Who enjoys flying? I do (on planes, of course) and birds certainly do as well (they better because they do a lot of it)! According to recent study, frigatebirds can drift in the skies for up to two months without landing (I think this makes them the biggest fans of flying, along with albatrosses, another ocean-faring flier). In order to do this, the seabird seeks out routes with strong and upward-moving currents to save energy on its flights across the ocean. By hitching a ride with favorable winds, frigates can fly more than 400 kilometers a day (which is the equivalent of a daily trip from Boston to Philadelphia) and avoid having to flap their wings as much.
For instance, the birds skirt the edge of the doldrums, windless regions near the equator. For this group of birds, that region was in the Indian Ocean. On either side of the region, the winds blow steadily. The winds come from cumulus clouds (the ones that look like fluffy cotton balls), which frequently form in the region. Riding upward-moving air currents underneath the clouds can help the birds soar to altitudes of 600 meters (about a third of a mile).
The birds don’t just stop there, though. Sometimes they fly higher into the [cumulus] clouds…[and] use the rising air inside the clouds to get an extra elevation boost. It can propel them up to nearly 4,000 meters (2.4 miles).
Interestingly enough, although frigatebirds spend most of their life over the open sea, their feathers are not waterproof, making them vulnerable to the ocean itself! Perhaps that is why they prefer to fly at such high altitudes, and not just because it’s more “convenient” for them.