Viability and Conservation of an Exploited Sage Grouse Population

We analyzed the viability of the Sage Grouse (Centrocercus urophasianus) population of North Park, Colorado, to evaluate its supposed decline due to hunting pressure and habitat degradation. Demographic data from 23 years of surveys were used to parameterize a post-breeding, female-based projection matrix with three life stages: juveniles, yearlings, and adults. The population was found to be approximately stable or in decline only if immigration and apparent surveying errors were factored from the data set. Adult and juvenile survival and adult and juvenile reproduction, respectively, were identified as the most limiting demographic factors. Empirical evidence from designed experiments with Sage Grouse has shown that these demographic factors respond markedly to habitat manipulations, especially brush manipulation. Several plausible management scenarios were evaluated with 100-year population projections generated through Monte Carlo simulation (1000 iterations), sampling from a normal probability distribution entraining the observed variability in each demographic parameter (95% confidence limits). Habitat manipulations to achieve moderate levels (~15% canopy cover) of sagebrush (Artemisia tridentata) are recommended. Regression analyses with power tests showed correspondence between hunting mortality and total mortality for juveniles and adults. Provided that habitat manipulations improve the survival of juveniles and adults, population viability may be conserved without reducing harvest by hunters. Analizamos la viabilidad de la poblacion de Centrocercus urophasianus en el Parque Norte, Colorado, para evaluar su supuesto declive ocasionado por presiones por caza y degradacion del habitat. Datos demograficos de 23 anos de estudios fueron utilizados para parametrizar una matriz de proyeccion posterior a la estacion reproductiva, basada en hembras y con tres estadios de vida: juveniles, organismos de un ano y adultos. La poblacion se encontro en una situacion aproximadamente estable o en declive unicamente si la inmigracion y errores aparentes de muestreo fueran eliminados de la base de datos. La supervivencia de juveniles y adultos y la reproduccion de adultos y juveniles respectivamente, fueron identificados como los factores demograficos mas limitantes. Evidencias empiricas de experimentos disenados con la especie han demostrado que estos factores demograficos responden marcadamente a manipulaciones del habitat, especialmente a la manipulacion por friccion. Diversos escenarios plausibles de manejo fueron evaluados con proyecciones poblacionales de 100 anos mediante simulaciones Monte Carlo (1000 repeticiones), muestreos de una distribucion de probabilidad normal incorporando la variabilidad observada en cada parametro demografico (95% limites de confianza). Se recomienda la manipulacion del habitat para alcanzar niveles moderados (~15% cobertura de dosel) de salvia arbustiva (Artemisia tridentata). Analisis de regresion con pruebas de poder mostraron correspondencia entre la mortalidad por caza y la mortalidad total de juveniles y adultos. Pensando que las manipulaciones al habitat mejorarian la supervivencia de juveniles y adultos, la viabilidad poblacional podria ser conservada sin reducir la cosecha por cazadores.

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