Saturday, May 08, 2010

How Far Can a Bird Fly Nonstop During Migration?

Bar-tailed Godwits / Image: Phil Battley

Recent studies using satellite telemetry or geolocators have shown that some bird species are capable of very long nonstop flight during migration, far longer than previously thought. Some of the longest belong to Bar-tailed Godwits, which have been tracked performing nonstop flights of over 11,000 km (or about 7,000 miles). Ruddy Turnstones perform similarly impressive flights. A new study in PLoS Biology tries to measure whether there are any limits to nonstop flights.

How long a bird is able to fly depends on a few factors. First, it needs to be able to use fuel efficiently. Bar-tailed Godwits do this very well, burning only 0.42% of their body mass per hour of flight. Ruddy Turnstones, Greater Knots, and Blackpoll Warblers have slightly lower efficiency. Flight speed is also important. Bar-tailed Godwits and Blackpoll Warblers have similar fuel efficiency, but a Bar-tailed Godwit can fly twice as far without stopping because it flies more quickly (see graph below). A faster bird will not only fly farther on the same fuel supply but also will be less likely to be blown off course by turbulence.

Potential flight range for the bar-tailed godwit (blue curve) and the blackpoll warbler (red curve).

Other factors that may influence long-distance flight include body shape and energy consumption. A long-distance migrant must be able to carry sufficient fuel supplies for the flight but do so in a very streamlined body. One way that godwits achieve this is by eliminating unnecessary organ mass and burning muscle mass in the latter stages of a migration flight. Other shorebirds share this trait.

A few other species like Sharp-tailed Sandpiper might attempt similar flights, but the Earth imposes its own limit on how far a bird might need to migrate. There are relatively few combinations of wintering grounds and breeding grounds that would require such a long nonstop flight. Some Pectoral Sandpipers breed in Central Asia and winter in South America, but they break up their migration into two stages. Arctic Terns have a longer trip (24,000 km!) but can feed along the way. It seems that the Bar-tailed Godwit's 11,000 km is about as far as a bird is likely to fly without stopping to feed.

ResearchBlogging.orgHedenström, A. (2010). Extreme Endurance Migration: What Is the Limit to Non-Stop Flight? PLoS Biology, 8 (5) DOI: 10.1371/journal.pbio.1000362