An oceanographic interpretation of seabird distributions in the Indian Ocean

How top avian predators are distributed at sea during the inter-breeding period remains poorly known. Here we focused on the pelagic seabird that is the single greatest avian consumer of marine resources: the macaroni penguin. Our aims were (1) to investigate where these penguins are distributed whilst at sea during winter, and (2) to determine how their distribution and trophic ecology varies in 1 colony between successive years and between 2 colonies from neighbouring localities at the same time. We surveyed a total of 30 penguins from Crozet and Kerguelen Islands (southern Indian Ocean). Penguins from Kerguelen were tracked in 2006 and 2007, and those from Crozet in 2007. Habitat use was investigated using miniaturised light-based geolocators, and trophic ecology by the use of stable isotope analyses. Results showed large-scale patterns of distribution over deep oceanic waters of the Polar Frontal Zone characterised by a temperature of 3.0 to 3.5°C during July. Birds from Kerguelen had a consistent inter-annual winter distribution at the population level. Birds tracked from Crozet were distributed in distinct areas, separate from the birds from Kerguelen. Trophic ecology (blood δ 15 N value) was very similar between years and colonies, and indicated that these penguins preyed upon low trophic level prey, most probably swarming crustaceans, at the end of winter. We conclude that inter-annual fidelity in winter habitat provides evidence of highly favourable and predictable foraging areas, while the distinct inter-colony distributions suggest very heterogeneous distribution of profitable feeding areas for this species in the southern Indian Ocean.

Section: Introductionmentioning

confidence: 99%

Inter-population segregation in the wintering areas of macaroni penguins

Thiebot¹,

Cherel²,

Trathan³

et al. 2011

“…For example, studies have quantified seabird habitat using physical parameters describing water masses, e.g. temperature and salinity (King 1974, Pocklington 1979, Ainley & Boekelheide 1983, Wahl et al 1989. Physical proxies for seabird distribution and abundance should include more than just temperature and salinity, since seabird habitat selection is most likely a function of prey abundance and/or availability and comprised of a mosaic of environmental variables.…”

Section: Introductionmentioning

confidence: 99%

Pelagic habitat of seabirds in the eastern tropical Pacific: effects of foraging ecology on habitat selection

Vilchis¹,

Ballance²,

Fiedler³

2006

A central tenet of ecology is the quantification of species-habitat relationships in order to explain spatial variability in the distribution and abundance patterns of animals. We quantified habitat preferences for 6 tropical seabird species representing a phylogenetically and ecologically diverse group within the eastern tropical Pacific (ETP). Seabird censuses were conducted aboard NOAA research vessels from August to November of 1989 and 1990 using 300 m strip transect methods. Simultaneously with the seabird censuses and from the same ships, oceanic habitat was quantified by measuring sea surface temperature, salinity, and chlorophyll, as well as thermocline depth and strength. We quantified seabird habitat using generalized additive models fitted with forward and backward selection algorithms based on minimizing the Akaike information criterion (AIC). In general, seabird habitat models performed well in explaining spatial variability in abundance, reducing the null deviance to ranges between 42.8 and 73.5%, and predicting seabird density patterns with an accuracy ranging from 56.6 to 80.5%. Relative abundance of the species modeled affected the outcome: the higher the abundance, the more robust the fit. Seabirds feeding on fishes and squids associated with habitats characterized by deep (>100 m) and strong (> 2°C 10 m -1 ) thermoclines, while planktivorous species preferred habitat characterized by shallower thermoclines with cooler surface temperatures (< 25°C) and a less stratified water column. Thus, seabirds in different feeding guilds have clear and distinct habitat preferences within the ETP. We propose thermocline topography as a key variable in predicting distribution and abundance of seabirds in this area, probably due to its influence on the availability of seabird prey.

“…continental shelf waters or nearshore rocky subtidal habitats) or seasonal migrations related to time and location of breeding (Ainley & Boekelheide 1984, Ribic et al 1997, Woehler et al 2003. Distinct seabird communities associated with different meso-scale habitats (usually related to different prey species) have been well described (Pocklington 1979, Abrams 1985, Wahl et al 1989, Ainley et al 1994, Veit 1995 At a finer scale of ≤1 km, co-occurrence patterns of different seabird species are more likely to be related to competition or commensalism. At this scale, seabirds often share similar prey species and forage together in mixed-species flocks (Hoffman et al 1981, Duffy 1983, Harrison et al 1991.…”

Section: Introductionmentioning

confidence: 99%

Co-occurrence and aggregation of marine birds and mammals in Monterey Bay, California, USA

Henkel¹

2009

Patterns of spatial and temporal co-occurrence or avoidance among different species of marine birds and mammals can provide insights into the degree to which these top predators compete for prey. I conducted at-sea surveys in nearshore waters of Monterey Bay, California, USA, and used a randomization technique to assess co-occurrence patterns of marine birds and mammals in 1 km transect segments. As expected, strongest positive associations were among members of 3 different foraging guilds: pursuit-divers, surface-feeders, and plunge-divers. Within guilds, pursuitdivers exhibited marked avoidance of one another (negative co-occurrence), although surfacefeeders often co-occurred with each other. The study was conducted during 2 yr, 1999 and 2000; during 2000, when predator abundance was greater and prey abundance may have been decreased, pursuit-divers exhibited more avoidance of one another than in 1999. These data suggest that competition reduces foraging ability for pursuit-diving species, making it more profitable for them to disperse more widely, whereas surface-feeding species (primarily gulls) benefit from flock foraging under most conditions. Larger animals tended to frequently co-occur, while the smallest member of each guild tended to avoid other species, indicating competitive exclusion of smaller predators.