May be scavenging energy in a jungle may not make the top of your priorities but still it is nice to see how technology is progressing...
Actually, the idea of scavenging energy in a jungle is just out the top of my head, and the idea came as I read a news from MIT about the discovery of a method to use water condensation as a source of energy, generating electrical power.
In 2013 two MIT researchers, Nenad Miljkovic and Evelyn Wang, discovered that when a water droplet detaches itself from a hydrophobic surface it carries along an electrical charge.
Now they have developed a generator made, as shown in the figure, by alternating set of hydrophobic and hydrophilic surfaces. When water condense into tiny droplets on the colder hydrophobic surface these tend to detach and move to the hydrophilic surface carrying along the electrical charge. Basically you have a power generator out of water condensation. And water condensation is what you get in cold places (fog) as well as in humid warm places (like a jungle...). This water condensation is for free and what you need is to have a temperature differential to make water condense. You can see condensation every morning on leaves, since their surface is slightly colder than the air, on window glasses whose surface, again, is colder than the air inside the room... This is also for free.
The generator has no moving part, is completely passive and just need to be located in a place where there is humidity and a temperature differential exist (e.g. by a river where the water is colder than the surrounding air, again something you can find in a jungle...).
The amount of power that can be generated is minuscule, the experiment has produced 15 picoWatts per square cm, but the researchers can see some easy ways to boost it to 1µW per square cm, which means that a generator the size of a camping cooler (small but still too bulky to fit in your pocket...) could recharge a cell phone in 12 hours.
It might just seem a curiosity with no application whatsoever given the low yield. On the other hand this applies to all scavenging technologies and we are starting to find important practical usage for them: powering sensors in the environment (jungle included).
Notice that Nature is making a fantastic job out of energy scavenging. And as we learn to reduce the power need of our circuits and disseminate them more and more these scavenging technologies will come very handy.