Cause-specific mortality and survival of northern bobwhite chicks

Abstract

Survival of northern bobwhite (Colinus virginianus) chicks is an important parameter influencing population dynamics. We determined cause-specific mortality and apparent daily survival of bobwhite chicks (n = 170) during 2018 and 2019 at Tall Timbers Research Station, Tallahassee, Florida, USA. We assigned cause-specific mortality to 58 chicks and unknown fates to 45 chicks. Of those with assigned fates, avian predation comprised the majority (n = 21, 36%) followed by snakes (n = 17, 29%), mammals (n = 16, 28%), and research-induced mortality (n = 4, 7%). Corn snakes (Pantherophis guttatus) were the primary snake species (13 of 17 snake predations) responsible for predation followed by northern cottonmouths (Agkistrodon piscivorus; n = 3) and 1 eastern diamondback rattlesnake (Crotalus adamanateus). We determined diel timing of mortalities during 2019. All corn snake predations during 2019 (n = 8) occurred during roosting (2100–0700 hrs), whereas the eastern diamondback mortality was a diurnal event; no cottonmouths depredated chicks during 2019. Nine of 11 mammalian events occurred during roosting. Two avian events occurred during 2019, both during daylight hours. Survival was best predicted by the model including the effects of chick age, hatch timing, year, and their interactions. Daily survival of chicks increased with age and reached an asymptote at approximately 70 days; late hatches (after 15 July) survived better than early hatches (β_{LateHatch×ChickAge} = 0.059, 95% CI =−0.003–0.121) and survival for late hatches was marginally lower in 2019 (β_{LateHatch×ChickAge×Year19} = −0.058, 95% CI = −0.137–0.022). Management focused on increasing survival during the first 2 months of life and early nesting season may substantially benefit bobwhite population abundance. Additionally, roosting appeared to be a vulnerable period for bobwhite chicks.