(Of birds the wild species, as has been stated, as a general
rule pair and breed only once a year. The swallow, however, and the
blackbird breed twice. With regard to the blackbird, however, its
first brood is killed by inclemency of weather (for it is the earliest
of all birds to breed), but the second brood it usually succeeds in
rearing.

Birds that are domesticated or that are capable of domestication
breed frequently, just as the common pigeon breeds all through the
summer, and as is seen in the barn-door hen; for the barn-door cock
and hen have intercourse, and the hen breeds, at all seasons alike:
excepting by the way, during the days about the winter solstice.