DOI: 10.5061/dryad.08kprr52r
title: Wandering Albatross observed and simulated GPS tracks from Crozet and Marion islands (2016-2019)

description: Sexual competition is increasingly recognized as an important
 selective pressure driving species distributions. However, few studies
 have investigated the relative importance of inter-
 vs. intrapopulation competition in relation to habitat
 availability and selection. To explain spatial segregation between sexes
 that often occurs in non-territorial and central place foragers, such as
 seabirds, two hypotheses are commonly used. The ‘competitive exclusion’
 hypothesis states that dominant individuals should exclude subordinate
 individuals through direct competition whereas the ’niche
 divergence’ hypothesis states that segregation occurs due to past
 competition and habitat specialization. We tested
 these hypotheses in two populations of an extreme wide-ranging
 and sexually dimorphic seabird, investigating the
 relative role of intrapopulation and interpopulation
 competition in influencing sex-specific distribution and habitat
 preferences. Using GPS loggers, we tracked 192 wandering
 albatrosses Diomedea exulans during four consecutive years
 (2016-2019), from two neighbouring populations in the Southern Ocean
 (Prince Edward and Crozet archipelagos). We simulated pseudo-tracks to
 create a null spatial distribution and used Kernel Density Estimates (KDE)
 and Resource Selection Functions (RSF) to distinguish the relative
 importance of within vs. between population competition. KDE
 showed that only intrapopulation sexual segregation was
 significant for each monitoring year, and that tracks between the
 two colonies resulted in greater overlap than expected from the null
 distribution, especially for the females. RSF confirmed these results
 and highlighted key at-sea foraging areas, even if the estimated
 of at-sea densities were extremely low. These differences
 in selected areas between sites and sexes were, however,
 associated with high interannual variability in habitat
 preferences, with no clear specific preferences per site and sex. Our
 results suggest that even with low at-sea population densities, historic
 intrapopulation competition in wide-ranging seabirds may have led to
 sexual dimorphism and niche specialization, favouring the ‘niche
 divergence’ hypothesis. In this study, we provide a protocol to
 study competition within as well as between populations of central place
 foragers. This is relevant for understanding their distribution patterns
 and population regulation, which could potentially improve management of
 threatened populations.
description: Wandering albatrosses from
 Possession Island, Crozet Archipelago (46°24’S, 51°46’E, henceforth
 abbreviated as ‘Crozet’) and Marion Island, Prince Edward Archipelago
 (46°54’S, 37°48’E, henceforth abbreviated as ‘Marion’), were individually
 sexed from field observations or from genetic analyses. GPS loggers
 (CatLog-S, Catnip Technologies, Hong Kong, and Igot-U GPS, Mobile Action
 Technology, at Marion, and Igot-U and X-GPS at Crozet, Weimerskirch et al.
 2018) were deployed on incubating birds and attached to the back feathers
 using Tesa© tape and left on birds for one (180 individuals) or two (12
 individuals) at-sea trips. Tracking was conducted synchronously at Marion
 and Crozet. A total of 192 birds (Crozet: 66 males and 55 females totaling
 121 birds; Marion: 44 males and 27 females totaling 71 birds, Table 1)
 were tracked during four subsequent years (2016-2019).
description: Due to the IUCN status of the species, GPS locations have been
 generalized to decimal degrees. Please contact the
 authors to access to the precise locations.
 <strong>Columns description</strong>:
 date: location dates id: individuals
 ID trip_id: foraging trip ID site:
 Crozet or Marion yr: monitoring year
 sim: simulations ID (but 0 for observed tracks)
 type_track: observed of simulated sst: sea
 surface temperatue (degree celsius) wind_speed: wind
 speed (m.s-1) bathy: bathymetry (m)
 pa: presence (1) absence (0) lon: projected
 and interpolated latitude, rounded to decimal degree
 lat: projected and interpolated longitude, rounded to decimal
 degree