An arctic tern soars over Iceland. These small birds have one of the longest annual migrations of any animal on Earth. Every year, arctic terns migrate from the Arctic Circle to the Antarctic Circle—a round-trip journey of about 30,000 kilometers (18,641 miles).

Photograph by Bob Feldman, MyShot
  • Arctic terns have one of the longest migrations of any animal on—or above—the Earth. These small, inconspicuous seabirds fly from the Arctic to the Antarctic every year . . . and then they fly back. The arctic tern's wings are ideally adapted for such long flights.

    Arctic terns have "high aspect-ratio" wings. Aspect ratio is a mathematical formula calculated by dividing the square of the wingspan by the total wing area. (This formula is used to calculate the aspect ratio of aircraft wings as well as the wings of birds, bats, and other flying creatures.)

    High aspect-ratio wings are long and narrow, ideal for slow, usually low-altitude flight. Birds with high aspect-ratio wings often glide and soar over long distances.

    1. Arctic terns are seabirds that feed primarily on fish. How do high aspect-ratio wings complement this feeding pattern?

      High aspect-ratio wings allow arctic terns to glide low over the ocean, using their beaks or feet to grab fish swimming near the surface.

    2. High aspect-ratio wings are common to many birds with long migration patterns. Why is this wing type beneficial to these birds?

      High aspect-ratio wings allow birds to glide and soar. Birds such as the arctic tern can travel long distances without using valuable energy to flap their wings to fly.

    3. What types of aircraft do you think use high aspect-ratio wings?

      Answers will vary! The wings of spyplanes usually have very high aspect ratios. Spyplanes often need to fly very long distances with minimal fuel. Both manned spyplanes (such as the U-2) and unmanned "drone" spyplanes (such as the Predator) have very high aspect-ratio wings.

  • Term Part of Speech Definition Encyclopedic Entry
    adapt Verb

    to adjust to new surroundings or a new situation.

    aircraft Noun

    vehicle able to travel and operate above the ground.

    altitude Noun

    the distance above sea level.

    Encyclopedic Entry: altitude
    Antarctic Noun

    region at Earth's extreme south, encompassed by the Antarctic Circle.

    Arctic Noun

    region at Earth's extreme north, encompassed by the Arctic Circle.

    Encyclopedic Entry: Arctic
    arctic tern Noun

    small bird that migrates from the Arctic to the Antarctic.

    aspect ratio Noun

    in aeronautics, the ratio of the square of an object's wingspan to its total wing area (planform).

    calculate Verb

    to reach a conclusion by mathematical or logical methods.

    formula Noun

    a general fact or rule expressed in letters and symbols.

    inconspicuous Adjective

    not easily noticed.

    migration Noun

    movement of a group of people or animals from one place to another.

    wingspan Noun

    the distance between the tips of a bird's wings when stretched out.