An Embr3⁄4ologicai, Comparison of the Domestic Fowl and the Red-winged Blackbird

TH• extensive investigations that have been carried on in the field of avian embryology have largely concerned the chicken as a representative subject. There are, however, two different general types of development among birds, namely: the nidifugous type, which results in the precocial condition at hatching, and the nidicolous type, which gives rise to the altricial condition. Various degrees and gradations of the two types are exemplified among the birds, but most embryological research has not considered the possible differences. Sutter (1950) in examining this problem stated, "Field ornithology has done much work in the domain of . . . contrasting postembryonic development of birds... but the comparative morphology of different types of ontogenesis is still at the beginning." The purpose of this investigation is to compare an example of ontogeny from a precocial order (Galliforrnes) with one of an altricial order (Passeriforrnes), noting especially morphological differences of large magnitude or time discrepancies, and attempting to throw some light on the problem of why one bird hatches in about 21 days while the other requires only twelve days. Much information was readily available on the chicken (Gallus domesticus), so it was the logical choice to represent the first order. Among the passefines, however, very little concentrated work on any one species has been done. Consequently, I selected the Thick-billed Red-wing (Agelaius phoeniceus fortis) to represent this group because of the accessibility of the nests and the large number of eggs available for collection and preparation. Prepared material of the Red-wing was compared to corresponding information on the chick as recorded in numerous sources, but mainly in Hamilton (1952), Patten (1951), and Arey (1954). Chick embryo microscope slides were also used to supplement the published material. Discussion of postembryonic development is omitted except where needed for clarification.