Metabolism Slows When Food Is Scarce

a hummingbird with bright magenta feathers on its head and a gray body is perched on a tree branch

Biological Strategy

Hummingbirds

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Image: Veronika Andrews / Pixabay / Free non-commercial use

Maintain Homeostasis

When a living system is in homeostasis, it means that internal conditions are stable and relatively constant. For example, a human’s internal temperature is approximately 37 degrees Celsius (98.6 degrees Fahrenheit) unless there’s an illness. The human body maintains this temperature despite external ambient temperature. However, as with all physiological processes, maintaining homeostasis requires communication and coordination. So living systems have ways to detect changes from the norm, mechanisms to cause an adjustment, and negative feedback connections between the two. A desert lizard called the Gila monster offers a good example of maintaining homeostasis. The lizard goes from eating large meals to fasting for extended time periods. To maintain its blood sugar levels at a steady level, when food is scarce, its endocrine system releases a hormone that raises its blood sugar levels.

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Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

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The metabolism of hummingbirds allows them to survive the night when food is unavailable by slowing to a hibernation-like state called torpor.

Image: Danny /

This hummingbird isnt in torpor, but its such a beautiful image.

“At night, when they cannot see to fly and the flowers have closed, the birds have no alternative but to shut down all their systems, lower their body temperature and, in effect, hibernate until dawn.” (Attenborough 1995:119)

“Hummingbirds use periods of inactivity between feeding bouts and
torpor to conserve energy and enable them to survive nocturnal
starvation.¹⁴ During torpor, the hummingbird metabolism is adjusted
downward to achieve up to 60% energy savings.” (Fowler and Miller 2003:235)

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