Bava Batra 80 - Buying Doves
If one buys the production of a dovecote from his fellow, he must allow the first pair of doves that is produced to fly with the mother - that is, to remain with her; they are not included in the sale.
It is the tendency of doves to lay a pair of eggs almost every month of the year. These eggs hatch and produce one male and one female, which themselves begin to mate at the age of two months.
In order to stay in the dovecote, the mother must have, in addition to her mate, her daughter as a companion. The daughter, too, must have her offspring as companions, since her mother is not company enough. The buyer must, therefore, leave all these pairs and not take them for himself.