Birds’ four-chambered hearts run larger than those of mammals, relative to body size, and they are coupled with extremely efficient cardiovascular systems. The energy demands of flight require these adaptations. An exercising human has a heart rate around 150 beats per minute. In contrast, an active hummingbird’s heart pumps at 1,200 beats per minute; a flying pigeon’s heart beats at 600.

More info and transcript at BirdNote.org.

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