The embryos in the uterus are all nearly of the same age, except for a month or two before birth, when two broods overlap.
Two broods seem to be common in the course of the season, and towards the end of summer the birds - the young greatly preponderating in number - collect in large flocks and move to the sea-coast, whence a large proportion depart for more southern latitudes.
It builds its nest in March, or early in April, in thick bushes or in ivy-clad trees, and usually rears at least two broods each season.
The ferret is remarkably prolific, the female bringing forth two broods annually, each numbering from six to nine young.
The number of young in each nest is generally five, sometimes only three, occasionally seven or eight, and at least two broods are produced annually.