Video clip of bird feeding chicks. Animated GIF file. 114KB. Wait for the first full cycle, then it speeds up.
In the expanded image below, you can see the chicks immediately get louder when the mother (or father) arrived at mark 0:05.0 (5) seconds and immediately get quieter when she (he) left at 0:35.0 (35) seconds.
Two chirps are seen in the frequecy spectrum image below. The scale on the right is in Hz. The scale on the bottom is in seconds. The chirp on the left is one chick. On the right, there are two chicks chirping, with one slightly higher in frequency than the other.
They alternate like this a lot of the time: one chick chirps, then two, then one chick, then two. With three chicks alternating, each has only to make one chirp every 2 or 3 chirp cycles, but somehow or another, the three of them make sure that at least one chirp is made every 1/2 second. They conserve their chirps, but they don't like silence and make sure the one chirp per 1/2 second cycle is kept up all day. They stop chirping only when the mother comes in for the evening. She doesn't stop her hectic pace until daylight is completely gone.
Here is the same 2 chirps in the regular time waveform:
Here are the same two chirps in sound.
There is a third chick that can sometimes be seen. In the frequency spectrum image below you can see 3 chicks in the chirp. One of them is slightly ahead of the other two.
The non-stop 14-hour fast and frenetic (but highly professional) pace and abilities of the parents combined with the unending precise and beautiful chirp-chirp-chirps of the chicks was a sight and sound to behold. Evolution clearly had a heavy hand in shaping the activity. A 30 minute show on the subject is not enough.
