Nature or nurture: which keeps birds in the best of health?


ANOTHER LIFE: THE BIRDS SEEM to take turns to show off. First the dawn solos of thrush and blackbird, then the chorusing sparrows and tits; now chaffinches take the stage. Mornings ring to the cock’s assertive trill from the big sycamore, with that piercing hiccup at the end.

An unmated cock can keep this up six times a minute, but ours seems more readily hushed. A brief performance to bring a female near, a bit of quiet display – he flashes his white wing epaulettes and turns sideways to show off his figure; she tweets and fluffs her feathers – and the pair are off on a mad sexual chase, whizzing like rockets between the trees.

If it’s not cock chaffinches squabbling at the nuts, it’s goldfinches, which have brought such heraldic colour to the feeders. Both sexes of goldfinch share the same plumage, but the male is bigger and has the brighter red Venetian mask.

There’s another, important difference between the two kinds of finch. Chaffinches, along with bramblings, are in the subfamily of fringillines – finches that rear their young on insects and defend big feeding territories, spreading themselves across the habitat.

Goldfinches, greenfinches and siskins, among others, are carduelines that feed their young mainly on seeds and that nest in loose colonies.

Siskins arrive with us on sudden forays from the conifer forest over the hill and seem to leave us as abruptly. But greenfinches: there’s a sad thing. It’s weeks since we’ve seen one – this in a garden that once welcomed flocks of them and their regular annual colony nesting in the hedges. When readers complain that a particular bird has vanished from their gardens, I routinely counsel patience. But the greenfinch, as most bird-lovers know by now, has been singularly prone to disaster.

Trichomonosis (sometimes trichomoniasis) is caused by a parasitic micro-organism, trichomonad, that swells the bird’s gullet, making it hard to swallow food. It struck first in these islands in 2005, mainly in greenfinches, and has since reduced the UK population – probably ours, too – by more than a third, Transmitted beak to beak in feeding, or picked up from messy bird tables or the droppings underneath, it also took hold in chaffinches, among them winter migrants that took it back to Scandinavia.

Something else, still mysterious, has produced it in the US. There, too, an epidemic of conjunctivitis in the eastern American house finches was linked to back-garden gatherings.

Feeding the birds is now a passion on both sides of the North Atlantic, and indeed across much of the world, explicitly encouraged by ornithological NGOs such as BirdWatch Ireland. Households in the UK and the US provide more than 500,000 tonnes of food. (We buy Argentinian peanuts by the sackload from the co-op.) So obvious are the virtues of helping more little songbirds survive the winter that any challenge to the notion seems odd.

Prof Darryl Jones isn’t odd, just Australian, and there, it seems, concerns about the impacts of feeding have produced something of a split. Many worry, he says, about “an alarming array of effects” on the birds and the environment, among them the spread of disease, support of unpopular species (including rodents) and – most often mentioned – the possible growth of dependence on anthropogenic foods. Many other Australians go on feeding, “aware of the apparent stigma of their hobby, but passionately committed to ‘their’ birds anyway”.

Jones, of the environmental futures centre at Griffith University in Queensland, does, indeed, appreciate his vastly different climate – also, that feeding the birds “may be a significant form of connecting with nature, and that, frankly, it is here to stay”. But, as he says, the arguments both for and against are based on very little evidence.

“Feeding really does change things,” he insists. He suggests that by educating those who do it, and recruiting them as “citizen scientists”, much more could be usefully learned.

Some answers may come from Ireland. In a pioneering study, Prof Stuart Bearhop of Queen’s University Belfast directed a “landscape-scale” team experiment in 10 well-spaced, deciduous woods in Co Down. Each wood was well provided with nest boxes, but only half of them offered unlimited peanuts to the blue tits from November until March, ending six weeks prior to breeding.

An average of 66kg of nuts were eaten at each “fed” site, and there the tits laid eggs an average of two and a half days earlier than those at the woods without peanuts. Their young were also more successfully fledged. So, to nobody’s great surprise, supplementary winter feeding is indeed found to have “the potential to alter bird population dynamics”. More tits, finches and blackbirds, more sparrows (and sparrowhawks) are helping to stock the wild from some very unnatural sanctuaries. But as amateur aviary-keepers we also owe some cleaner habits to the wider feathered world.

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