For more information on reducing power consumption, check out the following links:
- Power saving techniques for microprocessors. This is a great guide to reducing power consumption on an Arduino project that covers many of the power saving techniques used in this guide.
- Sleeping Arduino. This is a good series of blog posts that dive into the various sleep modes of the Arduino's processor.
- ATmega328P datasheet. Go straight to the source for information how low power sleep, watchdog, and other power saving functions of the Arduino processor work. Check out section 9 in particular for low power features.