Unbiased Survival Estimates and Evidence for Skipped Breeding Opportunities for a Female Bufonid

Abstract/Summary

1. Estimates of demographic parameters for females, in many organisms, are sparse. This is particularly worrisome as more and more species are faced with high extinction probabilities and conservation increasingly depends on actions dictated by complex predictive models that require accurate estimates of demographic parameters for each sex and species.

2. This study assesses demographic parameters, specifically temporary emigration and survival, for females, a class that has been difficult to investigate historically because of lack of data. Amphibians provide a particularly good example because there is global concern about amphibian decline yet most demographic parameter estimates are based on data from males, which we show can lead to erroneous conclusions.

3. We use 10 years of capture-recapture data from boreal toads (Bufo boreas) and the multi-state open robust design model to provide evidence for the occurrence of skipped breeding opportunities (i.e., temporary emigration) in females. This is the first time that the open robust design model has been applied to an analysis of an amphibian population that we are aware of.

4. We determined that the transition from breeder to non-breeder is obligate and the probability of a non-breeder remaining a non-breeder is 64%, thus temporary emigration is first-order Markovian in nature, where breeding probability is dependent on the previous year’s activity, i.e. if a female did not breed in year one, there is a 36% chance that she will breed in year two. With temporary emigration accounted for, we estimated between-year female survival at 87%.

5. Establishing the occurrence of temporary emigration not only reduces bias in estimates of survival probabilities, but also provides information about expected breeding attempts by females, a critical element in understanding the ecology of an organism and the impacts of outside stressors and conservation actions.