The difference in size between the two genders referred to above is quite marked, with females being about 25% larger than males.
Jackdaws have very rarely been recorded as prey although females often take largish birds like collared doves. More commonly,
the victims are smaller, including a wide range of songbirds.
Sparrowhawks were virtually extinct in southern and eastern England when I first began to take an interest in birds in the
early 1970s. Scientists at the Nature Conservancy, including two people I was later privileged to work with, Norman Moore and
Derek Ratcliffe, discovered why. Persistent agricultural poisons like DDT and dieldrin were once used as seed dressings and were
therefore ingested into the bodies of seed-eating birds. Birds of prey that specialised in hunting other birds – like peregrine
and sparrowhawk – thus suffered from a massive accumulation of these toxins. This either killed the adult birds or prevented
them from breeding successfully. After Ratcliffe and Moore had proved the link between DDT and the collapse of breeding
populations of raptors, DDT was eventually banned in Britain (although it is still widely used in many parts of the world).
When the ban began to take effect, numbers of sparrowhawks and peregrines rose rapidly.
If those people are right who maintain that sparrowhawks have an adverse effect on songbird numbers, then the absence of
sparrowhawks for 20 years or so should have resulted in an expansion in the numbers of blackbirds, song thrushes and other
birds. It did not, of course: no predator has such an effect on its prey. The birds which sparrowhawks kill would otherwise
die of other causes like starvation or hypothermia.
Sparrowhawks do now breed again in Kingston, though perhaps only one or two pairs. Many people will have seen them in the
gardens, often perhaps carrying off a hapless greenfinch, robin or blackbird. But pity for the victims is really misplaced:
sparrowhawks - and their chicks - must eat too!
I’d be interested to hear from others with experience of sparrowhawk kills or perhaps even have these birds nesting in their
garden or nearby. Although nests are often made high up in trees, they have also been recorded in low bushes.
If I were a serious chronicler of the parish birds, I would know approximately how many pairs of house martins nest in the
village each year and whether numbers fluctuate very much. I would also know whether their arrival dates are subject to much
variation. Alas, I have failed on all counts! My impression, though, is that there may be fewer pairs now than when I moved
here in 1994. Has anyone any evidence one way or the other?
House martins seem to resemble cats in that they often go where they are unwelcome! Conversely, people like me who would love
martins to nest on their houses are rarely so favoured. They may make a bit of mess on a temporary basis but surely more than
pay their keep by consuming vast numbers of aphids and providing entertainment for most of the daylight hours from May to as
late as October. House martins often produce two broods, so even if only a handful of pairs settles here in the spring, the
numbers setting off in the autumn for the journey to Africa can be quite substantial.
Where did martins nest before there were houses and bridges? Presumably on cliffs, although this would suggest a much smaller
population than there is now. There are reckoned to be about 500,000 pairs nesting in Britain each year.