A novel methodology for the rapid assessment of waterbird vulnerability to disturbance

Abstract

A methodology for rapidly assessing the vulnerability of waterbirds to disturbance was tested at Sabaki estuary, Kenya. Three variables were employed to measure the responses of 15 species: (1) bird density, (2) minimum distance of birds from a stationary disturbance and (3) recovery times following a moving disturbance. Spatial response metrics (1) and (2) were regressed against expected species densities (in the absence of disturbance). Normalised mean residuals then described species-specific deviations from the average spatial response to disturbance. A hypothetical model was constructed, whereby species were placed on a spatial response gradient and overlaid by the recovery metric (3). Greater Flamingo Phoenicopterus roseus, Lesser Flamingo Phoeniconaias minor, African Spoonbill Platalea alba and Terek Sandpiper Xenus cinereus exhibited the strongest avoidance responses. The two spatial metrics (1 and 2) achieved concordance for 73% of species, and all three metrics gave similar results for six of seven species at the extremes of the spatial response gradient. Non-concordance between response metrics is likely an effect of life-history traits (e.g. territoriality). Our results support the use of relative spatial response metrics (1 and 2) for robust and rapid identification of waterbird species that are most responsive and, by virtue, vulnerable to the effects of disturbance on tropical estuaries.