Be on the lookout

OK, I’ve noticed something curious on TV lately that isn’t important but has aroused my curiosity.

In the background of a number of Network series, Netflix programs and several commercials, flocks of impossibly large birds fly by in silhouette.  When you take into account perspective, they would have to be the size of small to medium airplanes, so they aren’t real, they are an added effect.

They play no part in the commercial or program, they are just briefly visible.

Is that some kind of inside joke by the video people? Or a signature for some effects company? Or just decoration?