Isn’t that the username of a Doper physician here?
As above: because the bugs were used to searching for food at ground level.
Thanks for the irrefutable proof that there are no insects up there and anthropomorphic insectivorous birds are just enjoying the views during some non-feeding leisure. I withdraw my obviously incorrect hypothesis that birds might be up there eating them.
You didn’t propose a hypothesis that they might be eating insects up there. you presented a logical conclusion that
I didn’t refute the possibility, I refuted the certainty.
They may be eating abundant insects at high altitudes-above-terrain (though this seems doubtful, given the rest of the information in this thread), or they may be flying high for other reasons, as I have suggested. Many animals, including birds, engage in play:
I would add high-altitude cruising (for insectivorous birds) to the list of locomotor play activities.
Small insects and the birds that eat them can be found thousands of feet up. The bugs are carried aloft by thermals and the birds follow them, taking advantage of the rising air, too. When flying in my glider I’ll keep an eye out for swallows/swifts as they are good thermal markers.
Neat. Never thought of it that way, although this thread is generally pursuing the matter, but reversed, from the zoological->physical answer.
Apropos, I always look for people swilling beer and stuffing themselves with cheeseburgers, because then I’ll know I’m in a city park.
ETA: I’m pretty sure in marine biology there’s a similar “_cline” definition based on species habitation. Anyone know it offhand?
According to this page: How High Can Insects Fly? | Live Science
I wonder how they collected those insects at those altitudes. 
Here is a rather old thread on the subject: Insects at altitude - Factual Questions - Straight Dope Message Board