Divergent post‐breeding distribution and habitat associations of fledgling and adult Black‐footed AlbatrossesPhoebastria nigripesin theNorth Pacific

Abstract

Past tracking studies of marine animals have primarily targeted adults, biasing our understanding of at‐sea habitat use toward older life stages. Anthropogenic threats persist throughout the at‐sea ranges of all life stages and it is therefore of interest to population ecologists and managers alike to understand spatiotemporal distributions and possible niche differentiation between age‐classes. In albatrosses, particularly little is known about the juvenile life stage when fledglings depart the colonies and venture to sea with no prior experience or parental guidance. We compared the dispersal of 22 fledgling Black‐footed Albatross Phoebastria nigripes between 2006 and 2008 using satellite telemetry and 16 adults between 2008 and 2009 using geolocaters from Midway Atoll National Wildlife Refuge, Northwest Hawaiian Islands. Following tag deployment, all fledglings spent several days within the calm atoll waters, then travelled northward until reaching 750–900 km from the colony. At this point, fledgling distributions approached the productive North Pacific Transition Zone (NPTZ). Rather than reaching the high chlorophyll a densities on the leading edge of this zone, however, fledglings remained in areas of low productivity in the subtropical gyre. In contrast, adult albatrosses from the same breeding colony did not utilize the NPTZ at this time of year but rather ranged throughout the highly productive northern periphery of the Pacific Ocean Basin among the shelf regions off Japan and the Aleutian Islands. The dichotomy in habitat use between fledglings and adults from Midway Atoll results in complete spatial segregation between age‐classes and suggests ontogenetic niche separation in this species. This research fills a large knowledge gap in at‐sea habitat use during a little known yet critical life stage of albatrosses, and contributes to a more comprehensive understanding of differential mortality pressure between age‐classes and overall conservation status for the vulnerable Black‐footed Albatross.

Ontogenetic changes in at-sea distributions of immature short-tailed albatrosses Phoebastria albatrus

“…Unlike immature and adult short-tailed albatrosses, other studies examining post-fledgling distributions of other albatross species have identified relatively low overlap between immatures and adults (Weimerskirch et al 2006, Alderman et al 2010, Gutowsky et al 2014a. Initially, fledgling shorttailed albatrosses departed from their colonies with more varied and oceanic trajectories than previously tracked adults from Torishima who tended to follow the coast of Japan north to the Kuril Islands before either continuing along the continental margins or traveling offshore to make the crossing to the Aleutians (Suryan et al 2006).…”

“…Segregation is even the case for shy albatrosses, where both adults and juveniles forage almost exclusively in Bass Strait and Southern Australian waters, yet show little overlap of core foraging areas (Alderman et al 2010). It is also the case for fledgling black-footed albatrosses (< 3 mo) who forage in subtropical waters, while adults prefer shelfbreak habitats in the North Pacific (Fischer et al 2009, Gutowsky et al 2014a). At present, competitive exclusion of preferred foraging areas by adult shorttailed albatrosses seems unlikely.…”

“…Juvenile seabirds are free of reproductive constraints, have different energetic requirements, are more naïve than adults, and thus often have distinctive behavior, foraging preferences, and distributions than adults (Wanless & Harris 1991, Gutowsky et al 2014a, Fayet et al 2015. They may also engage in riskier behavior than adults.…”

Individual-level Variation and Higher-level Interpretations of Space Use in Wide-ranging Species: An Albatross Case Study of Sampling Effects

“…Seabirds are generally seasonally colonial and migratory, thus specific regions are more heavily visited during different periods of their annual cycle. Defining period-specific space use can help to identify the source or severity of common or distinct threats posed at different periods in the annual cycle for a species, and for further sub-groups divided by for example age-class (e.g., Péron and Grémillet, 2013;Riotte-Lambert and Weimerskirch, 2013;Gutowsky et al, 2014a), or sex (e.g., Phillips et al, 2004;Hedd et al, 2014). At the colony level, individual-based tracking data have been used to discern period-and colony-specific space use and potential associated impacts for population dynamics for a variety of seabird species (e.g., Young et al, 2009;Catry et al, 2011;Gaston et al, 2011;Wakefield et al, 2011;Frederiksen et al, 2012;McFarlane Tranquilla et al, 2013).…”

Characterization of the seascape used by juvenile and wintering adult Southern Giant Petrels from Patagonia Argentina

“…During their first at-sea incursion, juveniles must go through their most critical stage (where mortality risk is higher) acquiring foraging skills over unknown areas (RiotteLambert and Weimerskirch, 2013). Despite the importance of this, juvenile dispersion in Procellariiformes is not well documented due to their high mortality and the difficulty on the recovery of devices because of their long periods at sea (Blanco and Quintana, 2014;Gutowsky et al, 2014). As far as we know, the at sea dispersion of this age class and its relationship with oceanographic features has been described in SGP and Northern Giant Petrel Macronectes halli through the study of ringed individuals (van den Hoff, 2011); and for the Wandering Albatross, Diomedea exulans, (Riotte-Lambert and Åkesson and Weimerskirch, 2014), the Scopoli's Shearwater, Calonectris diomedea, (P eron and Gr emillet, 2013), and the Black-footed Albatross, Phoebastria nigripes, (Gutowsky et al, 2014) through the use of satellite telemetry.…”