Sandhill crane colt survival in Minnesota

Age-structured population models require reliable estimates of cohort-specific survival rates, yet vital rates of younger age classes are often difficult to estimate because of the logistical challenges of monitoring young animals. As part of a study of sandhill cranes Antigone canadensis in the zone of contact between breeding distributions of the Eastern Population and Mid-continent Population in Minnesota, United States, we monitored first summer survival of 34 sandhill cranes (hereafter, “colts”) using VHF and/or GPS-GSM transmitters. We estimated daily survival probabilities from 19 to 120 days post-hatch using a generalized linear model accounting for interval censoring, resulting in an estimated period survival rate of 0.52 (90% confidence interval 0.36–0.71) over summer (100 days). Estimated daily probabilities of survival increased as colts became older and fledged (at 70–75 days post-hatch), when they presumably became less vulnerable to predation. Causes of mortality were mostly unknown aside from one case of a collision with a vehicle. There is a scarcity of published colt survival rate estimates for sandhill cranes and what is available varies widely by study site. Region-specific sandhill crane colt survival rate estimates can inform future management efforts and inform population dynamics research and overall natural history knowledge of sandhill cranes.