| Season
phenology: |
average |
|
|
Weather conditions: |
| The summer was wet and slightly cooler than usual. Mean air temperature for the summer period was +12.9°Ñ. The period from 30 June - 7 July was the hottest, with mean daily air temperatures +21.8°C on 3 July, +22.2°C on 4 July, and the record high value, +29.4°C, on 4 July. The lowest temperature (+0.1°C) was recorded on 12 July, when snow-fall occurred, and a 3-5 cm thick snow layer lasted for a period of over 24 hours at an altitude of above 150 m a.s.l. The total amount of precipitation was 99.8 mm, of which 9.74 mm were recorded on 24 July. Thunderstorms occurred on 4 days. High precipitation resulted in increased water level in the river in the period from 28 July to 5-6 August, and the freezing-over of the river in autumn occurred at a water level 1-2 m higher than normal. Windy days were rare, and the highest wind speed, 15 m/s, was recorded on 13 July. |
|
| Rodents abundance evaluation: |
average |
|
Breeding conditions:
|
Observations were carried out from 13 June to 25 July in the mouth of the Merku River, and from 26 July to 4 August in the course of rafting down the Kotuikan River to its confluence with the Iliya River. The total surveyed area was ca. 700 km2. The river was mostly running in canyons, incising the plateau of varying ruggedness with altitudes of 120-627 m a.s.l. Two vegetation belts, forest (up to 450-480 m a.s.l.) and mountain tundra, were at some places separated by a narrow belt of sparse forest. Forest was mainly represented by larch stands with dwarf shrubs and lichens with canopy projection 0.2-0.5. Herb-moss-dryad tundra was dominent on limestone plateaus, and mountain tops were occupied by desert-like landscapes with lichens and sparse herbs. Steep, almost bare slopes with stony tallus stretched from mountain tops to foothills. Shrub communities were found as a narrow riparian stripe in floodplain. Mires were represented on the terraces of the Kotuikan and Vyurbyur rivers, on small areas with the total size <10 km2. Lakes were very rare, and were situated only on fragments of the river terrace.
Arctic Foxes do not stay in this area permanently, and we did not observe them, but found some old tracks and fragments of carcasses. Fresh tracks of Wolves were seen almost daily, and one animal was seen outside of the study area, in the mouth of the Kotuikan River. The presence of Wolverine and Ermine was recorded.
Avian predators were rare. We did not record skuas, and very few Herring Gulls were observed. Judging by food remains in nests the diet of Rough-legged Buzzards included primarily Northern Pikas, small passerine birds, and juvenile Hares. The density of nesting buzzards was 6 pairs per 200 km2, or 1 pair/10 km of the Kotuikan River canyon. Each of two Buzzard nests found in inaccessible places contained 3 chicks. Nesting of Rough-legged Buzzards was probably successful. A nest of Gyrfalcons with 4 fledglings contained numerous remains of Willow Grouse, which contrasted with the absence of our observations of the latter species. Merlins bred and a pair of Ospreys nested in the Chuostakh River mouth, but we did not examine the nests of these species.
In total 45 bird species were recorded in the study area, including 24 confirmed and 8 presumed breeders. Composition of bird fauna is a more northern boreal than an Arctic one, with a number of breeding species typical for taiga (the Siberian Jay, Capercaillie, Common Sandpiper, Osprey). At the same time, a nesting pair of Pacific Golden Plovers was recorded on the mountain plateau. Noteworthy is presumed breeding of the Bohemian Waxwing, White-winged Crossbill, Spotted Redshank, Brambling, and observations of several House Martin colonies in a natural environment. Almost all species occurred at low densities, with the exception of the Willow Warbler, Arctic Warbler and Common Redpoll in the forest, and Wheatear in mountain tundra. Several common northern species were not recorded, including the Lapland Bunting, Shorelark and skuas. Waterfowl were common only on migration. Among waders Common Sandpipers and Grey-rumped Tattlers were recorded most often. The Arctic Tern was the most abundant species in river floodplain, and wandering Little Gulls were common downstream of the Emyakhsin-Yurykh River.
Hatching was recorded on 4 July in Common Sandpiper and Arctic Tern, on 8 July in Dusky Thrush, on 20 July in Black-throated Diver. Juveniles fledged on 4 July in White Wagtail, on 8 July in Common Redpoll and Little Bunting, and on 9-10 July in Willow Warbler, on ca. 14 July in Gyrfalcon, on 3 August in Rough-legged Buzzard.
Information on breeding success is scarce due to the small number of monitored nests (less than 20) and end of studies before fledging in most species. Loss of eggs and chicks was not recorded in monitored nests of the Black-throated Diver, Rough-legged Buzzard, Gyrfalcon, Common Sandpiper, Ruff, Arctic Tern, House Martin, Dusky Thrush, and Little Bunting. However, some broods, particularly in the mountains, could have been lost during the adverse weather period on 9-15 July. Chicks or fledglings were recorded in several species of birds: the Red-breasted Merganser, Capercaillie, Grey-rumped Tattler, White Wagtail, Siberian Jay and Willow Warbler. |
|