Anna’s Hummingbirds are a local humming bird species in coastal central California living in the region year round. A few migratory species such as the Allen’s Hummingbird migrate through the region spending winter in Central America and summer further north. The birds are very territorial and will fight for the best food sources. A hummingbird feeder in the backyard is an unlimited source of easy food that is worth fighting for (so long as the human residents keep filling it).
Fights can get aggressive between rival hummingbirds, but typically a sequence of chirps and sometimes a game of chase is all that is needed for one bird to flee and another to gain dominance over a territory. The chirps are in the frequency range of 6-10kHz and can often be heard while a bird approaches the food source.
I was curious to document this behavior and study these chirps. With the help of the Acoustic Camera provided by Polytec Inc. and GFAI which I was allowed to bring home for a weekend, I was able to capture video of the hummingbirds as they chirp and pinpoint the exact sound source for the birds as they fly through the air and to the feeder hanging in my backyard.
As a hummingbird flies into the frame of the Acoustic Camera, raw audio and video is captured as shown below with the audio displayed in the upper portion and video below. The audio is captured on 120 microphones at a 192kHz sampling rate while the video is capture at 30fps.
By using a beam forming analysis of the audio data captured and by using some more advanced digital signal processing to remove background noise, a sound map can be overlaid onto the video of the hummingbird. Additionally, for easier visualization of the color coded sound map, the video is processed to display outlines of objects in black and white and playback is slowed down. The sound can be seen coming from the flapping wings and from the beak of the bird as it chirps. The chirps can also be seen reflecting off the back wall behind the feeder.
The bird chirps as it approaches the feeder to warn other birds to stay away. This chirp is used to establish dominance. The sound of the chirp can be seen coming from the beak of the bird with the single frame image captured (below) at the time of the chirp.
When the bird is not chirping, the wings are still making noise during flight. Typical North American hummingbirds flap their wings 50 times per second. Sound not only resonates off the wings at this frequency (50Hz), but also at much higher frequencies (>2kHz) due to the movement of the air around the wings. This sound is captured and the sound of the wings flapping is visualized with the Acoustic Camera.
For videos with sound, download the file from the links below.