But wait-there's more. Loons have relatively heavy bodies and small wings-both adaptations for diving deep into water. With a complete set of flight feathers, their wings have just about the minimum amount of surface area to hold up their bodies. To minimize the time that they are flightless, loons molt all the feathers at once. It takes a lot of energy and body resources to grow feathers.
Loons grow a lot of large, stiff feathers all at once.
There are 11 primary feathers and 22-23 secondary feathers on each wing. Loons are flightless for about 2-3 weeks while their new feathers develop. This is the time when loons are in greatest danger. Not only are they unable to fly, but they must expend a lot of energy to grow feathers. Since they are using their energy stores they are less able to deal with diseases at this time.