Saturday, 11 December 2010

Sociable sparrows make a welcome return

It is good to see the House Sparrows return to the garden in force. Each morning they arrive from further down the street, a boisterous posse of grey-capped males and chattering females. This chattering becomes all the more evident once the birds have fed, the flock retiring to the thick of next door’s jasmine to indulge in communal banter. ‘Social singing’, as it is known, appears to be an important component of House Sparrow behaviour, its role tied in with social status and flock cohesion.

These are sociable birds and the winter flocks bring together individuals from several local colonies. Many of the youngsters present within these flocks will roost together in thick vegetation, while established pairs often retire to their nest site. Winter flocks of this kind not only provide benefits in the form of greater knowledge of food availability and lower individual risk of predation, but they also serve as the opportunity through which young birds can disperse away from the colony in which they were born.

Cohesion of sparrow society comes from the social hierarchy that is established through plumage and display, and ultimately backed up by force if necessary. In the eyes of a female, the badge which illustrates the suitability (and hence status) of a male is the size of his black bib. The most successful males are those with the biggest bibs and you will see subordinate birds quickly defer to these high-ranking males in many social situations (most notably in access to food, dust bathing opportunities and females).

Our House Sparrows were visitors when we first moved into this house but we lost them soon after, the landscaping of a neighbouring garden removing the cover they favoured and they ceased to venture this far up the street. Now that the vegetation next door has matured, we have seen their return. House Sparrows rarely venture far and for several years it has been frustrating to hear the colony further down the street, knowing they would only rarely reach our garden.

Cover is important for House Sparrows, providing feeding opportunities, protection from predators and a platform for the social singing. Other factors also play a major role in determining House Sparrow numbers, and key changes in the nature of urban landscapes have seen the House Sparrow population effectively halve since the early 1980s. The loss of nest sites, following the introduction of new designs of roofing tile and barge board, coupled with the clearance of scrubby habitats, increased use of pesticides within our gardens and increasing numbers of competitors and predators have all been linked to sparrow decline, even though we have yet to determine which of these is the most important.

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