Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 12

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych:  Corvus corone cornix
help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
The study area (16 km2) in "Ujście Warty" National Park, W Poland — was the valley of a lowland river at its confluence with the River Odra, covered by a mosaic of grassy vegetation and willow scrub. 111 breeding attempts were recorded during 2000-2002. The mean nest density (3.2 nests/km2) was higher than that recorded by other authors in agricultural landscapes, but lower than in urban areas. The nest construction was adapted to fit young willow trees. The mean clutch size was similar to that recorded in other populations (4.43), but eggs were smaller (41.2 mm x 29.1 mm). The hatching success was lower (76%) in comparison with other studies, but the mean number of fledglings (2.15 per nest and 2.96 per nest in successful broods) was relatively high. The main reasons for losses were unhatched eggs, predators, starved nestlings and poor nest construction. We hypothesise that the smaller egg size and lower hatching success recorded in this population was due to unfavourable and unpredictable feeding conditions (floods) during the period of egg formation and egg laying. Later in the season, receding floodwaters laid bare areas suitable for foraging on invertebrates; waterfowl eggs also became readily available. Predation was low (lack of nonbreeding stock of Hooded Crow). As a result of good conditions during chick rearing, the overall reproductive output was relatively high in comparison with other populations.
Changes in the numbers of corvids wintering in Warsaw (Central Poland), in the last sixteen years were analyzed. Four species were studied: Rook Corvus frugilegus L., Jackdaw C. monedula L., Hooded Crow C. corone cornix L. and Magpie Pica pica (L.) The results were based on density data for birds foraging in three urban parks. The bird counts were conducted in November and December 1988–2003. It was found that the number of wintering Rooks decreased significantly (0.5 fold), populations of Jackdaws and Hooded Crows – increased (4.25 and 3.95 fold, respectively), and no apparent trends were observed for Magpies during this period. Observed trends for Rooks as well as comparisons of limited data gathered earlier in other areas may confirm suggestions about the changing of migration routes of this species.
11
Artykuł dostępny w postaci pełnego tekstu - kliknij by otworzyć plik
Content available

Ptasie mądrale

44%
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.