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An important concern of conservation biologists is determining what conditions most limit the number of individuals in endangered populations. Because time is a constraint, narrowing the search for such factors is beneficial. Toward this end we used broad spatial and temporal data, to test the hypothesis that reproductive success (as measured by juvenile-to-adult ratios) of the endangered Attwater’s Prairie Chicken (Tympanuchus cupido attwateri) was not equal to that of the nonendangered Greater Prairie Chicken (T. c. pinnatus). We then tested the hypotheses that mean clutch size, egg hatchability, nesting success, and number of chicks per brood prior to brood breakup for Attwater’s Prairie Chicken were not equal to those of the Greater Prairie Chicken. We found that the mean ratio of juveniles to adults among Attwater’s Prairie Chicken was less than that of the Greater Prairie Chicken (p < 0.011), as would be predicted if reproductive success controls proportional changes in prairie-grouse numbers among years. Mean nesting success (32.2%) and number of chicks per brood prior to brood breakup (4.2) of Attwater’s Prairie Chicken were both less than those of the Greater Prairie Chicken (49.5 %, p = 0.0425, and 6.0 p = 0.0001, respectively). We suggest that researchers focus on determining what proportion of Attwater’s Prairie Chicken broods survive and why Attwater’s Prairie Chicken nesting and brood-rearing success are so poor relative to those of the Greater Prairie Chicken.

Una consideracion importante para biologos de conservacion es determinar cuales condiciones son mas limitantes para individuos de poblaciones en peligro de extincion. Porque el tiempo es constringente, enfocando la busqueda a tales factores seria beneficiosos. Hacia este fin probamos la hipothesis que el exito reproductivo (medido por la tasa de juveniles a adultos) de la especie en peligro de extincion, Tympanuchus cupido attwateri, no era igual que el de la especie no en peligro de extincion, T. c. pinnatus usando inforamcion con amplia extension geographic y temporal. Ademas probamons las siguientes hipothesis, que el numero promedio de huevos por nidada, salida del huevo, exito de anidacion, y el numero de polluelos por nidada antes de la dispersion de pollos, no eran igual al de T. c. pinnatus. Encontramos que la tasa promedio de juveniles a adultos de T. c. attwateri era menor que el de T. c. pinnatus (p = 0.011), que seria lo que se predeciria si el exito reproductivo es lo que controla los cambios proporcionales occurridos anualmente en el numero de gallinaceas de pradera. Para T. c. attwateri el promedio de nidos exitosos (32.2%) y el numero de polluelos por nidada, previo a la dispersion de los pollos (4.2), era menor que para T. c. pinnatus (49.5%, p = 0.0425, y 6.0, p = 0.0001, respectivamente). Sugerimos que investigadores se enfoquen en determinar que proporcion de las nidadas de T. c. attwateri sobreviven y porque el exito reproductivo y crianza de pollos de T. c. attwateri as tan bajo relativo al de T. c. pinnatus.