Impact of harvest on survival of a heavily hunted game bird population

Context.Despite their economic importance and intensive management, many game bird species, including the northern bobwhiteColinus virginianus, are in decline. Declinesmay be explained, at least in part, by low survival due perhaps to poor habitat quality, high predation or excessive hunting pressure. Aims.This study sought to estimate andmodel annual/seasonal survival probabilities, to evaluate factors influencing them and to determine the cause-specific mortality rates for northern bobwhites subject to varying levels of harvest on the Babcock–Webb Wildlife Management Area (BW area), south Florida, USA. Methods. We applied Cox’s proportional hazard models to data collected from 2066 radio-tagged bobwhites during 2002–2008 to test for intrinsic and extrinsic factors affecting survival and the non-parametric cumulative incidence function estimator to estimate cause-specific mortality rates. Key results. Mean annual survival (0.091 0.006) in the BW area was lower than most estimates reported for other bobwhite populations. Annual survival differed between adults (0.111 0.008) and juveniles (0.052 0.008), and varied among years. Survival in winter (October–March; 0.295 0.014) was similar to that in summer (April–September; 0.307 0.013). Density of food strips (i.e. long and narrow food plots) did not influence survival, but hunting effort (number of hunters per dayper km) had a substantial negative impact on survival. In the lightly huntedfield trial zone,winter (October–March) survivalwas significantly higher (0.414 0.035) than in the othermore heavily huntedmanagement zones (0.319 0.016). Cause-specificmortality analyses revealed that bobwhitemortality during summer (April–September) was mainly due to raptor (39.7%) andmammalian predation (35.6%), whereas huntingwas the primary cause ofmortality during winter (47.1%). Conclusions.Our results highlight the potential role of harvest as an important cause of the northern bobwhite population declines in southFlorida.Highmortality duringwintermay reduce recruitment of juveniles to the reproductive segmentof the population, and ultimately the population growth. Implications.Our results suggest that reduction in hunting pressuremay be necessary to reverse the declining population trends in heavily hunted game species in public lands, such as the northern bobwhites in the BW area.