Birds and Mammals of the Lena Delta Nature Reserve, Siberia

The Lena Delta is the largest arctic delta covered entirely by tundra. Protected since 1986, it is one of the richest areas in the Arctic north of 71° N for both species diversity and breeding densities. Between 6 June and 17 August 1997, 16 mammal species and 76 bird species were recorded in the Lena Delta Nature Reserve and the surrounding buffer zone. Several species are new to the region: far-eastern curlew, fieldfare, redwing, arctic warbler, red-breasted flycatcher, and common rat. New breeders are merlin and arctic warbler. These 1997 records, combined with those from earlier studies, give a total of 122 bird species for the region. Of these, 67 have been found breeding at least once. Densities ranging from 245 to 641 birds per km² were recorded in two restricted study areas. Such densities are unusually high north of 70° N for non-colonial breeding birds. Lapland longspur (100-300 individuals/km²), red phalarope (up to 200 ind./km²), and several Calidris species were the most common. Ruddy turnstone and dunlin had densities higher than those previously reported from the Lena Delta and other Siberian sites. Among the shorebirds, spotted redshank, pintail snipe, grey plover, dunlin, and curlew sandpiper may have extended their breeding range or increased in population during the last 15 years. But further evidence is still needed to confirm the westward extension of spectacled eider, long-billed dowitcher, and sharp-tailed sandpiper.Le delta de la Lena est le plus grand delta arctique totalement recouvert de toundra. Protégé depuis 1986, il est l'une des zones les plus riches de l'Arctique au nord du 71° de latitude N., tant par la richesse spécifique que par les densités d'oiseaux nicheurs. Seize espèces de mammifères et 76 espèces d'oiseaux ont été observées dans la Réserve naturelle du delta de la Lena et sa zone périphérique entre le 6 juin et le 17 août 1997. Plusieurs espèces sont nouvelles pour la région: courlis de Sibérie, grive litorne, grive mauvis, pouillot boréal, gobemouche nain et rat surmulot. Les nouvelles espèces nicheuses sont le faucon émerillon et le pouillot boréal. Combinés à ceux d'études plus anciennes, nos résultats portent à 122 le nombre total d'espèces d'oiseaux recensés dans cette région et à 67 celui des espèces s'y étant reproduit au moins une fois. Des densités comprises entre 245 et 641 individus au km² ont été trouvées sur deux zones d'étude restreintes, densités exceptionnelles au nord du 70° de latitude N. pour des espèces non coloniales. Les espèces les mieux représentées sont le bruant lapon (100-300 ind./km²), le phalarope à bec large (jusqu'à 200 ind./km²) et plusieurs espèces de Calidris. Le tournepierre à collier et le bécasseau variable avaient des densités plus fortes que celles précédemment rapportées pour le delta de la Lena et d'autres sites sibériens. Le chevalier arlequin, la bécassine à queue pointue, le pluvier argenté, le bécasseau variable et le bécasseau cocorli font partie des limicoles qui semblent avoir étendu leur aire de distribution ou augmenté leur population durant les 15 dernières années, mais d'autres travaux seront nécessaires avant de confirmer l'extension occidentale de l'eider à lunettes, du limnodrome à long bec et du bécasseau à queue pointue

Functional and numerical responses of four lemming predators in high arctic Greenland.

24 pagesInternational audienceThe high-arctic tundra ecosystem has the world's simplest vertebrate predator-/prey community, with only four predators preying upon one rodent species, the collared lemming (Dicrostonyx groenlandicus ). We document the functional and numerical responses of all the four predators in NE Greenland. Using these data, we assess the impact of predation on the dynamics of the collared lemming with a 4 yr cycle and >100-fold difference between maximum and minimum densities. All predator species feed mostly (>90%) on lemmings when lemming density is >1 ha-1, but the shapes of the predators' responses vary greatly. The snowy owl (Nyctea scandiaca) is present and breeds only when lemming densities at snowmelt are >2 ha-1, giving rise to a step-like numerical response. The long-tailed skua (Stercorarius longicaudus ) has a type III functional response and shifts from alternate food (mainly berries and insects) to lemmings with increasing lemming density. The skua surpasses all the other predators in summer by its total response. The type III functional response of the Arctic fox (Alopex lagopus ) starts to increase at much lower lemming densities than the responses of the avian predators, but it has only a weak numerical response. Finally, the stoat (Mustela erminea) is the most specialized predator and the only one with a clearly delayed numerical response. According to their specific functional and numerical responses, each predator plays a key role at some point of the lemming cycle, but only the stoat has the potential to drive the lemming cycle. Stoat predation is greatly reduced in the winter preceding the lemming peak, and it reaches a maximum in the winter preceding the lowest lemming summer density. Stoat predation appears to maintain low lemming densities for at least two successive years. Our study provides empirical support for the specialist predator hypothesis about small mammal population cycles