Analyses of Annual Surveys of White and Gray Squirrels (Sciurus carolinensis) in Olney, Illinois, 1977-1986

Abstract

Annual October surveys by over 30 Olney, Illinois, volunteer squirrel counters provide a decade of population indices for the white and gray phenotypes. These indicate that variation around an overall 10-year average of 22.6% white has been acceptably random. A weak and inconsistent decline in the numbers of both phenotypes is noted. Statistical analyses indicate that the counts of the two phenotypes have varied in synchrony over the past decade, with no evidence of competitive increases by either phenotype at the expense of the other. A weak correlation across survey districts between the population densities of squirrels and of trees greater than 15 cm dbh was detected. Above-median squirrel densities were clustered in the older central districts of Olney, with below-median densities in the newer suburbs. Some speculation is presented about the history of this Olney mutation before and after its first observation in 1902, and about the possibility that some degree of heterosis may explain the appearance of small white squirrel populations in at least 19 other North American communities. INTRODUCTION Mutations leading to albinism in gray squirrels (Sciurus carolinensis Gmelin) are apparently frequent. The best known of 20 contemporary white squirrel populations in North America is that in Olney, Illinois (38?32'N, 88?06W; population 9,000; area 10.6 kM2), where autumn white squirrel counts by 30 or more volunteers annually receive widespread publicity. This in turn has stimulated personal communications (to J.E.S., see Acknowledgments) reporting white squirrel populations in 19 other communities: Ballston Spa, New York; Brevard, North Carolina; Claremont, New Hampshire; Columbia, Michigan; Elgin, Illinois; Green County, Ohio; Greenwood, South Carolina; Kenton, Tennessee; Kettering, Ohio; Marionville, Missouri; Montello, Wisconsin; St. Paul, Minnesota; Trenton, NewJersey; Valparaiso, Indiana; Versailles, Illinois; Wabasha, Minnesota; Westby, Wisconsin; Xenia, Ohio; and in Exeter, Ontario, Canada. The Exeter, Ontario, population includes both white and black mutants in addition to the wild-type grays. The Olney volunteer squirrel counters (annually organized by J.E.S.) have now completed their 10th successive estimate (1977 to 1986 inclusive) of the white and gray squirrel populations of Olney. These estimates are the averages of separate 2-hr counts taken during the mornings of the last three Saturdays in October. For year-to-year comparisons these averages provide more reliable indices than any single count. They are necessarily smaller than at least the largest of the three annual counts, and are therefore underestimating annual populations by some unknown proportion we assume to be roughly constant from year to year. For these annual squirrel counts the City of Olney is divided into 33 contiguous districts, all of which are walked simultaneously by the community volunteers. Early newspaper accounts (Olney Advocate, 21 April 1932 and 8 August 1935) of the Olney white squirrels document the recollections of longtime residents who were in gen-