Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 4

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:  prey availability
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
This paper reviews the ecological advantages and disadvantages of very small body size in Sorex Linnaeus, 1758 shrews living at high latitudes with cold winters. It examines the feeding and foraging habits of small and large shrews in the context of prey supply, location of winter prey sources, territory requirements, habitat exploitation and inter-specific competition. Data on feeding habits and prey availability show that the major costs of small size are a reduction in food niche breadth and prey biomass resulting from restrictions on the type and size of prey eaten, and large territory requirements. Major benefits of small size are the ability to subsist on small, numerous and accessible arthropods with high encounter rates, enabling coexistence with larger congeners and exploitation of low-productivity habitats less suitable for larger earthworm-eating species. Small size, coupled with low per capita food intake, is shown to be of special adaptive value in cold winters when food supply is restricted mostly to small arthropods, and earthworms are few.
An increasing urbanization of habitats in which birds live influences their populations by modifying behaviour, dietary composition, causes of mortality and variables related to breeding. This study aimed to compare breeding periods and productivity among tawny owls, Strix aluco, inhabiting either an urban or an extra-urban area. Studies were conducted in parallel in two locations: central zone of Warsaw – the Polish capital – and the Rogów Forest – ca 70 km west of Warsaw. Number of fledglings and the beginning of the breeding period was assessed by direct observations and listening to calls of juveniles within tawny owl territories. Birds in the urban area were found to start breeding significantly earlier (from 5th February) than those in the extra-urban area (from 17th March). However, the two populations proved to be similarly productive, with 3.2 or 3.4 young per nest on average. The phenomenon of early breeding in city dwelling birds was confirmed in other tawny owl populations as well as other bird species. It can be potentially driven by factors such as higher temperature, artificial light and rich and stable food base.
The trophic ecology of Kuhl's pipistrelle Pipistrellus kuhlii (Kuhl, 1817) was in­vestigated monthly from May to October 1999. Nine insect and two arachnid orders were identified in faeces and classified in 24 different categories. The most frequently occurring prey categories were Culicidae, Lepidoptera, Chironomidae/Ceratopogonidae, Hymenoptera, unidentified Brachycera, Tipulidae and unidentified Coleoptera in de­creasing order. Other categories exhibited seasonal importance, such as the coleopteran Rhizotrogus sp. Prey availability was evaluated monthly using Malaise traps in known feeding areas. Bats preyed selectively through a temporarily changing pattern. Some taxa constituted an important part of the diet and were positively selected either monthly or in most of the months. Many of them were the largest prey featuring in the diet and changes of their relative profitability across time would determine their selec­tion index. The small size of some prey categories as well as P.kuhlii's morphofunctional constraints relative to flight and echolocation could explain their underexploitation or rejection. Our results suggest that P. kuhlii could be regarded as a 'selective op­portunist' species.
In highly seasonal temperate zones climate may cause fluctuations in the accessibility of prey for insectivorous bats. The main objective of this project was to evaluate if these fluctuations can result in resource bottlenecks that affect the body condition of a temperate zone bat — Myotis myotis. Seasonal changes in body condition followed different patterns in Portugal and Germany, which have different climates. In Germany bats use thermally better hibernacula, which allow them to minimize energy expenditure, but because of the longer winters they emerge from hibernation in poorer condition. Except during the hibernation period, food was always abundant in Germany, but the condition of the animals was poor when bad weather constrained foraging, particularly in early spring. In Portugal food was limiting during the long dry summer, and this affected the condition of the animals for several months. The conclusion that food resources can act as a limiting factor is relevant for conservation because, like other bat species, M. myotis forages mostly in agricultural and forestry habitats, and can be affected by practices that accentuate resource bottlenecks. Where necessary, the management of agroecosystems near colonies of M. myotis and of other threatened bats should aim at minimizing seasonal food bottlenecks.
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.