By Patrick McShea, Carnegie Museum of Natural History

Along the wave-washed margins of Pittsburgh’s rivers a four-inch high bird presents important lessons about nature’s ingenuity. Between late April and early September, small numbers of Spotted Sandpipers inhabit the beach-like zones between river bank vegetation and the water’s edge.

On first acquaintance, these seasonal residents are remarkable for their seeming perfect physical adaptation to the narrow ribbons of mud, sand, rocks, and tree roots that fluctuating river levels alternatively inundate and expose. A sandpiper’s grayish-brown back and brown-flecked white breast serve as excellent camouflage within this earth-toned habitat, a protection enhanced in places where wind and flowing water account for lots of background movement, by the bird’s incessant motion.

As they search for insects and other small prey, sandpipers pace about the river’s edge on spindly legs, occasionally bursting into a skittering rush to capture a fleeing bug, or skimming across the channel on stiff-looking wings to forage on the opposite shore. When not in forward motion the birds bob rhythmically, a behavior that in other parts of their extensive North American range has earned them colloquial names such as “teeter-peep” or “teeter snipe.”

The species would undoubtedly bear more intriguing nicknames if close observers of river edge fauna were aware of a phenomenon documented by two decades worth of research studies along the shorelines of Minnesota lakes: Spotted Sandpipers reverse many sex roles.

Male Spotted Sandpipers assume an inordinate portion of parental duties, including the 21-day incubation of a clutch of four eggs laid by his mate, and the shepherding of newly-hatched young for several weeks until they are old enough to fend for themselves. The male performs these tasks within a long narrow patch of shoreline claimed and defended by the female, a territory that in some instances is large enough to include one or two additional male mates caring for more eggs and young.

Polyandry is the term used to describe this type of breeding system in which one female mates with more than one male. Less than 2% of the world’s 9,000 bird species are polyandrous, and a significant portion of this minority consists of shore birds and wading birds that nest in the high Arctic. There polyandry appears to have evolved as a strategy to maximize the production and care of young during short summers. Females are able to devote enormous amounts of energy to egg production during a brief nesting season because multiple male mates devote enormous amounts of energy to the care of small sets of eggs and the young that hatch from them.

In this context Spotted Sandpipers can be thought of a species that extends this ongoing experiment in biological possibility into temperate regions, a textbook example on the edge of the Monongahela, Allegheny, and Ohio of how nature offers multiple solutions to the challenge of reproduction.

Patrick McShea works in the Division of Education at the Carnegie Museum of Natural History and he can be contacted by sending email to: McSheaP@CarnegieMNH.org .

Other Recent Articles by McShea Include:

Wood Ducks Spring Spectacle Almost Passes Unnoticed

Ospreys Call Pittsburgh’s Three Rivers Home for the Next Few Weeks

Links: To Lure Birds to Your Yard, Think Like One

Luring Hummingbirds

Monarchs Welcomed in Garden

5/18/2007