We mounted a video camcorder in a single-engine aircraft to estimate
nesting density along 10-m wide strip transects in black brant
colonies on the Yukon Delta National Wildlife Refuge, Alaska during
1990-1992. A global positioning system (GPS) receiver was connected
to the video recorder and a laptop computer to locate transects and
annotate video tape with time and latitude-longitude at 1-second
intervals. About 4-5 hours of flight time were required to record
30-40 minutes of video tape needed to survey large (>5,000 nests in >
10 km2)colonies. We conducted ground searches along transects to
locate and identify nests for determining detection rates of nests in
video images. Counts of nests from video transects were correlated
with actual numbers of nests. Resolution of images was sufficient to
detect 81% of known nests (with and without incubating females). Of
these, 68% were correctly identified as brant nests. The most common
misidentification of known nests was failure of viewers to see the
nest that the detected bird was incubating. Unattended nests with
exposed eggs, down-covered nests, and nesting brant, cackling Canada
geese, and emperor geese were identified in video images. Flushing of
incubating geese by survey aircraft was not significant. About 10% of
known nests were unoccupied in video images compared to 16% unoccupied
nests observed from tower blinds during periods without aircraft
disturbance.
