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 PETRELS. TUBE-NOSED SWIMMERS. (ORDER TUBINARES.) Petrels. (Family Procellariid^.) Petrels, or " Mother Carey's Chickens," are true chil- dren of the sea. Their home is the ocean, and they come to land only when nesting. To the etre s, landsman, therefore, they are strangers, Plate IV. ' •> J & J but to most people who have been to sea they are known as the Uttle, white-rumped swallow- like birds who on tireless wing follow in the wake of the ship day after day, patiently waiting for the food which experience tells them will be thrown overboard. Two species of Petrels are found off our coasts, Wil- son's and Leach's. The former has a yellow area in the webs of the toes and a square tail, while Leach's Petrel has the webs of the toes wholly black and a slightly forked tail. These differences, however, would not be appre- ciable at a distance. Wilson's Petrel nests in certain islands of the southern hemisphere in February, and. later migrates northward, reaching our latitude in May and spending the summer, or what in fact is its winter, in the North Atlantic. It is, therefore, probably the Petrel most frequently seen by transatlantic voyagers at this season. Leach's Petrel nests on our coasts from Maine north- ward, arriving from the South in May. The nest is made in a burrow in the ground or beneath a rock, and a single white egg is laid. Generally one of the birds spends the day on the nest while its mate is at sea, but at night the incubating bird leaves the nest, its place being taken probably by the one who has been feeding during the day.