A Wildlife Tip Sheet from Jacobi Jayne & Company
by ornithologist Chris Mead
Many people see Sparrowhawks as 'garden terrorists'. They watch these powerful birds swoop down to try to catch a tit, a finch or a Robin from a birdfeeder and feel that they are harming the very birds they are trying to help by putting out food.
Whilst this attitude is understandable, it is not the right one to take towards a perfectly natural component of the British wildbird community. By all means help the small birds evade the hawks - and this leaflet tells you how - but we should actually be very pleased to have the hawks coming to our gardens: they show that our wildlife is recovering well from a terrible episode of destruction wrought by modern chemicals.
Sparrowhawks were very badly affected by the poisoning of much of our wildlife 40 years ago through the use of toxic chemicals on farmland. The organo-chlorine compounds - including DDT, Dieldrin and Aldrin - that were designed to kill insect pests had a terrible effect on birds and other organisms high in the food chain. As well as the many direct deaths that resulted, there were awful effects on breeding birds since their metabolism was affected and they laid thin-shelled eggs which failed to hatch. Indeed, many eggs were crushed by the weight of the incubating female. Sparrowhawks were wiped out in large areas of the countryside and a whole generation of country dwellers was raised without Sparrowhawks being a normal component of the bird community. Their return in good numbers to much of the British countryside, and now also to towns, is a triumph for conservation.
The numbers of Sparrowhawks are controlled by the numbers of their prey - and not vice-versa - and they are definitely not responsible for the sad declines of small farmland birds over the last 25 years. It only takes a moment's thought to see that this must be true of a predator that preys only on small birds. As soon as the prey population suffers a decline, the predator's food becomes harder to find - and so the predator suffers long before the prey are wiped out.
Sparrowhawks and BirdfeedersSparrowhawks often work garden birdfeeding areas several times a day and the whirring of wings and alarm calls will alert the Human owner to the hunting foray. However, their hunting in these areas is often unsuccessful since there are usually large numbers of birds around birdfeeders and there is safety in numbers. The concentration of birds may attract the predator but, for it to be successful, it has to get in amongst the birds - each of whom has a pair of eyes. Seldom can the Sparrowhawk get near enough without being seen.
You can reduce a Sparrowhawk's chances of success still further by ensuring your birdfeeders are hung close to substantial cover such as trees and bushes. Low bushes can be clipped so that they cannot conceal a cat ambush and still provide ample cover for birds. Ideally birdfeeders should be placed no more than 18-inches from enveloping cover.
If you cannot place your birdfeeders near cover you can easily provide disruption to the predatory flights of Sparrowhawks. Placing feeders in a wire cage of 2-inch mesh will protect the birds inside because the hawk cannot enter. However, in most instances such an obtrusive structure is not necessary to give the small birds an advantage: instead just poke a few bamboo garden canes, 5 to 6 feet long, into the ground near the feeders to hinder the hawk when it swoops and enable the tits and finches to get away.
Unnatural Advantage?Sparrowhawks are predators that naturally depend on being able to feed on small birds but, of course, the world that the birds are living in around our gardens is severely modified by Human interests. It might be thought, therefore, that our birdfeeders unnaturally attract small birds and give the Sparrowhawks an 'unfair' opportunity. In fact, it is better to think of birdfeeders as being equivalent to the rich pickings that Chaffinches, Great Tits and Blue Tits would find under a Beech tree which has just dropped its mast. In these circumstances the local Sparrowhawk would regularly hunt at the tree to see if there was a lazy or slow bird. In most cases these would be sick or injured individuals that are just that little bit slower off the mark than the fully fit ones. Just because you are providing the food, you need not think that you should provide it in absolute safety from other natural members of the local avifauna!
The Effect on Small Bird PopulationsJust how much influence predators have on the lives of their prey (even in Britain's Man-modified landscape) was revealed in an interesting report published in 1995.
Throughout a long survey Great Tits and other species had been weighed and measured by bird ringers at various locations. This took place all over Britain but, particularly, near Oxford. During this time Sparrowhawks had gradually returned following their demise due to agricultural pesticides. It was therefore possible to compare the typical weights of Great Tits when the Sparrowhawks were not around with the typical weights after they had returned. Remarkably, the Great Tits had allowed their weights to rise when the hawks were not around but, as soon as they came back, their weights went down as they 'went to the gym' and became fitter, sleeker and faster! Throughout all this time the Great Tit populations were fluctuating but seemed not to be influenced by the presence or absence of the hawks in absolute terms.
The Great Tits in the study were often caught at places where there was a super-abundance of food. In some cases there were lots of birdfeeders and food available. In other cases, near Oxford for example, the abundance was entirely natural since it was only in years when there were good crops of beech mast (and in other years food was difficult to find). So the effect was real and not induced by differences in the food supply.
The analysis had concentrated on Great Tits since these birds are often taken by Sparrowhawks. So to be sure the weight change was due to the presence of the hawks, and not some other factor, the weights of Wrens over the same period were also analysed. Wrens are not taken so frequently by Sparrowhawks. Their typical weights had not changed at all.
Perhaps human obesity would quickly disappear if Tigers were introduced to the streets of London - and a fit Human could outstrip them in a sprint!