Observations on the Developmental Condition of Neonatal Birds

The artificial incubation of eggs of about 100 species of wild birds was attempted. Egg and clutch weights, egg volumes, incubation periods, neonatal weights, interims between hatchings within clutch es, number of days before hatching during which eggs float, and lengths of 6 of the long bones for neonates and adults are reported. Colors of natal down and of soft parts, especially of mouth linings, are given. Differences in extents of development at hatching are described, and some evolutionary postulates are discussed. This paper attempts to establish procedural standards under conditions that may allow for accurate and significant interspecific comparisons of incubation and neonatal condition independent of parental attentiveness and other environmental variables. INTRODUCTION The morphologic condition of development of hatching is used as an important criterion by ecologists and systematists in classifying birds (Daniel, 1957). An exhaustive search through North American museums in 1950 (Wetherbee, 1957), however, revealed that there were less than a dozen spirit specimens available that could confidently be called neonatal. Terms like precocial and altricial, nidicolous and nidifugous, to indicate the extent of development at hatching have been generally used in ornithology, but critical examination reveals that the categories are oversimplificatious and that there are actually a multitude of intermediate conditions. To re-examine this subject it was deemed necessary to have many specimens taken at the time of hatching. Evans (1891, 1892) in Scotland and Heinroth (1908, 1922) in Germany hatched out many Old World species, but they did not carry on morphological work. Baldwin and Kendeigh (1932), Kendeigh (1940), and Graber (1955) investigated some parameters of artificial incubation of eggs of a few species of wild birds. Wetherbee (1958 and 1959) described the artificial incubation of more than 100 species of wild birds. In spite of the above-cited works, ornithologists generally have the erroneous belief that eggs of wild birds, especially of passerines, cannot be incubated artificially. The lengths of 'natural incubation periods of birds' eggs have been recorded throughout history. A great deal of those data are untrustworthy as Nice (1953; 1954) has indicated in her exhaustive review of the subject. Unfortunately, however, even the information 1 Portions of these data were submitted to the University of Connecticut in partial fulfillment of the requirements for the Ph.D. degree. 2 Contribution of the Dept. of Poultry Science and Massachusetts Cooperative Wildlife Research Unit supported by the University of Massachusetts, Massachusetts Division of Fisheries and Game, U.S. Fish and Wildlife Service and Wildlife Management Institute.