Wednesday, July 28, 2004

Archie and Jughead:

Hello from Boulder, Colorado.

I'm here attending the annual GLOBE Program Conference.

Bill Hilton is one of the scientists that has funding from me, and he is here talking about his work with the Ruby-throated Hummingbird. I've posted about Bill and these birds before in April 2003, and April 2004, when the little guys first appear at our feeders. Bill has one of the best websites on this bird out there. Bill runs a nature center called the Hilton Pond Center, in York, South Carolina, where he does a lot of banding of birds, ruby-throats among them. After Bill bands a hummingbird, he puts green dye on their throat so that he doesn?t waste time recapturing them, because some of these cheeky rascals will re-enter the trap several dozen times a day! Bill is one of about one hundred people licensed to band hummingbirds in the U.S., and the only person permitted to put dye on them.

There are 338 species of hummingbirds in the world, all of them in the Western Hemisphere. Fifteen to seventeen species have a range in North America, but the only species in the Eastern U.S. is the Ruby-throated hummingbird, or RTHu in ornithological shorthand. Interestingly, the range for RTHus expands waaaay West in Canada, to just short of the B.C.-Alberta border.

In Costa Rica, there are 55 species. By the time you get to the Amazonian basin, there are 125 species. This increase in the number of species as you approach the equator leads us to believe that they originally speciated from the Amazon basin.

The first ever recapture of a migrating RTHu occurred in 1991. A hummingbird with a green throat was sighted in Loganville, Georgia by a lady who had returned the previous day from a birding trip to Costa Rica - she could not identify the bird, and called a friend who is a hummingbird specialist in Alabama. He jumped in his car and drove nine hours, captured the bird, and found that it was one of Bill Hilton's RTHu's, banded just 10 days previously in York, South Carolina. The bird had flown 270 miles in the ten intervening days. Not a new hummingbird species, but an exciting catch nonetheless.

The next recaptures occurred in 1997 and 2000 in Robertsdale, Alabama, 485 miles and 17 days from the banding in York, South Carolina, and then in Cameron, Louisiana, 790 miles from its banding. As you can tell, recaptures are extremely rare. There have been about 100,000 RTHus banded the U.S. since banding was started in the 1930's, but only 10-15 have ever been recaptured away from their original banding site. From the number of chicks hatched during the summer, we can tell that only about 20% of the migrating birds survive to return the next summer ? a staggering loss rate for any species, and one that makes the capture-recapture method extremely difficult to apply to migration.

The interesting thing about these recaptures is that they show a very strange migration pattern. Strange only because previously it was thought that the migration path for RTHus was through Florida and over water to the Yucatan peninsula (because drill rigs and boats in the area had seen RTHu's zooming by on their way, and because there have been sporadic reports of RTHus on Caribbean islands). These three recaptures show the birds moving West, rather than South, hinting that the majority of the RTHu population in North America may move overland around the Texas coast on their way to their wintering grounds on the Pacific coasts of Mexico and Central America.

No RTHu has ever been recaptured South of the Rio Grande, and the intent of the program is to train teachers and students in Mexico and Costa Rica in how to observe the birds so that they can be on the look-out for those green necks!

One interesting point Bill had was that the peak in feeder population that we observe around August is in fact made up of two distinct populations - those bird pairs and their chicks that actually nested in our area, and the early Southward migrators from Southern Canada.

I?m off this afternoon to an area in the Rockies at about 7,800 feet, where there are plenty of Black-chinned Hummingbirds, Rufous Hummingbirds, and Broad-tailed Hummingbirds. Stay tuned.


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