategic ringing project

Given the conservation importance of Gannet populations in Britain, and concerns about possible adverse impacts of offshore wind farms on Gannets as a result of collision risk, we advocate the establishment of strategic monitoring studies at key colonies. Colour ringing adult Gannets to measure survival at colonies close to and distant from offshore wind farms could indicate whether or not collision mortality has a detectable effect on adult survival. Colour ringing chicks could provide information on prospecting movements of immatures and colonies where birds recruit. Tracking studies of both adults and immatures would be highly desirable to complement improved monitoring of demography

Skipped breeding in common guillemots in a changing climate: restraint or constraint?

Climate change may have demographic consequences for marine top predators if it leads to altered rates of skipped breeding. Here we examine variation in skipping propensity at both the population and individual levels in common guillemots Uria aalge in relation to climate and oceanographic variables and explore the extent to which skipping may be adaptive or an unavoidable consequence of ecological or social constraints. We assumed a detection probability for birds present in the colony of 1.00 and skipping events were defined to include both resightings of non-breeders and failures to resight individuals known to be alive (not present at the colony but resighted in future years). Skipping frequency was higher in years where sea surface temperatures (SST) were higher in winter (both in the current and previous year), when guillemots from our study colony disperse widely across the southern North Sea. Individuals differed consistently in their average skipping propensity and their responses to SST. Males and females were equally likely to skip on average and the frequency of skipping increased in the oldest age classes. Birds that skipped in year t had lower breeding success in year t+1 if they laid an egg, compared to birds that did not skip in year t. Lifetime reproductive output was negatively related to individual skipping frequency. These results imply that skipping is driven more by individual-specific constraints, although we cannot rule out the possibility that birds benefit from skipping when environmental (or internal) signals indicate that breeding in poor years could be detrimental to their residual reproductive value. While future climate change might lead to guillemots skipping more often due to carry-over effects from wintering to breeding periods, the net demographic impacts may be subtle as the absolute frequency of skipping may remain low and individuals will not be equally affected

Reproductive performance of resident and migrant males, females and pairs in a partially migratory bird

We thank everyone from the Centre for Ecology & Hydrology (CEH) who contributed to data collection, and Scottish Natural Heritage for access to the Isle of May National Nature Reserve. We thank the Scottish Ornithologists’ Club (SOC) for their support, and all volunteer observers, particularly Raymond Duncan, Moray Souter and Bob Swann. HG was funded by a Natural Environment Research Council (NERC) CASE studentship supported by CEH and SOC, FD, SW, MPH, MN and SB were funded by NERC and the Joint Nature Conservation Committee, and JMR was part-funded by the Royal Society. Finally, we thank the Associate Editor and two reviewers for constructive comments on the manuscript. The data are available from the Dryad Digital Repository https://doi.org/10.5061/dryad.532j0 (Grist et al., 2017)Peer reviewedPublisher PD

Age-related effects on breeding phenology and success of common guillemots Uria aalge at a North Sea colony

Capsule: Common Guillemots Uria aalge show delayed breeding and marked age-related changes in reproductive success consistent with improved performance with experience. Aims: To determine age of first breeding and age-related effects on breeding phenology and success of Common Guillemots. Methods: Resighting data from a long-term colour-ringing study of Common Guillemot chicks were combined with observations of breeding phenology and success to follow the recruitment process, breeding phenology and success of 62 birds at a major North Sea colony over a 30-year period. Results: The median age of first breeding of Common Guillemots was 6.6 years. There were no detectable costs of first breeding on return rates or the likelihood of breeding the next season but first time breeders bred later and less successfully. Age of first breeding and lifetime breeding success both varied among individuals but there was no clear optimal age of first breeding and early first breeding was not associated with higher lifetime breeding success. Conclusions: Common Guillemots in the Isle of May population delayed breeding for 3–4 years beyond physiological maturity. The marked increase in breeding success with age was consistent with improved performance with experience rather than selection for higher quality individuals. Findings from this study will inform population models by providing improved estimates of age of first breeding and age-related changes in reproductive performance

Assessing the vulnerability of the marine bird community in the western North Sea to climate change and other anthropogenic impacts

Ocean warming and anthropogenic activities such as fishing, shipping and marine renewable developments are affecting marine top predators. Research has focussed on the impacts of single stressors on single species, yet understanding cumulative effects of multiple stressors on communities is vital for effective conservation management. We studied a marine bird community (45 species; 11 families) that used the Forth and Tay region of the North Sea for breeding, overwintering or migration between 1980 and 2011. Local sea surface temperature (SST) increased significantly over this period, with concomitant changes in lower trophic levels. Simultaneously, the region has been subject to fishing pressure and shipping disturbance and is a priority area for renewable energy developments. We used colony-based and at-sea data to quantitatively assess relationships between SST and counts, productivity and survival of 25 species for which sufficient data were available for analysis. For the remaining species, we applied a qualitative approach using published population trends, published climate relationships and foraging sensitivity. In total, 53% of species showed negative relationships with SST. Trends in counts and demography were combined with climate vulnerability to give an index of population concern to future climate warming, and 44% of species were classified as high or very high concern, notably cormorants, grebes, skuas, shearwaters, terns and auks, as well as species breeding in the region. Qualitative assessments of vulnerability to fisheries, pollutants, disturbance (including introduced predators), marine renewables and climate found that 93% of species were vulnerable to ≥2 threats, and 58% to ≥4. Our results indicate that the majority of birds in this region of the North Sea face an uncertain future, potentially threatening the resilience of this important marine bird community

Effects of an extreme weather event on seabird breeding success at a North Sea colony

Quantifying the effects of extreme weather is a critical question in population ecology since climate models predict increased climate variability. Effects will vary among and within species due to exposure or susceptibility, yet few studies have considered these sources of variation simultaneously. We investigated the effects of a summer storm on the breeding success of 4 seabird species at a North Sea colony in relation to aspect, height above sea-level, distance to cliff edge and laying date. The storm lasted 8 h with gusts of >60 m s−1. In exposed plots, razorbills Alca torda had higher failure rates (28.5%) than European shags Phalacrocorax aristotelis (15.1%), black-legged kittiwakes Rissa tridactyla (15.6%) and common guillemots Uria aalge (10.4%). Conversely, failure rates in sheltered plots were negligible (shags 0.0%; kittiwakes 1.9%; no guillemot or razorbill plots in sheltered locations). Guillemots breeding closer to sea-level were more likely to fail, but cliff edge proximity did not affect failure rate. In razorbills, pairs that laid early were more likely to survive the storm. In all species, some failed pairs re-laid, and success of re-lays was lower than that of pairs that survived. Thus, re-laying only provided partial compensation, and, overall, the storm caused a net reduction in annual population production of 4.6, 10.7, 8.9 and 22.8% for shags, kittiwakes, guillemots and razorbills, respectively. Increased storm frequency may therefore have important consequences on seabird populations, but orientation of storms relative to colonies and timing in relation to the breeding season are likely to be critical in determining the overall effect

Density-dependent foraging and colony growth in a pelagic seabird species under varying environmental conditions

Intra-specific competition for food resources affects both foraging behaviour and population growth rates in many species, highlighting a need to better understand how changing environmental conditions affect individuals in populations of different sizes. Using chick-rearing northern gannets as a model, we examined the influence of colony size on per capita population growth rates over 2 time periods (1994-2000 and 2000-2009) and on foraging trip durations in each of 2 years (2000 and 2009) at 10 colonies in 2 separate regions of the UK and Ireland (the North Sea and the Celtic/Irish Sea). The slope of the relationship between population size and foraging trip duration in 2009 was less than one quarter of that in 2000, suggesting a much weaker influence of population size in 2009, presumably due to less intense intra-specific competition for prey resources at sea. There was also regional variation, with colonies in the Celtic/Irish Sea growing substantially slower for their size over the period between 2000 and 2009 than did colonies bordering the North Sea, whilst observed trip durations in 2009 were on average 13% shorter than predicted from population size at colonies bordering the North Sea, but 32% longer than predicted at colonies in the Celtic and Irish Seas. These data suggest less favourable conditions for gannets in the latter region in recent years, and that annual variation in trip durations will be particularly marked at large colonies, making them especially vulnerable to adverse effects of low prey availability at sea

European shags optimize their flight behavior according to wind conditions

Aerodynamics results in two characteristic speeds of flying birds: the minimum power speed and the maximum range speed. The minimum power speed requires the lowest rate of energy expenditure per unit time to stay airborne and the maximum range speed maximizes air distance traveled per unit of energy consumed. Therefore, if birds aim to minimize the cost of transport under a range of wind conditions, they are predicted to fly at the maximum range speed. Furthermore, take-off is predicted to be strongly affected by wind speed and direction. To investigate the effect of wind conditions on take-off and cruising flight behavior, we equipped 14 European shags Phalacrocorax aristotelis with a back-mounted GPS logger to measure position and hence ground speed, and a neck-mounted accelerometer to record wing beat frequency and strength. Local wind conditions were recorded during the deployment period. Shags always took off into the wind regardless of their intended destination and take-off duration was correlated negatively with wind speed. We combined ground speed and direction during the cruising phase with wind speed and direction to estimate air speed and direction. Whilst ground speed was highly variable, air speed was comparatively stable, although it increased significantly during strong head winds, because of stronger wing beats. The increased air speeds in head winds suggest that birds fly at the maximum range speed, not at the minimum power speed. Our study demonstrates that European shags actively adjust their flight behavior to utilize wind power to minimize the costs of take-off and cruising flight

The need for year-specific correction factors (k values) when converting counts of individual common guillemots Uria aalge to breeding pairs

Long-term studies at two Scottish colonies show that the k value used to convert counts of individual Common Guillemots Uria aalge to pairs has changed substantially in the last 15 years due to decreases in survival and colony attendance. Any future wide-scale census of this species needs to collect concurrent k values if counts of individual birds are to be used to determine changes in breeding populations since the previous survey

Among-individual and within-individual variation in seasonal migration covaries with subsequent reproductive success in a partially migratory bird

Acknowledgements: We thank Raymond Duncan (Grampian Ringing Group), whose insatiable enthusiasm for ringing was inspirational. We thank everyone who contributed to fieldwork, especially Mike Harris and David Hunter; Roger Pradel for generous advice on CMR mixture models; and UK Natural Environment Research Council for funding (NE/R000859/1, NE/P009719/1). Data accessibility Data are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.pvmcvdnhv [46]. Electronic supplementary material is available online at https://doi.org/10.6084/m9.figshare.c.5054649.Peer reviewedPostprin