Navigation by stars

One of the little birds that has been a frequent visitor to the bird feeder this spring is the Indigo Bunting.  Its striking blue color makes it a favorite discovery, and it has a rather cheerful song.

bunting and goldfinch

But what is really special about these birds is their phenomenal ability to navigate their way from wintering areas in Central America and the West Indies to breeding areas in North America at night, using cues from the patterns of stars overhead.

When I was a grad student at Cornell, I took a class from Steve Emlen, who earned his Ph.D. by finding out just how the Indigo Buntings navigated.  He designed something really sophisticated (called “Emlen cages”) to measure his captive buntings’ migratory activity and direction at different times of year.

The bird stands on an ink pad, surrounded by a funnel of blotter paper with a wire mesh top (not shown).  When exposed to the night sky, a migratory bird hops from the ink pad upward landing on the blotter paper, leaving footprints that indicate its preferred direction (N in the spring, S in the fall).

The bird stands on an ink pad, surrounded by a funnel of blotter paper with a wire mesh top (not shown). When exposed to the night sky in a planetarium, a migratory bird hops from the ink pad upward landing on the blotter paper, leaving footprints that indicate its preferred direction (N in the spring, S in the fall).

But the night sky constantly changes as constellations rotate into and out of view, so what were the birds really using as cues for direction?  Emlen even tried to confuse the buntings by showing spring migrants the fall night sky, but they still oriented northward.

The answer was that the birds used the North Star, not individual constellations, and their orientation (toward the north or toward the south) depended on what time of year their biological clock told them it was.  Yes, birds can tell time — most animals can.  Hormones that tell them it’s time to breed are also telling them go north.  A slightly different mix of hormones tell them it’s time to leave the breeding ground and  fly south.

The amazing wonders of the natural world…

Yes, it was a long trip, but I'm a guy and don't need to ask for directions.

Yes, it was a long trip, but I’m a guy and don’t need to ask for directions.

7 thoughts on “Navigation by stars

    • Some birds can navigate short distances (up to a few hundred miles) using magnetic cues (homing pigeons do this), but most animals migrate in response to their internal (biological) clock stimulating a change in behavior that is appropriate for a changing environment.

  1. Pingback: A crazy day in the backyard | Back Yard Biology

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