Seabirds as Marine Animals

Processes that underlie impacts of global warming on marine organisms at upper trophic levels are largely unknown. Long-term studies of seabirds indicate that inter-annual decreases in fledging success are correlated with El Niño years, when sea surface temperatures (SSTs) are above long-term averages. These studies propose that seasonal processes are most likely responsible. To date, no work has focused on the potential impacts of elevated SSTs on seabird reproduction at finer time scales, i.e. within a breeding season. We directly measured the influence of SST variability on foraging success in the wedge-tailed shearwater Puffinus pacificus within and among 3 breeding seasons at Heron Island in the southern Great Barrier Reef, Australia. We found that changes in foraging success (meal size and feed frequency) and chick growth were negatively correlated with daily variations in SST both within and among seasons. Our findings suggest that forage resource availability fluctuated daily in direct association with small-scale variation in SST. This is evidence that declines in seabird breeding success, previously coupled exclusively with large-scale El Niño conditions and processes, may also involve fine-scale mechanisms. Consequently, observed El Niño scale impacts may include season-specific outcomes of day-to-day trophic interactions that operate within all breeding seasons.

Section: Discussionmentioning

confidence: 99%

Sea surface temperature constrains wedge-tailed shearwater foraging success within breeding seasons

Peck¹,

Smithers²,

Krockenberger³

et al. 2004

“…The use of at-sea surveys allows investigation of the distribution of seabirds in relation to marine-environmental features (Schneider 1990, Hunt 1991, Pakhomov & McQuaid 1996. However it is impossible to determine the breeding status of seabirds at sea, to observe their individual behaviour and often to determine their prey based on simple observations (Brown 1980. Hunt & Schneider 1987.…”

Section: Introductionmentioning

confidence: 99%

Exploitation of distant Antarctic waters and close shelf-break waters by white-chinned petrels rearing chicks

Catard¹,

Weimerskirch²,

Cherel³

2000

The foraging ecology of white-chinned petrels Procellaria aequinoctialis rearing chicks was examined at the Crozet Islands in the Southern Ocean, based on satellite tracking, diet and provisioning studies. White-chinned petrels from the Crozet Islands exploit a wide variety of marine environments ranging from sub-tropical waters to the limit of pack-ice at the edge of the Antarctic continent. This capability was made possible by the use of a 2-fold strategy whereby adults exploit alternatively distant oceanic waters and neritic slope waters in the v~cinity of the breedng grounds. On average the birds conducted a long foraging trip followed by 2.2 short trips. During trips of long duration over oceanic waters, birds tended to commute mainly to cold, deep Antarctic waters where most foraging activity took place. They commuted from and returned to Crozet at high speeds (mean 31 and 34 km h-' respectively) with a mean foraging range of 1868 km (maximum 2421 km). In Antarctic waters, the white-chinned petrel appears to feed mainly on pelagc fishes and on Antarctic knll Euphausia superba and concentrates its efforts in waters with sea-surface temperatures of 2°C. During short trips the birds commuted to the Crozet shelf break, where they fed mainly on fish. Diet samples delivered to chicks after short trips indicate that adults relied at least in part on food made available by longliners as baits and discards. Despite its small size compared to albatrosses, the white-chinned petrel from Crozet appears to be a particularly wide-ranging species and an opportunistic feeder in terms of the marine environment exploited, which explains its wide dstribution in the Southern Ocean. This study highlights the particular importance of Antarctic waters for this sub-Antarctic species during the chick-rearing period, i.e. in summer when the retreat of the pack-ice makes abundant resources such as Antarctic krill available.

“…Increased consumer activity at fronts may result from increased primary production, or from secondary concentrating mechanisms at fronts, in the absence of increased phytoplankton production. Qualitative effects have been reported for several consumer groups (Holligan, 19811, including marine birds (Brown, 1980;Ainley and Jacbos, 1981). For mobile marine consumers such as seabirds, numbers or biomass may not be correlated with feeding activity.…”

mentioning

confidence: 97%

Fronts and Seabird Aggregations in the Southeastern Bering Sea

Schneider¹

1982

A number of recent studies suggest that biological activity may be enhanced at fronts, which mark the boundary between water masses. Concurrent bird and physical oceanographic data were collected along a transect that crosses 3 fronts in southeastern Bering Sea. A simple regression-against-distance model was used to describe location and structure of bird aggregations along this transect. Significant bird aggregations coincided with 2 of the 3 fronts, 1 at the shelf break and 1 associated with the 50 m isobath. Aggregations at the shelf break front were composed of surface foraging birds (fulmars and petrels). Aggregations near the shallow sea front were composed of subsurface foraging birds (murres and sheanvaters). The sizes of these aggregations suggest that high rates of carbon flux to upper trophic level consumers may occur in limited areas.