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Identifying natural populations that might be considered separate units using morphology, genotype or both is important in understanding the process of speciation and for conservation. We examined the relationships between the only two subspecies of the most numerous Arctic seabird, the Little Auk Alle alle, using both morphological (wing and head-bill lengths) and genetic data (482 base pairs of the mitochondrial control region and seven nuclear microsatellite loci). We found significant morphological differences between the subspecies, A. a. polaris being significantly larger than the nominate A. a. alle. However, we did not find the subspecies to be differentiated at either mitochondrial DNA or at microsatellite loci. Consequently, one evolutionary significant unit is proposed. The similarity of the two subspecies at neutral genetic markers may be due to contemporary gene flow between populations, as well as large population sizes both in the present and in the past, combined with recent post-glacial colonization of the Artic.

8 páginas, 5 figuras, 1 tabla., Arctic climate change has profound impacts on the cryosphere, notably via shrinking sea-ice cover and retreating glaciers, and it is essential to evaluate and forecast the ecological consequences of such changes. We studied zooplankton- feeding little auks (Alle alle), a key sentinel species of the Arctic, at their northernmost breeding site in Franz-Josef Land (80°N), Russian Arctic. We tested the hypothesis that little auks still benefit from pristine arctic environmental conditions in this remote area. To this end, we analysed remote sensing data on sea-ice and coastal glacier dynamics collected in our study area across 1979–2013. Further, we recorded little auk foraging behaviour using miniature electronic tags attached to the birds in the summer of 2013, and compared it with similar data collected at three localities across the Atlantic Arctic. We also compared current and historical data on Franz-Josef Land little auk diet, morphometrics and chick growth curves. Our analyses reveal that summer sea-ice retreated markedly during the last decade, leaving the Franz-Josef Land archipelago virtually sea-ice free each summer since 2005. This had a profound impact on little auk foraging, which lost their sea-ice-associated prey. Concomitantly, large coastal glaciers retreated rapidly, releasing large volumes of melt water. Zooplankton is stunned by cold and osmotic shock at the boundary between glacier melt and coastal waters, creating new foraging hotspots for little auks. Birds therefore switched from foraging at distant ice-edge localities, to highly profitable feeding at glacier melt-water fronts within, This study was conducted in the specially protected area of the Franz-Josef Land State Federal Refuge, within the framework of the joint international expedition of National Park Russian Arctic and a National Geographic ‘Pristine Seas Expedition FJL 2013’. The expedition was funded by National Geographic, Blancpain and Davidoff Cool Water. DG and JF are funded by CNRS and the European Union (Marie Curie CIG; Project 631203 to JF), and by the French Polar Institute (ADACLIM program No. 388).

During the last decade, increasing information on little auk (Alle alle) biology, ecology and behaviour has been reported. However, only a few of these studies have focused on the breeding population in the Avanersuaq (Thule) district of Northwest Greenland, where 80 % of the global little auk population is estimated to breed. This study reports on the chick diet composition from one of the largest colonies, the Paakitsoq colony, located on the south-eastern margin of the North Water (NOW) Polynya. Results revealed the highest proportion of Calanus hyperboreus, a large lipid-rich copepod, in chick diet reported for any little auk colony. Results confirmed that the cold, highly productive waters of the NOW Polynya are favourable foraging grounds for the little auks during the breeding season. Species diversity within and between the chick meals was low, which probably reflects a high availability of a few preferred prey species. Individual chick meals were generally low in number of prey items and total energy content compared with other published results. This may be explained by a higher feeding frequency or by the samples being collected late in the breeding period (during late chick rearing), when chicks have a reduced growth rate and may require less energy than at earlier developmental stages.

The role of seabirds as sea-land biovectors of nutrients is well documented. However, no studies have examined whether and how colonial seabirds that differ in diet may influence terrestrial vegetation. Therefore, the purpose of the study was to describe and compare plant communities located in the vicinity of the two most common types of seabird colonies in Arctic, occupied by piscivorous or planktivorous species. Within 46 plots arranged in four transects in the vicinity of planktivorous (little auk, Alle alle) and piscivorous colonies (mixed colony of Brunnich’s guillemot, Uria lomvia, and black-legged kittiwake, Rissa tridactyla) we measured the following: guano deposition, physical and chemical characteristics of soil, total nitrogen and its stable isotope signatures in soil and plants, ground vegetation cover of vascular plants and mosses, and the occurrence of lichens, algae and cyanobacteria. Using LINKTREE analysis, we distinguished five plant communities, which reflected declining influence along a birds fertilization gradient measured as guano deposition. SIMPROOF test revealed that these communities differed significantly in species composition, with the differences related to total soil nitrogen content and δ15N, distinctive levels of phosphates, potassium and nitrates, and physical soil properties, i.e., pH, conductivity and moisture. The communities were also clearly distinguished by distance from the bird colony. The two colony types promoted development of specific plant communities: the immediate vicinity of the planktivorous colony characterized by a Deschampsia alpina–Cerastium arcticum community while under the piscivorous colony a Cochlearia groenlandica–Poa alpina community was present. Despite the similar size of the colonies and similar magnitude of guano input, differences between ornithogenic communities were connected mostly to phosphate content in the soil. Our results show that the guano input from seabirds which have different diets can affect High Arctic vegetation in specific and more complex ways than previously realized.

Climate change results in the alteration of the size structure of plankton, which consequently may affect higher trophic levels, such as planktivorous seabirds. In this study Laser Optical Plankton Counter measurements were performed over seven summer seasons (2010–2016) to test the ratio of large versus small zooplankton in relation to environmental conditions. Investigated transects were repeated during the same time of the year (July/August) in different zones of the West Spitsbergen Shelf crossing the Arctic front. The plankton particles were grouped into two size fractions: “Calanus”, potentially consisting of a majority of the high-energetic, older life stages of the preferred prey for little auk (Alle alle) and the “small” fraction including less preferred items. The vertical availability of the Calanus fraction was tested on the background of usually abundant smaller zooplankton, which may hinder the detection of larger zooplankters by little auk. Larger zooplankton were found closer to the coast, in the upper 20-m depth layer in years characterized by significantly lower mean temperatures. Potential availability of prey for the little auk thus could be higher in colder years than in warmer years. Additionally, our study indicated the tendency of the small plankton fraction to concentrate near the locations of the highest chlorophyll fluorescence, in the 20–30-m water layer. The high spatial and temporal resolution of the data indicated a variation in the proportion of large versus small zooplankton, and thus in the availability of Calanus to little auk with respect to temperature.

The complete diet composition structure of the most numerous planktivorous sea bird, little auk (Alle alle), in the European Arctic, is still not fully recognized. Although regular constituents of little auk chick diets, the copepods, Calanus glacialis and C. finmarchicus have been previously relatively well described, more taxa were frequent ingredients of the bird’s meals. Therefore, the role of the little auks supplementary diet components (SDCs) at two colonies in the Svalbard Archipelago, Hornsund and Magdalenefjorden, in 2007–2009, is a main subject of this comparative study. Because the SDCs often consisted of scarce but large zooplankters, this investigation was focused on biomass as a proxy of the SDCs’ energy input. Although the total biomass of the food delivered to chicks in both colonies was similar, in Magdalenefjorden, the proportion of SDCs was twice that found in Hornsund. The main SDCs in Hornsund were Decapoda larvae (with predominating Pagurus pubescens) and Thysanoessa inermis, whereas the main SDCs in Magdalenefjorden were C. hyperboreus and Apherusa glacialis. Previous investigations, which indicated lipid richness of SDCs, together with our ecological results from the colonies, suggest that this category might play a compensatory role in little auk chick diets. The ability to forage on diverse taxa may help the birds to adapt to ongoing Arctic ecosystem changes.

International audience; Tradeoffs between current reproduction andfuture survival are widely recognized, but may only occurwhen food is limited: when foraging conditions arefavorable, parents may be able to reproduce withoutcompromising their own survival. We investigated thesetradeoffs in the little auk (Alle alle), a small seabird with asingle-egg clutch. During 2005–2007, we examined therelationship between body mass and survival of birdsbreeding under contrasting foraging conditions at twoArctic colonies. We used corticosterone levels of breedingadults as a physiological indicator of the foraging conditionsthey encountered during each reproductive season.We found that when foraging conditions were relativelypoor (as reflected in elevated levels of corticosterone),parents ended the reproductive season with low body massand suffered increased post-breeding mortality. A positiverelationship between body mass and post-breeding survivalwas found in one study year; light birds incurred highersurvival costs than heavy birds. The results of this studysuggest that reproducing under poor foraging conditionsmay affect the post-breeding survival of long-lived littleauks. They also have important demographic implicationsbecause even a small change in adult survival may have alarge effect on populations of long-lived species.