Foraging and breeding behaviours and their relationships with breeding performance in a pelagic seabird

Supervisor: Maite Louzao (AZTI)
During the breeding cycle, animals adopt different foraging strategies depending on the stage to meet the energetic requirements and nutritional needs. Pelagic seabirds behave as central place foragers during the breeding season, when breeding individuals forage at sea while they are spatially constrained to return to their colonies on land. Therefore, they need to trade-off between prey availability and distance to foraging grounds (i.e., foraging effort) and time in the nest incubating the egg or feeding their chick (breeding effort). Within this context, our main objective was to provide a broad understanding of the contribution of foraging and breeding behaviour to the breeding performance of a central-place forager, the Balearic shearwater Puffinus mauretanicus. We focused on the southern population of a critically endangered species, breeding in the west coast of Ibiza, Balearic Islands. Based on global location sensing (GLS) devices for the period 2011-2013, we estimated 4 foraging indices (trip durations and percentages of time sitting on the water, foraging and flying) and 2 breeding indices (overall percentage of time spent in the nest and time interval between nest attendances) for both incubation and chick-rearing stages. Based on Generalised Linear Models developed within the Information-Theoretic framework, we found that both breeding and foraging indices of the two stages were influencing the breeding success. The percentage of time on land during incubation was the most important factor, when successful birds spent more time on land than failed breeders (52% vs 41%). This result is relevant since incubation is the most critical stage for successful breeding (when most of the breeding failures occur) and once hatched, the probability of survival of the chick is higher. Foraging effort during the incubation was less important than breeding effort, but model coefficients show that successful breeders spent more time foraging at sea (52% vs. 47%), while taking shorter foraging trips (2.0 d vs. 2.5 d). During chick-rearing, the most important factor was the percentage of time flying, with successful breeders spending a larger proportion of time flying than those who failed (20% vs 17%). The time spent on land during the chick-rearing had a negative effect on breeding success (12% and 16% for successful and failed breeders, respectively). This study is the first attempt to analyse in depth the temporal geolocator activity during the breeding cycle of the Balearic shearwaters and provides a novel methodology applicable to other pelagic seabirds.