Ecologia espacial e trófica de uma população antártica de petrel-gigante-do-sul Macronectes giganteus (Gmelin, 1789)

Abstract

The breeding season is a critical moment in the life history of a seabird. Due to the need of alternate between self-feeding foraging trips and trips to attend the nest, individuals suffer restrictions upon their foraging ranges and resource use. This restriction causes the increase in intraspecific competition. The Southern Giant Petrel (SGP) Macronectes giganteus is a top predator species of the Southern Ocean. It has generalists feeding habits and a marked sexual dimorphism in size. As a strategy to reduce competition, females and males usually show spatial and resource use segregation, which varies temporarily and in intensity according to degree of restriction in each breeding stage. Studies indicate that individuals from generalist species, such as the SGP, can minimize competition even more through the reduction of their niche breadth, becoming specialists at the individual level. In comparison to other regions where SGPs breed, the spatial and isotopic ecology of SGP breeding in the Antarctic region is poorly investigated, mainly due to logistical difficulties. Thus, the overall goal of this dissertation is to describe the trophic and spatial ecology of an Antarctic southern petrel population (Macronectes giganteus) throughout the breeding season. Remote tracking data of females and males breeding at Elephant Island, Maritime Antarctica were used to estimate foraging areas (FA, kernel UD) across the different stages of the breeding season (incubation, guard and chick-rearing); and also to quantify the degree of spatial overlap among sexes; Individual FAs were used to estimate consistency in space use. The ratios of stable isotopes δ13C and δ15N from different tissues (red blood cells and feathers) were analyzed to investigate temporal variations in habitat and resource use and on the degree of intersexual overlap in the isotopic niche and also to test the occurrence of individual consistency in these traits. Results showed that males and females were highly overlapped in space across the breeding season; both foraged in pelagic waters of the Antarctic and Subantarctic Zone. As expected, the greatest restriction in FAs was in guard, when the chick is still thermally dependent and requires constant feeding. The isotopic niche of males and females was also overlapped in most stages, but during chick-rearing. In this stage, breeding constraints loosen up, but food availability decreases. Niche positions varied among periods, especially in terms of used water masses. These reflect changes in foraging areas according to the feeding needs of adult and chick. Males usually fed on higher trophic levels than females, except during incubation. A high individual consistency among stages in large-scale space use was found. However, unlike expected, there was no individual specialization in resource and habitat use, due to a high within individual variation in both axes of the isotopic niche. This is the first study to analyze spatial distribution and trophic data of SGP in a matching temporal scale and to report the breeding distribution of SGP from Antarctica. The level of sexual segregation found in this study are consistent to patterns of Subantartic and Patagonian populations. The absence of individual consistency in the isotopic niche suggests the population of SGP from Elephant Island is a type A generalist, where all individuals are generalists. However, we suggest that within individual variation should be further investigated taking into account different stages of the annual cycle, breeding seasons of different years and variation in environmental conditions.