Birds have really high blood glucose levels. Of course, you may surmise that they need it with the high energy demands of flight. They also use a lot of energy to keep a high body temperature, 4oC higher than ours. Also of note, birds have very low levels of glycogen, a compound that the rest of us vertebrates other than some big lizards hold as quick energy reserves in muscles.
The detailed story is told in the May 29th issue of the journal Nature by Chang Zhang and colleagues from 14 research institutions in China. Here are some questions to ponder. One is that high blood glucose in diabetic humans leads to damage to blood vessels. Why not in birds? Do they not live long enough with the condition? But parrots live long lives!
Another is why even flightless birds such as emus maintain high blood glucose levels. This may exemplify phylogenetic constraint: if your whole evolutionary line had the trait, there may be no genetic variation left to shed it. Zhang’s team dug deeper into the high glucose study. The level is maintained with persistent activity of a receptor protein for glucagon. Hmm. A chicken with this gene knocked down gets lower blood glucose, lower metabolism, and a chubby life style.
Evolution is often deliciously complex. Some of its products such as chickens are just delicious to the omnivores among us.
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org.
Source: Nature 641: 1287-1297 (29 May 2025)
Image: 328. bird glucose levels.jpg, from the article
