PLAN OF STUDY. 
xiii 
young student, upon reading this very questionable doctrine, turn 
to this Dictionary,* he will learn that Colonel Montagu uniformly 
found the nests cold, and that taking into account the chemical 
principles of fermentation, it was impossible they could be warm. 
But Pennant also mentions a circumstance of much more in- 
terest in reference to the original inquiry, when he says that this 
bird ‘‘ lays five or six white eggs, and always covers them ivhen it 
quits the nest,'' — the very point to ascertain which the research 
was begun. With this authority, supported as it is by Montagu, 
most students might rest satisfied, but the ardent naturalist never 
arrives at any conclusion like this, without bringing all the facts 
within his knowledge to bear upon it, in order to elucidate con- 
necting causes and consequences ; for the fact being ascertained 
of the mother bird covering her eggs, it becomes interesting to 
inquire why she does this. 
It is admitted by all the naturalists already quoted, that the 
nest in question is built on moist ground, if not actually touching 
the water, and that part at least of the materials consist of moist 
water plants. Now it is indispensable to hatching, that the eggs 
be kept at a high temperature, and not be suffered for a moment 
to cool. The natural heat of the bird itself is sufficient for this 
purpose, without the heat of fermentation, erroneously supposed 
by Pennant ; but if she quits them for a moment to go in pur- 
suit of food, or to withdraw the attention of an intruding water 
spaniel, or a prying naturalist, their near vicinity to moist plants 
or to water, would certainly prove fatal to the embryo chicks. 
In order then to prevent her brood from being destroyed by cold, 
the careful bird covers the eggs with a quantity of dry hay, to 
keep them warm till her return. 
By keeping this interesting fact in his mind, our young natu- 
ralist may subsequently find that other birds employ the same or 
similar devices. The carrion-crow (Corvus corone) for example, 
who lines her nest with wool and rabbits’ fur, always covers her 
eggs with a quantity of this before leaving her nest, no doubt for 
the same reason that the dabchick employs hay. Again, several 
birds of very different habits, such as the wood- wren [Sylvia sibi- 
latrix) and the hay bird, [Sylvia trochilus,) construct a perma- 
nent arch of moss and dried grass over their nests, leaving a nar- 
* Page 127. 
