Monitoring Butterfly Populations Using the Fourth of July Butterfly Count

Abstract

-The Xerces Society's Fourth of July Butterfly Count (4J), patterned after the popular Christmas Bird Count (CBC), is a nationwide, volunteer, annual 1-day census of butterflies and skippers at selected sites. The ornithological literature is reviewed, although not exhaustively, to summarize the methods for analyzing CBC data and to list the types of studies using these data. Applications of ornithologists' experiences with, concerns about, and uses for, CBC data to 4J studies are discussed, as well as issues, problems and opportunities specific to the Lepidoptera and 4J. This discussion is augmented by the results of a survey of midwestern 4J compilers. Two prototype studies using 4J data are offered: a nationwide analysis of monarch data 1979-1988 and an analysis restricted to the Midwest 1986-1989 on the fluctuations of immigrant species. DESCRIPTION AND PURPOSES OF BUTTERFLY COUNT The Xerces Society started the Fourth of July Butterfly Count (4J) in 1975 and has sponsored it annually since. The methods of the butterfly count are patterned after the highly successful Christmas Bird Count (CBC), founded in 1900 and sponsored by the National Audubon Society, except for the time of year. The 4J count period informally extends several weeks before and after this holiday, although counts outside this time period are also accepted. People initiating a count establish a 15-mile diam count area, which is to remain the same each year the count is conducted. In a 1-day period, participants keep track of the number of each species of butterfly (i.e., butterfly and skipper) seen, method of identification, time in the field, weather, number of observers in how many field parties, and distances traveled and how (car, foot, etc.). Results are published annually by the Xerces Society (10 Southwest Ash Street, Portland, Oregon 97204). Like the CBC counts, the 4J counts are diverse. Some counts census city parks, campuses, arboretums or nature centers, while others census more natural areas. Amateur lepidopterists conduct some counts, while professional lepidopterists conduct others. Some counts are held for fun, while others are part of research or monitoring projects. Nature centers also conduct counts as educational ventures for their members or the general public. Many counts census both developed and wild areas and mix amateur and professional lepidopterists as counters. The butterfly count was started for various reasons. Most important, it was meant to be a pleasant and educational experience both for people interested in butterflies and the general public, who often help out. The program presents butterflies, and by association invertebrates in general, in a positive and appealing way to the public. A secondary purpose of the 4J count was as an informal tool for studying and monitoring butterfly populations, especially to learn more about the ranges and sizes of butterfly populations and how weather and other variables affect butterflies. I surveyed the 16 count compilers active any year(s) from 1986 to 1988 inclusive in the Midwest (Ohio to Iowa and Michigan to Minnesota, hereafter Midwest). They filled out a separate survey for each of the 19 count circles counted in one or several of those three years. Responses from 14 compilers representing 17 counts were received. As for how midwestern counts got started, word of mouth from someone familiar with 4J was the most frequent method of recruiting a count's compiler (n = 7), although membership drives for the Xerces Society were nearly as effective (n = 5). R. M. Pyle's