Researchers have indexed abundance of the northern bobwhite (Colinus virginianus; hereafter, bobwhite) during autumn by counting the number of coveys heard during early morning call surveys. However, critical assumptions about call rates, survey timing, and seasonality have not been tested, and the effects of weather and bobwhite density on call rates are unknown. Therefore, we quantified covey-calling activity of 219 radiomarked coveys at 5 sites during September–December 1997–1999 to assess the effects of these variables. Across all sites, the average proportion of coveys that called prior to leaving the roost site was 58% (range = 48–87%). Coveys began calling 23.4 ± 0.5 (x̄ ± SE) min before sunrise, and they produced 31.4 ± 1.9 calls/call event; most calls (87%) occurred 35–15 min before sunrise. Using data collected in 1998, we fit 15 logistic regression models to predict the probability of a covey calling. The selected best model (Akaike weight [w] = 0.48) included variables for the number of adjacent calling coveys, wind speed, cloud cover, and barometric pressure change with number of adjacent calling coveys having the greatest effect on covey calling (odds ratio of 1.4). A less parsimonious model, which also included biweekly periods and interaction terms, was potentially as likely (w = 0.41) as the selected model, with the 16–31 October biweekly period having most effect (odds ratio of 1.8) over other biweekly periods. We tested selected best models using observations collected in 1999 from 2 of the sites monitored in 1998. During peak calling periods, predicted call rates were <0.06 from observed covey-call rates. Given the accuracy of predicted call rates, we recommend adjusting covey-call counts by an estimated calling rate to better measure fall bobwhite abundance.
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Vol. 68 • No. 3