Yellow-billed Cuckoo - Everglades, Florida

Traditionally, migratory songbirds are thought to follow a fairly standard life history.  Breed in the United States and Canada during the spring and summer and then migrate to Central and South America for the winter to avoid the harsh weather conditions and food scarcity found across much of North America.  However, new scientific evidence may turn that on its head, at least for a few species.

Researchers from the University of Washington in Seattle have presented evidence that at least five species, Yellow-billed Cuckoo, Cassin’s Vireo, Yellow-breasted Chat, Hooded Oriole, and Orchard Oriole, may not follow this pattern exactly.  Their evidence points to a second breeding season, where at least some portion of the population migrates to North America and breeds, then departs for an early southbound migration in midsummer.  However, instead of going all the way to the tropics, they stop in western Mexico to breed a second time in the thorn forest there.  This second breeding season corresponds with an influx of rain and pulse of insect life.

Sievert Rohwer and his colleagues not only documented breeding of each of these species but, using both physiological observation and stable isotope analysis, demonstrated that many of these individuals had bred previously that year outside of western Mexico.  Females displayed worn brood patches, featherless areas on the belly of the bird used for incubating eggs, suggesting that these birds had previously bred earlier in the season.  Stable isotope analysis demonstrated through chemical signatures that these individual birds had spent time farther north and not spent the entire spring in the thorn forest.

Breeding patterns like this have never been recorded in the New World and only twice in the Old World.  It may have major conservation implications as, while we don’t know the percentage of individuals from these five species that follow this migratory double breeding pattern, the thorn forests of western Mexico may prove crucial to supporting the entire species populations.

The researchers also raised numerous other life history questions.  How do young birds from the first breeding season and the young birds from the second both find their way to similar winter grounds despite being born thousands of kilometers apart?  How do these birds regulate their physiological condition altering between migratory condition (northbound), breeding condition (first season), migratory (southbound), breeding condition (second season), and migratory again?

This fascinating research has uncovered a phenomenon in several species and only through further study can we begin to understand how important this second breeding season may be to these and other birds.

Source: Rohwer, Sievert, Keith A. Hobson, and Vanya G. Rohwer. “Migratory double breeding in Neotropical migrant birds.”  Proceedings of  National Academy of Sciences 106.45 (2009): 19050-19055.

Nature Appreciation Day hosted by the Nature Photographer’s Network – Sunday, October 4^th, 2009 will be the first annual Nature Appreciation Day.   The basic idea is to get out and take some photos in the outdoors.  The theme is “What Nature Photography Means to Me – why we enjoy the pursuit of nature photography and how focusing on the beauty of nature through the camera’s viewfinder provides an escape from the stress of daily living.”  If you don’t know NPN, it is a great community of nature photographers that can be a great learning resource.  I’ll be on a plane flying back to New York most of the day but will try to get out and get some photos when I get home.  Read the full Press Release here.

The National Parks: America’s Best Idea – Tonight is the final night for the 6 part series filmed by Ken Burns focusing on our nation’s national parks.  This is a major multimedia release with the film, a cd, and a book all focused on this project.  I haven’t had a chance to watch the series myself but have recorded the first 5 episodes and will be watching it in the coming weeks.   I’ve heard great things so far.  If you have missed the series, they are available online at PBS.  Read more and see the full series here.