Tree frogging adventures

The mountain chicken isn’t the only species of amphibian found on Montserrat. The two others are the tiny tree frog Johnston’s whistling frog (Eleutherodactylus johnstonei) and the introduced cane toad (Rhinella marinus). Neither of these species are affected by chytrid but both carry it and act as disease reservoirs which infect the mountain chickens.

Video of a Johnston's whistling frog calling - a very common sound every night in Montserrat! 

Indeed it is this little tree frog that is thought to have been how chytrid got to Montserrat in the first place. Montserrat imports almost all of its fresh fruit and vegetables from neighbouring Caribbean islands with Dominica being a major exporter. Tree frog’s carrying the disease most likely came over in shipments of bananas and other goods, escaped into the wild and spread the disease leading to the population crash in mountain chickens.

One of the important bits of information the team has been collecting in Montserrat over the last three years is on chytrid itself. How widespread is it? Is it more abundant at certain times of the year than others? All very important questions in our understanding of the disease dynamics. How to do this? Catch and swab lots and lots of tree frogs!

Tree-frogging (as we call it) takes place once a month at all four of the main field sites. Along a 500m transect the team walk and aim to catch at least 60 tree frogs at night which takes about 4 hours. Not so easy when they are small, hide in the leaf litter and are very quick! When they are caught each frog is swabbed using something that looks like large cotton bud. This is done twice for each frog to ensure that any errors or unusual results in analysis can be tested. These swabs are stored in cool conditions before eventually being sent back to the UK for testing in laboratories at London Zoo.

Swabbing a tree frog for chytrid (Photo: S-L Adams)

When handling frogs all surveyors wear gloves and change them in between frogs to prevent cross contamination. To ensure that the surveyors don’t collect the same frog again once processed the frogs are put inside the glove and the gloves stapled to the trees - which look very strange! Don’t worry the frogs are perfectly fine in there (amphibians need a lot less oxygen than mammals) and once the survey is finished they are all released back into the night.

Tree frogging and the strange gloved trees that appear! (Photo: S-L Adams)

Some initial findings from this research are that chytrid loads in tree frogs (that is how much of it they have on them) correlates to rainfall. Specifically loads are higher if the drier the preceding month, which is vital information for helping plan any future releases or treatments.