We assessed song rates among male Cerulean Warblers (Dendroica cerulea) in Ozark riparian forest in southeastern Missouri to characterize song rate variation and estimate how many males may be missed during censuses. Average (± SD) songs per 5-min intervals for continuous 4-hr observation periods varied from 3.1 ± 4.8 (mated males) to 36.0 ± 18.7 (unmated males; n = 24 males). Unmated males averaged twice the number of songs per 5-min periods than mated males. Considerable song rate variation existed even among mated males. Song rates slightly declined over the 4-hr observation period. Song rate differences between Cerulean Warblers in Ontario and southeastern Missouri suggest caution when making assumptions about breeding status based on auditory surveys. Average male Cerulean Warbler territory size (n = 20) was 0.9 ± 0.1 ha with 27 of 31 males having at least one abutting conspecific territory. All males (n = 24) were silent for 32.7 ± 21.5 and 21.8 ± 17.4% of the 5-min and 10-min periods, respectively. Unpaired males (n = 5) were silent for 2.9 ± 3.15 and 1.2 ± 1.86% and mated males (n = 19) were silent for 37.9 ± 18.8 and 25.4 ± 16.2% of the 5-min and 10-min periods, respectively. These data demonstrate that when auditory clues are used for detection, not incorporating song rate will result in significant underestimates of density.
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Vol. 121 • No. 2