| Season phenology: |
average
|
|
|
Weather conditions: |
| Snow melt started in the very end of May according to the weather station data, and June was relatively warm. Mass appearance of broods of waders and passerines in early July indicated favourable weather conditions at the start of breeding by birds. The weather was dry and warm in July, with the exception of the period from 9-14 July when snowfalls occurred daily and air temperatures dropped below freezing at night, which could have affected adversely survival of wader chicks. August was cool and rainy, September was relatively warm with temperatures above freezing on most days.
|
|
| Rodents abundance evaluation: |
low
|
|
|
Breeding conditions:
|
Numbers of Snowy Owls were low, but they occurred in small numbers in all landscape regions at an average summer density 0.21 bird/km (lim 0-1, total transect length=1197.4 km). Density of owls in the study plot (45 km2) halved compared to all previous years and was decreasing from 0.27 bird/km in late June to 0.16 bird/km in late August. The highest density of owls was observed in June - August in the study plot at the center of the island, and in September at the southern plain in the Somnitelnaya River area.
Solitary pairs of Snowy Owls attempted reproduction, but failed due to low abundance of lemmings. Only 7 nest scrapes of in total 122 surveyed across 81 breeding territory in different parts of the island gave some signs of unsuccessful reproduction by owls. It means that lemming numbers were so low even during snow melt that owl males failed to supply females with a minimal amount of food required. Not a single chick was recorded during the whole survey period until 20 September, which indicated complete breeding failure in Snowy Owls on Wrangel Island.
In the study plot Snowy Owls were distributed among breeding territories, and 2 records of territorial conflicts were made. Owls hunted lemmings despite low numbers of the latter. Actively use of alternative food by owls was aided by high numbers of tundra birds, e.g. numerous broods of waders crowding into floodplains of springs in early June. We did not observe intensive hunting of owls on moulting geese, while Snow Buntings were actively taken by owl males, and Long-tailed Skuas also suffered from strong predation pressure by owls. We observed Snowy Owls feeding on carcass of a reindeer taken by wolves, but owls were never recorded on mummified carcasses of reindeers perished during the winter. Owls were observed hunting lemmings on the southern coast in September, although ducks and phalaropes were abundant in the bay.
Numbers of Arctic Foxes were very low everywhere on the island, and reached the lowest value on record since the start of observations in 1990 on the study plot, 0.13 fox/km2. Mean density of on excursions was 0.11 fox/km (range 0-0.26). A decreasing trend in Arctic Fox numbers during the last 3 years was following a similar thend in lemming abundance, as availability of alternative food had no considerable effect on dynamics of island population of Arctic Foxes.
In spite of the low lemming numbers Arctic Foxes bred, and some pairs were successful breeders. Low lemming numbers should have had stronger impact on reproductive effort of territory faithful Arctic Foxes than on nomadic Snowy Owls, but this was not the case. Reproduction of Arctic Foxes in 2005 was probably made possible by high level of mortality in reindeers in February-March, but in spite of the abundance and availability of frozen reindeer carcasses a proportion of Arctic Foxes attempting breeding did not exceed one third of the population surviving winter. Density of breeding pairs was low everywhere and had mean value 0.024 pairs/km (range 0-0.08, n=196 km of counts). Density of dens was 0.02 den/km2 on the study plot, and shortest neighbour distances between dens with broods ranged from 35 to 60 km (n=6). Den occupation generally on the island was 10.5% (n=57), which represents a three-fold decrease compaired with a previous minimum recorded since 1990. Solitary cubs were raised by adult foxes in few pairs, and we expect low numbers of Arctic Foxes in 2006 on the island.
We found 5 Arctic Fox dens dug out by wolves. Wolves and wolverines destroyed 10% (n=50) of Arctic Fox dens during the last 5 years, which indicated a considerable pressure by increasingly abundant predators on fox population.
Solitary Pomarine Skuas were rarely recorded on migration along the island coast, but they were not observed inland during breeding period. Long-tailed Skuas nested everywhere on the island, but a proportion of breeders in the population accessed on the study plot was 74% (n=38). Nesting density was 0.31 pair/km2 in late June. Breeding success was very low in Long-tailed Skuas and we found only 4 broods with fledged chicks in different parts of the island. Given favourable weather conditions low reproductive performance should have been related to low lemming abundance, although normally Long-tailed Skuas breed successfully using alternative food like insects and chicks of waders, and the latter were abundant in 2005. Mass migration of Long-tailed Skuas started earlier than average, and most of them left inland areas by mid August. We observed solitary pairs on the Yuzhnaya Plain in September.
Birds of prey were recorded in different parts of the island since 20 August, and 6 of 7 records were eagles or sea eagles which was probably explained by abundance of reindeer carcasses. BIrds identified with certainty included Gyrfalcon, juvenile Golden Eagle and Bald Eagle.
Brent Geese and most of Common Eiders did not breed, presumably due to absence of breeding Snowy Owls. Common Eiders were common in the inland areas of the island, but we found isolated nests in different parts of the island, while eider colonies in the surveyed territories of owls (n=81) were absent. Among 13 eider nests found 54% were within owl territories, and the rest of them in the vicinity of rivers or springs. Predators, presumably Arctic Foxes, destroyed 11 nests and captured female eiders on 2 nests.
Snow Goose colonies were not found within 81 surveyed territory of Snowy Owls, and geese broods were not recorded on the study plot in the period of mass movement of broods. However, approximately 60 pairs of moulting geese with broods were recorded in the Mamontovaya River valley, 1 brood in the Gusinaya valley and approximately 10 broods in the vicinity of Blossom Cape. Mean brood size was 3.4 goose chick (range 2-5, n=10) in the Mamontovaya River valley. While geese broods in the latter locality could have originated from the main colony in the Tundrovaya River valley (similar movements were recorded in 1985), broods at the Gusinaya River and Blossom Lagoon could not be related to the main colony. Thus, a small number of geese was probably breeding within owl territories and survived to hatching due to low numbers of Acrtic Foxes. A major part of the Snow Goose population bred successfully at the main colony in the Tundrovaya River valley.
Counts of geese with broods were carried out in the fledging period from 4-7 August in the Tundra of Academy, Tundrovaya River valley, at transect 37 km. We recorded 3-4 thousand of geese, and mean brood size at fledging was 3.1 juveniles (range 1-10, n=58). Four remains of geese were found including 1 adult bird and 3 chicks. Chicks which damaged legs did not allow to move normally were recorded in 3 flocks, while normally they did not survive to fledging. No signs of predatory activities by wolves and wolverines were found; Arctic Foxes were very rare and Snowy Owls rare. Thus predation pressure on geese in the brood-rearing period was low.
We observed adult female Polar Bear persueing a flock of geese with broods in the Neizvestnaya River valley, but the outcome of this hunt was not determined due to presence of observers.
|
|