Phylogeny of the Waxwings and Allied Birds

by M. Dale Arvey

NEST BUILDING

There are numerous papers concerning the nesting of waxwings. B. garrula, owing to its nesting in the far north, where observers are few, has received less attention than B. cedrorum. There is, on the other hand, no literature that deals with the nesting habits of the majority of the Ptilogonatines, with the exception of Phainopepla, on which there is considerable literature (Merriam, 1896; Myers, 1907, 1908). No detailed study of the nesting of Dulus has been reported, although Wetmore and Swales (1931) have described carefully the large communal nest of this genus.

In Bombycilla, both members of a pair apparently aid in the construction of the nest (Crouch, 1936; Swarth, 1932). Although the sexes are alike in plumage and general appearance, most students of the nesting of waxwings agree that one bird, assumed to be the female, does most of the arranging of the material, and does the shaping of the nest, whereas both birds carry materials to the nest site. As is characteristic of many passerine birds, both members of the pair gather materials and fly back to the nest site, where the female takes the more active part in the construction of the nest itself.

Both species of American waxwings build bulky nests, with the base or platform composed of a large amount of twigs and sticks, from which there often trails a mass of sticks and moss or string. Softer materials such as moss, plant fibers, and string, are placed inside the platform; moss is readily available to, and preferred by, B. garrula according to Swarth (op. cit.:271), and various plant fibers and string are used by B. cedrorum. The inner lining consists of soft plant fibers or down, dry grasses, and feathers. The nest is usually unconcealed in a tree either adjacent to a trunk or on a main side branch, but sometimes in a fork. Nest building by both Cedar and Bohemian waxwings is rapid, taking from three to five days, and is followed immediately by egg laying.

Nesting by waxwings is late in the season; June is the month in which the nest is usually started. This is readily explainable in Bohemian Waxwings, since adverse weather would prohibit earlier nesting in the area in which they spend the summer. Crouch (op. cit.:1) remarks that B. cedrorum possibly evolved in the far north where it was impossible for it to start nesting earlier, and that the habit has been retained. Perhaps, on the other hand, nesting is delayed until the berry crop is ripe, to insure sufficient food for the young.

Desertion of the nest is not uncommon in waxwings, despite the tolerance to other animals that is shown by the birds. A new nest may suddenly be begun before the first one is finished, and all the materials from the first nest may be removed, or the nest may be abandoned before it is completed. The eggs may be left at any time up to hatching, and the young may be deserted, especially in the earlier stages of development.

The very large and bulky communal nest of Dulus is not radically different from the nest of waxwings. In the absence of sufficient nesting sites, a pair of gregarious birds such as Dulus could combine their nest with those of other pairs, retaining for their own territory only the nest cavity, and in this way communal nests might have evolved. The nest of Dulus is communal probably because of the lack of suitable trees for nesting sites, and only incidentally does this type of nest afford better protection from natural marauders. Large numbers of Palm-chats work together in the construction of the nest platform, and both sexes probably take part in the work.

In Phainopepla the nest is built mostly by the male (Merriam, 1896; Myers, 1908), although the female does some of the work, especially in the shaping and lining of the nest. In this genus, the nest is usually a compact structure, but exceptional nests are of considerable bulk. The nest is commonly placed in a fork near the main trunk of a tree, in a conspicuous location, and generally is 10 to 20 feet from the ground. In shape and location, the nest closely corresponds to that of Bombycilla, but the materials used for a base are stems of annual plants, whereas Bombycilla uses more woody twigs. The finer materials used by Phainopepla are more readily obtainable in the ecological association inhabited by Phainopepla than would be heavier twigs such as Bombycilla uses.