Decline of the House Sparrow
and other small garden birds
Observations from 1947 - 2000
compiled by: David Cottrell & Mary Hodgson
INTRODUCTION
We contend that the drastic decline in the house-sparrow population must be considered together with the decline in small songbird populations. While it might be simplistic to attribute these declines to one single cause we feel strongly that there is one major cause, namely the rising number of sparrowhawks and a change in their nesting practices, brought about by the increasing urbanisation of rural areas.
Formerly the sparrowhawk nested in woodland or forest where it found its prey. In any natural situation the relative numbers of predators and prey are controlled by the availability of prey and attacks on predators by other predators. Sparrowhawks have virtually no enemies, their numbers in the past being reduced by gamekeepers and farmers if they got out of control.
After the catastrophic effect of organochlorine pesticides was discovered in the fifties, sparrowhawks were put on the protected list and their numbers subsequently increased. At the same time massive post-war housing projects were underway. Farmland, woodland and open countryside disappeared under new housing estates, thus depriving an increasing sparrowhawk population of some of their possible nesting sites.
The network of small gardens on a housing estate, where bird-lovers attract birds by feeding them and providing nesting-boxes, can often support a larger number of small birds (the so called 'garden' birds and songbirds) than the same area did previously. This provides a wealth of prey for raptors.
Most modern urban planners try to preserve small woodland and other open areas in and around new housing estates. These areas, while not being widespread woodland, can provide a considerable number of nesting sites for sparrowhawks. Trees bordering commuter railway lines can also offer such sites.
Sparrowhawks breed in the spring as do song and other garden birds. The hen, larger than the cock, can deal with birds up to pigeon size, but when she is sitting on the eggs the cock has to do all the hunting. He can only carry smaller birds and over a limited area, so to nest in or near an area rich in small bird prey is an obvious choice.
The following pages offer local detail to support our contention but we can say here in the past it was very rare for sparrowhawks to attack pigeons in the vicinity of their lofts in urbanised areas. Since about 1993, however, these attacks have become all over the country. This suggests that as sparrowhawk numbers returned to and finally surpassed their previous levels, during which time increased urbanisation deprived them of old woodland nesting sites, they found the new food source available in housing estate gardens and moved in to nest within its reach.
This concentrated predation on small birds at their own breeding time must seriously affect their future population. Each bird taken means a potential breeding loss for the victims, plus possible loss of small chicks deprived of parents. The three small birds needed daily to feed one adult sparrowhawk must be doubled for the pair, and multiplied by an unknown factor of loss in potential breeding and replacement.
In the short term, this loss of local birds could be made up later by surviving birds outside the area coming in to fill the gap when the sparrowhawks have departed.
Until lately, local residents have reported the reappearance of e.g. sparrows around August-September time. Recently there has been no reappearance. In inner cities and big conurbations, where the disappearance of the house-sparrow is causing such concern, there is rarely such a peripheral environment to draw on.
The behaviour of small birds in the estates has also changed. They no longer sit out in the open but stay under cover or very close to the shelter of hedges and shrubs. This indicates an awareness of predator activity. Such restricted movements also restrict their feeding area. Starlings are the exception, still feeding in the open because they rely on the safety of being in a flock, and also being mostly too big for the cock bird to carry.
Sparrowhawks have not only recovered their numbers but have increased enormously. In 1986 Newton gave their numbers as 32,000 pairs, with probably an equal number of single birds. He also said they were now at capacity levels as permitted by habitat and food supply, occupying all possible breeding sites in the country. However, according to the Report of the Raptor Working Party their numbers have risen to at least 34,000 pairs, which we feel may be an understatement.
We contend that predation by sparrowhawks is one major factor in both the disappearance of the house-sparrow and the current fast-disappearance of small garden birds and songbirds which is not currently recognised.