I have tagged a lot of hares with gps collars and we used drop off, but i had a lot of problems when i did it because a little mud and hair are enough to block the release mechanisms. then we decided to recover collars in a different way: probably you will not like my suggestion but take into account also the possibility tho recover the collars shooting the hares because the percentage of failure in the drop off mechanisms for these collars is still high. another solution could be to recapture the hares with nets. it works but it needs people trained to do this work. Ciao

Hi, contact the Swedish company Followit.se, email [email protected]. They have this feature on their GPS collars. Good luck! Mats Amundin, Kolmarden Wildlife Park, Sweden.

Unfortunately, I have not any idea this topic... :(

Have you checked out Telemetry Solutions? They have mini GPS collars with optional drop off feature that may suit your needs.

http://www.telemetrysolutions.com/track-wildlife/gps-for-hare.php

On a first step, it depends on the environment where the drop off "mechanism" is supposed to work. I was using e-obs gps-loggers on langurs (small primates with a body weight of ~7kg) in the Vietnamese rainforest. Due to the moist tropical climate, we didn't trust the mechanical solutions, because of bad experiences in other projects due to the reasons Marco mentioned already. Therefore, we asked e-obs to directly integrate leather and/or fabric parts into the collar that would decay and break after a while. Depending on the environmental conditions, it is tricky to calculate the life span of such a collar, and material testing might be necessary - but nevertheless, it's better to have the collar off the animal sometime than having the animals running around with such a collar for the whole of their life because of a mechanical failure...

I used Followit collars, which have a drop off, on dingoes but I believe mine were the lightest that Followit make (215g) which is too heavy for small mammals.

I agree with Kristy, try Telemetry Solutions, as they have a 30-50g collar with drop off. I've used their trap alert devices and have found them to be well made and reliable, and the TS staff are very professional and helpful. If your study animals weigh more than about 600-1000g then these collars will still be too heavy.

A consideration you should take into account is that drop off only works if the battery has power. I calculated my tracking duration and fix rate using a calculator supplied by the manufacturer. However, all of my collars used up their battery power well before the expected date and I had to stalk my study animals and manually (UHF) command them to drop off. I think this is because the battery life is calculated on an expectation of a given success rate when searching for satellites. I work in wet tropical areas which included dense forests, and the collars spend more time searching for satellites than they would in more-open habitats. Thus they chew through the batteries faster.

As others have said, you could also build in weakness into the strap. The rusty wire idea is a good one. What about dissolvable thread such as is used for suturing wounds?

I tracked pygmy possums (approx. 8g) using tiny VHF transmitters and affixed them using a drop of surgical glue on the fur between their shoulder blades. The transmitters typically fell off after 1-2 weeks. Depending on the size of your GPS, something like that might work.

As mentioned before, drop off mechanisms are not 100% reliable.

When I was working on large mammal telemetry, we used pure cotton straps and integrate it into the collar's belt (additional to drop off mechanism) - just to make sure that the collar will get off the animal. Cotton will deteriorate depending on weather conditions. We used a Swedish "recipe" in Slovenia and it worked perfectly (we have similar moderate climate). For one year study period on an infant bear or deer we used one strap of 4 cm wide cotton, for adult female 2, and for adult male 3 straps.

@Damian, what kind of 8 g VHF you used? Can you give a reference to company? Thanks

Hi Linas. Sorry I wasn't very clear. The possums were 8g, the VHF transmitters were 0.35g. I got them from Holohil Sytems in Canada. They specialise in small VHF transmitters down to 0.22g.

http://www.holohil.com/transmitters.htm

very interesting! A pity they do not present thier prices. Can you help? ([email protected]) how much your university paid per one unit?

Use cat gut or vicryl to suture the collar or harness, I've used in primates and the time of disolvation is variable, depends on environmental conditions like temperature and Relative humidity

http://en.wikipedia.org/wiki/Catgut

http://en.wikipedia.org/wiki/Vicryl

HI, I am interested in experience regarding brown hare (Lepus euroaeus) tracking devices.

When is the best time to set up a tracking device for brown hare that need to be released from the rearing farm in to the hunting ground.

It is clear before we release him, but there is a fear that he will under huge stress during fastening on. Is there any safe way to do this?

Anne Berger Damian Stuart Morrant Linas Balciauskas Robin Andrés Poches @

I agree with previous comments on using fabric collars, or introducing a strap of fabric into the collar belt. I worked with the critically endangered Tehuantepec jackrabbit (Lepus flavigularis) in a neotropical savanna in Oaxaca, México. We did not use automatic release mechanisms that rely on batteries or relocation of individuals. Lepus flavigularis did not chew the collar belt of marked conspecifics. If your study species chews the collar belt it would be good to use chewable materials. In humid environments, cotton has the problem of getting wet easily and not drying easily when is used as a neck collar, and the animal would have a wet collar most of the time, which may not be comfortable. We used collar belts made from nylon tubular tape; the one used by professional rock climbers. The material is comfortable to wear on the neck and does not accumulate water. For young individuals we cut the belt (using fabric scissors) into two pieces and added a very little piece of elastic fabric (like the one we use in our human underwear) with instantaneous glue. The nylon tape is tubular, so you can instert the elastic inside the "tube" on both sides of the cut-belt. The elastic must allow just enough room for growth, and the glue would eventually decay and release the collar. For adult individuals we used elastic too, or we made a cut on the nylon belt, of about one third of its width, and that was the release mechanism. The cut must be done on the edge of the belt that is less close to the body of the animal, in such a way that the belt does not get too loose on the neck, to prevent that the animal could get a forelimb stuck in the collar (not very feasible, but it can happen). The cut in the belt would slowly continue breaking until the collar is finally released. The elastic-glue decayed sooner (but lasted for at least 1 year) that the cut-belt.