Tuesday 10 April 2012

One of the black and white mallards seems to be a girl, as for a couple of days she has been hanging around with a normally coloured drake.

One expects these odd-coloured birds to be male. But that is a misunderstanding of the way in which the patterns of birds' plumage are generated. The basic pattern of repeated brownish mottling seen on female ducks and many other birds is actually a very delicate balance, and any disturbance causes it to break up into blocks of plain colour. The slight disturbance caused by male hormones produces the pattern of a typical drake or other gaudy male bird. A more severe disturbance caused by some genetic accident produces a black and white bird, and a disturbance so severe that it breaks the patterning mechanism entirely gives a pure white bird.

You can see an analogous process in Wolfram cellular automatons, where a coloured pattern is generated by assigning colours to a row of numbers and then adding, subtracting or multiplying adjacent numbers to form the next row down. Here are two examples: left, a repeating pattern made by repeating a sequence of numbers; right, a broken pattern caused by disturbing the regularity of the numbers.

Another odd couple has been seen on the lake for the past three years: a pair of a Canada-greylag goose hybrid with a pure greylag. These hybrids always have Canada fathers, since the sexually aggressive Canada gander jumps on the greylag female. The offspring imprint on their greylag mothers and consider themselves greylags, and they are accepted by their peers.

There are now several family groups of long-tailed tits taking their newly fledged young around to feed them. The male tawny owl was in his usual spot, but the family have been off the map for the past three days. The little owl was in his usual lime tree, and was calling to his mate, who seldom bothers to answer.

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