Girton Birdwatch - October 2011
I picked up a second-hand copy of Simon Barnes's book 'How to be Wild' a few months ago. The theme of the book is his belief that humans have a 'soul-deep' need for non-human forms of life. In its pages he explores what he believes is an essential truth: that by enjoying the wild world, and by trying to understand it, our own lives become that much richer and satisfying. In Chapter 5 he hears, and turns to contemplate, a bird with which we all are familiar: the lapwing, which is now 'promoted to the status of Special Bird. Once a bird you mostly ignored, for, like the 49 bus, you knew there'd be another one along in a minute. Now a bird that lifts the heart. That's one of the triumphs of human life: to take an everyday bird and turn it into a living national treasure. As if love can only ever be too late'.
I was reminded of this observation when reading a newspaper article by Stephen Moss, himself a man with a deep and abiding passion for the natural world. Moss was writing about another familiar, 'everyday', bird: the great tit, and lamenting the fact that like the house sparrow (and lapwing), it's a bird which tends to be overlooked or ignored until it's in trouble. We see it virtually every day but don't register it; it's not exotic or rare or unusual. However, Moss urges us to take another look at the great tit: 'If you had never seen one before, imagine how you would react to the appearance of this black-and-yellow vision on your garden bird feeder. Look closer at the charcoal-black head, contrasting with those snow-white cheeks; the broad black stripe down the chest, bisecting two patches of custard-yellow; and that rich moss-green shade on the bird's back. Absolutely stunning.'
Moss was driven to eulogise the great tit because it's in trouble. It had made the news because one unfortunate bird had been eaten alive by a carnivorous pitcher plant, then suffered the indignity of being wrongly identified as a blue tit (another lovely bird often taken for granted). More disturbingly, in the greater scheme of things, are the reports that great tits are suffering from avian pox, a new and virulent disease that appears to be sweeping through our garden birds at a worryingly rapid rate. So if you are missing some of your regular visitors - and despite the fact that many garden birds are still out in the fields taking advantage of the autumn bounty - this may be part of the reason.
The potential fate of the great tit sent me hurrying to a 'bible' of mine: Cocker & Mabey's 'Birds Britannica', a source of fascinating detail on most British birds. Writing of happier times, Cocker & Mabey make reference to the great tit's adaptability and flexibility in explaining its widespread geographical distribution. One reason for its success is its vocal repertoire; in a single great-tit population the birds will employ an average of 40 different song types in a year. This, it has been argued, allows the great tit to give the impression that his territory is more densely occupied than it is, thereby discouraging competition. Not everyone accepts this hypothesis in its entirety, but there does seem to be strong evidence to suggest that great tits with large vocabularies are socially dominant and breed more successfully.
Another key to the pecking order is the thickness of the black stripe down the centre of the great tit's under parts. In females it narrows and then stops on the lower belly but in males, which are larger and dominant, it spreads as a black patch right to the undertail coverts. As well as this visual 'flag', size is also critical to the great tit hierarchy, but Cocker & Mabey point to recent research which indicates unexpected developments in this variable feature. Apparently, during the period when the sparrowhawk, the tit's main predator, was suffering from pesticide poisoning, the most dominant great tits were also the heaviest. However with the hawk's recovery, the fatter birds were the most susceptible to predation and the impact was for dominant birds to lose excess weight and to rely on their social ascendancy to secure access to food resources. They are quite literally the fittest to survive. Subordinate great tits, which may be excluded from food in periods of shortage, are obliged to carry energy reserves for just such hard times and thus are more vulnerable to sparrowhawk attacks. The overall flexibility in the bird's response to this renewed challenge meant that its numbers didn't decline despite the recent dramatic increase in the sparrowhawk population. And then along comes avian pox. We should keep our fingers crossed and attend even more scrupulously to our feeder hygiene.