Fairies rely on 3 principal powers in order to survive out in the wild.
Fairy Power is the basis of most of a fairy's non-magical, physical abilities. It's akin to their health, strength, lung-capacity, &c.
Wing Power is the basis of a fairy's flight, but also for their source of their ability to produce Erogel, and is akin to their Stamina and Willpower.
Quiver Power is the basis of a fairy's ability and willingness to seduce, and is akin to their morale, .
All 3 powers contribute to a Fairy's magical abilities (See: Magic),
Powers can be "stressed" or "spent". A stressed power causes part of the gauge to darken, while spending power causes part of the relevant gauge to clear.
If any one power is completely spent, the rescue teams are called in, to teleport the fairy back to town.
Power-meters in the current UI have a circle on either end, indicating a "last-point" and "first-point". It's an easy way to tell the difference between a bar that is full, near-full, empty, or near-empty. Although the "last-point" circle may seem useless since a fairy will be rescued as soon as a power is depleted, some abilities let you stress the last bit of a power without spending it, waiving additional point-cost, so having that indicator is important.