Sparrowhawk

A top predator

Juvenile sparrowhawk
The very close and sensitive link between sparrowhawks and their prey makes the hawks a monitor of the health of the ecosystem.

As a top predator, sparrowhawks can only thrive if their prey - in this case songbirds - is present in good numbers and has a healthy population.

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 - long-term scientific studies have shown that sparrowhawks have no impact on overall songbird populations.

A number of studies found that songbirds were no more common when sparrowhawks were absent  than when they were numerous. The sparrowhawk population was decimated by pesticides entering the food chain in the 1960s and 70s and songbirds numbers remained the same in the hawks' absence.

It is also worth remembering that sparrowhawks and songbirds have existed side by side for thousands of years without any detrimental effect occurring on the populations of the songbirds.

Balancing act

The number of sparrowhawks in an area is naturally rectricted by food availability and the number of suitable nesting sites. If songbird numbers increase, sparrowhawk numbers increase. If songbird numbers go down, so do sparrowhawk numbers. 

This very close and sensitive link between sparrowhawks and their prey make the hawks a monitor of the health of the ecosystem. The very presence of sparrowhawks is evidence of a healthy environment with strong populations of songbirds.

A natural surplus

Small birds can rear between five and 15 young in a season. 

In the absence of predation by predators such as sparrowhawks, the vast majority of these would die anyway, of starvation or disease. The reason that small birds raise so many young is precisely because so many will die. 

Only one or two young birds need to survive in order to maintain the numbers of that species and keep the population stable. They couldn't all survive to breed because there aren't enough nest holes, caterpillars or territories to support such numbers.

Sparrowhawks also take mainly the most common species that have large populations, able to withstand losses.

Survival of the fittest

Sparrowhawks remove the most vulnerable individuals, so those with the best escape tactics survive. This brings immense stability to the system, as the fittest and healthiest individuals survive. These are much more likely to breed successfully themselves and produce a greater number of fitter young birds that have a better chance of survival.

If habitat is diverse and contains plenty of food and cover for small birds, the balance is tipped further in favour of the prey. In contrast, reducing the quality of the habitat can make songbirds more vulnerable to predation from predators such as sparrowhawks. 

The sparrowhawk has no serious predators itself, although its chicks and fledglings are taken by pine martens and goshawks. Both of these are scarce in the UK.

Versatile hunters

The female takes prey up to wood pigeon size, but the smaller male doesn't catch anything bigger than the mistle thrush.

Sparrowhawks employ many hunting techniques, depending on the habitat and prey. They are not built for stamina and long chases, so they have to be able to approach their prey closely and undetected to have any chance of success. The usual flying speed is 30-40 kph, but a sparrowhawk is capable of up to 50 kph in short bursts.

Once they have been spotted by their prey, sparrowhawks only have about three seconds to grab the prey before it escapes. Because the hawk is quite easily seen, and small birds warn others to fly for cover with calls, only about one attack in ten results in capture.

Last modified: 03 July 2006

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