Why is there a bat flying around in circles outside?

Seeing a bat flying around in circles outside might seem odd but it’s quite normal. Insectivour bats often fly in circular patterns when hunting bugs. But most people that see bats flying outside their house or elsewhere see them flying in a crazy, erratic fashion, so catching a glimpse of a bat flying in a near-perfect circle can seem strange. We’ll discuss two main types of scenarios where you might observe circular bat flight patterns:

  1. A single bat flying in circular flight
  2. A group of bats flying in a circle together

But first, let’s talk about why we normally see bats flying in crazy patterns.

Why do bats fly erratically?

Bats circling under a bridge rather erratically. I wouldn’t call this case a ‘bat doughnut’ since they didn’t yet create a collective vortex.

Experts can learn quite a bit from bats’ flight patterns. For example, with training people can identify species of bats in their region by flight patterns and bats’ flight height.

But to most of us, bats seem like their fly in bizarre patterns. Yet they have a system to their madness. First, catching bugs ain’t easy. Some of the insects that insectivore bats prey upon use flight patterns designed to help the insects evade their predators. That means bats need to make sharp, quick adjustments in mid-flight to catch their prey.

Second, some bugs can detect bats’ echolocation sounds. Some moths and beetles can ‘hear’ bats’ sonar sounds. To hide their location from their prey, bats will fly in more erratic patterns than usual when stalking beetles and moths that can detect bats.

Why did I see a single bat flying in near-perfect ovals?

Some folks hypothesize that seeing a single bat flying in a regular circular or oval pattern in the early evening or early morning might a bat’s version of warming up. It could be that, like humans, bats need to allow their muscles and nerves to warm up for more intense work. This makes sense to me.

I would add that they might also be doing some cognitive warming up because it could be they have to somewhat calibrate their sonar detection mechanisms after sleeping during the day.

Video of a bat circling the evening sky a few times (likely warming up its wings for hunting).

I’ve also read a hypothesis that bats circling primarily after sleeping and before they start hunting might be related to geolocation. Perhaps it helps them remember where they roosted before they head out for hunting. This seems feasible to me too. We see something like this in honey bees, for example, where physical dances can indicate directions toward food sources.

Why did I see a group of bats join a lone bat in a circular flight path?

Next, some groups of bats communicate and coordinate their hunting efforts. This likely explains the majority of cases we see where groups of bats (bat colonies) seem to be flying regular circles somewhat in sync. Bats use sonar communication to coordinate their movement with other bats.

Sometimes you can observe bats’ coordinated hunting behavior. For example, in the video below, Paul observed one bat flying in a circle at first. Then, seemingly suddenly, around 20 to 30 bats joined the lone bat—all the bats circling together. What likely happened, was that the first bat discovered a patch of air ripe with bugs and communicated this to its fellow bats. This allowed the bats to work together to hang the group of insects in the air outside Paul’s home.

Group of 20 to 30 bats flying in circles and figure eight-like patterns in the evening.

Research on bats’ flight patterns

A group of animals or insects flying in coordinated, circular patterns is referred to as ‘collective vortex behavior’ in the scientific literature. The collective vortex behavior of bats is referred to as a ‘bat doughnut,’ and you can see in the video below why scientists dubbed it as such—they make the shape of a doughnut. You can clearly see a ‘bat doughnut’ form in the video below.

A group of bats displaying ‘collective vortex behavior’ in the Malaysian sky. Really cool phenomenon.

Delcourt et al. argue that “in some species, vortices increase feeding efficiency and could give protection against predators…” and that “vortices could improve collective decision-making and information transfer.”

It seems to me that this could be true of bats because hawks and owls are predators of bats and it seems it seems more difficult for raptors and owls to nab bats from mid-air when they’re flying collectively in doughnut patterns.

For example, it is more difficult for large fish to grab smaller fish if the smaller fish stick to their school. I suppose a vast mass of moving bats (or fish) makes it difficult and slow for a predator to decide which specific bat to focus on grabbing. Perhaps bat donuts create a fast paralysis by analysis in their predators, making bats’ predators mostly inefficient.

Video of natterers bats circling inside a barn loft before departing for the evening

Frequently Asked Questions about bats flying in circles

Why do bats circle around my garden?

If you keep seeing bats circling around your garden, they are likely hunting insects and indirectly helping you out with garden pest control and putting a dent in your yard’s mosquito populations. This is a win-win for you. Fewer bugs for you. Full tummies for the bats. Some people even put up bat houses near their garden because they enjoy the bats’ help in reducing insects in their yard and garden area. For fun, you can gently flick a small rock or piece of dirt up in the air near the bats’ flight path and watch how quick and agile the bats respond to it.

What does it mean when a bat circles you?

If a bat circles you outdoors, there are likely bugs above your head the bat is hunting. The bat isn’t after you. If a bat circles you inside, the bat is likely trying to find its way outside. To help it, close doors to any surrounding rooms and open one door or window to the outside. Normally a bat can find its way outside within five minutes if you reduce its options like this. You can learn more about what to do if you get a bat in your house here.

Why would a bat fly in circles during the day?

Bats often begin hunting at the beginning of the evening. They’re likely circling to help find insects, but if you see a bat circling from late morning to early afternoon, it could be that the bat was flushed out of its roost or the bat might be sick. Bats with distemper or rabies can exhibit abnormal behavior, including flying during the day. Also, baby bats separated from their mothers fly during the day in an attempt to reunite with their mothers. Finally, sometimes sharp changes in temperature seem to confuse bats about the time, which can also lead to daytime flying behavior.

Video showing fruit-bats circling around their roost in daytime
Published
Categorized as Bats

By David Jackson

I enjoy learning about new pest control strategies and sharing what I learn at NeverPest.com. I aim to create a reliable resource for people dealing with all sorts of pest issues.

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