Encounter rates from road-based surveys of rio grande wild Turkeys in Texas

Traditional index-based techniques have indicated declines in Rio Grande wild turkey (Meleagris gallopavo intermedia; hereafter, wild turkey) populations across much of Texas, USA. However, population indices can be unreliable. Research has indicated that road-based surveys may be an efficacious technique for monitoring wild turkey populations on an ecoregion level. Therefore, our goal was to evaluate applicability of road-based distance sampling in the Cross Timbers, Edwards Plateau, Rolling Plains, and South Texas ecoregions of Texas. We conducted road-based surveys in each ecoregion during December 2007March 2008 to estimate wild turkey flock encounter rates and to determine survey effort (i.e., km of roads) required to obtain adequate sample sizes for distance sampling in each ecoregion. With simulations using inflatable turkey decoys, we also evaluated effects of distance to a flock, flock size, and vegetative cover on turkey flock detectability. Encounter rates of wild turkey flocks from road-based surveys varied from 0.1 (95 CI= 0.00.6) to 2.2 (95 CI= 0.86.0) flocks/100 km surveyed. Encounter rates from surveys restricted to riparian communities (i.e., areas ≤1 km from a river or stream) varied from 0.2 (95 CI= 0.10.6) to 2.9 (95 CI= 1.56.7) flocks/100 km surveyed. Flock detection probabilities from field simulations ranged from 22.5 (95 CI= 16.329.8) to 25.0 (95 CI= 13.639.6). Flock detection probabilities were lower than expected in all 4 ecoregions, which resulted in low encounter rates. Estimated survey effort required to obtain adequate sample sizes for distance sampling ranged from 2,765 km (95 CI= 2,5972,956 km) in the Edwards Plateau to 37,153 km (95 CI= 12,861107,329 km) in South Texas. When we restricted road-based surveys to riparian communities, estimated survey effort ranged from 2,222 km (95 CI= 2,0922,370 km) in the Edwards Plateau to 22,222 km (95 CI= 19,78225,349 km) in South Texas.