Behavioral Ecology Blog

I’d be remiss if I didn’t mention this very nice study by a fellow IB grad student and associate of the MVZ published this month in the Proceedings of the Royal Society London B. It represents the bulk of the dissertation research of Chris Clark, who has studied sound production in The Anna’s Hummingbird.

As I understand it, the majority of the work was done right here in Berkeley (over in the Waste land between the Berkeley Marina and Golden Gates Racetrack). Aside from a bunch of close calls with violent homeless residents of this area, he captured some amazing video, and has uncovered a novel mechanism for sound production in birds.

The Title of the Paper: The Anna’s hummingbird chirps with its tail: a new mechanism of sonation in birds

The Abstract:

A diverse array of birds apparently make mechanical sounds (called sonations) with their feathers. Few studies have established that these sounds are non-vocal, and the mechanics of how these sounds are produced remains poorly studied. The loud, high-frequency chirp emitted by a male Anna’s hummingbird (Calypte anna) during his display dive is a debated example. Production of the sound was originally attributed to the tail, but a more recent study argued that the sound is vocal. Here, we use high-speed video of diving birds, experimental manipulations on wild birds and laboratory experiments on individual feathers to show that the dive sound is made by tail feathers. High-speed video shows that fluttering of the trailing vane of the outermost tail feathers produces the sound. The mechanism is not a whistle, and we propose a flag model to explain the feather’s fluttering and accompanying sound. The flag hypothesis predicts that subtle changes in feather shape will tune the frequency of sound produced by feathers. Many kinds of birds are reported to create aerodynamic sounds with their wings or tail, and this model may explain a wide diversity of non-vocal sounds produced by birds.

The production of this sound appears to be associated with either mate choice or male-male competition, as it is performed only by males, and only within the context of these “dives” that the hummingbird does during the breeding season. Most of you in CA will have seen this dive, but for the unlucky ones, Chris describes it:

The display of the male Anna’s hummingbird, a green-backed hummingbird with green head and red throat and weighing less than a nickel, is one of the most dramatic of the hummingbirds. During the breeding season, which lasts from November through May, males ascend rapidly to a height of 100 feet or more, then execute a looping dive at speeds of over 23 meters per second (50 miles per hour), Clark and Feo calculated from their video. When they reach the bottom of their dive and round upward near a perching female or intruder, the birds produce a loud chirp.

The whistle is very evident, but the “pop” is much less so. I have never heard the pop, and have witnessed these dives many times.. My hearing must be bad..

Here is the video: LINK

So near the end of the video, you see the tail feathers spread- well turns out this is exactly the time that the ‘pop’ sound. Chris experimentally manipulated the configuration of the feathers, and simulated the effect in a wind tunnel…The sound, sure as rain, comes from these feathers in this specific configuration..Here is the pop sound (WAV file)

Clark, C.J., Feo, T.J. (2008). The Anna’s hummingbird chirps with its tail: a new mechanism of sonation in birds. Proceedings of the Royal Society B: Biological Sciences, -1(-1), -1–1. DOI: 10.1098/rspb.2007.1619