Autor:
Tytuł:
Changes in the house sparrow population in Britain
Tytuł publikacji grupowej:
Temat i słowa kluczowe:
wróblowe ; ornitologia ; Wielka Brytania
Abstract:
The number of House Sparrows has declined markedly in mid-latitude western Europe in the last 25-30 years. This was first noticed in Britain in farmland about 1979, though after a fall of about 60% the population appears to have stabilised at this lower level. It is now generally accepted that this decline was a consequence of reduction in the availability of food resulting from intensification of agricultural practices. ; There has also been a reduction in built-up areas, though it is considered that, with little interchange between the two populations, the two declines are not directly related. The urban decline did not become obvious until about 1990, where in the centres of some large towns the decline, unlike that in farmland, took place at an increasing rate leading to virtual extinction. Closer examination shows that the situation in the built-up areas is far from uniform, with a similar decline to that in the urban centres occurring in the so-called "leafy affluent suburbs", but any decline being much less pronounced in the inner residential areas and modern housing estates. ; The main cause of the urban decline is again reduced availability of food, but here compounded by reduced availability of nesting sites and increased predation by cats and Sparrowhawks, with these factors having differing impacts in the different built-up habitat types. The House Sparrow is a social species, breeding in loose colonies, which depend on social stimulation for successful breeding. ; It is suggested that, when the colony size falls below a certain level, the birds cease to breed because of the lack of social stimulation and the colony collapses (the "Allee Effect"). This stage has been reached in the centres of some large towns, where lack of nesting sites has been the critical factor, and in the "lafy suburbs", where the separation of the buildings on which the birds prefer to nest leads more rapidly to lack of social stimulation than in the case of the other residential areas where the houses are much closer together. Any decrease in these latter areas has occurred though an increased spacing of the colonies rather than by a decrease in colony size.
Wydawca:
Zielona Góra: University of Zielona Góra, Institute of Biotechnology & Environmental
Data wydania:
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Źródło:
International Studies on Sparrows, vol. 30