Evaluation of road-based surveys of Rio Grande wild turkeys in Texas

Many techniques have been used to index or estimate abundance, density, and trends of Rio Grande wild turkey (Meleagris gallopavo intermedia) populations. Though traditional index-based monitoring techniques can indicate trends in wild turkey populations, they were not designed with the sensitivity necessary to detect anything but drastic changes. Recent research on line transect-based distance sampling from roads has indicated road-based surveys may provide an efficient, effective, and inexpensive technique for monitoring wild turkey populations on an ecoregion scale. Our goal was to evaluate the applicability of road-based distance sampling in the Cross Timbers, Edwards Plateau, Rolling Plains, and South Texas ecoregions of Texas. Our research objectives were to: (1) quantify the association of male and female Rio Grande wild turkeys to roads according to ecoregion, season, and time of day, and examine potential biases associated with using roads as transects for distance sampling; (2) conduct road-based surveys in each ecoregion to determine wild turkey flock encounter rates and the amount of survey effort required to obtain adequate sample sizes for road-based distance sampling; and (3) conduct field simulation surveys using inflatable wild turkey decoys to determine flock detection probabilities and evaluate factors affecting wild turkey flock detectability.

We found that Rio Grande wild turkey populations are randomly distributed around roads from 1 December-15 March in most areas. Our results suggested that road-based surveys conducted during that period will produce generally unbiased results. We conducted road-based surveys in 4 ecoregions of Texas from 1 December 2007-15 March 2008. Encounter rates of wild turkey flocks obtained from road-based surveys varied from 0.1 (0.0-0.6; 95% CI) to 2.2 (0.8-6.0) flocks/100 km surveyed. Encounter rates from surveys restricted to riparian communities varied from 0.2 (0.1-0.6; 95% CI) to 2.9 (1.5-6.7) flocks/100 km surveyed. Flock detection probabilities obtained from field simulations ranged from 22.5% (16.3-29.8%; 95% CI) to 25.0% (13.6-39.6%). Flock detection probabilities were lower than expected in each ecoregion, which resulted in low encounter rates. Estimated survey effort required to obtain adequate sample sizes for distance sampling ranged from 2,765 km (2,597-2,956 km; 95% CI) in the Edwards Plateau to 37,500 km (33,333-42,857 km) in South Texas. When road-based surveys were restricted to riparian communities, estimated survey effort ranged from 2,222 km (2,092-2,370 km; 95% CI) in the Edwards Plateau to 22,222 km (19,782-25,349 km) in South Texas. Our modeling efforts suggested that distance to the flock and vegetative cover combined played important roles in wild turkey flock detectability. Frequent rains during the 2007 growing season created dense understory vegetation that made flock detectability difficult in every ecoregion. Our results indicated that too much survey effort was required to make road-based surveys a feasible technique for monitoring wild turkey populations in most ecoregions of Texas. However, when surveys were restricted to areas within 1 km from a river or stream, the technique was feasible for monitoring wild turkey populations in the Edwards Plateau and Rolling Plains ecoregions.