A trip to Baxter State Park is a birder’s dream, and this time was no exception. Blackpoll warblers, winter wrens, white-throated sparrows and the occasional boreal chickadee serenaded us when we stopped at Basin Pond for a refreshing break on our hike out from Chimney Pond.

Most memorable about our stop was the appearance of a spotted sandpiper.

We first became aware of the bird’s presence by a series of calls it gave. The strident “per-weet, per-weet” reached us across the rocky shoreline as the bird flew with stiff, shallow wing beats along its territory.

We watched it moving among the rocks, occasionally pausing to survey its surroundings. It continually bobbed its rear-end up and down, appearing as if it were unbalanced. This comical behavior is a helpful characteristic when identifying the bird.

The spotted sandpiper is one of the few shorebirds that breeds in Maine. It nests near secluded inland lakes and ponds, and forages near the water’s edge for flies, worms, beetles, small crustaceans and fish.

It also has an interesting breeding biology. Unlike most other bird species, spotted sandpipers exhibit a reversal of sex roles. It is the female that arrives first in the spring, selects and defends a territory from other females, and initiates mating with the male.

She doesn’t stop there, however. Once she mates with a male and lays her eggs, she may leave him to do all the incubating and raising of the young while she finds another male to mate with. Researchers have reported a female mating with four or five males.

The last male she mates with is the luckiest, though – she may stay and help him incubate and raise the young. If a predator destroys the nest, the birds will make another nesting attempt within five days. Likewise, if they are disturbed during nest building, they will desert the nest and build elsewhere.

Like other shorebirds, young spotted sandpipers are born covered with down and able to walk and forage for food soon after hatching. They will stay with their parents for three weeks, until they are able to fly. Until then, their parents will watch over them, and even brood them in a shallow scrape in the ground in inclement weather.

The young are easily distinguished from their parents before the fall molt by their clear, unspotted breasts. It is not as easy to tell the male and female apart, however. Females will on average be larger than males, and will have more heavily spotted breasts – but this is only likely to be noticeable if the two are together for comparison.

Spotted sandpipers will begin their migration south in September or October, as will the killdeer profiled in last week’s column.

Chris Corio, a volunteer at Fields Pond Nature Center, can be reached at fieldspond@juno.com.