XIV 
PLAN OF STUDY. 
row entrance in tlie side. Having recently had occasion to inves- 
tigate the structure of various nests, with some minuteness, I have 
been led to adopt the opinion, that the arched coping or dome, so 
remarkable in several small birds, for ingenious and beautiful work- 
manship, is designed to preserve their animal heat from being dis- 
sipated during the process of incubation ; an opinion which appears 
to be corroborated by the fact of our native birds that thus cover in 
their nests at the top, being all very small. Among these, besides 
the wood-wren and the hay-bird, are the common wren, the chiif- 
chaff, [Sylvia hipolais,) the gold-crested wren, the bottle-tit, [Pa- 
rus caudatus^ Ray,) and the dipper, [Cinclus aquaticus, Bech- 
STEiN.) There are other birds, no doubt, little larger than these, 
such as the blackcap and the babillard, [Curruca garrida^ Bris- 
SON,) which do not build domed nests; but it is worthy of remark, 
that the latter usually lay much fewer eggs ; the babillard sel- 
dom more than four, and the blackcap four or five ; while the 
gold-crested wren lays from seven to ten, the bottle-tit from nine 
to twelve, and the common wren from eight to (some say) four- 
teen, and even twenty. It will follow of course, that in order to 
hatch so large a number, these little birds require all their animal 
heat to be concentrated and preserved from being dissipated. The 
dipper, indeed, lays but five or six eggs, and weighs from six to 
eight times more than any of our other dome builders ; but it is 
to be recollected, that, from its being a water bird, and building 
near water, it may have more occasion to use “ all appliances” 
to concentrate its heat.* In tropical countries, where the heat is 
great, such domed nests are very common, and are probably in- 
tended to protect the mother birds, while hatching, from the intense 
heat of a perpendicular sun;'|' though most naturalists think they 
are designed to avert the intrusion of snakes, — forgetting that 
snakes would more naturally run their heads into a nest with a 
small side entrance, than if it were open above, A circumstance 
which fell under my observation, corroborative of this remark, 
I have recorded under the article Hay Bird. Other birds, in 
warm countries, leave their eggs during the day exposed to the 
heat of the sun, and only sit upon them during the night or in 
* See a paper on the Contrivances of some Animals to j secure Warmth, by 
J. Rennie, in the Journal of the Royal Institution for May, 1831 . 
t See Architecture of Birds; Chapter on Dome Builders, page 307 . 
