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1 September 2005 Influence of precipitation on demographics of northern bobwhites in southern Texas
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Abstract

Northern bobwhite (Colinus virginianus) populations in southwestern rangelands are influenced by precipitation; populations increase during relatively wet periods and decrease during drought. Understanding the demographic responses of bobwhites to fluctuations in precipitation might provide a basis for identifying mechanisms responsible for the phenomenon. We compared 10 population variables (bobwhite survival, nesting-season length, nest success, hen success, percent hens nesting and renesting, nesting rate, percent juveniles in fall harvest sample (Nov–Feb), clutch size, and egg hatchability) between a dry (Sep 2000–Aug 2001; 51 cm precipitation) and wet period (Sep 2002–Aug 2003; 93 cm precipitation) in Brooks County, Texas. We monitored radiomarked bobwhites on 3 sites during the dry (n=263 bobwhites) and wet period (n=191 bobwhites) to obtain estimates of survival and reproductive effort. Bobwhite survival curves differed between the dry period (0.30±0.04; Ŝ±SE, n=102 bobwhites) and wet period (0.60± 0.06; n=71 bobwhites; P≤0.001) during fall-winter (Sep–Feb). A lower proportion of hens nested during the dry period (95% CI: 52.6±22.5 %; n=19 hens) compared to the wet period (100%; n=15 hens). Of hens that nested, the dry period exhibited a lower nesting rate (95% CI: 1.2±0.3 nests/hen) compared to the wet period (95% CI: 2.3±0.5 nests/hen). The dry period also experienced a shorter nesting season (69 days) compared to wet period (159 days). Lastly, percent juveniles (Nov–Feb) was lower during the dry period (95% CI: 69.3±0.3 %; n=740 harvested bobwhites) compared to wet period (95% CI: 78.3±2.1%; n=1,415 harvested bobwhites). Our field study highlights 4 demographic variables (i.e., survival, percentage of hens nesting, nesting rate, and nesting-season length) that warrant further research to identify causal factors responsible for the boom-and-bust phenomenon in bobwhites. Further, our data suggest that drought negatively impacts bobwhite reproductive effort such that harvest should be reduced or ceased during drought (e.g., <50 cm annual precipitation).

Fidel Hernández, Froylán Hernández, Juan A. Arredondo, Fred C. Bryant, Leonard A. Brennan, and Ralph L. Bingham "Influence of precipitation on demographics of northern bobwhites in southern Texas," Wildlife Society Bulletin 33(3), 1071-1079, (1 September 2005). https://doi.org/10.2193/0091-7648(2005)33[1071:IOPODO]2.0.CO;2
Published: 1 September 2005
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