Though none of the news sites (or PR) directly reference it the paper
is online at

http://www.pnas.org/content/early/2009/10/23/0908121106.abstract

> Migratory double breeding in Neotropical migrant birds
> Sievert Rohwer a, Keith A. Hobson b, and Vanya G. Rohwer a
> Author Affiliations
>
> a Burke Museum and Department of Biology, University of Washington,
> Seattle, WA 98195; and
> b Environment Canada, Saskatoon, SK, Canada S7N 0H3
>
> Abstract
> Neotropical migratory songbirds typically breed in temperate regions
> and then travel long distances to spend the majority of the annual
> cycle in tropical wintering areas. Using stable-isotope methodology,
> we provide quantitative evidence of dual breeding ranges for 5
> species of Neotropical migrants. Each is well known to have a
> Neotropical winter range and a breeding range in the United States
> and Canada. However, after their first bout of breeding in the
> north, many individuals migrate hundreds to thousands of kilometers
> south in midsummer to breed a second time during the same summer in
> coastal west Mexico or Baja California Sur. They then migrate
> further south to their final wintering areas in the Neotropics. Our
> discovery of dual breeding ranges in Neotropical migrants reveals a
> hitherto unrealized flexibility in life-history strategies for these
> species and underscores that demographic models and conservation
> plans must consider dual breeding for these migrants.
>

The full paper isn't free unfortunately and I've not found a preprint
on the web. If you know of one let me know.

The UW PR is at

http://uwnews.washington.edu/ni/article.asp?articleID=53093

On Oct 28, 2009, at 8:45 AM, Dennis Paulson wrote:

>> http://www.sciencedaily.com/releases/2009/10/091026152806.htm

--
Kevin Purcell
kevinpurcell at pobox.com
twitter: at kevinpurcell