Oceanographic and climatic factors differentially affect reproduction performance of Antarctic skuas

Abstract

We studied how environmental conditions affect reproduction in sympatric skua species that differ in their reliance on marine resources: the exclusively marine foraging south polar skua Catharacta maccormicki, the terrestrially foraging brown skua C. antarctica lonnbergi and mixed species pairs with an intermediate diet. Egg size, clutch asymmetry and hatching dates varied between species and years without consistent patterns. In the south polar skuas, 12 to 38% of the variation in these parameters was explained by sea surface temperature, sea ice cover and local weather. In mixed species pairs and brown skuas, the influence of environmental factors on variation in clutch asymmetry and hatching date decreased to 10-29%, and no effect on egg size was found. Annual variation in offspring growth performance also differed between species with variable growth in chicks of south polar skuas and mixed species pairs, and almost uniform growth in brown skuas. Additionally, the dependency on oceanographic and climatic factors, especially local wind conditions, decreased from south polar skuas to brown skua chicks. Consistent in all species, offspring were more sensitive to environmental conditions during early stages; during the late chick stage (> 33 d) chick growth was almost independent of environmental conditions. The net breeding success could not be predicted by any environmental factor in any skua species, suggesting it may not be a sensitive indicator of environmental conditions. Hence, the sensitivity of skuas to environmental conditions varied between species, with south polar skuas being more sensitive than brown skuas, and between breeding periods, with the egg parameters being more susceptible to oceanographic conditions. However, during offspring development, local climatic conditions became more important. We conclude that future climate change in the Maritime Antarctic will affect reproduction of skuas more strongly through changes in sea ice cover and sea surface temperature (and the resulting alterations to the marine food web) than through local weather conditions. KEY WORDS: Maritime Antarctic · Sea surface temperature · Sea ice cover · Catharacta spp. · Breeding parameter · Chick growth · Life history 334: 287-297, 2007 spp.) comprise the key resource for almost all higherorder predators in the Antarctic, either representing the main prey for penguins, fishes and whales, or indirectly affecting top predators such as seals and skuas that prey on krill-consuming species. Because the Antarctic food web is comparatively simple (Hempel & Kerry 1990), environmental changes affecting lower food chain levels can also rapidly influence reproduction and population dynamics of top predators (Fraser & Hofmann 2003. Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESSMar Ecol Prog SerIn studies of polar seabirds, oceanographic factors like sea ice cover and sea surface temperatures have been used as proxies for food accessibility and availability, as the...

Long-term changes in population size, distribution and productivity of skuas (Stercorarius spp.) at Signy Island, South Orkney Islands

“…Although diet seems to have diversified in response to declining resources, timing of breeding on Signy Island does not appear to have changed since the 1950s/early 1960s; mean hatching dates in 1963/ 64-1965/66, 1982/83 and 2013/14 were all in the first week of January (Richards 1958;Burton 1968;Hemmings 1984; this study), and were similar to those recorded for brown skuas at King George Island in 1983/84 to 2003/04, and at South Georgia in 2000/01 and 2002/03 (Hahn and Peter 2003Phillips et al 2004;Hahn et al 2007). Although some brown skuas at Signy Island occupy feeding territories in penguin colonies, which can sustain skuas for much of the season Hahn and Bauer 2008), other birds at Signy Island feed in penguin colonies that are not defended consistently by another pair of skuas, or elsewhere on small petrels and marine prey (see above).…”

“…This would explain the slight decline in breeding success from the 1950s/early 1960s to the present. However, even if this somewhat reduced breeding success is the result of density-dependent competition for resources, it is important to note that productivity of brown skuas at Signy Island remains similar to levels reported for populations breeding elsewhere (0.5-1.8 chicks fledged/pair) (Reinhardt 1997;Phillips et al 2004;Hahn et al 2007). There is no evidence of any substantive long-term change in breeding chronology of penguins at Signy Island (Lishman 1985; British Antarctic Survey unpublished data).…”

Taxonomic recommendations for British birds: seventh report

“…In addition, sympatrically breeding Brown and South Polar Skuas differ significantly in several long call parameters (Pietz 1985) and further differ in ecological and reproductive traits (Pietz 1987, Ritz et al. 2006, Hahn et al. 2007).…”

Ecología trófica y áreas de forrajeo del escúa polar del sur, <i>Stercorarius maccormicki</i>, en dos localidades antárticas

“…Dada la versatilidad registrada en el comportamiento de los escúas alrededor del continente antártico, es necesario incrementar los estudios del EPS, para extender y profundizar el conocimiento general de esta especie. Los resultados obtenidos en este estudio, coinciden con trabajos previos, particularmente con aquellos realizados en poblaciones ubicadas en la Península Antártica (Pietz, 1986, Hahn et al 2007, 2008, aunque también revelan nuevas evidencias del impacto de la variabilidad en la disponibilidad de los recursos sobre el comportamiento de alimentación. Los predadores tope marinos explotan un ambiente heterogéneo tanto en la escala espacial como temporal (Hunt et al 1999), y en respuesta a ello pueden exhibir variaciones considerables en su ecología de alimentación o distribución en el mar (Lescroël y Bost 2005).…”

“…La cronología y el éxito reproductivo de los escúas, que es generalmente bajo, están influenciados por distintos factores (Young 1994, Reinhardt 1998. Se pueden identificar factores extrínsecos o ambientales como la extensión del hielo marino (Pietz 1986, Parmelee 1978, tormentas (Wood 1971) y disponibilidad de alimento (Trivelpiece et al 1990, Hahn et al 2007) y otros factores que son propios de los individuos como la edad de reproducción y la experiencia (Ainley et al 1990, Ritz et al 2005. En el EPS se ha determinado que el tamaño de los huevos y el inicio temprano de la reproducción pueden reflejar condiciones favorables al comienzo de la temporada (Pietz 1986, mientras que la performance reproductiva y en especial el crecimiento de los pichones pueden ser un indicador sensible de las condiciones ambientales locales durante el periodo de cuidados parentales (Ricklefs 1983, Cairns 1987, Montevecchi 1993, Boersma y Parrish 1998.…”