The crucial role of seabirds in the enrichment of nutrient-poor polar terrestrial ecosystem is well-known. However, no studies have examined the potentially different impacts associated with piscivorous and planktivorous bird colonies on the surrounding tundra soils. Therefore, we compared guano deposition and physical and chemical parameters of soil near two large seabird colonies, one of planktivorous little auks (Alle alle) and the other comprising piscivorous Brunnich's guillemots (Uria lomvia) and kittiwakes (Rissa tridactyla). The two colonies generated similar levels of guano deposition, with the intensity of deposition decreasing away from the colony. Guano deposition adjacent to both colonies was considerably higher than that in control areas. The increased guano supply around colonies significantly enhanced soil conductivity, nitrogen (NO 3 -, NH 4 ? ), potassium (K ? ), and phosphate (PO 4 3-) ion concentrations and led to reduced pH values. Guano deposition explained 84 % (piscivorous colony) and 67 % (planktivorous colony) of the total variation in the tested soil parameters. Planktivore and piscivore colonies affected adjacent tundra in different ways. The phosphate content and pH value of soil influenced by piscivores were significantly higher than values measured in planktivore-influenced soil. The gradient of guano deposition and associated ion content in the soil decreased more rapidly with distance from the piscivore colony. Climate-induced changes in populations of planktivorous and piscivorous seabirds are expected in the study region and may therefore have substantial consequential effects on Arctic terrestrial ecosystems.

Knowledge of foraging behaviour is essential to understand both the ecological roles of seabirds and the constraints acting upon them in marine ecosystems. Here, we investigated foraging trips of a small planktivorous alcid, the little auk Alle alle, using miniature GPS loggers. We performed the study in 2 large breeding colonies in west Spitsbergen (Hornsund and Magdalenefjorden) with contrasting oceanographic conditions (Arctic and Atlantic environments, respectively). Generally, in both locations little auks foraged in areas with low sea surface temperature (Arctic-type water, marginal ice zone, and frontal zones) where preferred zooplankton are commonly abundant. In the Arctic environment (Hornsund), birds foraged significantly closer to the colony (up to 60 km) compared to up to 150 km in the Atlantic environment (Magdalenefjorden). Hatching and breeding success and chick survival up to 20 d as well as chick body mass parameters were similar in both studied colonies. However, chicks in the Arctic environment (Hornsund) achieved both peak body mass and fledging age earlier, suggesting faster chick growth than in the Atlantic environment (Magdalenefjorden). The importance for breeding little auks of nearby cold water foraging grounds may make them sensitive to predicted climate change with serious negative consequences for body condition, future survival and breeding success.

Despite a widespread recognition of the role of seabird colonies in the fertilization of nutrient-poor polar terrestrial ecosystems, qualitative and quantitative data documenting any consequential influence on soil invertebrate communities are still lacking. Therefore, we studied community structure and abundance of springtails (Collembola) in ornithogenic tundra near two large seabird colonies in Hornsund, south-west Spitsbergen. We found considerably (5-209) higher densities and biomass of Collembola in the vicinities of both colonies (the effect extending up to ca. 50 m from the colony edge) than in comparable control areas of tundra not influenced by allochtonous nutrient input. The most common springtails observed in the seabird-influenced areas were Folsomia quadrioculata, Hypogastrura viatica and Megaphorura arctica. The latter species appeared the most resistant to ornithogenic nutrient input and was found commonly closest to the bird colonies. Collembolan abundance decreased with increasing distance from the seabird colonies. However, relationships between collembolan density and specific physicochemical soil parameters and vegetation characteristics were weak. The most important factors were the cover of the nitrophilous green alga Prasiola crispa, total plant biomass and soil solution conductivity, all of which were correlated with distance from the colony and estimated amount by guano deposition. Community composition and abundance of springtails showed no evidence of being influenced of seabird diet, with no differences apparent between communities found in ornithogenic tundra developing in the vicinity of planktivorous and piscivorous seabird colonies. The study provides confirmation of the influence of marine nutrient input by seabirds on soil microfaunal communities.

During the chick-rearing period, little auks Alle alle adopt a bimodal foraging strategy, alternating long trips with several short ones. It has been postulated that they reach more remote areas during long feeding trips than during short ones. However, the range of their foraging Xights has never actually been measured. The aims of this study were to Wnd the exact location of the little auk feeding grounds and to investigate whether they reach remote areas during long foraging trips using miniature GPS and temperature loggers. The study was conducted in 2009 in Magdalenefjorden (79°34ЈN, 11°04ЈE), one of the main breeding grounds of little auks on Spitsbergen. The temperature logger records indicated that during short trips, little auks visit warmer waters (situated close to the colony) than during long ones. The tracks of two GPS-equipped birds indicated that during long trips little auks foraged in the distant, foodabundant marginal sea ice zone, at least 100 km away from the colony. During long trips, birds make several stops at sea, perhaps sampling the foraging area with respect to prey distribution. Since food conditions near the studied colony are usually suboptimal, little auks may be exploiting distant feeding areas to compensate for the poorer-quality food available at nearby foraging grounds. The extended duration of long foraging trips may enable birds to collect food for chicks on food-abundant, remote foraging grounds as well as acquire, process and excrete food needed for selfmaintenance, reducing the costs of Xight to the colony.

Here, we model current and future distribution of a foraging Arctic endemic species, the little auk (Alle alle), a small zooplanktivorous Arctic seabird. We characterized environmental conditions [sea depth, sea surface temperature (SST), marginal sea ice zone (MIZ)] at foraging positions of GPS-tracked individuals from three breeding colonies in Svalbard: one located at the southern rim of the Arctic zone (hereafter ‘boreo-Arctic’) and two in the high-Arctic zone on Spitsbergen (‘high-Arctic’). The birds from one ‘high-Arctic’ colony, influenced by cold Arctic water, foraged in the shallow shelf zone near the colony. The birds from remaining colonies foraged in a wider range of depths, in a higher SST zone (‘boreo-Arctic’) or in the productive but distant MIZ (second ‘high-Arctic’ colony). Given this flexible foraging behaviour, little auks may be temporarily resilient to moderate climate changes. However, our fuzzy logic models of future distribution under scenarios of 1 °C and 2 °C SST increase predict losses of suitable foraging habitat for the majority of little auk colonies studied. Over longer time scales negative consequences of global warming are inevitable. The actual response of little auks to future environmental conditions will depend on the range of their plasticity and pace of ecosystem changes.