Good Neighbours?

We often have a tendency to believe that other species, and birds in particular, live lives of peace and goodwill to all other creatures. Quite unlike we wicked humans. Not so, not at all so. I happened upon the following account of the home life of Cliff Swallows while re-reading Colin Tudge’s excellent book, The Secret Life of Birds.

Here is the real community spirit of our avian friends … (quote):

The sexual and social lives of Cliff Swallows are so complicated that biologists are still trying to make sense of them, although few birds are studied more intensively these days. In essence, Cliff Swallows are monogamous, or at least they live in monogamous pairs. But the pairs group together to form colonies, in nests shaped like small pitchers, side by side, up to 5,000 at a time. The result, as Stanford University biologist Joan Roughgarden puts it in Evolution’s Rainbow, ‘amounts to a city of mud huts’ – although some Cliff Swallows are content simply to be villagers, and live in groups of twenty nests or so.  Some males, too, just hang about, out of town, with no nests to call their own. In short, their living arrangements overall are as varied as those of human beings. Indeed, says Professor Roughgarden, socially speaking ‘Cliff Swallows are perhaps our closest cousins”. The city of the Cliff Swallows, as Roughgarden puts the matter, features ‘a hot real estate market, trespassing, robbery, hanky-panky with the neighbours, plus presumably some compensations’ — just like, say, Los Angeles.

 
The nests are very close together: so close that they may block each other’s entrances, so that residents sometimes find themselves trapped, and starve. Or their home may be engulfed in droppings from above. The whole urban stew is a hotbed for pathogens, a veritable shanty. Sometimes the swallows — usually males — trespass on each other’s property, either barging in or following the owner home and blocking the entrance. The single most common reason for this, so scientists have shown — accounting for I4 per cent of all trespass in one study – is simply to steal grass, to line their own nests; in human terms, popping next door to nick a duvet. In 7 per cent of intrusions the trespassers steal mud that is not yet dry, to build their own nest. Do the birds know what they are doing, one might whimsically ask? Do they feel the frisson of forbidden fruit? Or do they simply feel that grass is grass and mud is mud, and next door is as good as place as any to get them from?

 
But sometimes the visits would, if this were a human city and we were being anthropomorphic, attract the attention of the social services or even the serious crime squad. In one study, in about one in ten visits a male trespasser forced himself on his neighbour’s ‘wife’. In about one in thirty intrusions, a female laid an egg in her neighbour’s nest — or carried one in in her bill, ready-laid, the strategy known as ‘brood parasitism’. Usually the nests she favoured with her surplus eggs were close to her own — not more than five doors away — and usually it was when the neighbour was not at home. Sometimes she would seize the opportunity to throw out one of her neighbour’s eggs, but often she would just add one to the existing clutch. Not all females in any one colony are likely to practise brood parasitism: in one study, only about one in three females did this.

 

Sometimes the female Cliff Swallow would bring in a chick, ready-hatched, and add it to the resident family. But in one in a hundred visits a visiting female would also toss one of the resident chicks out of the door, like Judy, the lovely wife of Punch, as if to keep the numbers even.

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