108 OBSERVATIONS ON BIRDS. 



nest, has amounted in some years to nearly a hun- 

 dred dozens ; to say nothing of the old birds which 

 are occasionally destroyed at all seasons of the year. 

 Yet I feel satisfied that the general aggregate of the 

 nests in spring, as also of the individuals forming 

 the immense flocks we see in autumn, is much 

 the same as it was thirty years back. So too with 

 the sparrows, which abound in such multitudes, to 

 the great annoyance of the farmer ; they are not, to 

 my thinking, more or less abundant than they were 

 formerly, though here, as in other places, the parish 

 officers give rewards for their destruction every year. 

 My idea in regard of this matter is, that species, 

 which, like the rook and sparrow, are generally dis- 

 persed over the kingdom, have a tendency to 

 equalize their numbers throughout the different 

 parts of it ; deficiencies from accident, or any other 

 cause, in one locality, being made up by supplies 

 from another, in which there happens to be an 

 excess. It seems also not improbable, that, without 

 a diminution of numbers in any one place to induce 

 strangers to settle there, the numbers in another are 

 not allowed to increase beyond a certain limit, in 

 consequence of the law which impels old birds to 

 drive away their offspring, as soon as they are suffi- 

 ciently matured to shift for themselves. If there 

 be convenient space for them in the neighbourhood, 

 without interfering with the old birds, they may be 

 suffered to remain ; but otherwise they are forced to 

 go elsewhere ; and if there is no colony near, allow- 

 ing of increase, to which they can attach themselves, 

 they found a new colony, wherever circumstances 



