Whilst the wild tribes of birds choose this time of the year from their
acquired knowledge, that the mild temperature of the air is more convenient
for hatching their eggs, and is soon likely to supply that kind of
nourishment, that is wanted for their young.

If the genial warmth of the spring produced the passion of love, as it
expands the foliage of trees, all other animals should feel its influence
as well as birds: but, the viviparous creatures, as they suckle their
young, that is, as they previously digest the natural food, that it may
better suit the tender stomachs of their offspring, experience the
influence of this passion at all seasons of the year, as cats and bitches.
The graminivorous animals indeed generally produce their young about the
time when grass is supplied in the greatest plenty, but this is without any
degree of exactness, as appears from our cows, sheep, and hares, and may be
a part of the traditional knowledge, which they learn from the example of
their parents.

_Their Contracts of Marriage._

Their mutual passion, and the acquired knowledge, that their joint labour
is necessary to procure sustenance for their numerous family, induces the
wild birds to enter into a contract of marriage, which does not however
take place among the ducks, geese, and fowls, that are provided with their
daily food from our barns.

An ingenious philosopher has lately denied, that animals can enter into
contracts, and thinks this an essential difference between them and the
human creature:--but does not daily observation convince us, that they form
contracts of friendship with each other, and with mankind? When puppies and