Just to recap the idea - the mini batteries are charged up during the day by the solar panels. The Weevils are silent during the day but when evening comes a light sensor kicks the sound circuit into life and the Weevils perform a dusk chorus until their power drains and they quieten for the night.
The design actually had to be changed at the last minute - tests with the SuperCapacitors from MUTR hadn't been so great, so a change was made to using miniature NiMH rechargeable batteries. These behave in a much more stable and long-lifed way and allowed the addition of LEDs driven by the 3 oscillators. Blinky, clickety, squeek-noise.
This project will be mutated sometime in the future, but there's not much sun around these parts at the moment so I reckon its hibernation time until spring.