Hello all! Welcome back to local wildlife weekly.

For those of you who have been watching the Seaside Center’s summer video series (courtesy of yours truly), you will at this point have learned about many more species than I have covered here (albeit in less depth). If you have no idea what I’m talking about, oh no! You can find the entire playlist here.

At the end of my last video, I touched briefly on a species of bird that deserves more time in the spotlight. The black skimmer is a truly remarkable animal and, while it remains unusual on the Sound, its numbers seem to be increasing— excellent news for committed birders and amateur nature-lovers alike.

So, what makes the skimmer so special? If only there was one reason: the skimmer is visually and audibly enchanting, unique in behavior and ecology, and it’s always found in excellent habitat. What’s not to love? Also, as is typical of the species profiled in this series, the skimmers’ natural history is a gateway to some interesting and contested topics. Let’s explore why!

Introducing: The Black Skimmer

A Black Skimmer at Nickerson Beach in Lido Beach, NY. Photo by Brendan Murtha.

The black skimmer, Rhynchops niger, is one of three skimmer species found around the world. These three species (Black, African, Indian) straddle the global tropics, and are similar enough to be considered a “superspecies.” A superspecies is a collection of populations who have diverged allopatrically (as a result of geographic isolation) from a single parent population, but who remain genetically similar enough that successful hybridization would likely occur were the populations to meet. It is thus an “umbrella” for the species it contains, and is the necessary inverse to the subspecies, of which Rhynchops niger has three: R. n. niger (North America), R.n. cinerascens (Northern/Western South America), and R. n. intercedens (Southeastern South America). Each of these subspecies are similarly allopatric, a largely isolated population, and here we see the constant “pull-and-tug” tension at the heart of contemporary species classification: superspecies, species, and subspecies are not clear-cut categories, but exist only in relation to one another– sort of an endless dance between evolving populations. In fact, the three current skimmer species were once considered a single species, with a pan-tropical range, and what we now call black skimmer could similarly be “split” into multiple full species in the future.

Skimmers are in the family Laridae, alongside gulls and terns. In this family they occupy a puzzling space, as it’s not clear where their divergence occurred: while morphologically similar to terns (lithe and long-winged) DNA studies suggest skimmers split off from the common ancestor of the whole group, placing them “equal distance” from gulls and terns alike. The latter groups have undergone a great deal of diversification, radiating widely, but as we’ve discussed the skimmers all remain similar and unique: why?

The name “skimmer” speaks to the superspecies’ cohesion, as none of its populations have abandoned the namesake behavior. Skimmers are all “skimmers,” impeccably adapted for the act, and the birds’ divergence from early Laridae was likely along the lines of such specialization. Early specialization isn’t exactly conducive to niche diversification, and as other Larids diversified to occupy neighboring niches the likelihood of skimmers “abandoning” the behavior to try something new would have been minimal: competition and limited resources would keep them relatively unchanged within their lane, where they held an early monopoly. You know what they say: “If it ain’t broke, don’t fix it…” In this sense, despite the skimmers superspecies-species-subspecies stretch, what constitutes a skimmer is quite clear (and designated by the genus Rhynchops, or the “subfamily” Rhynchopidae).

So, what does constitute a skimmer? Let me not get ahead of myself: we haven’t even specified what “skimming” entails, or how it works!

Skimmers with a Common Tern, another member of family Laridae. Photo by Brendan Murtha.

One of the most notable features of a skimmer is its odd bill, which is laterally compressed (like a knife). On this bill the lower mandible extends beyond the upper one, giving skimmers a unique “underbite.” Rather than being a misshapen anomaly, this bill is a potent weapon. To feed, skimmers fly low over shallow water and let their extended lower mandible run beneath the surface. Hyper-sensitive, this mandible will make contact with small fish, which are “uprooted” from the water: the upper mandible then snaps down to make the meal. At this angle of attack skimmers hover just over the surface of the water, not casting a shadow from above: the poor fish never see them coming. To make matters worse, skimmers often feed communally, flying in v-formation: a flock will tear through a school of baitfish, turning the glassy surface into a cauldron of frantic activity. Through this commotion the birds leave long wedged wakes, which mirror the wide angle of their wings mid-glide: the combined effect of all this is simply breathtaking to observe. It’s made all the better by skimmers’ crepuscular preferences: the birds feed mostly at dusk and dawn, and the patterns they trace on the surface look best under such dramatic lighting. How convenient!

As you might guess, the skimmers’ feeding strategy works only in very shallow water or water brimming with fish. If the fish dip just a few centimeters below the surface they are beyond the skimmers grasp: unlike other Larids, skimmers will neither dive nor dabble for their food. These restricts them to habitats like tidal flats, marsh pools, or salt-pannes. They also avoid turbulent waters, which tend to keep fish deep: as a result you will not see skimmers feeding in the surf of an open beach. Skimmers often “chase the tide,” as it’s called, criss-crossing the water’s leading edge, and they’ll also flock around the sheltered pools that build up behind sandbars. Fortunately for skimmers, these waters often attract huge concentrations of small fish. Baitfish seek out shallows, where they’re safe from larger aquatic predators and diving birds… or so they think. Skimmers exploit these refugee congregations, proving once and for all that, if you’re a baitfish, truly nowhere is safe.

On the east coast of North America skimmers range as far north as Cape Cod and the Islands (Martha’s Vineyard, Nantucket, etc.) This is a northern range cap for many coastal species: north of the Cape the coast turns rocky and supports a whole different ecosystem. The barrier beaches and extensive marshes of the coastal plain provide perfect skimmer habitat: they nest colonially on the open beach and can feed on the sheltered waters behind the barrier. On the South Shore of Long Island, for example, roads that run along the barrier beach often see large movements of skimmers overhead: the birds move back and forth from the beach to the marsh, bringing food to chicks in the colony. Being around big groups of skimmers is always a treat, especially when they’re vocal: the birds call to each other with alien barks, a sound with no local corollary. When driving these barrier-beach roads it’s always a good idea to roll your windows down: the skimmer calls float through the breeze and, at least to me, quickly become an inseparable part of the summer soundscape. Skimmer populations that nest north of North Carolina do not spend the winter; they’ll head down to southeast beaches and the gulf coast in late fall.

Despite it technically being within their range, skimmers have always been scarce on the Long Island Sound. Colonies in the northeast are local to begin with, as their beloved barrier beach habitat is patchy and diminished north of Long Island. This scarcity was exacerbated by human disturbance. Like many other birds, skimmer colonies were historically raided for their eggs, and, coupled with development, this drove many to collapse. By the turn of the 20th century the skimmers’ range had seen its northern fringe lopped off, the population too sparse to repair itself. The birds have staged a significant natural comeback since then, and have been breeding on Cape Cod and Long Island for decades: yet throughout this time they’ve remained quite unusual on the Sound. The historical status of skimmer on the Sound is unclear, but it’s likely that, if there were historic colonies, they were always quite small and scattered. The Sound doesn’t offer up great skimmer habitat, with rocky shores and minimal beachfront. Small flocks often appear during the summer, but they rarely stick around. Such localized disparity always amazes me: skimmers can be downright abundant on the opposite shore of Long Island, only a dozen miles away (a stone’s throw for a bird).

That being said, skimmers are becoming more and more common on the Sound. In fact, this summer, Connecticut hosted its first established skimmer colony in many years– small, for sure, but successful! Situated on a sand-spit in West Haven, the nesting skimmers chose well; their new site has all the necessary characteristics, with open swaths of sandy beach abutting a sheltered lagoon and extensive, shallow-water flats. Whether or not this colony will persist, grow, and/or birth new ones, for now it’s to be celebrated: to see fledgling skimmers on a Connecticut beach was a dream come true for myself and many other Connecticut birders. While adult skimmers may be the epitome of grace, young ones are downright goofy: they appear big-headed and uncomfortable, and their attempts to skim are uncoordinated and rarely successful. It’s cool, it’s cool… I can totally relate. I hope that, while watching adults float over ember tides, the young birds know such grace is within their reach: how inspiring that must be!

A “digiscoped” photo of a young skimmer, fledged from the new CT colony this summer! Photo by Brendan Murtha.

My fingers are crossed; hopefully our new skimmer colony is occupied annually and more colonies appear around the Sound. I dream of the day skimmers are a familiar species for naturalists and non-naturalists alike (they’re certainly hard to ignore) and, in the meantime, I hope this post has at least made you, reader, aware: keep your eyes out! As skimmers numbers increase, your chance of catching a glimpse gets higher and higher. If that’s not exciting, I don’t know what is.

I will leave you on this hopeful note, for unfortunately this is the last installment of “Local Wildlife Weekly.” The summer is drawing to a close and, like a shorebird, I too am packing to go. Few birds head north in the fall, but I am no bird: Maine is beckoning and, while I’ll be sad to bid the Sound goodbye, I am excited– the woods and shores of my adopted-home also hold a special place in my heart. I hope you’ve enjoyed this series as much as I’ve enjoyed writing it, and I hope you’ve learned something about the wildlife we’re lucky to count as neighbors. If anything, I hope these posts have made you more curious, more attentive: there is so much to see when you look close, and looking is the first step in a miraculous journey.

Signing off! Thank you all!

- Brendan Murtha, 2020 Seaside Center Naturalist