Migration of Birds

As Summer slowly quietens into Autumn, so the birds too slide gently from the frantic frenzy of being a parent to the more decorous state of grandparent-hood. The season’s young have been packed off to fend for themselves as best they can, and the parents can now potter about satisfying only their own simple needs. With a nest full of hungry chicks, nearly all our bird species are driven to find an almost unending supply of good insect food; protein for the fast growing youngsters. Once the chicks are fledged and self sufficient, the pressure to find protein-rich food is gone and the exhausted parents can take a well earned break from bug-hunting. Now a vegetarian diet of fruit and berries with an occasional nutritious worm is quite enough to keep body and soul together.

As winter approaches it is interesting to note how many of the local trees choose this seemingly inhospitable time of year to fruit. One good explanation of this phenomenon is that if the trees fruited in summer when insects abound, the birds would not be interested in such second-class food as berries, and the trees would not benefit in the dispersal stakes.

There are of course another group of birds not at all interested in helping the trees move their “children” around. These are the Palaearctic migrants who have come here to enjoy our summer and must now take the long and arduous journey back to Europe and Britain to breed. The European or Barn Swallow is a good example, along with the Willow Warbler, Spotted Flycatcher and many others. These birds must actually put on weight in order to have enough energy for the long flight ahead so need all the protein they can find. A small bird can actually increase its weight by half again without falling out of the sky! Migrating birds do feed along the way but seem to beef up before leaving just in case the wayside cafes are not up to scratch. Aerial feeders like the swallow stand a better chance of finding food en route, whereas a bird that has to land to feed can get into all kinds of trouble.

Sally Johnson

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