Hi everyone,

I'm hoping to tap into the community's experience with GPS tracking technologies for birds in particularly challenging environments.

I work on the restoration of the critically endangered Hawaiian crow (ʻalalā). Our release site is located in dense montane rainforest at approximately 1,800 m elevation on the slopes of a dormant volcano. It's a difficult environment due to dense forest, frequent cloud cover and rainfall, and limited (if any) cellular coverage.

During previous releases, birds generally remained within about 12 km of the release site, so we don't require long-distance tracking. Our priority is obtaining reliable, high-quality GPS locations over a long deployment period. Birds spend considerable time beneath the forest canopy but also make flights above the canopy. We would also like to be able to remotely download data and update tag programming after deployment. Ground-based tracking is still valuable for mortality investigations, but our primary goal is reliable remote tracking.

We've tested a couple of commercially available solar GPS tags over the years. While both have provided useful information, we've experienced challenges with inconsistent GPS fix quality and location acquisition in this environment. I'm interested in hearing what has worked well for others working in similar conditions.

A few questions for those with experience in tropical forests or other difficult GPS environments:

• Have you found a tag or manufacturer that performs particularly well under dense canopy or in areas with little to no cellular connectivity?
• Has satellite-based data transmission been more reliable than cellular?
• How well have solar-powered tags performed under prolonged canopy cover?
• Are there programming strategies (fix intervals, duty cycles, scheduled fixes above the canopy, etc.) that noticeably improve fix success in these habitats?
• Are there any emerging technologies or systems that you think are especially promising for this type of application?

We're looking for relatively small (approximately 10–15 g), solar-powered backpack-mounted transmitters that can be reprogrammed remotely after deployment and ideally include mortality alerts.  Internal antennas would be best.

I'd really appreciate hearing about your experiences—both successes and lessons learned. Thanks in advance!