This article first appeared in the January 2004 issue of the San Antonio Audubon News.
Am I the only one out there who gets actual nausea looking at shorebirds? I sometimes stare at them for so long through binoculars looking for obscure field marks that I suffer from motion sickness. Needless to say, I will not be expounding much here on the finer points of separating Long-billed (Limnodromus scolopaceus) and Short-billed Dowitchers (L. griseus). What does fascinate me are the “whys” and “wheres” of shorebirds, how they travel such enormous distances to grace our local mudflats, and how the various species efficiently divide up the habitat between them, each feeding in a somewhat different manner.
The methods of prey capture in this group are more complex than at first appears. Some clearly locate prey on the surface by sight. Others probe in the water and mud, locating prey by touch, while yet others feed by filtration, sieving the mud and water through their bills. Closer inspection blurs these convenient distinctions: some may probe based upon visual clues, and bills may be designed such that capillary forces and filtration are employed while probing, and even the most specialized probers and filterers can capture prey opportunistically by sight. What does emerge is that shorebird bills are amazingly complex structures, both sensitive and flexible, and cleverly designed to make use of natural forces when capturing prey.
The dowitchers are believed to be most closely allied to the similarly long-billed Snipes and Woodcocks, but unlike these birds they commonly occur on open mudflats far from cover. Dowitcher flocks are usually easy to spot: they are compact, medium-sized shorebirds with long, straight bills. They usually feed in shallow water, probing the mud with a distinctive, rapid sewing-machine motion.
Female Dowitchers average both larger and longer-billed than their mates, such that considerable overlap in these traits exists between the two species. Although rather subtle plumage differences exist, the species are perhaps most easily separated by their calls. The differences in their voices along with the habitat and season can offer important clues for identification.
Short-billed Dowitchers breed in wet grassy meadows and wetlands in the boreal zone. Three subspecies occupy separate ranges in the eastern (L. g. griseus), central (L. g. hendersoni) and western (L. g. caurinus) regions of the North American sub-Arctic. Short-bills migrate south prior to molting, adults passing through our area from late June, the juveniles following in late July and August. All winter primarily in salt water habitats from the southern United States to South America. The flocks of these birds that occur seasonally on our coasts were once decimated by market gunners.
On the breeding grounds, both dowitcher species form monogamous pairs. Both sexes help construct a simple nest and initially incubate the four spotted eggs. The females then leave the males who tend the precocial young alone. The fact that males commonly outnumber females in the Short-bill at least may indicate a tendency towards polyandry.
Long-billed Dowitchers nest in moist Arctic tundra and muskegs in far Northwest Alaska and adjacent Siberia, wintering from the Gulf States and Washington State south through Mexico. The genus Limnodromus is otherwise represented in the Old World by a single species, the Asian Dowitcher (L. semipalmatus), and is absent altogether from Europe and much of Siberia except as strays, most often Long-bills. Long-bills enter into a post-breeding molt prior to moving south, consequently the adults do not appear in our area until the end of July, and the juveniles not until September. Although a degree of habitat overlap exists, Long-bills prefer freshwater habitats at all seasons. Any Dowitcher found in our local area in the fall and winter is almost certainly this species.
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