Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

First evidence for a second breeding season among migratory songbirds

27.10.2009
Biologists for the first time have documented a second breeding season during the annual cycle of five songbird species that spend summers in temperate North America and winters in tropical Central and South America.

It was known that these species, which migrate at night when there are fewer predators and the stars can guide their journey, breed during their stay in temperate regions of the United States and Canada.

But it turns out that they squeeze in a second breeding season during a stopover in western Mexico on their southward migration, said Sievert Rohwer a University of Washington professor emeritus of biology and curator emeritus of birds at the Burke Museum of Natural History and Culture at the UW.

"It's pretty much unheard of to have a nocturnal migrant with a second breeding season. It's a pretty special observation," Rohwer said. "We saw these birds breeding and we were completely surprised."

Migratory double-breeding has been observed in two Old World bird species on their northward migration, but this is the first documented observation of "migratory double breeders" in the New World, and the first anywhere for the southward migration, Rohwer said.

The scientists traveled to the lowland thorn forests of coastal western Mexico to survey and collect songbirds that had raised their young in the United States and Canada and then immediately migrated to Mexico to molt, or shed and replace their feathers.

But during July and August in three consecutive summers, 2005-2007, the researchers found individuals from five species – yellow-billed cuckoos, orchard orioles, hooded orioles, yellow-breasted chats and Cassin's vireos – that were breeding rather than molting.

They found evidence that the birds had, in fact, bred earlier that year. Females of all five species examined in July had dry and featherless brood patches, indicating they had bred earlier that summer. (To more efficiently transfer heat to eggs, the abdominal brood patch becomes featherless and thickened with fluid when females are incubating, but as the young mature it dries out and remains featherless.). In the Mexican breeding ground, there was a complete absence of young birds, indicating the females had not bred in the area of the thorn forests.

Active nests were found for two species and males of all five species were singing and defending territories or guarding females, behaviors associated with breeding. In addition, isotopic analysis of the birds' tissues showed that many had recently arrived in west Mexico from temperate areas farther north.

Rohwer is lead author of a paper describing the findings, published the week of Oct. 26 in the online edition of the Proceedings of the National Academy of Sciences. Coauthors are Keith Hobson of Environment Canada, a national agency charged with preserving environmental quality, and Vanya Rohwer, a graduate student at Queen's University in Kingston, Ontario. He is Sievert Rohwer's son and took part in the work while a UW undergraduate. The research was funded by the Burke Museum Endowment for Ornithology, the Hugh and Jane Ferguson Foundation, the Nuttall Ornithological Club and Environment Canada.

The observation is much more than an oddity in bird behavior, Sievert Rohwer said. He noted that orchard orioles might raise a first brood in the Midwestern and south-central U.S. and a second on Mexico's western coast, yet both sets of offspring find the same wintering area in Central America. The question is how both groups find the right place, since they must travel in different directions.

Then there is the yellow-billed cuckoo, once commonly seen throughout the western United States and as far north as the Seattle area but now seldom seen along the West Coast. Disappearing habitat in the U.S. is usually cited as the reason.

But Rohwer believes the real problem could be the transformation of thorn forests of southern Sonora and Sinaloa, states in northwestern Mexico, into irrigated industrial farms. That loss of habitat, he said, could mean not enough young are produced in the second breeding season to sustain the populations previously seen on the U.S. West Coast.

"It turns out that many of those migrants, both molt migrants and the newly discovered migratory double breeders, are dependent on the low-altitude thorn forests that become very productive during the monsoon," Rohwer said.

The thorn forests lie in an arid and forbidding scrubland that springs to life with the monsoon lasting from June through August. The monsoon brings virtually all of the area's annual rainfall. The small trees leaf out and insects become abundant, making an ideal stopover for migrating songbirds.

However, with plenty of biting insects, temperatures often at 100 degrees Fahrenheit and humidity hovering near 100 percent, it is a difficult place for researchers to work, so there has been little previous documentation of life in the thorn forest. The new findings could spur more work there.

"For western North America, the conservation implications are pretty serious," Rohwer said. "Biologists know theoretically that they should pay attention to these migration stopover sites, but they've been largely ignored for their conservation implications."

For more information, contact Rohwer at 206-543-4066 or rohwer@u.washington.edu

Vince Stricherz | EurekAlert!
Further information:
http://www.uw.edu
http://www.washington.edu

More articles from Life Sciences:

nachricht Repairing damaged hearts with self-healing heart cells
22.08.2017 | National University Health System

nachricht Biochemical 'fingerprints' reveal diabetes progression
22.08.2017 | Umea University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Cholesterol-lowering drugs may fight infectious disease

22.08.2017 | Health and Medicine

Meter-sized single-crystal graphene growth becomes possible

22.08.2017 | Materials Sciences

Repairing damaged hearts with self-healing heart cells

22.08.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>