Post-weaning survival in kangaroos is high and constant until senescence: Implications for population dynamics

Large herbivores typically have consistently high prime-aged adult survival and lower, more variable, juvenile and senescent survival. Many kangaroo populations undergo greater fluctuations in density than other large herbivores, but age- and sex-specific survival of kangaroos and their response to environmental variation remain poorly estimated. We used long-term capture-mark-recapture data on 920 individuals to investigate the survival component of eastern grey kangaroo (Macropus giganteus) population dynamics. Forage availability and population density were monitored quarterly and included as predictors of survival in Bayesian Cormack-Jolly-Seber models. Annual survival probabilities were estimated for 5 age classes: 0 years (juveniles), 1–2 years (sub-adults), 3–6 years (prime-aged adults), 7–9 years (pre-senescent adults), and ≥10 years (senescent adults). Survival of juveniles varied widely during our 12-year study, ranging from 0.07–0.90 for females and 0.05–0.92 for males. Sub-adult survival was 0.80–0.93 for females and 0.75–0.85 for males, while that of prime-aged adults was ≥0.94 for females and ≥0.83 for males, despite large fluctuations in forage and density. The survival of pre-senescent adults spanned 0.86–0.93 for females and 0.60–0.86 for males. Senescent survival was variable, at 0.49–0.90 for females and 0.49–0.80 for males. Male survival was significantly lower than female survival in prime-aged and pre-senescent adults, but not in other age classes. Although most models supported by WAIC selection included one or a combination of environmental covariates, none of these individual covariates had a discernable effect on survival. Temporal variability in overall survival was mostly due to changes in survival of juvenile and senescent kangaroos. Kangaroo survival patterns are similar to those of ungulates, suggesting a strong role of sex-age structure on population dynamics.