PARENTAL INSTINCT IN BIRDS. 251 
the eggs would require to be large, which, as I have pointed out, 
would be an impossibility with incubating species. 
Even admitting that the size of the egg may not be the all- 
important factor, and assuming that it is the precocious develop- 
ment of the nervous system, allowing of co-ordination of move- 
ment, which regulates the conditions of chicks at birth, there 
must still remain the objection that precocity does not ever mean 
physical strength, and five minutes’ chat with a gamekeeper 
soon convinces one of the delicate susceptibilities of Grouse and _ 
Pheasant chicks. So it is necessarily an advantage to a bird 
capable of caring for them to produce a few—say, four or five— 
helpless though healthy young rather than a large number 
of delicate and precocious ones. 
Superficially, it looks a convenience at least for any species to 
sive birth to young able to look after themselves ; but the chicks, 
for example, of the Partridge must run a greater number of 
risks than the parent, possessing at the same time less ability to 
cope with them. Consequently the Partridge has to produce as 
many as ten young at a brood, not because it has less parental 
instinct than the Thrush (who would assert that ?), who produces 
four, but because its young are active and run into all kinds of 
dangers. Active young are really antagonistic to the parental 
instinct, and hence the advantages of helpless young to a species 
which has developed this instinct. 
