Tell-Tale Tits

THERE is a rook I feel I know, the one that croons to itself as it flaps across the acre: it's a low-pitched, reflective, Barry Manilow sort of sound. There was another rook, once, that used to perch on the hen-run fence and imitate, as best it could, the crowing that accompanied the laying of an egg. But that's as far as I've gone in telling apart the residents of the rookery down the hill. They are black, and have a bare bit around the base of their bills, for digging after earthworms, and that's it.

On my rare trips to the capital (two years, now) I sit in the train amazed by all the different people. I am riveted by the individuality of the human face the infinitely variable identikit of eyes and ears and noses. Staring at particular and often extraordinary arrangements of muscle, fat and skin-folds, I wonder about the significance of all this morphological subtlety.

To shuffle and reshuffle 200,000 human genes just to let people recognise each other and bond in pairs does seem extravagantly complicated, even for, nature. Anthropologists have given up trying to decide how many human "races" there are - perhaps as many as 60 - yet it is within the races that people seem most alert to nuances of physiognomy (do the Irish look all the same to the Japanese?).

When humans start to study the behaviour of animals in the field, the effort of telling the difference can become even more exacting. Women may be better at it than men: one thinks of naturalists such as Jane Goodall with the chimpanzees, Diane Fossey with gorillas, Shirley Strum with baboons - even Anne Rasa with mongooses (not mongeese).

When it comes to studying birds, the scope for sorting one from another is somewhat limited, even more so when both sexes look the same. It took a man, naturally, to find an engineering solution. J.H. Burkitt county surveyor of Fermanagh in the 1920s, hit on the notion of giving the robins in his garden. different coloured rings on their legs, thus introducing the standard tool of modern ornithology.

All the more poignant, then, to find a young woman scientist, not a hundred miles from Fermanagh, raiding a flag for bird research that depends upon more refined powers of cognition. So confident is Susan Fitzpatrick of recognising the blue tits, great tits and coal tits that eat the bags of peanuts at her bird table in suburban Belfast, that she has based a whole study on her certainty.

Ms Fitzpatrick, of the School of Applied Biological and Chemical sciences at the University of Ulster, publishes her paper "Utilisation of Provisioned Peanuts by Suburban Tits in Belfast" in Irish Birds, 1995, just published by the IWC. It is a fairly technical dissertation, using such things as regression equations to measure the tits' individual rates of peanut consumption.

But what really impresses is Ms Fitzpatrick's ability to know one tit from another. Granted, she has been feeding them with nuts (the usual sort, in red mesh bags) continuously since 1990, and watching them almost every day, but still, she has a great eye. Sexing tits is helped by the males' greater brightness of colour, but she also knows her resident birds and a few "regular intruders" from their plumage patterns. Try this on birds at your feeder.

"IN blue tits, variations in the colour of the crown, size and shape of the white forehead patch, the width of the white supercilium [stripe over the eye] and nape band encircling the blue crown, the width of the dark eyestripe and nape band, and the width of the dark border around the white ear-coverts all combined to give an individual an identifiable head-pattern; the shade of yellow on the underparts and width of the breast stripe also differed between individuals.

"Great tits differed recognisably in the width and shape of the breast-stripe, the shade of yellow on the breast, and, in males, the extent of the black diamond on their bellies. Females also varied in the greenishness of the mantle. Coal tits differed in the extent and shape of the black bib, the shape of the white ear-coverts patch at its junction with crown and nape, and in a dark marking at the side of the breast just above the folded wing."

Such meticulous practice was also brought to the measurement of peanut consumption. Thus: "The tendency of tits to remove pieces of nut from the bag and retire to cover to eat them produces inherent variability in nut intake rates due to differing sizes of the piece removed and the time taken to extract it." Nonetheless she was able to calculate that on average, during each visit a male blue tit would obtain peanuts at a rate of 0.0256 g/min plus 0.027g as a `take-away'; a female blue tit would get 0.0247 g/min plus 0.011g, and great tits get 0.024 g/min plus 0.015g as `take-away'."

This was in the mild winter of 1995, but even so, the contribution of peanuts to the energy requirements of the smaller tits was similar to or even greater than the contribution of provisioned sunflower seeds to the winter diet of black-capped chickadees in rural Alaska.

For the resident tits of this Belfast garden, watched for three eight-hour days in winter and again in spring, the nuts accounted for a big part of their diet - the resident male blue tit, for example, got close to half his winter energy this way and more than a quarter of what he needed in the spring.