Thursday, May 8, 2014

Spotted Sandpipers - Ring's Island, Salisbury - May 7, 2014

Spotted Sandpiper by Margo Goetschkes


I saw three Spotted Sandpipers yesterday morning at Salisbury's Town Pier on the Merrimack River.  The Spotted Sandpiper's name, Actitis macularia,  translates as follows: Actitis in Greek means "coast dweller", and macularlia in Latin means "possessing a spot or mark". This small shorebird, only 7-8 inches from head to bobbing-tail, weighs just less than two ounces.

On this cool morning, the Spotties' efficient feathers layered one over the other like shingles on a roof warmed them.  I recognize their 15 inch wingspan and a flight that's weak and stiff - appearing arthritic in gait and cadence - as they settled on a dock.  I've watched their teetering accelerate when they're unsettled and nearly stop when they're content.  When they forage, they're recognized by their endless nodding and teetering.  They're visual feeders and can catch a flying insect. It's the Spotted Sandpipers' life history that interests me. I wondered if these three were a group of females on a journey to establish and defend breeding territories by arriving earlier than the males.  In other species of migratory birds, it is the males who establish territories by arriving first. The Spotted Sandpiper females are nearly 25% larger than males.  These freshwater breeders are found across most of the United States and Canada. Spotted Sandpipers are not social birds and are seldom seen in flocks. Pete Dunne's Essential Field Guide Companion states that they migrate in flocks of fewer than a dozen individuals.

Spotted Sandpipers are ground nesters. Females may copulate with up to five mates, but they leave the job of incubation and chick rearing to the males. Males incubate a maximum of four eggs for up to three weeks, and the young fledge in 17-21 days. By having multiple mates, a female is able to boost her reproductive efforts. The female may store seminal fluid for nearly a month.  That means that the eggs she lays for one male may be sired by another from a previous mating. The male provides the parental care, and it is possible that those young have none of his genetic material.

The Birder's Handbook [Ehrlich, Dobkin and Wheye] states "Spotted Sandpipers thus forgo the advantages of having two parents to care for eggs and chicks. At least in the study population, however, that does not seem to affect the fledging rate greatly, and the Spotted Sandpipers' reproductive strategy seems to be highly successful." The text also states that Spotted Sandpipers breed at an early age and live a relatively short time [breeding females live an average of only 3.7 years]. These three Spotted Sandpipers rested, fed and then moved on to get started on the rigors of creating the next generation. In a few weeks, the season's insects hatch out to nourish the young.  As the days shorten, fall migration begins in July.  I'll be watching for the polyandrous females, those nurturing males and the young of the Class of 2014 as they linger to forage for insects and aquatic invertebrates along many shores, building their fat stores to fuel their southern journey to Chile, Argentina or Uruguay. 
Good birding,
Sue

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