Hi Eric,

What kind of habitat range and size (m2) are you hoping to detect the dendrobatid amphibian population moving through in the tree tops, and at what kind of accuracy / location? Micro VHF transmitters are typically about 0.27g and 1cm in size, but the antenna will be longer than 30mm (possibly 40mm) and battery life is 15 - 20 days typically with a limited range in wet humid rainforests (as well as actual localisation).

At 30mm SVL I would think that your most viable option may be a very small passive RFID tag or UV paint, but the attachment method would need R&D work to achieve < 0.3g for it to be viable.

I have had several conversations with researchers using UV paint to track partula snails, requiring fixed UV sensitive cameras but you'd need a good array. RFID tags glued on could be 5mm x 5mm, and you'd probably use a similar array to get the ID of a passing amphibian. You could get a highly accurate location with RFID placed strategically (but again - the habitat range would be quite small unless you can get enough receivers out and you have a good idea of the connectivity from the release site to adjacent trees.