Bats are the only mammals capable of true, sustained flight. They typically become active just as the light begins to fade, presenting a unique identification challenge due to their speed, small size, and the low-light conditions. Learning to distinguish them requires paying close attention to distinct visual cues and using specialized tools to decode their non-visual communication. Analyzing flight timing, movement, and sound allows for specific wildlife identification.
Differentiating Bats from Other Flyers
The first step in identifying a bat in flight is confirming it is not a bird or a large insect. A reliable indicator is the time of day, as bats generally emerge for foraging at dusk or later, while most small birds have already settled into their roosts. Although certain birds, like swallows or nighthawks, may fly at dusk, their wing movements and body shapes are distinctly different from bats.
Bats never stop flapping their wings, unlike birds that frequently glide or pull their wings in when diving. A bat’s wingbeat appears more irregular and fluttery, often described as a “twinkly” motion, while birds tend to have more deliberate, steady strokes. Furthermore, bats engaged in hunting fly in highly erratic, zig-zagging, and looping patterns as they chase insects.
The silhouette provides a clear anatomical distinction, even in low light. A bat’s wing is a flexible membrane of skin stretched over elongated arm and finger bones, giving it an angular, segmented appearance. Unlike birds, the bat’s wing membrane connects to its hind legs and ankles. If the flying animal is larger than a robin, it is likely a bird, as most local bats are quite small.
Visual Identification: Analyzing Flight Patterns and Silhouette
Once confirmed to be a bat, the flight pattern offers the next level of identification, as different species employ styles suited to their preferred prey and habitat. Bats that hunt insects in open air, known as hawking, often display erratic, looping, and diving movements. This acrobatic style is necessary for intercepting fast-moving targets.
In contrast, bats that forage along linear features, such as tree lines or over water, may exhibit a straighter, more direct flight path. For example, some species of Myotis bats fly low over the surface of water, occasionally scooping up insects with their feet, a behavior called trawling. The speed of flight is also a clue; larger bats with longer, narrower wings, like the Noctule, tend to fly high and fast, making steep dives when feeding.
The silhouette can further narrow the possibilities, focusing on size and wing shape. Bats with broad, rounded wingtips are slower and more maneuverable, which is helpful for navigating dense environments. Conversely, bats with long, narrow wings are built for sustained, fast flight in open spaces. Observers may also look for a visible tail membrane or the tail projecting beyond the membrane, a feature characteristic of free-tailed bats.
Auditory Identification: Understanding Echolocation
The most definitive method for identifying bats in flight relies on their primary sensory tool: echolocation. This involves emitting ultrasonic sound waves that are too high-pitched for the human ear to perceive. These sound waves bounce off objects, and the returning echoes allow the bat to create a detailed acoustic “image” of its surroundings for navigation and hunting.
To make use of this non-visual data, a specialized electronic tool called a bat detector is necessary to translate the ultrasonic pulses into audible clicks or chirps. Different bat species have evolved unique call patterns, which vary in frequency, duration, and structure. Some species use frequency-modulated (FM) calls, where the frequency rapidly drops, while others use constant-frequency (CF) calls, and many use a combination of the two.
By tuning a bat detector to different kilohertz (kHz) settings, an observer can determine the peak frequency of the calls, which often corresponds to a specific species or group. For instance, one type of Pipistrelle bat often calls loudest around 45 kHz, while a closely related species peaks at 55 kHz. When a bat detects and closes in on an insect, its call repetition rate increases dramatically, creating a distinct sound called a “feeding buzz.”