Estimating harvest rate and the effects of hunting pressure on northern bobwhite survival

Abstract

Harvest limits are an important component of wildlife management but evaluating whether realized harvest rates are close to established regulations is often not done in practice. Also, managers typically only partially control harvest rates via changes to metrics such as season length and hunting party size, but the relationships between these proxies and harvest rate are often unknown. We studied a population of northern bobwhite Colinus virginianus over a three-year period to estimate harvest, survival and relationships between harvest rate and proxies of hunting pressure. We captured and marked bobwhite with only bands (n = 479) or bands and radio-transmitters (n = 592). We monitored radio-marked individuals weekly until radio failure, lost signal or death. A comparison of annual survival rates indicated birds marked with only bands survived at similar rates (14.5%, 95% CI: 7.6, 21.4%) compared to those marked with both bands and radio-transmitters (10.6%, 95% CI: 7.9, 13.3%). A cumulative incidence function for cause-specific mortality produced an annual harvest rate estimate of 12.0% (95% CI: 8.6, 15.4%). However, this estimate was likely negatively biased in the presence of undocumented crippling loss. We also derived a 14.4% annual harvest rate using average observed levels of hunting pressure and a joint live–dead model that was not dependent on classification of mortality sources. We predicted annual harvest rates over a range of population sizes and hunting pressures to inform managers of possible thresholds to target. Hunting pressure was an important predictor of harvest rate. For instance, we estimated that adding approximately two more hunters per week would push seasonal harvest rates past the targeted harvest threshold, indicating managers should carefully regulate hunting pressure to avoid exceeding set harvest limits. Estimating relationships between weekly survival and hunting pressure can provide information to evaluate different management scenarios and help develop hunting regulations.