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Effects of broadcasting calls during surveys to estimate density and occupancy of northern bobwhite


  • Associate Editor: McDonald


We assessed the effects of using a broadcast caller during surveys and increasing survey duration to estimate northern bobwhite (Colinus virginianus) density and occupancy. From 15 May 2009 to 15 August 2009, we conducted repeat-visit breeding bobwhite surveys at 180 sites in Delaware, USA. Increasing survey duration from 3 min to 7 min, or using a broadcast caller, improved detection probability for a single visit by 52% and 42%, respectively. However, density estimates when using a broadcast caller were biased high—≥3 times greater compared to passive-listening surveys. Density estimates for 3-min and 7-min passive surveys were not different. Additionally, bobwhite occupancy was similar among all 3 survey treatments. Use of a broadcast caller to survey for bobwhites appears to violate the assumption of distance sampling that an individual is detected prior to movement. Use of a broadcast caller is inappropriate for determining density estimates through distance sampling, but may be appropriate for determining site occupancy. © 2011 The Wildlife Society.