Fluctuations in Numbers of Birds in the Toronto Region

J. Murray Speirs
1939 The AUK: A Quarterly Journal of Ornithology  
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more » ... he Auk. THE numbers of any animal species present in a given region fluctuate year by year. In some cases there has been a tendency for the years of greatest abundance to occur at regular intervals. The purpose of this paper is to put on record certain periodic fluctuations which have been detected in the Toronto region, in the winter populations of Northern Shrike, Snowy Owl, American Rough-legged Hawk, Pine Grosbeak, Horned Owl, and Goshawk. In this paper the Toronto region is that area within twenty-five miles of the Toronto city limits. This area reaches to Burlington on the west, to Newmarket on the north, and includes Whitby on the east. The years of greatest abundance will be called peak years, or simply peaks. The records from which the conclusions presented in this paper have been derived consist of a great mass of data of varying quality. Few of the identifications have been made from collected specimens but with the increased use of binoculars and with the increased quantity and quality of reference books it is no longer necessary to identify birds by collecting them, certainly not for a statistical work where exceptional records automatically play an insignificant r6le. The largest source of data used in this study is the mass of sight records recorded by local bird students. The chief sources of records are as follows: 1. The file of checking cards in the Royal Ontario Museum of Zoology. These cards list all the species of birds which have been identified in the Toronto region in recent times. Spaces are provided for indicating the number of each species seen on a trip, the locality, the date, the name of the observer, the time spent observing, and the weather. The file contains continuous records since 1885. Records previous to 1920 have been obtained from the diaries of a number of naturalists. 2. The author's records. These consist of daily lists of all species observed, starting from January 1, 1924. Numbers were used in a few cases before 1931 and starting in January, 1931, all the lists have included estimates or counts of the numbers of each species seen. From these two sources about 10,000 complete daily lists are available and about 3,000 lists that are more or less nearly complete. The number of available daily lists varies from about ten per day in late July to about forty-five per day in early May. 3. These data are supplemented by numerous scattered records in the following sources: the records of the Brodie Club and the Toronto Ornitho-
doi:10.2307/4078792 fatcat:mvotn32mobdcdd2pol7y7s56ee