SCIENCE

Hummingbirds have evolved a clever way of coping with the cold—one we might mimic on a mission to Mars. (Nat Geo News)

It’s hard to take a bad photo of a hummingbird, but this is one of our favorites.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• Why are winter temperatures hard on North America’s hummingbirds?
  • Harsh winter weather means there is less food available.
    • In the wild, hummingbird food is mostly super-sweet nectar (hummingbirds prefer nectars that are more than 25% sugar) and insects. In fact, “hummingbirds are carnivores (nectar is just the fuel to power their flycatching activity), and depend on insects that are not abundant in subfreezing weather.” (Nectar-bearing flowering plants are also not-so-abundant in cold weather.)
    • Hummingbirds need to eat a lot, and almost constantly. They consume about half their weight in pure sugar every day.
      • Nectars fuel hummingbirds’ amazing metabolism—the highest of any endothermic animal on Earth. (Many insects have higher metabolisms.) This high metabolism means hummingbirds need an enormous amount of energy (calories) for their quick-winged flight, rapidly beating heart, and even restful perching. In fact, hummingbirds spend about 75% of their time perching and digesting.

• If less food is available in winter, and hummingbirds will die of starvation or cold without a nearly constant source of energy, why don’t they just migrate to warmer climates during the winter?
  • Most do! Most hummingbirds in North America migrate to sunnier climates in Mexico, the Caribbean, and even South America. The rufous hummingbird makes the longest migration relative to size of any bird on Earth—from Alaska to Mexico every year.

• Fewer hummingbirds are migrating, however. Why? How are they surviving the cold winter weather?
  •  Human activity has contributed to two sources of steady food supplies in cold winters.
    • Backyard hummingbird feeders are supplied all year, allowing many hummingbird species to stay in the area.
    • Climate change has altered ecosystems, allowing flowering plants to blossom through winter and insects to breed all year.

• The Nat Geo News article attributes general hummingbird hardiness to a phenomenon called torpor. What is torpor?
  • Torpor is a nightly energy conservation mode similar to hibernation. During torpor, a hummingbird’s heart rate can plummet from 1,260 beats per minute to fewer than 50 beats per minute, and its body temperature can drop from 40°C (104°F) to 18°C (65°F).
  • Even during torpor, hummingbird metabolism is so high, they lose about 10% of their body weight every night.

• Do other animals experience torpor?
  • Yes! Many species of mice, bats, and marsupials experience periods of torpor to save energy.
  • NASA has researched putting astronauts into an extended period of torpor to cut the cost of long-duration space missions, such as an expedition to Mars. Torpor would reduce the food, temperature, and activity necessary for explorers to survive such a journey.

TEACHERS TOOLKIT

Nat Geo: How the World’s Smallest Birds Survive the Winter

Nat Geo: Hummingbird in Flight photo

NASA: Torpor Inducing Transfer Habitat For Human Stasis To Mars