Radar measures of bird density and flight heights during evening flight.

<p>Time series depicting the change in A) mean radar reflectivity (i.e., index of bird density) and B) mean height of birds aloft during evening flights around the KDAX radar during the winters of 1998–1999 and 1999–2000 (<i>n</i> = 44 days). Error bars denote ±1standard error of the mean.</p

Maps of wintering waterfowl distributions.

<p>Maps of the 5-km-bandwidth kernel density of radio-marked northern pintail locations (<i>n</i> = 3 102) and the mean radar reflectivity (i.e., index of bird density) around the KDAX radar (<i>n</i> = 18 days) during winter 1998–1999. White areas denote regions where radar data were masked from analysis.</p

Study area within the Central Valley of California.

<p>Locations (stars) and names of weather radars and their associated 80 km radius surveillance areas are shown. Also shown are capture locations of radio-marked northern pintail and mallard during winters of 1998–1999 and 1999–2000. Dark grey-shaded areas denote where radar data were masked because of persistent ground clutter contamination or partial radar beam blockage.</p

Accuracy, precision, and detection range of radar observations of birds during evening flight.

<p>Time series depicting the change in radar data accuracy, precision, and detection range as measured, respectively, by A) the mean correlation between mean radar reflectivity (i.e., index of bird density) and the mean kernel density of radio-marked waterfowl locations within a 0.5 km bandwidth, B) the kernel density bandwidth size of the maximum mean correlation coefficient between mean radar reflectivity and mean kernel density of radio-marked waterfowl locations, and C) the mean maximum range that the radar detected birds in the air around the KDAX radar among 2 000 bootstrapped samples of 30 individual sample volumes during the winters of 1998–1999 (<i>n</i> = 18 days) and 1999–2000 (<i>n</i> = 26 days). Standard errors for plots A and C were too small for display.</p

Mean evening flight initiation time for wintering dabbling duck species at various locations.

<p>Mean evening flight initiation time for wintering dabbling duck species at various locations.</p