Buffers, and sanctuary area for migratory birds: a novel approach

Migratory bird refuges provide sanctuary from human disturbance, but limited information is available to quantify the effectiveness temporal refuges and estimate sanctuary area. We used aerial transect and ground surveys to monitor the distribution and behavior of waterfowl and other waterbirds in response to a gradient of spatial and temporal disturbances from hunting in a restored floodplain wetland complex, Emiquon Preserve, along the Illinois River, USA. Using ArcMap and spatial interpolation of waterbird densities as a novel approach to quantify sanctuary area, we estimated that approximately 64%-76% of Emiquon Preserve functioned as refuge relative to temporal disturbances. However, in a similar analysis using overall waterbird density estimates from previous years when hunting pressure was less, we estimated 41%-52% of Emiquon Preserve was classified as sanctuary and mean area for individual species ranged from 13%-44%. We detected no changes in sanctuary area across varying levels of disturbances indicating that temporal refuges were ineffective at increasing sanctuary area when disturbances were absent. Disturbance buffer distance (i.e., the non-sanctuary area around each disturbance event) varied by species, location within the Preserve, and daily hunting intensity, but overall was 224 m (range = 0 - 1,046 m). We question the effectiveness of short-term temporal refuges for waterbirds and recommend others use our analytical approach to quantify disturbance buffers and refuge area in the future. Our data indicate that temporal refuges were ineffective at providing sanctuary conditions (i.e., non-hunted) and that significant tradeoffs exist in balancing provision of sanctuary and allowing human use of a restored floodplain wetland complex.