"The Birds"

I have a story I haven't shared yet about birds here.

Every evening....and it IS everyday.....there are all these birds who fly around overhead. They just do lazy circles over and over.....they are black in color....but not crackles. Actually, there have been all kinds of birds doing it from time to time....I know cause I watch. Tonight, for example, there were to of those grey color crane type birds with them.

I have seen as few as 50 and then there times there are so many I can't even guess a count.

Now, the reason this is intriguing to me? Trees top out at probably 40-50 feet around here. The birds are are way up higher than that. At least another 100 feet or so. What can they possibly be doing way up there? And why do they do this every night??