Seabird Ecology; Migration Ecology

Knowledge about the spatial distribution of seabirds at sea is important for conservation. During marine conservation planning, logistical constraints preclude seabird surveys covering the complete area of interest and spatial distribution of seabirds is frequently inferred from predictive statistical models. Increasingly complex models are available to relate the distribution and abundance of pelagic seabirds to environmental variables, but a comparison of their usefulness for delineating protected areas for seabirds is lacking. Here we compare the performance of five modelling techniques (generalised linear models, generalised additive models, Random Forest, boosted regression trees, and maximum entropy) to predict the distribution of Balearic Shearwaters (Puffinus mauretanicus) along the coast of the western Iberian Peninsula. We used ship transect data from 2004 to 2009 and 13 environmental variables to predict occurrence and density, and evaluated predictive performance of all models using spatially segregated test data. Predicted distribution varied among the different models, although predictive performance varied little. An ensemble prediction that combined results from all five techniques was robust and confirmed the existence of marine important bird areas for Balearic Shearwaters in Portugal and Spain. Our predictions suggested additional areas that would be of high priority for conservation and could be proposed as protected areas. Abundance data were extremely difficult to predict, and none of five modelling techniques provided a reliable prediction of spatial patterns. We advocate the use of ensemble modelling that combines the output of several methods to predict the spatial distribution of seabirds, and use these predictions to target separate surveys assessing the abundance of seabirds in areas of regular use.

Estimations on the influence of evolutionary and ecological forces as drivers of population gene diversity and genetic structure have been performed on a growing number of colonial seabirds, but many remain poorly studied. In particular, the population genetic structure of storm-petrels (Hydrobatidae) has been evaluated in only a few of the 24 recognized species. We assessed the genetic diversity and population structure of the Black Storm-Petrel (Hydrobates melania) and the Least Storm-Petrel (Hydrobates microsoma) in the Gulf of California. The two species were selected because they are pelagic seabirds with comparable ecological traits and breeding grounds. Recent threats such as introduced species of predators and human disturbance have resulted in a decline of many insular vertebrate populations in this region and affected many different aspects of their life histories (ranging from reproductive success to mate selection), with a concomitant loss of genetic diversity. To elucidate to what extent the population genetic structure occurs in H. melania and H. microsoma, we used 719 base pairs from the mitochondrial cytochrome oxidase c subunit I gene. The evaluation of their molecular diversity, genetic structure, and gene flow were performed through diversity indices, analyses of molecular and spatial variance, and isolation by distance (IBD) across sampling sites, respectively. The population genetic structure (via AMOVA and SAMOVA) and isolation by distance (pairwise p-distances and Fst /1-Fst (using Phi-ST) were inferred for H. microsoma. However, for H. melania evidence was inconclusive. We discuss explanations leading to divergent population genetic structure signatures in these species, and the consequences for their conservation.

Lunar phase and illumination are known to affect nocturnal behavior of many organisms, particularly through predator-prey interactions. Visual predators can benefit from higher light levels to increase their activity, while prey may decrease their activity to avoid predation. The lower number of nocturnal seabirds observed on colonies during full moon nights has been mostly interpreted as a predation avoidance strategy. However, it is also possible that shearwaters take advantage of the moon's illumination to feed also at night, and stay at sea to forage during full moon nights. We used miniaturized GPS-loggers to obtain 179 tracks from 99 wedge-tailed shearwaters breeding in New Caledonia, to investigate moonlight effects on individual behavior. Lunar phase significantly predicted self-provisioning trip duration, with individuals performing longer trips around the full moon. However, this relationship was not significant during chick-provisioning trips when adults have to frequently return to the colony. Adults mostly returned to the colony during moonlit periods, refuting the predation avoidance theory. Tracked individuals showed an unexpectedly high amount of nocturnal foraging activity (28% of total activity), positively influenced by the presence of the moon. δ15N stable isotope values were significantly related to the percentage of nocturnal foraging, but with a weak relationship, impeding our ability to confirm that wedge-tailed shearwaters fed on different prey when foraging at night. This study suggests that reduced colony attendance around the full moon may be linked to greater at-sea foraging opportunities in distant oceanic areas than to increased predation risk on land.

Little is known of the endangered and declining western North Atlantic population of the Roseate Tern Sterna dougallii outside the breeding season, when most mortality probably occurs. We used geolocators to track Roseate Terns in 2007 and 2009 and retrieved six units with useful data. In the post-breeding period in July–August, all six birds staged around Cape Cod, close to the breeding site. They started southward migration from 28 August to 14 September and flew directly across the western North Atlantic Ocean to staging areas around Puerto Rico and the Dominican Republic. We identified five major areas and four minor areas in the West Indies and along the north and east coasts of South America where birds stopped over for 2–24 d during southward and northward migrations. Birds arrived at (Northern Hemisphere) wintering areas from Guyana/Suriname on the north coast of South America to eastern Brazil between 3 October and 2 November. They left wintering areas from 7–23 April and arrived back at the breeding area from 5–30 May. Although this study is based on data for only six birds, it identifies several stopover and wintering areas that should receive priority for future studies and potential conservation measures. Geolocators did not impair Roseate Terns’ ability to raise young in the year the devices were attached, but lower than expected rates of return suggest that the geolocators reduced survival, and most of the birds that returned had lost body-mass and did not breed in the year of return.