OBSERVATIONS ON THE CUCKOO. 61 
of birds, they have the power of retaining the egg in 
the uterus after it is perfected, and that while it 
remains there the embryo is progressively advanced 
towards maturity by the internal heat of the parent’s 
body*. Now, without having observed a single cir- 
cumstance in the whole course of my inquiries which 
at all tends to corroborate this opinion of Montagu’s, 
I have discovered a curious fact which appears to 
render such a supposition altogether unnecessary. 
On the 5th of May, 1822, I saw a Cuckoo in the act 
of watching a pair of Titlarks construct their nest. 
The Larks had just commenced building, and did not 
seem to be at all disconcerted at the presence of the 
Cuckoo, which sat on the ground, about seven or 
eight yards from the spot, attentively observing them, 
and when disturbed flew away with great reluctance, 
and only to a short distance. This nest, which was 
on Kersal Moor, where the races are annually held, 
was too distant from my residence to permit me to 
examine it frequently, and to make such numerous 
and minute observations as I wished; but on the 
12th of May I again visited it, in the confident ex- 
pectation that it would contain a Cuckoo’s egg, and I 
was not disappointed. IJ may further remark, in con- 
firmation of this discovery, which, by exhibiting a 
curious and hitherto unnoticed instinctive propensity 
of this bird, forms an interesting addition to its 
history, that Cuckoos almost invariably deposit their 
* «Ornithological Dictionary,’ Introduction, p. 15. 
