Thursday, 8 March 2007

Majestic menace

For many, the mute swan is the most graceful and serene of our birds. At this time of the year, however, a different and less pleasant side may be seen. The lengthening days initiate the urge to breed and sexually mature swans begin to establish territories within which to raise a family. Pair formation is a slow and serious business for the mute swan, beginning when individuals are still in their grey-brown juvenile plumage. At this young age they may engage in recognisable courtship greetings, interacting with potential mates within the winter herd (a group of swans is known as a herd, rather than a flock.) Over the following months, young birds increase the degree of courtship behaviour so that by the time they reach their second summer they will have acquired a mate. Even then, they typically do not breed, but instead go through an engagement period before finally breeding at the age of three or four. At this stage, they will establish and defend a breeding territory of their own.

For pairs that have already bred successfully, the establishment of a territory also requires them to see off any of their young that have yet to disperse. This can be a difficult process; the bonds between parents and young, so important earlier in life, now have to be broken, forcing the young to become independent. The primary means of seeing off young birds and would-be intruders is centred on a display of strength. This involves the bird adopting a characteristic posture (known as busking), with the wing feathers raised over the back to give an arched appearance. At the same time, the neck feathers are fluffed out – making the neck appear thicker and more solid, and the head and neck are coiled back. This swan will then swim at the intruder; the jerky nature of this motion resulting from the swan using both its feet simultaneously to force it forward in the water. Normally this is sufficient to see off the interloper but sometimes a more direct attack is needed, with the aggressor launching itself forward with powerful strokes of its great wings. In exceptional cases, the swan will actually see the attack through and there are instances where young swans, unable to escape, have been drowned by an attacker. The willingness to see attacks through highlights the value placed on securing a breeding territory. Interestingly, though, a small minority of pairs (such as those at Abbotsbury in Dorset) are colonial, nesting as close as 2-m together. Under such circumstances there is no place for aggression. So, while the busking display of a swan may seem majestic, it is worth remembering that this monarch means business.

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