Sparrowhawks and songbirds
It is a misconception that sparrowhawks control the number of songbirds.
Concerns about sparrowhawks
Some people are worried that sparrowhawks eat too many small birds and cause their population to fall or even become extinct. This is unlikely to happen, since the hawks take mainly the most common species, and since they would starve to death before a significant drop in overall prey numbers. Small birds can rear between five and 15 young in a season, while only one or two need to survive to keep the population stable. The vast majority die before the following breeding season: of starvation, illness or injuries.
So sparrowhawks may alter the way in which birds die, and perhaps also the seasonal pattern of mortality, but not the overall number that die.
The Breeding Bird Survey for 2006 showed that the UK sparrowhawk population declined by 1 per cent between 1994-2006, whereas common prey actually increased in numbers: blackbirds by 18 per cent, robins by 18 per cent, great tits by 54 per cent, collared doves by 39per cent and song thrush by 17 per cent.
Deterring sparrowhawks from your garden does not stop them hunting, but will simply move the action elsewhere. Consequently, using deterrents is entirely for human benefit- it will make no difference whatsoever to the birds. Rather than deter them, try to learn to admire the skill and beauty of this very specialised hunter.
* From Sparrowhawks and songbirds, RSPB Birds, Summer 1997 (Newton, I and Perrins, C)