Leviticus 1:14

Of turtledoves, or of young pigeons - The offering of a bird was permitted to one who was too poor to offer a quadruped. (Compare the marginal references.) But in certain rites of purification birds were appointed for all, whatever might be their circumstances. See Leviticus 15:14, Leviticus 15:29; Numbers 6:10. The limitation of the age of the pigeons may be accounted for by the natural habits of the birds. It would seem that the species which are most likely to have been the sacrificial dove and pigeon are the common turtle and the bluerock pigeon, a bird like our stock-dove, and considerably larger than the turtle. The turtles come in the early part of April, but as the season advances they wholly disappear. The pigeons, on the contrary, do not leave the country; and their nests, with young ones in them, may be easily found at any season of the year. Hence, it would appear, that when turtledoves could not be obtained, nestling pigeons were accepted as a substitute.