Birds or bats?

I want to know if there’s any good way to tell the difference between a bird and a bat under low light conditions, and when the creature is flying around so crazily that you can’t get a good look at it.

Here’s the situation: I was sitting on my lakeside dock (in Tampa, FL) at sunset, around 8:45 pm. Six or seven small dark flying creatures appeared. They were the size of small birds. Their flight was erratic, zig-zagging, diving, almost instantaneously reversing direction, never in a staight line. Obviously they were pursuing a dinner of flying insects. Their wings were beating so fast that I couldn’t get a good look at their shape, and they never stopped beating; they never soared. They were also totally silent. I assumed they were birds, but when one of them swooped by quite close to me I thought it looked more like a bat.

For the last two days I have been outside from 8:45 to 9:00 observing these creatures (they only appear for 15 minutes or so) and I have not been able to form a definite opinion as to whether they are birds or bats. If anyone has any good way to tell the difference, such as by their flying characteristics, please let me know.

Bats fly like that so it is likely that they were bats. However, there is at least one type of common bird that flies roughly the same way as well. Barn Swallows fly in a darting manner as well often changing direction quickly in straight lines. That makes it hard to say based on your description.

My money’s on bats. The ones I’ve seen fly like a UFO with two hyperactive monkeys fighting over the controls.

Swifts, martins ans swallows do fly a bit like that, but are (I think) most active during the day, and although they don’t soar, their flight patterns tend to be a bir more graceful and sweeping than bats, of which many species fly exactly as Scupper describes.

If they are flying like that and appear at dusk, they are certainly bats. Swallows and swifts may fly acrobatically, but rarely as erratically as bats; and they would not be likely to appear only at dusk, being active mainly during the day. The only nocturnal bird that would be flying around in the air where you are is a Nighthawk, and they have a much steadier flight than you describe.

Bats flap their wings a lot more than birds and are more erratic when flying, they change directions a lot more.

If you can get close enough, throw a piece of worm up into the flock. If something eats it in midair, they’re probably bats.

Not to contradict you, Colibri, but I live next door to a house whose upper nooks house swifts which are quite crepuscular in their activity. While one may occasionally (rarely) see one on the wing during the day, they tend to begin hunting about an hour before sunset and continue well past dusk. Their flight pattern is also very much what is described here, with smooth glides alternated with “jinks” and other aerial acrobatics, presumably to catch flying insects. Since we also have bluebirds, it may be an adaptation to a local opportunistic microniche, but I can validate that (a) they are swifts, and (b) they are predominantly – almost exclusively – crepuscular.

Polycarp, I seem to recall you are in the eastern US so your birds must be Chimney Swifts. Chimney Swifts are most often seen at dawn and dusk as they gather near their roosts, usually in chimneys or buildings. During the day they are more dispersed as they forage far and wide, sometimes quite high up, and are thus less conspicuous. They spend most of the night in the roosts. Your birds are probably getting in some crepuscular foraging before retiring for the night; but they most likely have been out for most of the day. (Do you actually see them in their roosts during the day?)

I suppose **Can’t Handle the Truth’s ** critters could be swifts if, like you, he lives close to a roost. And yes, swifts do jink quite a bit (and more so than swallows), but usually less so than bats.

However, the fact that CHTT’s critters are appearing over a lake at dusk suggests to me that they are bats; if there were swifts around you would most likely notice them flying over the lake during the day as well.

Well, based on all the replies, I’m going to say they are bats. I’ve been seriously birdwatching here since February (I’m talking 2 to 4 hours per day) and I’ve become quite familiar with all the birds who are out during the daytime, including chimney swifts, whose “flying cigar” shape is unmistakeable. These creatures I see at dusk are different from any birds I see in the daytime.

Here’s a description of Florida’s bats.