Hourly variation in transect counts of birds

Abstract

We examined hourly variation in numbers of birds detected during morning line transect counts in northern Wisconsin and Upper Peninsula Michigan . We analyzed hourly variation by month (May-September), year (1986, 1987 ; 1985-June only), and state . Mean number of individuals detected generally was highest during the first or second hour in each state. Hourly differences in total individuals were significant in 1 of 1 1 monthly samples in Wisconsin and in 4 of 11 in Michigan . Lowest counts of total individuals were recorded during the fourth hour. No significant difference among hours was detected in mean number of species detected per hour in Wisconsin. Differences were significant in three Michigan samples and approached significance (P < 0.06) in a fourth . Lowest counts of total species occurred during the fourth hour. Individual species varied in hourly trends ; some increased during the morning, some decreased, and others showed no consistent pattern in number of individuals detected per hour. Hourly differences in abundance of individual species were significant in 12 of 61 comparisons (20%) in Wisconsin but in only 1 of 62 (2%) in Michigan .