Wednesday, December 20, 2006

Are we giving songbirds their last supper? (Bird Feeders)

A 1992 study published in the American periodical Virginia Wildlife concluded that the state's one million domestic and feral cats kill up to 26 million birds a year. Fifty-five million are killed annually by eight million pet cats in Britain. Feeders attract birds into the cat's domain. Thus, the argument goes, feeding exposes birds to the risk of an untimely death.

Wherever birds of a feather flock together, disease is also likely. Salmonella, trichomoniasis, aspergillosis and avian pox are all associated with garden birds. All are transmitted through close contact, or food and water contaminated with faeces or bodily fluids. Hence, feeders have been implicated in their spread. Another killer, mycoplasmal conjunctivitis, reached epidemic proportions in eastern North America’s house finch population after it was identified in 1994. House finches visit feeders often.

Apparently, though, the biggest killer of garden birds is invisible. In a 1992 Cornell Laboratory study into mortality, 51 per cent of deaths resulted from birds flying into windows. Garden birds startle easily, and in the city, glass is rarely far away. A 1993 report summarizing public observations estimated up to 10 birds are killed annually for every building in North America.

These figures have been used by critics to suggest there is a strong ecological case for discouraging feeding. Yet, evidence that bird populations are seriously depleted by deaths attributable to feeders is lacking. Indeed, research has suggested that the risk of death from predation and disease is no greater in the presence of feeders than it is elsewhere. Conservation organizations advocate covering windows close to feeders, or placing feeders away from buildings and roads. If limiting deaths from this cause is that easy, depriving birds might be counter-productive.

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