To compare behaviors of radio-marked and unmarked mallards, we used data collected on paired females from late April through June. Weighting by the square root was a compromise between giving each female equal weight and weighting by the number of observations per female. For unmarked females, the number of individuals observed and the distribution of observations among them were unknown. Thus, the percent time observed in each category could not be weighted and averaged, and standard errors could not be calculated. For the statistical comparison of unmarked and radio-marked birds, we assumed that the percent time unmarked females were observed in each behavioral category was measured without error.
All percentages reported are back-transformed values.
Sample sizes are given in Table 1 . Nests of most radio-marked birds were found by using telemetry. These searches commenced in late April or early May, after trapping and radio-tagging operations had ended. Clutch size was recorded as the maximum number of eggs found in completed clutches. We assumed that the samples of nests found by telemetry and chain dragging contained comparable proportions of first nesting attempts.