A BIRD'S GEOGRAPHY AND ARITHMETIC. 189 
a limit which they rarely exceed or fall very far 
short of. 
Others are much more definite. Thus, as noted 
among some plovers, three or four eggs are very 
regularly the rule. With a few it is definitely three. 
We have seen already that a bird can lay more eggs 
than she usually deposits, having a reserve, it seems, 
for emergencies, such as robbery, etc. She soon fills 
another nest if one is broken up. 
If also, in many birds, as they are laying, an egg 
be taken daily, the mother will continue to replace it, 
to the limit of her egg-laying capacity, so long as she 
perceives the number too small; and one may, in this 
way, just at this time get an egg or eggs for study 
without destroying the bird’s prospects. Now this 
argues that the bird can count up to her needs in this 
respect. 
It is not likely, however, that she has a “ one-two- 
three,” etc., sort of appreciation of the numbers as she 
goes along. It may be just an estimate in the lump 
of when the nest is properly filled. 
As noted, the cowbirds are well known to be para- 
sitic upon other birds in laying their eggs. Meadow- 
larks’ nests have been found with their proper number 
of eggs deposited, but with one or more thrown out 
and a cowbird’s egg or eggs in their place. It appears 
as if the parasitic mother felt that there were too many 
in the nest for hers to have the proper chance in incu- 
bation. 
It would be straining our theory too far to sup- 
pose that she instinctively knew what was the proper 
