Michael Walter's latest report:
One of my abiding memories, growing up in the suburbs of London, is the regular “crack crack” sound of a song thrush smashing snail shells on a favoured anvil in our back garden. This behaviour has becomeincreasingly unfamiliar to succeeding generations as the bird grew scarcer, and it is nearly 18 months since I last saw one in my present garden. The finger of blame has been pointed at the intensification of farming methods, the use of chemicals to kill slugs and snails in gardens, and drier summers when the birds are unable to extract earthworms from hardened soil; but the truth is that we don’t really know why a once abundant species should have dwindled away to such an extent. Surprisingly, on the reserve’s monitored plot there has been no consistent downward trend, but numbers have fluctuated fairly wildly between five and 27 pairs. This spring’s total of 23 singing males was in fact the second highest count, which might be cause for optimism, were it not for the fact that, givenits past erratic record, song thrush numbers could quite easily be down to an-time low next year. The nuthatch has ploughed a slightly different furrow: having enjoyed a faltering recovery after the almost total collapse of the population fifteen years ago, this spring we were back down to a dispiriting ten pairs after fifteen in the previous two years. As there is nothing that we can do in the short term to improve the habitat for these engaging little birds, we can only sit tight, hoping that the current slump is just a blip in what is really a continuing upward trend.
An interesting record supplied by a visitor recently was of a Norfolk hawker dragonfly. Until very recently this was an extremely rare species restricted to the Broads in, yes, you’ve guessed it, Norfolk. For reasons that are poorly understood, a species will occasionally expand rapidly out of an area to which it has been restricted for hundreds of years, suddenly colonising completely new swathes of territory, as happened with the collared dove in its dramatic explosion westwards from Turkey in the 1940s and 1950s. Some change in the climate, habitat or even the dragonfly’s behaviour, has enabled it to abandon the confines of the Norfolk Broads and colonise marshes along the north Kent coast in the past five years. Nevertheless, it seems remarkable that a female should have turned up in Blean Woods, with negligible suitable habitat, but the person who identified the insect may well have been witnessing an important element of the dragonfly’s ability to expand its range – namely a willingness to fly over miles of unsuitable habitat in search of an area that will meet all its ecological needs. My guess, therefore, is that this particular individual has long since moved on, or simply died in its quest for pastures new.
After a disappointing spring for humans and wildlife alike, the early summer is proving very lacklustre for butterflies. With a peak count of just 230 in late June, the heath fritillary had its worst season for twelve years. Recent management at one small site has produced easily the best area of cow-wheat on the reserve, but it may have come too late, as I never saw more than three individuals there this spring. All hinges on successful breeding and a healthy survival rate for their vulnerable caterpillars. If that is the case, then there could be plenty of butterflies next summer to strengthen its population at that site; if, however, all the butterflies I saw were males, or if most of the larvae are eaten by predators, this particular patch could just as easily see its heath fritillary population extinguished, despite having the potential to become the largest colony in the whole wood. The colony is on a knife edge, and I shan’t know which way the pendulum has swung until this time next year.
Below is a photo of a Norfolk hawker taken by Mark Chidwick, as mentioned above: