The Datasheet on their site has some tech details:

http://icarusinitiative.org/sites/default/files/ICARUS%20SP%...

That one doesn't seem to be loading for me, but the Internet Archive has a version:

https://web.archive.org/web/20160331224522/http://icarusinit...

>The first-generation models will weigh 5 grams but the team wants to get them down to just one, which would allow them to track even the lightest fliers like swifts. Each tag comes equipped with a solar panel, GPS, and a huge memory, and can measure acceleration, temperature, bearing, pressure, light intensity, and more. Unlike the smallest current data-loggers, they can transmit information, too. They can even be reprogrammed from space.

I thought this was a pretty decent amount of info for a non-tech news source.