A bird migration study

To: Birding Aus <>
Subject: A bird migration study
From: L&L Knight <>
Date: Wed, 28 Feb 2007 17:47:19 +1000
I'm not sure how much the following item applies to waders and sea

Why migrate? It's not for the fruit
Some flock to search for food, some migrate

Public release date: 27-Feb-2007
 University of Chicago Press Journals

Why do some birds fly thousands of miles back and forth between
breeding and non-breeding areas every year whereas others never travel at all? One textbook explanation suggests that eating fruit or living
in nonforested environments were the precursors needed to evolve
migratory behavior. Not so, report ecologists W. Alice Boyle and
Courtney J. Conway of the University of Arizona, Tucson, in the March
issue of the American Naturalist. Conway is also a research scientist
with the U.S. Geological Survey. The two showed the pressure to migrate comes from seasonal food scarcity. It's the first time the technique called phylogenetic independent contrasts has been used to identify the causes of bird migration. "It's not just whether you eat insects, fruit, or candy bars, or where you eat them – it matters how reliable that food source is from day-to-day," Boyle said. "For example, some
really long-distance migrants like Arctic Terns are not fruit-eaters."

The new research indicates that one strategy for dealing with seasonal changes in food availability is migration. The team also found that
birds that forage with others of the same species are less likely to
migrate. "Flocking can be an alternative way of dealing with food
shortages," Boyle said. When birds band together to search for food,
the group is more likely to find a new patch of food than is one lone
individual. To figure out the underlying pressures that drive some
birds to leave home for the season, Boyle and Conway focused on 379
species of New World flycatchers from the suborder Tyranni. For all
those species the scientists compared the species' size, food type,
habitat, migratory behavior, and whether the birds fed in flocks. A
universal assumption about bird migration has been that short-distance migration is an evolutionary stepping stone to long-distance migration. The team's work contradicts that idea by showing that short-distance
migrants are inherently different from their globe-trotting cousins.


W. Alice Boyle and Courtney J. Conway, "Why migrate? A test of the
evolutionary precursor hypothesis" American Naturalist 169:344-359

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