Sunday, December 19, 2010

Exceptionally late Broad-winged Hawk migration

juvenile Broad-winged Hawk

I'm back in El Salvador. Yesterday, I went on a field excursion organized by the Salvadoran branch of Partners in Flight (PIF), the principal club of bird observers in El Salvador. We went to Walter Thilo Deininger National Park near the coastal town of La Libertad, where we saw a fair number of interesting birds - really more than any of us had expected.

By far the most noteworthy sighting, however, was of a group of 17 Broad-winged Hawks - later followed by smaller groups for a total of at least 40 individuals - apparently migrating over the site!

All birds were juveniles.

juvenile Broad-winged Hawks kettling over the park

As far as I'm aware, this late migration of juvenile Broad-winged Hawks has not been previously described - for Central America, or indeed any other site. The species winters in northern South America and throughout Central America; a small number winters in southern Florida and the lower Mississippi Delta and coastal Texas. The majority of birds that winter in the US are juveniles (Goodrich et al. 1996).

juvenile Broad-winged Hawks in a glide over the park

Highly gregarious in migration, the species can be seen in large congregations in the northeastern US during the second half of September, Texas late September, Mexico early October. Fall migrants are noted in Costa Rica and Panama from late September to mid-November, but most pass through in October (Goodrich et al. 1996). 

juvenile Broad-winged Hawk

Separate migration of age classes is well-known during spring migration, when the majority of adult Broad-winged Hawks precede the majority of juveniles by about two to three weeks. In fall, all ages usually migrate together (pers obs).

Flying with the broadwings were single individuals or small groups of two or three Turkey Vultures. This surprised me less, as a small percentage of Turkey Vultures is known to linger and migrate opportunistically. Mexican hawk counters in Veracruz told me it is often possible to see Turkey Vulture movement well into December.

Goodrich, L. J., S. C. Crocoll and S. E. Senner. 1996. Broad-winged Hawk (Buteo platypterus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

1 comment:

Oliver Komar said...

John, it was fun to bird with you on yesterday's field trip. I wonder if this December wave of migrating Broad-wings was due to the two exceptional cold waves that passed through the southeastern US last week, with freezing temperatures all along the Gulf Coast. Perhaps these juveniles were lingering (wintering) up there, and got the message that they should be wintering farther south. Another bird we saw during yesterday's field trip at Parque Deininger (El Salvador), that struck me as exceptional, was the Chuck-will's-widow. This species is normally only a fall transient in El Salvador. But some birds apparently winter along the Gulf coast of the US. Once again, the December cold wave may have created a December passage wave for Chuck-will's-widow too, or pushed those US wintering birds to winter here in Central America.