ELF Communications System Ecological Monitoring Program: Bird Species and Communities: Annual Report 1988-1989

Abstract

This investigation was designed to isolate effects of electromagnetic (EM) fields produced by extremely low frequency (ELF) antenna systems on bird species breeding in or migrating through Wisconsin and Michigan. Specifically, we seek to determine if bird species richness and abundance differ between areas that are close to the antenna and those that are far enough away to be unaffected by the antenna. We are pursuing this question at both the community and species level. Characteristics examined include total species richness and abundance, abundances of common bird species, and abundances of birds within selected guilds. Our monitoring program includes bird censuses over a five month period from May to September (1986-1989). Additional data were collected in June of 1985 and August-September of 1984. Here we summarize results of our 1989 research activities. The Michigan transmitter began 150 amp tuning and testing intermittently in the first part of May. On the 14th of May, the transmitter began continuous 150 amp operation for 16 hrs/day on weekdays and all day on weekends. On October 7th, the Michigan transmitter began full power continuous operation. We therefore consider May 1989 to be a transitional period, and June through September to be impact periods. Bird abundance and species diversity were highest in June and July in Michigan and in May and June in Wisconsin. No significant differences in community level parameters (total individuals, total species) were noted in either state. Considerable annual variation in numbers of individuals and species was noted. Particularly abundant species (all seasons included) included the Nashville Warbler, Ovenbird, White-throated Sparrow, Red-eyed Vireo, Black-capped Chickadee, Hermit Thrush and Golden-crowned Kinglet. The most abundant species present on treatment and control segments varied among seasons and between states. Among "abundant" species (>1 individual observed/500 m segment), five of 34 comparisons (over all seasons) revealed a significant difference between treatment and control XII segments in Michigan; four indicated a greater abundance on control segments. Six of 31 comparisons indicated a significant difference between treatment and control segments in Wisconsin; four indicated a greater abundance on control segments. Previous analyses of vegetation on Wisconsin and Michigan study sites (Blake et al. 1988) revealed differences between treatment and control plots. The difference most likely to influence bird populations was distribution of coniferous and deciduous habitats. Treatment segments supported more coniferous and lowland habitats than did control areas, in both states. To account for differences in habitat between treatment and control segments in Wisconsin, we paired treatment and control segments on the basis of habitat similarity and compared bird abundances on these paired segments (N = 15 pairs). (The Michigan study is designed as a "before-and-after" experiment and, thus, differences in habitat pose less of a problem for interpretation of bird distribution patterns.) Two of 31 comparisons of abundant species showed significant differences between paired segments in Wisconsin; in both cases, numbers were higher on treatment segments. The final report for Wisconsin will consider effects of vegetation on results from previous years and on distribution patterns of guilds. Eighteen of 105 comparisons of common species (based on prominence values) between treatment and control segments (all segments) in Michigan and 20 of 100 in Wisconsin were significant. Values were higher on control segments in Michigan in 9 cases; 6 of 20 were more abundant on control than on treatment segments in Wisconsin. Few species were consistently and significantly more abundant on either treatment or control segments among seasons within a year or within seasons between years. Differences between treatment and control segments are most likely due to habitat differences. Species were classified into guilds on the basis of foraging behavior and preferred breeding habitat. Few significant differences in abundances of birds within different guilds were found between treatment and control segments. Differences were most consistent for habitat categories, providing further evidence that habitat differences are responsible for many of the observed differences in bird distribution patterns between treatment and control segments.