Wild Side : Martha's Vineyard naturalists catalog mid-summer butterflies
Photo by Matt Pelikan
Last Sunday, July 17, five liberally sunscreened butterfly enthusiasts took to the field for the 12th annual Vineyard Butterfly Count. Coordinated by the North American Butterfly Association, the so-called "Fourth of July Butterfly Count," or 4JBC, takes place in a window from late June into late July. Participants tally all the butterflies they can find in a circle 20 miles in diameter, or, in the case of the Vineyard, across the entire Island.
Begun in 1999 (we missed one year due to weather), this relatively new tradition resembles the more familiar Christmas Bird Count. Part of national networks of hundreds of similar efforts, both counts enlist amateur observers to collect data used for long-term monitoring of wildlife populations.
Naturally, five observers can't count every single butterfly on the Vineyard. But even a single observer can do a surprisingly thorough job in a particular field or meadow. And since much of the Vineyard features wooded habitat that holds few if any butterflies at this season, count participants focus their attention on the limited areas that butterflies prefer. By adjusting numbers to account for more or fewer observers, each individual 4JBC produces a fairly accurate snapshot of what butterflies are around, in what kind of numbers. And over time, the hundreds of counts nationwide add up to an overview of population trends and changes in distribution of butterflies.
Allan Keith, of Chilmark, covered Aquinnah, Chilmark, and much of West Tisbury; Oak Bluffs and Vineyard Haven were the province of Judy Holland; and I covered Edgartown, with the assistance of Soo Whiting and Greg Palermo, of Edgartown. Rob Culbert reported some additional sightings. Unfortunately, Chappy went uncounted this year.
Both the number of species (33) and the number of individuals tallied (924) place this count right about in the middle of our historical results — though allowing for the small number of observers, these figures suggest that the season is a very good one for Vineyard butterflies. The most common species were common wood nymph (134), a larger species with dark wings sporting a yellow patch near the wingtips; American copper (120), a tiny gray-and-orange job; and dun skipper, a nearly black, moth-like butterfly barely a half-inch long.
The stars of the show were the hairstreaks, a group of small, grayish butterflies with intricate markings that are unusually common this season. Coral (22) and banded (30) hairstreaks produced especially welcome numbers, with most of these coming from the western half of the Island. (Such small-scale, local variations in abundance are very common with butterflies.)
Surprisingly scarce or absent were American ladies (just three individuals), painted lady (none at all), and red admiral (also missed entirely, amazing for a species that sometimes turns up by the hundreds in this count). These species are migratory, re-colonizing the Vineyard every spring, but this season, something clearly has prevented their re-establishment here in their usual numbers.
Also scarce or missing were pearl crescent and Peck's skipper. Sometimes abundant on the Vineyard, both of these species are "between flights" here: members of a spring generation have finished their lives, and their offspring have not yet reached maturity.
From my own perspective, the day had two high points. The first came relatively early in the day, when Greg Palermo, participating in his first-ever butterfly outing, spotted a beautifully fresh-striped hairstreak on a milkweed flower at Sheriff's Meadow's Tuthill Preserve in Edgartown.
The tiny, ornate butterfly was partly hidden in the cluster of blossoms, and in spotting it, Greg showed his rapidly developing ability to detect the subtle cues that signal the presence of the butterfly. Moreover, this striped hairstreak proved to be the only one tallied on the entire count — showing that an alert beginning observer can significantly influence the count's outcome.
My second high point came in Correllus State Forest, where I walked a couple of miles of fire lane under a very hot afternoon sun. Along with several species of aster, wild indigo was everywhere and in full bloom — I've never seen this plant have a year like this. As I walked, I turned up a steady stream of hairstreaks and skippers nectaring on these two flowers. The butterflies turned up as singletons, rarely in groups, but I never had to walk more than a few yards between butterflies, and the numbers steadily grew. In particular, gray hairstreaks were unusually common, and the day's total for this species, 36, ended up setting a count record for this species.
So-called citizen science projects like the Christmas Bird Count and the 4JBC have grown steadily in popularity in recent years, and they have also gained credibility among professional scientists. Any given count shows year-to-year swings in numbers that have nothing to do with long-term population trends. And there are sometimes limitations in the effort and accuracy that amateur observers exhibit. But over time, and across a vast geographical area, these variations average out; taken together, complete 4JBC results represent the best picture we have of how butterflies are doing across the continent.