The role of breeding experience on the foraging specialization of a pelagic marine predator, the Cory's sheawater

Abstract

Experience is believed to be an important factor determining the foraging success of animals, but there are still very few studies investigating how foraging abilities develop over time. In this study, the spatial distribution and foraging tactics of inexperienced and experienced individuals of a Procellariiform seabird species, the Cory’s shearwater (Calonectris diomedea borealis) breeding on the Portuguese continental shelf was compared. Kernel analysis and a multivariate analysis (MADIFA) showed that while the experienced birds were relying on known static features such as the bathymetry of the area, inexperienced birds were using larger areas that were explained by different static and dynamic variables each year. The foraging areas of the two groups overlapped less and less for each year, while stable isotope signatures were becoming more and more similar, as inexperienced birds were foraging on higher trophic prey closer to the coast, like the experienced birds. Linear mixed models comparing home ranges and foraging areas calculated for each group showed that the experienced birds were in general more successful in detecting favourable foraging grounds, except in 2011, when the results showed the opposite. Interestingly, the reproductive success of the inexperienced birds was significantly higher than for experienced birds during that season.

A experiência é considerada um factor importante para o sucesso de procura de alimento dos animais, mas há ainda muito poucos estudos que investiguem como as habilidades de procura de alimento se desenvolvem ao longo do tempo. Neste estudo, foi comparada a distribuição espacial e as tácticas de procura de alimento de indivíduos experientes e inexperientes de uma espécie de Procellariiforme, a cagarra (Calonectris diomedea borealis), cuja população se reproduz na plataforma continental Portuguesa. A análise de Kernel e uma análise multivariada (MADIFA) mostrou que, enquanto as aves experientes dependiam de variáveis estáticas, tais como a batimetria da área, as aves inexperientes utilizaram áreas mais vastas respondendo em cada ano, a diferentes variáveis estáticas e dinâmicas. Os modelos lineares mistos comparando as características de habitat nas áreas de utilização com as áreas de procura de alimento entre ambos os grupos, mostraram que geralmente as aves experientes têm mais sucesso na detecção de locais de procura de alimento mais favoráveis, excepto em 2011, quando os resultados mostraram o oposto. Curiosamente, o sucesso reproductor das aves inexperientes nesse ano foi superior aquele das aves experientes.