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IN many avian species visual signals are very important and powerful, whether the bird concerned is juvenile or adult. In zebra finches, the colour of the bill of a juvenile is black and that of an adult female is red. This is the only visible difference between the juvenile and the adult. In experiments it has been observed that if red colour is applied to the beak of a juvenile, it is instantly courted by adult males and even by its own father. As soon as the red colour is removed the ‘anti-sex’ signal of the juvenile colour comes into operation again and the bird is left alone.
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| It has recently been discovered that in
the colonies of these birds a third of the nests contain
one or more eggs that have been laid by a female other
than the occupant. Apart from avoiding the
responsibilities of the nursery, this female gains
another advantage — by laying eggs in other nests
she can produce more offspring than she could rear in her
own nest. However, she must move quickly and discreetly
if the legitimate tenant is not to detect her egg and
destroy it. As it happens, no zebra finches have have
ever been observed laying eggs in another’s nest,
although DNA tests on the finches’ eggs prove
without a doubt that clandestine laying takes place. It
would seem, therefore, that for zebra finches rearing
their own brood of chicks, laying a few more in a
neighbour’s nest is the equivalent of adding some
icing to the genetic cake. Hawfinch, member of the same family as the zebra finch, has the most powerful bill and jaw muscle of any bird of its seed. Cherry and olive stones are very hard to crack but this 18 cm long bird can exert a pressure of nearly 50 kg with its massive bill to break them open. Its over-sized bill has four rounded knobs at the base — two on the inner side of each mandible — and by placing a stone between them the force for cracking it is shared equally by the muscles on each side of the head. Genus ‘Serinus’ includes 32 species of small to medium-sized birds with small to fairly large conical bills. They have mainly yellow, brown, green and grey streaked plumage. Being good singers they are popular cage birds. These seed-eaters inhabit open woodland, cultivated land and forests and nest in trees. In the USA the success
in the propagation of wild marijuana is attributed to
birds, mainly the canaries who are member of the genus
‘Serinus’. Around New Jersey and New York this
hemp plant grows at such a large scale that if all of it
were harvested it would produce millions of cigarettes.
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Among birds passerines have a
prolonged breeding season and the maximum number of a
brood raised in the wild is generally six, but in
captivity zebra finches where a suitable environment is
created reported to have raised as many as 21 consecutive
broods. Inhabitant of the dry parts of Australia, water
is so important for this bird that in the wild it will
only breed after the rains have come. Behaving as a
opportunist breeder this species has no fixed breeding
season, but comes into full reproductive condition within
days of a storm and a good drink of water. To help the
bird breed better, breeders create an artificial
environment inside the aviary by spraying water and
planting green grass.