Foraging economics and performance of polar and subpolar Atlantic seabirds

Seabirds of high latitudes in the North and South Atlantic (chiefly penguins, Procellariformes, alcids, shags, Gannet and Kittiwake) are compared (on absolute and energy-, mass- and time-specific scaled bases) in terms of the rate at which they supply energy to their offspring, the rate of offspring growth, and the duration of the dependence (fledging) period. For a smaller suite of species, time and energy budgets during complete foraging cycles (including time ashore) and while at sea are compared. The broad-scale comparisons show storm petrels to have consistently low provisioning and growth rates, and Kittiwakes, Gannets, shags and some penguins to have consistently high rates. Penguins (except the Gentoo Penguin) and albatrosses spend most of a foraging cycle at sea; murres, shags, gannet and kittiwake spend at least half the time ashore, guarding their offspring. Energy budgets are much more similar, because of the disproportionate cost of at-sea activities, although the time spent flying, swimming, resting, and diving varies widely between species and is often difficult to interpret in terms of active foraging. Other apparent anomalies include the large amount of time Common Murres spend resting at sea and the high resting and low flight metabolic rates of kittiwakes and gannets. Assessments of foraging performance need to be more broadly based than hitherto and to take account of both physical constraints and ecological contexts. Further development of these approaches, especially critical interspecies comparisons, requires better discrimination of activities at sea, measurement of activity-specific energy costs and more accurate data on provisioning rates to offspring, particularly of North Atlantic species, notably Gannets and shags

Albatross foraging behaviour: no evidence for dual foraging, and limited support for anticipatory regulation of provisioning at South Georgia

Many pelagic seabirds are thought to regulate reproductive effort by adopting a dual foraging strategy, alternating or mixing short foraging trips over local shelf waters (maximising provisioning rates) with longer trips over distant oceanic water (allowing restoration of lost condition). Many species also respond to chick condition, decreasing food supply to over-fed, and sometimes increasing it to under-fed chicks. Analysis of tracking data from 4 albatross species breeding at South Georgia provided evidence that adults responded to prevailing environmental conditions, but did not provide evidence for a dual foraging strategy. Trip durations and maximum foraging ranges tended to follow a positively skewed, unimodal distribution, with the exception of the light-mantled albatross for which no significant modes were apparent. Individual distributions deviated from this, but none were strongly bimodal or showed regular alternation of trip lengths, trip distance or predominant bathy-metric regime. There were significant relationships between meal mass and trip duration, time since the last feed and chick condition on return, reflecting responses to current rather than predicted chick needs. On average, adults returned with smaller meals after 1 to 2 d trips, but otherwise stayed away until a threshold payload was obtained; consequently, provisioning rate (g d(-1)) was much greater after shorter trips. Lack of dual foraging may reflect the diversity of foraging zones available in this highly productive region. By inference, this would mean that adoption of dual foraging elsewhere is a consequence of greater heterogeneity in resource availability in waters surrounding those colonies

Understanding Oceanic Migrations with Intrinsic Biogeochemical Markers

Migratory marine vertebrates move annually across remote oceanic water masses crossing international borders. Many anthropogenic threats such as overfishing, bycatch, pollution or global warming put millions of marine migrants at risk especially during their long-distance movements. Therefore, precise knowledge about these migratory movements to understand where and when these animals are more exposed to human impacts is vital for addressing marine conservation issues. Because electronic tracking devices suffer from several constraints, mainly logistical and financial, there is emerging interest in finding appropriate intrinsic markers, such as the chemical composition of inert tissues, to study long-distance migrations and identify wintering sites. Here, using tracked pelagic seabirds and some of their own feathers which were known to be grown at different places and times within the annual cycle, we proved the value of biogeochemical analyses of inert tissue as tracers of marine movements and habitat use. Analyses of feathers grown in summer showed that both stable isotope signatures and element concentrations can signal the origin of breeding birds feeding in distinct water masses. However, only stable isotopes signalled water masses used during winter because elements mainly accumulated during the long breeding period are incorporated into feathers grown in both summer and winter. Our findings shed new light on the simple and effective assignment of marine organisms to distinct oceanic areas, providing new opportunities to study unknown migration patterns of secretive species, including in relation to human-induced mortality on specific populations in the marine environment

Factors affecting the solution of a parental dilemma in albatrosses: At what age should chicks be left unattended?

With rare exceptions, avian offspring are continuously attended by one parent for at least the first few days after hatching. The duration of this phase of the nesting cycle is regulated by a trade-off between the benefits of brooding/guarding and those of foraging.We manipulated offspring age in grey-headed albatrosses, Thalassarche chrysostoma, by swapping chicks between nests. Parents given chicks 6 days older than their own shortened brooding by only 1.2 days, and parents given chicks 6 days younger than their own extended brooding by 1.4 days. Despite being relatively unresponsive to chick age, parents adjusted brooding in relation to calendar date and to chick condition. The results suggest that adults do not use chick age per se as a cue, but instead probably use an internal timer, and fine-tune the decision to end brooding according to date and chick mass. The duration of brood guarding did not correlate with adult body condition, suggesting that adults had a sufficient safety margin to allow them to respond to chick needs without compromising their own residual reproductive value. Chick survival at the end of brood guarding was strongly dependent on calendar date (early and late chicks suffered higher mortality), which suggests that greyheaded albatrosses benefit from breeding synchronously. We conclude that the length of the brood-guarding period is dependent on chick condition and seasonal variation in chick predation risk

Proximate drivers of spatial segregation in non-breeding albatrosses

Many animals partition resources to avoid competition, and in colonially-breeding species this often leads to divergent space or habitat use. During the non-breeding season, foraging constraints are relaxed, yet the patterns and drivers of segregation both between and within populations are poorly understood. We modelled habitat preference to examine how extrinsic (habitat availability and intra-specific competition) and intrinsic factors (population, sex and breeding outcome) influence the distributions of non-breeding grey-headed albatrosses Thalassarche chrysostoma tracked from two major populations, South Georgia (Atlantic Ocean) and the Prince Edward Islands (Indian Ocean). Spatial segregation was greater than expected, reflecting distinct seasonal differences in habitat selection and accessibility, and avoidance of intra-specific competition with local breeders. Previously failed birds segregated spatially from successful birds during summer, when they used less productive waters, suggesting a link between breeding outcome and subsequent habitat selection. In contrast, we found weak evidence of sexual segregation, which did not reflect a difference in habitat use. Our results indicate that the large-scale spatial structuring of albatross distributions results from interactions between extrinsic and intrinsic factors, with important implications for population dynamics. As habitat preferences differed substantially between colonies, populations should be considered independently when identifying critical areas for protectio

Threats to seabirds: A global assessment

We present the first objective quantitative assessment of the threats to all 359 species of seabirds, identify the main challenges facing them, and outline priority actions for their conservation. We applied the standardised Threats Classification Scheme developed for the IUCN Red List to objectively assess threats to each species and analysed the data according to global IUCN threat status, taxonomic group, and primary foraging habitat (coastal or pelagic). The top three threats to seabirds in terms of number of species affected and average impact are: invasive alien species, affecting 165 species across all the most threatened groups; bycatch in fisheries, affecting fewer species (100) but with the greatest average impact; and climate change/severe weather, affecting 96 species. Overfishing, hunting/trapping and disturbance were also identified as major threats to seabirds. Reversing the top three threats alone would benefit two-thirds of all species and c. 380 million individual seabirds (c. 45% of the total global seabird population). Most seabirds (c. 70%), especially globally threatened species, face multiple threats. For albatrosses, petrels and penguins in particular (the three most threatened groups of seabirds), it is essential to tackle both terrestrial and marine threats to reverse declines. As the negative effects of climate change are harder to mitigate, it is vital to compensate by addressing other major threats that often affect the same species, such as invasive alien species, bycatch and overfishing, for which proven solutions exist

Summer distribution and migration of nonbreeding albatrosses: individual consistencies and implications for conservation.

Abstract. Many birds show a surprising degree of intraspecific variability in migratory tendency and choice of wintering site. In this study, we tracked the seasonal movements of 35 nonbreeding Black-browed Albatrosses Thalassarche melanophrys from South Georgia, including 24 birds followed in two consecutive years. This revealed consistent patterns of status-related, sex-specific, and individual variation in wintering strategies, and provided the first description of the summer distribution of failed/deferring breeders. Individuals exhibited a striking degree of site fidelity, returning to the same region (southwest Africa or Australia) and showing correlated centers of distribution, as well as remarkable consistency in the chronology of their movements, in consecutive years. Nonetheless, a degree of behavioral flexibility remained, and particularly on the return migration, birds moved between, or bypassed, alternative intermediate staging sites depending on local circumstances. Initiation of the outward migration varied according to breeding status, timing of failure, and sex: deferring breeders and those that failed early departed two months before successful birds, and successful females departed 1-2 weeks earlier than males. Sex-related latitudinal variation in distribution was also apparent, with females wintering farther north within the Benguela system. Moreover, the only migrant to Australia was a male, supporting an apparent tendency for male-biased breeding dispersal inferred from genetic analyses. Distribution and timing of movements appeared in general to relate to avoidance of competition from congeners and conspecifics from other populations. From a conservation perspective, the study indicated that, for the declining Black-browed Albatross population at South Georgia, the primary focus should be toward improving the management (especially reducing bycatch levels) of fisheries in the central and eastern South Atlantic

The M81 Group Dwarf Irregular Galaxy DDO 165. II. Connecting Recent Star Formation with ISM Structures and Kinematics

We compare the stellar populations and complex neutral gas dynamics of the M81 group dIrr galaxy DDO 165 using data from the HST and the VLA. Paper I identified two kinematically distinct HI components, multiple localized high velocity gas features, and eight HI holes and shells (the largest of which spans ~2.2x1.1 kpc). Using the spatial and temporal information from the stellar populations in DDO 165, we compare the patterns of star formation over the past 500 Myr with the HI dynamics. We extract localized star formation histories within 6 of the 8 HI holes identified in Paper I, as well as 23 other regions that sample a range of stellar densities and neutral gas properties. From population synthesis modeling, we derive the energy outputs (from stellar winds and supernovae) of the stellar populations within these regions over the last 100 Myr, and compare with refined estimates of the energies required to create the HI holes. In all cases, we find that "feedback" is energetically capable of creating the observed structures in the ISM. Numerous regions with significant energy inputs from feedback lack coherent HI structures but show prominent localized high velocity gas features; this feedback signature is a natural product of temporally and spatially distributed star formation. In DDO 165, the extended period of heightened star formation activity (lasting more than 1 Gyr) is energetically capable of creating the observed holes and high velocity gas features in the neutral ISM.Comment: The Astrophysical Journal, in press. Full-resolution version available on request from the first autho