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Prelaying period in cory’s shearwater: Foraging ecology and behavior

2010Pre-breeding period in Cory's shearwater: bird quality and foraging behaviourCHIU WERNER Antje (Peru)
Organisation:University of Coimbra, Coimbra (PT)Supervisor :Jaime ramos (UC) & Vitor paiva (UC)
Summary: The pre-breeding period in Cory’s shearwater Calonectris diomedea is certainly the less studied stage in the life cycle of this species. Yet, it is especially during this period when the purposes of energetic expenditure vary between sexes leading to possible dimorphisms in their foraging ecology. Namely, females will have to cope with the costs of egg production whereas males will engage in nest defense from conspecific competitors. During the incubation and chick rearing period, the foraging ecology patterns are determined by the presence of the egg and later the chick. However, no studies have yet assessed which traits influence the foraging ecology of this species during the pre-breeding period and moreover for each sex. Thus, this study focused on two major aspects that could influence the foraging ecology of Cory’s shearwater in males and females during the pre-breeding period: the nest quality and ocean productivity. To do so, nests were characterized by their physical features, previous breeding success and current occupancy rates. On the other hand, 33 individuals (16 females and 17 males) were instrumented with GPS-loggers to record their at-sea behavioural patterns. This data was then analyzed with low and high resolution remote sensing measurements of marine primary productivity (Chl-a, SST and bathymetry) to additionally test for the influence of the resolution of remote-sensing spatial and temporal resolution on the interpretation of behavioural patterns displayed Cory’s shearwaters and other marine predators. Results show that male’s behavioural patterns are strongly influenced by nest variables associated to quality. Furthermore, this study suggests that the success of males in gaining a proper nest during the pre-laying will define the outcome of the coming breeding season for that pair, revealing that only high quality individuals will get the chance to breed. Yet, such quality differences within males were not obvious in terms of at sea behavioural patterns and foraging ecology. Females on the other hand did not show any specific patterns related to nests, however they showed to forage at considerable less productive areas than males during this period suggesting that they might be searching for very specific nutrients rather than prey availability. Furthermore males and females showed to forage in areas that are slightly less productive than the richest areas found within their home range, which suggests that a small mismatch with respect to primary productivity still exists. Last but not least, the results of this study suggest that the use of low-resolution remote sensing products in combination with highly-accurate tracking devices may lead to Type I errors. The design of marine important bird areas (mIBAS) in the North Atlantic System is strongly based on Cory’s shearwaters foraging ecology. Behavioural dimorphisms in foraging ecology of this species during the pre-laying period should be taken into account in the design process as they reveal different patterns and habitat use as during the incubation and chick-rearing period.