Hi Carl and everyone, how are you? I'm leading a local project to try to tag a giant armadillo (Priodontes maximus), I've done some comparative technologies and prices, we come to conclude that is better to buy company devices and not try to make them since some researches told us that was a waste of time and money.
Those researchers tried to build their own devices and have failed on the customizing, humidity got in (it has to be water proof), hard case and long lasting this was too heavy and didn't last enough time (logged some information), most of devices got damaged by environmetal factors. Attachement technique suggest screw on scales (plus you can use epoxy to improve the attachment) and the decive should not weight over 1.5% of the animals body weight.
You have 2 options.
GPS+Long range data download+VHF: it depends on how close you can get to the animals, and how often, lets say every 15 or 30 days (half field work, try to think about how much money you will spend on it) for about 50-700 mts (depends on the forest density and other obstacles and if animal is on the ground or up on the canopy), the device must have a VHF transmitter so you can do homing and try yo get close to donwload the data (preprogram schedule), GPS life is based on how many coordinate/fixes you want per day, also you can set up accelerometer and other sensor to establish behaviour. You will need a special transceiver unit (modified tablet and long range UHF panel antenna)
GPS+Iridium+VHF: This might be the best option, since Iridium will try to send data every 10 data rows, this device will weight aroung 190 gr, you can also attach the GPS+Iridium in one scale and the VHF on other scale, but eventually either unit can fall off, and then you might not be able to retrieve in case of refurbishment, this option seems expensive but this can last for about 12 months with 4 fixes per day, or 8 months with 8 fixes per day, that's a lot of data.
We conclude that one company suit our needs in price, time and weight, it was Telenax from Mexico, they have build devices for pangolies in the past. Telonics was expensive and too heavy and only offer GPS+long range device, Lotek offer a short lifespan and was expensive.
We're wainting for the GPS+Iridium units for 2020, when we will start our project.
I hope this helps.