Wednesday, 28 April 2010

Sparrowhawks: The Truth

I'm indebted to Beleaguered Bryan for passing on this titbit:

Sparrowhawk Blitz Caused Sparrow Plunge

Newly published research provides compelling evidence that the decline of House Sparrows in Britain has been caused by intense predation pressure from resurgent Sparrowhawk populations.

Sparrowhawks were wiped out over much of Britain in the 1950s because of the effects of organochlorine pesticides, but since these were banned in the 1970s the number of Sparrowhawks has quadrupled, and they started to colonise cities for the first time in the 1980s. Urban sparrows were easily picked off because of their bold behaviour, which had developed in the absence of a significant threat from an aerial predator.

Dr Christopher Bell, who led the research, said “The study shows that variation in the timing of the disappearance of Sparrows from gardens across Britain can be explained by variation in the year that Sparrowhawks began to be seen hunting birds in the same gardens. This overturns previous assumptions about the effects of predation on bird populations, and exposes flaws in studies apparently showing that Sparrowhawk predation has no effect.“

Several puzzling aspects of Sparrow decline are explained by these results. Urban Sparrows have tended to disappear from the more affluent districts of cities such as London, Bristol and Norwich, while continuing to thrive in less well-off areas, such as large council estates. This is because the affluent parts of cities provide safe nesting places for Sparrowhawks in the large gardens of grand houses, and in private grounds and restricted areas of parkland, whereas no such nesting opportunities occur in poorer districts.

The results also explain why Sparrow decline happened later in the cities than in the countryside. Sparrowhawks re-occupied most of the British countryside during the 1970s, coinciding with the decline of rural Sparrow populations, but only started to move into urban areas in the late 1980s and 1990s, which coincides with urban Sparrow declines.

The study also explains regional variation in the extent of Sparrow decline across Britain. Scottish and Welsh Sparrows experienced a relatively small decrease in numbers, and have since recovered strongly, whereas Sparrow numbers in southern and eastern England have continued to plummet. Meanwhile, Sparrowhawk numbers in Scotland and Wales have been stable for many years, after undergoing a relatively small increase in the 1960s and 70s, but in south and east England Sparrowhawks have undergone a massive increase in numbers, which has continued until quite recently.

The results emerging from this study are potentially embarrassing for organisations involved in Sparrow research and conservation such as the RSPB, which have consistently denied that increasing numbers of Sparrowhawks and other predators can affect populations of wild birds. Instead they have promoted the idea that food shortage caused by changes in agriculture and urban development is behind Sparrow decline, but have found little evidence for this theory despite investment of at least £500,000 in Sparrow research. Conservation organisations have also promoted measures known as ‘agri-environment schemes’ to reverse the supposed effects of agricultural changes on wild birds. Farmers are now required to implement these measures to receive their subsidies under EU legislation, with £½ billion spent on such schemes each year in the UK alone. However, despite the fact that over two-thirds of farmland in England is now managed under agri-environment schemes, bird populations show no signs of recovery, suggesting that predators may be the real reason behind bird declines in the countryside.


Quite so. This is typical of that sinister organisation the RSPB, which won't hear a word against any of our feathered friends. Anyone with a garden could tell them that there have been dramatically fewer songbirds since predators started moving in from the countryside - magpies, jays, crows and raptors. Most of us have seen them at work, taking eggs and killing both adult and juvenile birds - but the RSPB (and others) insist on blaming it all on cats. Sparrowhawks are particularly effective killers, seldom seen until they've struck. The RSPB line has always been that they are misnamed as they rarely if ever attack sparrows. The old Duke of Wellington knew better. When Queen Victoria, concerned at the numbers of sparrows nesting on the partly finished Crystal Palace, asked his advice on how to get rid of them, he replied, 'Sparrowhawks, ma'am'. He was right; when the Palace opened, there was not a sparrow to be seen.

3 comments:

  1. I've watched a peregrine falcon and a Cooper's hawk lunch on sparrows in my tiny city garden. I also suspect the declining numbers of raptors in the past may have had as much to do with hunters as with pesticides.

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