Depending on the viewing angle and position of their wings, birds could appear just as a dark spot like that.
Songbirds, for instance, do the flutter/fold technique, where often their wings are completely against their body as if at rest.
I live in the Northern Hemisphere, currently at night it is frequently below freezing. Last night was no exception, and when I went outside this morning, there are still flies making an appearance.
I'm not saying your photos are definately bugs or birds, I feel that has to be considered as a possibility.
I don't believe you can discount that.