Sparrowhawk

“Sparrowhawks, Ma’am”. This is the answer supposedly given by the Duke of Wellington to Queen Victoria when the latter asked for advice as to what to do about the sparrows flying inside the vast glass pavilion built for the 1851 Great Exhibition. Several large trees had been enclosed within the covered arena, and the birds in the trees were causing a nuisance with their droppings. Clearly, letting off shotguns inside a glass structure was not a good idea, hence the question to the elderly Duke, who lived nearby.

Whether or not the story is true, and there is some doubt about it, the remedy would certainly have worked. If a sparrowhawk appears in my own neighbourhood, all other birds disappear from view and all birdsong ceases. For virtually any garden bird from the size of a woodpigeon downwards, the sparrowhawk is the most feared airborne predator they are likely to encounter.

Appearance

Sparrowhawks, at 28 to 38 centimetres (11 to 15 inches) in length are not all that large when compared to many other British birds of prey. However, the size range cited above is due to the females being much larger than the males, and therefore likely to challenge larger birds as prey.

The plumage of male birds is grey or brown above and whitish with orange-brown barring below. They also have orange-brown patches behind the eyes. Females lack much of this colouring, their underparts being mostly white and grey. The tails of both sexes are long and square, with dark grey banding.

Behaviour

Sparrowhawks are woodland birds, either coniferous or mixed, although they hunt beyond the confines of the trees. As with most hunters, be they birds or animals, they will always go for the prey that takes least effort to catch, so smaller birds that are old, young or sick are in most danger. Indeed, it is estimated that, during the summer, around 40% of their prey consists of birds that have only recently fledged.

The advantage of woodland hunting is that the sparrowhawk can take prey by surprise after a short pursuit between the trees. Once a bird is aware that it is a target it has about three seconds to escape, after which the sparrowhawk will be forced to abandon the chase. The chances are generally in favour of the target, as only one in ten chases results in a kill.

Breeding

Although sparrowhawks breed and winter in the UK, many birds disperse from their breeding grounds in winter, only returning in March or April. Males are the first to arrive, with the females following later. It is common for pairs to select two trees, one for the nest and the other as a resting and feeding place. The latter tree can often be identified by the food pellets at its base composed of undigested food that has been regurgitated.

In the nest, formed of twigs lined with hair, up to six eggs will be laid that are incubated by the female for up to 32 days while the male brings food to her. Incubation is timed so that the eggs will hatch at intervals, so that the chicks will be of different sizes in the nest. This must be some sort of insurance policy, because it is common for the larger chicks to eat the smaller ones if there is insufficient food being brought to them.

At first, the male bird hunts for the whole family, plucking the prey clean of feathers at the “feeding tree” before handing it to the female who will then take her share and pass smaller pieces to the chicks. After about a week, the female will also hunt, and later still the male will take food directly to the chicks when they are able to tear it for themselves. After about 30 days the young are able to hunt for themselves.

Conservation

The question has been raised as to whether sparrowhawks are a good or bad thing as far as local bird populations are concerned. As mentioned above, healthy adult birds only form a small proportion of their food, and it must also be remembered that a pair of birds will hunt over an area up to five kilometres in diameter. It can therefore be seen as a sign of a healthy bird population if there are sparrowhawks around; if they could not sustain themselves they would not be there.

Another factor that has affected sparrowhawk populations in recent years has been the use of farmland pesticides that have accumulated in the birds and caused problems such as the thinning of eggshells which reduces their chance of hatching.

Sparrowhawks are not long-lived, and only half the broods are likely to result in chicks maturing to adulthood. Although the RSPB (Royal Society for the Protection of Birds) does not regard the sparrowhawk as a threatened species, it is important that it has legal protection. However, it is food supply that will determine the success of the species in a particular area.

© John Welford