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Journal of Wildlife Management 75 1 61 70 2011 DOI 10 1002 jwmg 4 Research Article Simulating Northern Bobwhite Population Responses to Nest Predation Nesting Habitat and Weather in South Texas MICHAEL J RADER 1 Caesar Kleberg Wildlife Research Institute Texas A M University Kingsville Kingsville TX 78363 USA LEONARD A BRENNAN 2 Caesar Kleberg Wildlife Research Institute Texas A M University Kingsville Kingsville TX 78363 USA KYLE A BRAZIL 3 Caesar Kleberg Wildlife Research Institute Texas A M University Kingsville Kingsville TX 78363 USA FIDEL HERNA NDEZ Caesar Kleberg Wildlife Research Institute Texas A M University Kingsville Kingsville TX 78363 USA NOVA J SILVY Department of Wildlife and Fisheries Sciences Texas A M University College Station TX 77843 USA ABSTRACT Nest predation is thought to be one of the major factors limiting northern bobwhite Colinus virginianus populations We examined the relative impact of altering nest predation rate nesting habitat and weather i e temp and precipitation on northern bobwhite population dynamics in a hypothetical 15 000 ha subtropical rangeland ecosystem in south Texas using a simulation model The systems model consisted of a 3 stage i e eggs juv and ad bobwhite population with dynamics in uenced by variables affecting production recruitment nest predation and mortality We based model parameters on data collected from a 3 yr nest predator study employing infrared camera technology from ongoing eld research using a radio marked population of wild bobwhites and from the literature The baseline simulated bobwhite population dynamics corresponded closely to empirical data with no difference between medians of simulated n 30 yr and observed bobwhite age ratios over a 28 yr period Similarly a time series comparison of simulated and observed age ratios showed most 89 observed values fell within the 5th and 95th percentiles of the simulated data over the 28 yr period We created simulated population scenarios representing 1 baseline historical conditions 2 predator control 3 low precipitation 4 low precipitation with predator control 5 high temperature 6 high temperature with predator control 7 reduced nest clump availability and 8 reduced nest clump availability with predator control that resulted in considerably different median bobwhite densities over 10 yr For example under simulated predator control populations increased by about 55 from the baseline scenario whereas under simulated reduced nest clump availability populations decreased by about 75 from the baseline scenario Comparisons of time series for each scenario showed that reduced nest clump availability low precipitation and high temperature reduced bobwhite densities to a larger degree compared to a natural nest predation rate Reduced nest clump availability resulted in the most substantial decline of simulated bobwhite densities Simulations suggested that management efforts should focus on maintaining adequate nest clump availability and then possibly consider nest predator control as a secondary priority 2011 The Wildlife Society KEY WORDS bobwhite Colinus virginianus drought nesting habitat nest predation population predator control simulation south Texas stochastic modeling Northern bobwhite Colinus virginianus populations are potentially limited by many factors including predation weather and habitat Stoddard 1931 Lehmann 1984 Roseberry and Klimstra 1984 Guthery 2002 In south Texas bobwhites exist in a unique ecological context characterized by a diverse predator community recurrent drought extensive and contiguous semiarid subtropical rangeland subject to livestock grazing and fee lease hunting Lehmann 1984 Herna ndez et al 2002 Rader et al 2007b South Texas is one of the few regions where bobwhite populations have not experienced signi cant longterm declines in North America Brennan 1991 Church et al 1993 Link et al 2008 Recent trends indicate large cattle ranches characteristic of south Texas have increasing economic incentives to emphasize sale of bobwhite and white tailed deer Odocoileus virginianus hunting opportunities over livestock production This development has resulted in economic incentives to maintain rangeland in a Received 30 April 2010 Accepted 12 May 2010 1 Present Address Wisconsin Department of Natural Resources 5301 Rib Mountain Drive Wausau WI 54401 USA 2 E mail leonard brennan tamuk edu 3 Present Address P O Box 1370 Lampasas TX 76550 USA Rader et al Bobwhite Population Model condition bene cial to bobwhites and a variety of other wildlife Fulbright and Bryant 2002 Numerous biotic and abiotic factors in uence bobwhite production in South Texas Nest predation is the main cause of bobwhite nest failure and is a recurrent management concern for bobwhites and other ground nesting galliformes Stoddard 1931 Klimstra and Roseberry 1975 Lehmann 1984 Hurst et al 1996 Rollins and Carroll 2001 Apparent bobwhite nest losses to predation generally fall between 37 and 76 Lehmann 1946 Simpson 1976 Staller et al 2005 Rader et al 2007a Sandercock et al 2008 Thus there is evidence that predation might limit potential bobwhite production but the impact of nest predation on fall and spring bobwhite densities is not clear In fact predator removal studies have been shown to have minimal positive effects on south Texas bobwhite populations Beasom 1974 Guthery and Beasom 1977 Lehmann 1984 Sandercock et al 2008 observed that nest success was fourth in overall importance after chick survival adult summer and adult winter survival with respect to annual population growth Nesting habitat is another variable potentially amenable to management and a perennial concern for managers in south Texas Kiel 1976 Guthery 1997 Kopp et al 1998 Numerous studies have documented bobwhite nest site selection and susceptibility to predation Spears et al 1993 Guthery 1997 61 Herna ndez et al 2003 Lusk et al 2006 Rader et al 2007a Additionally other studies have highlighted potential deleterious effects of grazing on bobwhite habitat and production Cantu and Everett 1982 Wilkins and Swank 1992 Drought is a recurrent feature in south Texas and is thought to be the driving mechanism of the characteristic boom bust phenomenon exhibited by bobwhite populations in the region Lehmann 1984 Lusk et al 2001 Herna ndez et al 2002 Herna ndez et al 2007 Both reduced precipitation Kiel 1976 Bridges et al 2001 Herna ndez et al 2005 and high operative temperatures Guthery et al 1988 2001 2005 Forrester et al 1998


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