Aerial survey of waterbirds on wetlands as a measure of river and floodplain health

1. This study highlights the use of waterbird communities as potential meas ures of river and floodplain health at a landscape scale. 2. The abundance and diversity of a waterbird community (54 species) was me asured over 15 trips with four aerial and three ground counts per trip on a 300-ha lake in arid Australia. 3. Aerial survey estimates of individual species were significantly less pr ecise (SE/mean) than ground counts across two (11-100 and > 1000) out of lo ur abundance classes of waterbirds: 0-10, 11-100, 101-1800 and > 1000. Stan dard error/mean as a percentage decreased with increasing abundance from ab out 60% for the lowest abundance class to 18% for the largest abundance cla ss. 4. Aerial survey estimates were negatively biased for species in numbers of less than 10 and greater than 5000 but unbiased compared to ground counts for other abundance classes. Aerial surveys underestimated numbers of water birds by 50% when there were 40000 waterbirds. Three ground counts found ab out seven more waterbird species than four aerial surveys. One ground count took about 150 times longer than two aerial surveys and cost 14 times more . 5. Regression models were derived, comparing aerial survey estimates to gro und counts for 31 of 36 species for which there were sufficient data. Aeria l survey estimates were unbiased for most of these species (67%), negativel y biased for six species and positively biased for one species. Estimates w ere negatively biased in species that occurred in small numbers or that div ed in response to the aircraft. 6. River system health encompasses the state of floodplain wetlands. Waterb irds on an entire wetland or floodplain may be estimated by aerial survey o f waterbirds; this is a coarse but effective measure of waterbird abundance . Aerial survey is considerably less costly than ground survey and potentia lly provides a method for measuring river and floodplain health over long p eriods of time at the same scale as river management.