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Roosting birds of certain species can be agricultural pests, hazards to aircraft on takeoff and landing, and a purported health hazard. Locating roosts of pest bird species and estimating the numbers of birds using them is time-consuming field work, especially when use of different roosts changes seasonally. Since the middle of the previous century, radar has been used to observe early morning bird echoes, then called “ring angels”. Today, large Doppler radars designed for meteorological work can routinely observe bird roosts, even when birds fly at treetop height. Radar images can often locate all roosts within a certain distance from the radar and can provide an indication of the number of birds using each roost and the general location of their food sources. Single images from the lowest tilt angle (lowest elevation) of different radars show roosts in several areas of the country, and successive scans of a research radar across an area becomes an animated picture of the detailed spatial behavior of birds leaving the roost. Applying a computer image recognition technique, the Hough Transform, to single radar-derived images of bird roosts results in objective numerical estimates of roost location and other data. Data are shown comparing ground-truth visual counts of European starling and brown-headed cowbird departures with such quantitative radar-derived data. The radar correctly estimated the central tendency of flight speed of the birds (20 m/sec), time of morning flight (mean 13.2 min past civil sunrise), and roost location (modal error about 2 km). Sometimes (5.1% of identifications) the algorithm found a “roost” that could not be located by field observers; occasionally there were other sources of confusing echo such as vehicles or migrating birds.

The appropriate selection or combination of packages such as HOMERANGE, TELEM88 and KERNELHR is necessary to analyze the dispersal of animals. The software includes graphic display, home range estimation and habitat analysis. Fewer general-purpose packages serve the purpose better than a wide variety of software packages.

A recently developed radar-based technique permitted empirical re-evaluation of the established but poorly supported theory that migrating North American waterfowl (Anatidae) use landscape features such as rivers as leading lines. Ducks departing the Illinois River Valley in the autumn of each of 15 years travelled SSE with a mean track that was 68° different from the 220° course of the Illinois River ( P ≤ 0.001). We conclude that leading lines were unimportant navigation aids for ducks leaving this major stopover site in autumn and suggest that rivers have less effect on the spatial course of duck migration than previously thought. Timing of departures was examined in a representative subset of 8 years and found to be consistent, with a mean start time of 44 min after civil sunset. [ABSTRACT FROM AUTHOR]