PS 9-82 - Investigating breeding conditions and population size of an endangered amphibian to optimize reintroduction success

Background/Question/Methods

The boreal chorus frog (Pseudacris maculata) is a threatened species in portions of Canada, mainly due to habitat loss and fragmentation. To mitigate the decline of Great Lakes, St. Lawrence, and Canadian Shield protected populations, captive breeding and reintroduction have been considered. We developed a collaborative, interprovincial project to reintroduce the species and monitor the establishment of reintroduced populations in southwestern Quebec at parc national du Mont-Saint-Bruno for a period of five years. Our objective was (1) to identify the optimal conditions for calling during the spring breeding season, to estimate population size in natural wetlands, and (2) to estimate the short-term survival of captive-reared juveniles introduced in restored ponds. In 2021, we used a combination of automated call recorders and capture-mark-recapture to study two natural populations of boreal chorus frogs during the breeding season. We also released 732 metamorphs into restored wetlands to study their weekly survival using capture-mark-recapture.

Results/Conclusions

Results showed that the two natural populations were small with only 10 (95% CI: [8,16]) and 28 individuals (95% CI: [23,38]), respectively. Twenty years ago, these populations numbered hundreds of individuals. These low population size estimates were also supported by a low occurrence of choruses, the latter being highest at 7–15°C and during the first week of the breeding season (April 4–9, 2021). The weekly survival probability of captive-reared juveniles released into the restored ponds was 0.27 (95% CI: [0.19, 0.40]). Our study highlights that the species occurs at alarmingly low population sizes. These results will help managers to target the best period to conduct call surveys at natural sites, but also inform models of population viability of reintroduced populations.