We used multiple‐linear‐regression methods to simultaneously assess effects of vegetative disturbance and weather on the production of sharp‐tailed grouse (Tympanuchus phasianellus) on Valentine National Wildlife Refuge (NWR) in Nebraska using a long‐term data set of harvest‐age ratios as production indices. After developing the model, we plotted the model‐averaged predictions of sharp‐tailed grouse production indices for Valentine NWR against actual sharp‐tailed grouse production indices for our reference area, Samuel R. McKelvie National Forest (NF) in Nebraska. Model‐averaged estimates of production provided reasonable predictions of actual production indices on Valentine NWR, although prediction intervals were large. The most useful predictor variables according to cumulative Akaike's Information Criterion weights were weather variables, emphasizing the significant influence of weather on sharp‐tailed grouse production. As hypothesized a priori, “May Average Temperature,” “June Average Temperature,” and “Cumulative Precipitation from 1 January‐31 July” were positively correlated with sharp‐tailed grouse production, while “June Number of Heat Stress Days” and “June Number of Days of Precipitation >2.54 mm” were negatively correlated with sharp‐tailed grouse production. The drought index, Cumulative Precipitation from 1 January‐31 July, explained the most variability in sharp‐tailed grouse production indices. The model developed on Valentine NWR overpredicted sharp‐tailed grouse production indices on Samuel R. McKelvie NF by 0.77 juveniles per adult, when averaged across years. Further experimentation is needed to support our hypothesis that vegetative disturbance on Samuel R. McKelvie NF is negatively affecting sharp‐tailed grouse production at its current levels.
The ratio of juveniles to adults in the fall harvest is a common index of production for Galliformes. The percentage of juvenile birds in the harvest has been shown to decline as the hunting season progressed for many galliforms, resulting in a biased index of production. Therefore, we used wing samples of plains sharp‐tailed grouse (Tympanuchus phasianellus jamesi) and greater prairie‐chickens (T. cupido pinnatus) from 4 public land areas in the Nebraska Sandhills, Nebraska, USA, to assess the potential for bias in harvest‐age ratios across time. We hypothesized that the ratio of juveniles to adults in the harvest could change over time if susceptibility to harvest and/or fall survival were different between the juvenile and adult prairie grouse (Tympanuchus spp.) in the Nebraska populations. We found no change in the harvest‐age ratio over time in either the sharp‐tailed grouse or greater prairie‐chicken data. Our findings were consistent with the published literature on harvest‐age rates for sharp‐tailed grouse but inconsistent with the greater prairie‐chicken literature. Therefore, we maintain that analysis of the harvest data for bias due to a changing harvest‐age ratio as the hunting season progresses is an essential adjunct to subsequent analysis or comparisons of production indices based on harvest‐age ratios. In addition, limitations of harvest‐age ratios must be known and care must be taken to minimize other potential biases before using harvest‐age ratios as an index to production.
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