Factors influencing Northern Bobwhite recruitment, with implications for population growth

Abstract

Understanding and quantifying demographic parameters that influence population growth is necessary to effectively maintain population persistence in the presence of recent changes in climate and land use. We used a combination of capture–recapture and harvest information from a 42 yr dataset to create an integrated population model that estimates population abundance, annual survival, and per capita recruitment in Northern Bobwhite (Colinus virginianus). We evaluated the associations of commonly reported population metrics (age ratios from harvests, annual survival, and recruitment) to population growth rate using correlation analysis. We also modeled the effects of population abundance, breeding-season temperature, breeding-season precipitation, fall minimum temperature, and fall precipitation on recruitment. Recruitment averaged 1.55 (range: 0.82–2.21) and was most strongly correlated with population growth (r = 0.78, 95% confidence interval [CI]: 0.63–0.88), followed by annual survival (r = 0.38, 95% CI: 0.09–0.61). We found a weak correlation between fall age ratios and population growth rate (r = 0.11, 95% CI: −0.19 to 0.40). Recruitment exhibited weak, nonlinear, negative density dependence (β1 = −0.13, 95% credible intervals [CRI]: −0.17 to −0.08 and β2 = −0.03, 95% CRI: −0.07 to 0.004). Breeding-season maximum temperature and breeding-season precipitation had a significant, positive effect on recruitment (β3 = 0.15, 95% CRI: 0.11–0.19 and β4 = 0.10, 95% CRI: 0.05–0.16, respectively). Fall minimum temperature and fall precipitation both had negative but uncertain effects on recruitment (β5 = −0.03, 95% CRI: −0.08 to 0.01 and β6 = −0.02, 95% CRI: −0.07 to 0.01, respectively) but less so compared to weather in the breeding season. Our results illustrate that recruitment (1) can be estimated without data on fecundity and chick survival by using integrated population models and (2) is highly correlated with population growth in Northern Bobwhites. We encourage natural resource managers to focus on actions that increase Northern Bobwhite recruitment.