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Farm and Woodland Bird Declines and the
Re-colonisation of Britain by Sparrowhawks
by Dr Chris Bell

Dr Chris Bell
The decline of birds on British farmland over the past 40 years is both a wildlife catastrophe and something of a scientific mystery. Numbers have halved since the late 1970s, and the finger of blame has been pointed firmly at farming and the intensification of agriculture, leading to the widespread implementation, since the 1990s, of agri-environment schemes. However, despite copious funding for research on farmland bird declines, these schemes have failed deliver the promised recovery in bird populations, and the government’s Farmland Bird Indicator continues to flatline, as it has for almost 20 years. The knee-jerk response is again to blame the farming community for failing to implement these schemes properly, but there is another seldom discussed possibility, which is that the scientists have been looking in the wrong place. 
House Sparrow

One of the best studied species has been the House Sparrow, and great effort has been expended in the attempt to link its decline with disappearing stubble fields and the spread of secure grain silos. But changes in farming techniques can’t explain the equally sharp decline among urban house sparrows, which has until recently been a media cause célèbre. Lack of insect food for nestlings has been proposed as an alternative explanation for urban sparrow declines, but studies such as the RSPB’s London Sparrow Feeding Project and London Sparrow Parks Project, which were designed to substantiate this idea, have failed to produce any convincing evidence in its favour.
A much more likely explanation for the decline in urban sparrows through the 1990s was the unprecedented influx of Sparrowhawks into towns and cities over the same period, following their recovery from the adverse effects of widespread organochlorine-based pesticide usage. 

I decided to test this theory, using data from the British Trust for Ornithology’s (BTO) Garden Bird Feeding Survey, and the results proved to be compelling. Throughout Britain, House Sparrows began to decline just after the re-appearance of Sparrowhawks in their locality, with populations remaining stable wherever the hawks remained absent. So if Sparrowhawks appeared at a site in the mid-1970s, that’s when sparrows would go south. If at another site the hawks’ appearance was delayed until the mid-1990s, then so would be the beginning of sparrow decline.
So if Sparrowhawks are responsible for the decline of garden-dwelling sparrows, the question naturally arises, what about sparrows and other birds in the wider countryside? The data required to answer this question may exist in the form of the BTO’s Common Birds Census scheme which ran from 1962 to 2000, but despite approaching research institutes and university departments across the country I’ve been unable to find a partner with whom to implement such a project.
Now, however, SongBird Survival has stepped into the breach by providing the sponsorship needed to access the BTO’s data and carry out the study. Analyses are currently underway, and early indications are that the study will produce some fascinating and important results.   
Graph Showing decline in House Sparrows
Graph showing Increase in Sparrowhawks

Related Research
House Sparrow
The role of the Sparrowhawk in the decline of the House Sparrow 2010
Dr. Christopher Bell and a team from Cambridge University conducted this study which analysed data from the British Trust for Ornithology (BTO). It clearly shows that the decline in the house sparrow has been driven by intense predation pressure from resurgent sparrowhawk populations in both rural and urban environments.


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Corvid Research Project
Corvid Breeding Biology
Keith Duckworth Project - Gardens for birds

SongBird Survival is a charity commissioning research into the decline of Britain’s songbirds. With your support and membership we hope to reverse their decline. 
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