Weather and Pheasant Populations in Southwestern North Dakota

Abstract

High productivity and survival of ring-necked pheasants (Phasianus colchicus) were correlated with high rainfall and cool temperatures in May and June during an 8-year period in southwestern North Dakota. These findings differed markedly from those of several earlier studies in the less arid midwestern United States where cool, wet weather in the spring generally affected pheasant populations adversely. General trends in the pheasant population could be explained on the basis of precipitation in May and June. The population was relatively high during the mid-1950's when wet and dry May and June periods occurred in alternate years but declined markedly after 2 consecutive years of spring and summer drought. The population remained at a static low during 1960 through 1963 when wet and dry spring and summer periods again occurred alternately. This paper presents the results of a study on the relation of weather to ring-necked pheasant population fluctuations in southwestern North Dakota. The study was initiated after pheasants decreased markedly throughout southwestern North Dakota in conjunction with a period of drought. We surmised that poor reproductive success, caused by the drought, was responsible for the population decline, and we set out to test this possibility by examining weather records and data on pheasant productivity. During the work it became apparent that annual survival was important in the population fluctuations and also appeared to have been affected by weather. Much has been published on the effects of weather on pheasant populations but the results of most studies have differed from ours. Biologists in eastern and midwestern portions of pheasant range have generally concluded that high precipitation and cool temperatures in the spring and summer have adverse effects on productivity (Perry 1946, Allen 1947, Dustman 1950, Kozicky et al. 1955). However, Wandell (1949:374376) cautioned that this is not always true and cited findings in Illinois and Montana where adverse weather and excessive rainfall did not result in decreased pheasant populations. The present study was done in a region of limited precipitation and the results suggest that drought, rather than excessive rainfall, was the factor that limited the pheasant population. We wish to thank the many biologists and game wardens of the North Dakota Game and Fish Department for collecting data, Jack Samuelson and Lloyd Oldenburg for suggestions relating to the analysis, A. D. Geis, A. J. Godin, and R. I. Smith for reviewing the manuscript, and A. J. Godin for preparing the figures. DESCRIPTION OF THE REGION Primary pheasant range in western North Dakota is south and west of the Missouri River (Fig. 1) with highest densities of pheasants in the south-central part of the region. This region is within the Missouri Plateau section of the Great Plains and is locally called the Area. Glaciation (Iowan stage) barely extended south and west of the present Missouri River. The topography of the Slope Area is almost wholly the result of erosion, with much of 1 This paper is a North Dakota Game and Fish Department contribution supported by funds from Federal Aid Project W-67-R-2. 2 Present address: Migratory Bird Populations Station, Laurel, Maryland.