Re-introductions of Chiricahua leopard frogs in southwestern USA show promise, but highlight problematic threats and knowledge gaps

Summary

Chiricahua leopard frogs (Lithobates chiricahuensis), listed Threatened under the US Endangered Species Act and threatened by the chytrid fungus Batrachochytrium dendrobatidis (Bd), non-native predators and habitat loss across Arizona, New Mexico and Mexico, were the subject of coordinated recovery efforts under a 2007 federal recovery plan reviewed here through three contrasting case studies. In the Upper East Verde River area, 3,542 captively reared metamorphs and late-stage tadpoles were released across 13 sites in 2009-2010, and breeding was confirmed at four sites within 10 months, producing 32 wild egg masses and demonstrating that reintroduced frogs could disperse and reproduce at new localities. In the Pajarita Wilderness area, eradicating invasive bullfrogs in 2008, rather than reintroducing frogs directly, allowed native Chiricahua and lowland leopard frogs to naturally recolonize eleven previously unsuitable sites by 2011, some more than 7.9 km away, showing threat removal alone can be sufficient. In the Black River area, repeated small releases of captive-reared frogs at four historical sites since 1996 failed, with the species undetected there since 2009 despite the absence of Bd, for reasons that remain unclear. In New Mexico, high chytrid susceptibility has instead forced a strategy of establishing eight genetic-refuge lineages in confined tanks rather than direct reintroduction, though two refuge source populations have since died off. The project rates its three case studies as one Successful, one Partially Successful, and one Failure overall, concluding disease remains a major barrier to reintroduction success in parts of the range.