The foregoing paper discusses accidents in which large numbers of night-migrating birds are killed. A brief historical review of ornithological interest in such occurrences is given, and the types of data provided by the accidents are listed and discussed. In particular, recent accidents occurring in early October, 1954, through much of eastern United States are cited, and detailed analysis is presented of a sample of 1090 birds killed one mile west of Topeka, Shawnee County, Kansas, between September 25 and October 23, 1954. At Topeka during the period mentioned, 1090 birds representing 61 species were collected and were processed at the University of Kansas. For all specimens, weight, sex, age, and fat condition were recorded, and certain species were measured as well. Some notes on molt were taken. A total of 193 birds was preserved as study skins, and 49 as skeletons. Comments on weight, size, sex, age, subspecific identity, and status in Kansas are presented in an annotated list. Randomness of this and other similar samples is discussed. A theoretical computation is given for several nights of the numbers Differential migration of sex- and age-groups as shown by the larger samples taken at Topeka (Catbird, Red-eyed Vireo, Nashville Warbler, Yellow-throat, Mourning Warbler, Dickcissel, Lincoln Sparrow) is discussed and the history of theories on this subject reviewed. It is shown that age and sex must both be taken into account in studies of differential migration. Several patterns of migration are displayed by the species analyzed, adults migrating earlier than immatures in some instances, young earlier than adults in others, but all seemingly being complicated to varying degrees by differential migration of sexes within age groups. It is suggested that explanations of these patterns may be sought in the life histories of the species involved. Molt in relation to migration is discussed briefly, and it is held that there is an important relationship between molt and time of migration. Specimens noted to be in molt are listed. Size differences, in wing length, tail length, and weight are discussed in relation to sex and age, and variation in one or more of these characters is analyzed as found in the Topeka samples of Nashville Warbler, Mourning Warbler, Yellow-throat, Dickcissel, and Lincoln Sparrow. It seems that in some instances significant size differences prevail between adults and immatures and that these age classes should be separated in taxonomic work with species where differences in size are known to exist. When the facts are not known they should be determined, and the large samples collected in accidents to nocturnal migrants present excellent opportunities for ascertaining the facts. Other uses of material obtained in large migration accidents are discussed, such as computations of longevity and the problems of processing large, accidentally-killed samples. Care should be taken to select samples as nearly random as possible when all birds cannot be processed. Repeated and thorough analysis of accidental kills should provide a mass of valuable data bearing on many questions and problems which have thus far been little studied. |