September Nature Sightings

This past week, I encountered two interesting and new (to me) wildlife sightings while doing field surveys.

The first was at the site of a September 12, 2021, otter roadkill, where a small tributary of the Nissequogue River passes through a culvert under Route 27A in Smithtown. The problem here is one that otters face in many watersheds on Long Island: a dam on one side of the road that presents a barrier in the form of a 6-foot-tall vertical wall.

Otters traveling from the Nissequogue River upstream along the small creek can navigate through the 4-foot-diameter concrete culvert under Route 27A, but then they encounter the dam. All four sides of the narrow spillway between the dam and the culvert are vertical concrete. In order to make its way upstream to Willow Lake, the otter is forced to go back downstream through the culvert, up the embankment and onto the busy road.

While taking measurements of the dam and spillway for a possible otter-friendly ramp, I noticed a large, unusual-looking crab clinging to some vegetation on the pond side of the dam and feeding near the surface. The only freshwater crab-like organism that I’m familiar with is the crayfish, and this was no crayfish: It lacked the latter’s distinctive, lobster-like abdomen. What most caught my attention was the dark growth covering all but the tips of its white claws. I took some photos to see if I could identify it back home.

An online search of “freshwater crabs of New York” led me directly to a State Department of Environmental Conservation link for “Invasive Chinese Mitten Crab,” and a photo of a long-legged crab somewhat resembling our saltwater spider crabs (Libinia spp.) but with a covering of an odd, dark brown, hair-like growth on its claws, for which it gets its common name, mitten crab.

I soon realized that I should have collected the specimen.

The Chinese mitten crab (Eriocheir sinensis) is an invasive species native to East Asia and first found in New York in 2007, in the Hudson River near the Tappan Zee Bridge. According to the website, this species has not been reported from anywhere on Long Island.

If you happen to encounter one, collect it, if possible, or at least get a photo and report your sighting at dec.ny.gov/animals/35888.html.

The Chinese mitten crab spends most of its time in freshwater, migrating to brackish or saltwater to reproduce. The young are capable of moving several hundred miles upstream to find suitable freshwater habitat, where they will spend up to five years developing before returning downstream to reproduce.

As the otter did, when it encountered the dam, the mitten crab is capable of leaving water to move upstream around barriers. It’s amazing that, unlike the agile and fast-moving otter, the crab managed to avoid getting run over while crossing the road!

Later that day, I met up with Seatuck colleagues Enrico Nardone and Arielle Santos for some field work on the marsh islands of the Great South Bay. Our first stop was to check on a new bald eagle nest site on a large island with a small grove of trees west of Captree.

A bushwhack through poison ivy-infested shrubs led to the tree that, until recently, contained the formidable nest — but the entire structure now lay on the ground. Fortunately, reports from this site confirmed that at least one chick successfully fledged this summer. It will be interesting to see if the adults rebuild this winter.

Our next stop was a low marsh island that is home to the largest concentration of nesting common terns (Sterna hirundo) in the area. I associate common tern nesting habitat with the beach, their typical nest being a simple scrape in the sand above the high tide line and seaward of dense dune vegetation. Here, there was no sandy beach and no upland area without very dense vegetation. The entire island was covered with dense and healthy patches of typical salt marsh grasses: Spartina alterniflora, Spartina patens and Distichlis spicata.

It was hard to believe that common terns nested here, and it took some time to develop the “search image” to locate the nests. But there was no mistaking them, as quite a number had an unhatched tern egg still sitting there.

They were in all three vegetation zones of the marsh, utilizing a bit of wrack debris to elevate the nest above the average high tide mark. The number of intact but unhatched eggs found may reflect poor hatching success this year due to a storm surge during the critical incubation period.

The DEC lists this species as “threatened” in the state, and reports on their website that “many colonies are being forced to breed in salt marsh habitats as a result of the increased human use of beaches, and competition with herring and great black-backed gulls.” Both herring gulls and great black-backed gulls are relatively new breeding species on Long Island, with nesting first recorded here in the 1930s for the former and the 1940s for the latter.

One of Seatuck’s conservation campaigns is to monitor these unique and precarious marsh nesting sites and look for ways to enhance tern productivity. It will be a challenging task.

En route back to the marina, we came upon a large flock of terns feeding. Unlike common and least terns, these birds were not plunging into the water but just flying low and dipping the bills in. Roseates was the first guess, but on closer inspection they were Forster’s terns in their nonbreeding plumage.