Earth Science News  





. Why Do Birds Migrate

A royal flycatcher shows his stuff. This homebody is content to stay put in Costa Rica year-round. Credit: Copyright 2004 Alice Boyle.
by Staff Writers
Tucson AZ (SPX) Mar 07, 2007
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 either eating fruit or living in non-forested environments were the precursors needed to evolve migratory behavior. Not so, report a pair of ecologists from The University of Arizona in Tucson. The pressure to migrate comes from seasonal food scarcity.

"It's not just whether you eat insects, fruit, nectar or candy bars or where you eat them -- it matters how reliable that food source is from day-to-day," said W. Alice Boyle. "For example, some really long-distance migrants like arctic terns are not fruit-eaters."

Boyle, an adjunct lecturer in UA's department of ecology and evolutionary biology and co-author Courtney J. Conway, a UA assistant professor of natural resources and a research scientist with the U.S. Geological Survey, report their findings in the March 2007 issue of American Naturalist.

To figure out the underlying pressures that drive some birds to leave home for the season, the team wanted to examine a related set of species and compare their size, food type, habitat, migratory behavior and whether they fed in flocks.

Boyle and Conway focused on 379 species of New World flycatchers from the suborder Tyranni. One of the largest groups of New World birds, the Tyranni includes kingbirds, flycatchers, phoebes and such southern Arizona birdwatchers' delights as vermillion flycatchers and rose-throated becards. Tropical members include manakins and cotingas.

First the scientists had to construct the first "supertree" for New World flycatchers.

"No one has ever compiled all those birds together into one megafamily tree," Boyle said, adding that "supertree" is a technical term among evolutionary biologists.

Having the tree let the researchers compare a variety of traits across the many species of Tyranni by using a computer analysis called phylogenetic independent contrasts.

The technique allowed the scientists to sort out whether a bird was migratory because that's what species on their side of the family tree always did or whether the bird's travel habits had some ecological correlates.

Food scarcity was the number one issue that predicted a species' migratory behavior, the team found. Boyle said, "Food availability is the underlying process, not diet and habitat."

One strategy for dealing seasonal changes in food availability is migration. The team also found that species that forage in flocks are less likely to migrate.

"If you are faced with food scarcity, you have two options," Boyle said. "You can either forage with other birds or you can migrate."

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, she said. "Flocking can be an alternative way to deal with food shortages."

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.

Email This Article

Related Links
Alice Boyle
Courtney Conway
News at University of Arizona
Darwin Today At TerraDaily.com

Some Corals Might Be Able To Fight The Heat
Ithaca NY (SPX) Mar 05, 2007
While humans can survive large temperature fluctuations, such species as corals are only comfortable within a 12-degree temperature range. And rising global temperatures appear to be threatening their survival, according to Drew Harvell, Cornell professor of ecology and evolutionary biology.

.
Get Our Free Newsletters Via Email
  



  • Indian Army Airlifts Thousands Stranded On Kashmir Highway
  • Rescue Teams Scramble To Help Indonesia Landslide Victims
  • Agreement Between ESA And The European Maritime Safety Agency Signed Today
  • Conflicting Signals Can Confuse Rescue Robots

  • Banning New Coal Power Plants Will Slow Warming
  • The U.N.'s War On Global Warming
  • Wet Desert Of India Drying Out
  • Heatwave On The Top Of The World

  • Satellite Scientists Set To Descend On Hobart
  • CSIRO Imagery Shows Outer Great Barrier Reef At Risk From River Plumes
  • ITT Passes Critical Design Review for GOES-R Advanced Baseline Imager
  • Scientists Gear Up For Envisat 2007 Symposium

  • Wen Says China Must Stop Wasting Energy
  • Iran Seeks Closer Naval Ties With Oil-Starved India
  • Researchers Study Superconductivity, Magnetism In Novel Material
  • Software Patch Makes Car More Fuel-Efficient

  • Researchers Reconstruct Spread Of Bird Flu From China
  • Troubling Trends In AIDS Cases
  • Two Weapons Ready For AIDS Fight
  • Bird Flu Spreading In Central Russia

  • Why Do Birds Migrate
  • Some Corals Might Be Able To Fight The Heat
  • Scientists Invent Real-Life Tricorder For Chemical Analysis
  • Fish, Trees, Cuddly Mammal Up For Protection From Human Trade

  • Asian Pollution Linked To Stronger Pacific Storm System
  • Canada's Oil Sands To Keep Polluting
  • As An Economy Blossoms An Ancient Capital Suffocates
  • Carnegie Mellon Researchers Study Harmful Particulates

  • Time For TV Detox
  • DNA Study Explains Unique Diversity Among Melanesians
  • Eating Ice Cream May Help Women To Conceive But Low-Fat Dairy Foods May Increase Infertility Risk
  • First Direct Electric Link Between Neurons And Light-Sensitive Nanoparticle Films Created

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2006 - SpaceDaily.AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA PortalReports are copyright European Space Agency. All NASA sourced material is public domain. Additionalcopyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement