Feather corticosterone levels on wintering grounds have no carry-over effects on breeding among three populations of great skuas (<i>Stercorarius skua</i>)

Environmental conditions encountered by migratory seabirds in their wintering areas can shape their fitness. However, the underlying physiological mechanisms remain largely unknown as birds are relatively inaccessible during winter. To assess physiological condition during this period, we measured corticosterone concentrations in winter-grown primary feathers of female great skuas (Stercorarius skua) from three breeding colonies (Bjørnøya, Iceland, Shetland) with wintering areas identified from characteristic stable isotope signatures. We subsequently compared winter feather corticosterone levels between three wintering areas (Africa, Europe and America). Among females breeding in 2009, we found significant differences in feather corticosterone levels between wintering areas. Surprisingly, levels were significantly higher in Africa despite seemingly better local ecological factors (based on lower foraging effort). Moreover, contrary to our predictions, females sharing the same wintering grounds showed significant differences in feather corticosterone levels depending on their colony of origin suggesting that some skuas could be using suboptimal wintering areas. Among females wintering in Africa, Shetland females showed feather corticosterone levels on average 22% lower than Bjørnøya and Iceland females. Finally, the lack of significant relationships between winter feather corticosterone levels and any of the breeding phenology traits does not support the hypothesis of potential carry-over effects of winter feather corticosterone. Yet, the fitness consequences of elevated feather corticosterone levels remain to be determined

Activity patterns of wintering Great Skuas Stercorarius skua

Capsule Great Skuas Stercorarius skua wintering in different areas spent different amounts of time in flight (foraging or searching for food) and so may be experiencing different feeding conditions. Aims To compare the daily percentage of time spent in flight (foraging or searching for food) between different wintering areas. Methods In 2008, loggers equipped with a saltwater sensor were deployed on adult Great Skuas at three colonies in the northeast Atlantic, and the data used to compare foraging activity between the five main wintering areas. Results The five areas used by 22 Great Skuas in winter were widely separated, from the northwest Atlantic to northwest Africa, and differ substantially in oceanography. The main difference in foraging effort among areas for individuals that were site-faithful was that the percentage of time per day spent in flight off northwest Africa was much lower than elsewhere. Among five birds that travelled between wintering areas, one reduced the percentage of time in flight after switching from Iberia to northwest Africa. Conclusion The data suggest that feeding conditions were better off northwest Africa than elsewhere, at least during winter 2008/09. This allowed Great Skuas wintering in that region to spend more time resting, so probably reducing their overall energy expenditure

Year-Round Movements of Sooty Terns (Onychoprion fuscatus) Nesting Within One of the Atlantic’s Largest Marine Protected Areas

Seabirds are among the most threatened birds as a result of acute exposure to many anthropogenic threats. Their effective conservation requires a detailed understanding of how seabirds use marine habitats. Recently, one of the largest no-take marine reserves in the Atlantic was designated in tropical waters surrounding Ascension Island, on which the largest Atlantic population of sooty terns (Onychoprion fuscatus) breeds. Although they are the most abundant tropical seabird, they appear to have suffered marked population declines on Ascension Island as they have elsewhere. Here, we describe year-round movements and habitat use of male and female sooty terns between 2011 and 2015. On average, birds traveled 47,000 km during their 8 months of migration, during which they remained within 2,900 km of the island. They spent most of the day and night in flight, only touching down briefly on the ocean most likely to feed. Habitat suitability models successfully predicted foraging ranges of birds and their atsea distributions varied considerably between seasons, years and sexes. Considerable variation in range overlap between birds and the new marine protected area (MPA) suggests that similar such studies of other marine taxa are urgently needed. The range of sooty terns mainly falls in the high seas outside of the new MPA, highlighting the very large areas that many oceanic seabirds forage across and the challenges their conservation present

Parameter estimates for type III general linear model (GLM) assessing the influence of wintering area (i.e., Africa, America and Europe) and breeding colony (i.e., Bjørnøya, Iceland and Shetland) on feather corticosterone levels of breeding great skua (<i>Stercorarius skua</i>).

<p>Parameter estimate values are given for the following factors: Colony: Bjørnøya; Winter: Africa. Numbers in bold indicate significant p-values (p<0.05). NA, not applicable; s.e., standard error.</p

Individual feather corticosterone concentrations in winter grown primary feathers of great skuas (<i>Stercorarius skua</i>) breeding in three different colonies: Bjørnøya (black triangles), Iceland (white circles) and Shetland (black stars) in relation to their wintering quarters: Africa, Europe and America.

<p>Individual feather corticosterone concentrations in winter grown primary feathers of great skuas (<i>Stercorarius skua</i>) breeding in three different colonies: Bjørnøya (black triangles), Iceland (white circles) and Shetland (black stars) in relation to their wintering quarters: Africa, Europe and America.</p

Influence of breeding colony (i.e., Bjørnøya, Iceland and Shetland) and wintering area (i.e., Africa, America and Europe) on reproductive phenology traits of breeding female great skuas (<i>Stercorarius skua</i>).

<p>The F- and p-values were calculated using type III general linear models (GLM). Numbers in bold indicate significant p-values (p<0.05). Values (means ± standard errors) are reported for the 3 different breeding colonies. For each row reporting significant differences between colonies, lowercase letters (a–c) indicate a significant difference in means (Tukey's HSD <i>post hoc</i> tests).</p

F-, p-values and parameter estimates for the analyses of covariance between life-history traits (dependent variables) of breeding female great skuas (<i>Stercorarius skua</i>) and winter feather corticosterone levels (pg/mm) and breeding colony (i.e., Bjørnøya, Iceland and Shetland) used as independent variables (additive model excluding the interaction).

<p>Parameter estimate values are given for the following factor: Colony: Bjørnøya. Numbers in bold indicate significant p-values (p<0.05). s.e., standard error.</p

Relationships between daily growth rate of A-chicks (until day 10 of age) and persistent organic pollutants (∑OC and ∑BDE) in the blood of female great skuas in nests receiving different treatment (supplied extra food and controls).

<p>Data from Iceland 2009.</p

Hatching body conditions (hatching weight controlled for egg size) of the A-chicks and B-chicks in great skua broods in relation to the mothers’ plasma concentrations of ∑OC and ∑BDE.

<p>Data from Iceland in 2009.</p

Returning probability (± SE) of great skuas between breeding seasons (A) at Bjørnøya (2009–2012) and (B) Shetland (2009–2010) in relation to plasma concentrations of ∑OC and ∑BDE (log, ng/g wt weight).

<p>Returning probability (± SE) of great skuas between breeding seasons (A) at Bjørnøya (2009–2012) and (B) Shetland (2009–2010) in relation to plasma concentrations of ∑OC and ∑BDE (log, ng/g wt weight).</p