Variable harlequin frogs Atelopus varius have declined significantly throughout their range as a result of infection with the fungal pathogen Batrachochytrium dendrobatidis (Bd). The Panama Amphibian Rescue and Conservation Project maintains an ex situ population of this Critically Endangered species. We conducted a release trial with surplus captive-bred A. varius individuals to improve our ability to monitor frog populations post-release, observe dispersal patterns after freeing them into the wild and learn about threats to released frogs, as well as to determine whether natural skin toxin defences of frogs could be restored inside mesocosms in the wild and to compare Bd dynamics in natural amphibian communities at the release site vs a non-release site. The 458 released frogs dispersed rapidly and were difficult to re-encounter unless they carried a radio transmitter. No frog was seen after 36 days following release. Thirty frogs were fitted with radio transmitters and only half were trackable by day 10. Tetrodotoxin was not detected in the skins of the frogs inside mesocosms for up to 79 days. Bd loads in other species present at sites were high prior to release and decreased over time in a pattern probably driven by weather. No differences were observed in Bd prevalence between the release and non-release sites. This trial showed that refinements of our methods and approaches are required to study captive Atelopus frogs released into wild conditions. We recommend continuing release trials of captive-bred frogs with post-release monitoring methods, using an adaptive management framework to advance the field of amphibian reintroduction ecology.

The activity of the water opossum Chironectes minimus was studied in Atlantic forest rivers in south-eastern Brazil using radiotracking, from October 2004 to October 2008. There were 439 nocturnal fixes of 11 males and four females. Activity patterns of the water opossum were compared among sexes and seasons, using linear and generalized linear mixed models. The water opossum is active mostly at night, showing a unimodal pattern, with activity increasing after sunset and decreasing thereafter along the night. Females were more active in the first quarter of the night and males in the second one. The activity period of males was longer in the dry season, while for females it was longer in the wet season. Sex and season were important determinants of the water opossum activity patterns, mainly because of different sex strategies in a promiscuous/polygynous mating system. However, despite those influences the overall distribution of activity along the night was similar to most Neotropical marsupials. Therefore, similarities in the activity patterns are probably due to phylogenetic constraints and to the absence or weakness of selective pressures modifying the activity of the water opossum.