MANNER OP MIGRATION. 55 ciated with the young. Some fly by day, some by night, and others by botli day and night. This fact was iirst established by Mr. WilHam Brewster, who, in his admi- rable memoir on Bird Migration, writes : " Timid, seden- tary, or feeble-winged birds migrate by night, because they are either afraid to venture on long, exposed jour- neys by daylight, or unable to continue these journeys day after day without losing much time in stopping to search for food. By taking the nights for traveling they can devote the days entirely to feeding and resting in their favorite haunts. Good examples are Thrushes (except the Robin), Wrens, AVarblers, and Yireos. " Bold, restless, strong-winged birds migrate chiefly, or very freely, by day, because, being accustomed to seek their food in open situations, they are indifferent to con- cealment, and being further able to accomplish long dis- tances rapidly and with slight fatigue, they can ordi- narily spare sufficient time by the way for brief stops in places where food is abundant and easily obtained. Under certain conditions, however, as when crossing large bodies of water or regions scantily supplied mth food, they are sometimes obliged to travel partly, or per- haps even exclusively, by night. Excellent examples are the Robin {Merula), Horned Lark [Otocoris), and most Icteridai [Bobolink, Blackbirds, and Orioles]. " Birds of easy, tireless wing, which habitually feed in the air or over very extensive areas, migrate exclusively by day, because, being able either to obtain their usual supply of food as they fly, or to accomplish the longest journeys so rapidly that they do not require to feed on the way, they are under no necessity of changing their usual habits. The best examples are Swallows, Swifts, and Hawks." While migrating, birds follow mountain chains, coast- lines, and particularly river valleys, all of which become
