Authors Posts by Matt Pelikan

Matt Pelikan

Matt Pelikan
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Juvenile Coopers Hawk

Last weekend, while looking for butterflies along a fire lane in the State Forest, I was surprised by a sudden halt in the bird songs that were providing the soundtrack for my stroll. A prairie warbler, which had been reciting its ascending buzz with the regularity of a clock, missed his cue; a chipping sparrow bit off his song in mid-trill.

This sort of thing makes birders look up. So I did. And as is supposed to happen at such moments, I found myself trading stares with a smallish hawk passing almost over my head. A long tail, and short, rounded wings marked this as a Cooper’s hawk; its modest size, clearly smaller than a crow, marked it as a male. Gripped in its feet, pulled snuggly against its belly like a football in a fullback’s hands, the hawk carried a small, gray item – probably a meadow vole, hardy unprecedented but not quite a typical prey item for a Cooper’s, since this woodland hawk specializes in catching birds.

The hawk, making good time on firm, steady wingbeats and clearly aiming for a nearby stand of evergreens, did not appear happy to see me. It instantly veered off course and rapidly climbed. In a few seconds, it was in full soar, wings out straight and tail fully fanned, perhaps 200 feet above me. It circled a couple times, then banked steeply and dove toward a point on the other side of the evergreens it had originally been flying to. I lost sight of it, and in a few minutes, the birds were singing again.

It was not hard to figure out what was going on, and indeed, this kind of thing happens quite often these days. A hawk making a bee-line with prey in its talons in early June is on its way back to a nest, on the way home from doing some shopping for its mate and offspring. The sudden change of direction by the hawk I observed was aimed at concealing the location of the nest. The steep climb and circling simply reflected the bird taking a good look around, making sure I was alone and that no other threats were in the area. And the sudden plunge was probably the start of a more discreet approach to the nest, through the back door. I was probably standing within 100 yards of so of an active Cooper’s hawk nest.

The relationship between humans and Cooper’s hawks has not been a happy one. The hawks, being optimized for bird-hunting, have a hard time passing up chickens. And farmers, not wanting to lose chickens, for many years responded by shooting the hawks. Sport gunning for these “undesirable” birds of prey also took a heavy toll. While never really close to extinction, in the early 20th century the Cooper’s hawk was largely erased as a breeding bird in well-settled areas in our region.

Legal protection, a regional decline in farming, and a better appreciation of wildlife has resulted in fewer Cooper’s hawks being shot, and the species has steadily rebounded in numbers over the past few decades. Long a staple of the fall hawk migration on the Vineyard, Cooper’s hawks began (or, more precisely, resumed) breeding on the Vineyard about 20 years ago. It’s hard to tell how many pairs nest here, because these birds travel widely in search of prey, and they do their best to be discreet when they have eggs or young. But based on how often and how widely I see this species during the breeding season, I’d put our current nesting population somewhere around 20 pairs, and I’m convinced the number is growing slowly but steadily.

While known to nest in a wide range of settings, Cooper’s hawks are said to have a special fondness for nesting in white pines, and on the Vineyard at least, I think they almost always nest in evergreens of some kind. Concealment is surely the reason. While adult Cooper’s hawks have little to fear from other predators, the relationship between crows and Cooper’s hawks is one of mutual detestation. Crows simply can’t see one of these hawks without harassing it; they’d eat the hawk’s eggs or nestlings if they got the chance, and by mobbing adult hawks whenever they see one, crows spoil the hunting and delay the return of adult hawks to the nest.

Cooper’s hawks remain a common fall migrant on the Vineyard, their numbers peaking in early October, with some birds lingering on the Island through most winters. The species is much less obvious, and probably less numerous, during spring migration. One puzzle is whether our nesting population migrates south, or, as with our red-tailed hawks, reflects a distinctive, sedentary population of a generally migratory bird.

In any case, the Cooper’s hawk appears well established as a breeding bird here, and the eerie silence as songbirds catch sight of an approaching Cooper’s hawk will be a common event for alert Vineyard naturalists for years to come. Don’t forget to look up.

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What was this tiny golden beetle, hidden within the petals of a tulip?

The great outdoors can produce baffling mysteries. MVTimes Wild Side columnist Matt Pelikan tries his best to solve them. Got a question for the Wild Side? Send it to onisland@mvtimes.com

Dear Wild Side,

I found this beautiful bug in an equally beautiful tulip today. Pretty sure it’s a golden tortoise beetle, but thought you could elaborate for our readers?

Thanks.

Danielle Zerbonne

Vineyard Haven

The Pelikan brief:

Interesting little beetles — the use by larvae of feces cakes as a defense mechanism is quite amusing!

The longer answer:

This odd creature is a so-called “tortoise beetle,” named for its vaguely turtle-like shape. The beetle’s exoskeleton extends outward, forming a transparent apron, which may offer protection from predators. As is often the case with common names for insects, “tortoise beetle” is really a generic term: taxonomically speaking, tortoise beetles are a “tribe” or part of a sub-family, with about 30 species occurring in the United States and more than 1,700 existing worldwide. I can’t tell for sure which species Danielle photographed, but only a few tortoise beetles occur in our region, and of these, the species that seems closest to Danielle’s bug is Charidotella purpurata. Like the vast majority of insects, this beetle is not well enough known to have acquired an English name, though it’s a widespread and apparently fairly common species. Another possibility is Charidotella bicolor, known as the golden tortoise beetle, a close relative which is also widespread.

Tortoise beetles, both larval and adult, feed on plants, and in general this group specializes in eating members of the plant family Convolvulaceae (this is the family that contains, among other plants, the sweet potato and the morning glory). In warm climates, some kinds of tortoise beetles can be agricultural pests, devouring enough sweet potato leaves to damage a crop. But these beetles do not appear to be especially common on the Vineyard, and sweet potatoes are not a local crop, so it is safe to assume that Danielle’s beetle is doing nobody any harm. (Ornamental sweet potato vines are widely available as annual container plants, and it might be fun to grow one and see if tortoise beetles turn up on it.)

Tortoise beetles lay eggs in spring, usually on the underside of the leaves of the plant the adult prefers to feed on. The eggs hatch into remarkably homely larvae, flattened, slug-like, and equipped with branching spines. The larvae of some species are said to assemble a sort of shield, consisting of debris pasted together with feces, which they hold over themselves as protection from would-be predators. It would surely deter me! Tortoise beetle larvae mature over a period of a few weeks, pupate, and emerge as adults, and then enter a dormant state called “diapause” to overwinter. The onset of warm weather rouses the adults, which seek out an appropriate food source, and mate and lay eggs if they are female, starting the next generation.

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What the heck is this alien-looking growth on a West Tisbury tree?!

The great outdoors can produce baffling mysteries. MVTimes Wild Side columnist Matt Pelikan tries his best to solve them. Got a question for the Wild Side? Send it here.

Dear Matt,

I saw this growing on a cedar in West Tisbury. They seem prone to strange orange growths;  I have noticed similar ones before.  Alien looking thing! Any idea what it is?

-DZ, West Tisbury

Dear DZ,

Appearances to the contrary, your cedar trees have not been infected by space aliens! Those knobby growths, sprouting orange tentacles under a mild spring rain, are a common fungus known as cedar-apple rust.

As the name of this odd organism suggests, it’s a parasite that alternates between two different species of plants as hosts. Spores produced in the orange fingers on the knobs on your cedar drift through the air (potentially as far as several miles!) and, if they’re lucky, land on a tender, young leaf on an apple tree that is starting to break dormancy. If conditions are warm and wet enough to suit the fungus, it infects the apple leaf, producing reddish lesions that persist through the season and may eventually kill the leaf.

Triggered by warm spring rain, the production of spores by the cedar-dwelling generation of cedar-apple rust is timed to coincide with the period when apple leaves are most susceptible to infection. When mature, the fungal growth on the apple produces spores that, echoing the springtime process, can infect red cedars, completing the fungus’s complicated life cycle.

Cedar-apple rust doesn’t seem to hurt cedar trees much. But in its apple-eating avatar, this fungus can defoliate and kill apple trees, or mar the fruits and make them unmarketable. Apple varieties differ in how well they resist the fungus, so choosing stock carefully can help avoid problems in areas where cedar-apple rust is a problem. And orchard owners can also treat their trees with fungicide in spring, when incoming spores are prevalent. In theory, removing all the cedars (or apples) in an area would also eradicate the fungus by breaking its life cycle, but this solution is rarely practical. I remove the fungus from the cedars in my yard, at least the ones I can reach, to try to reduce the risk that a neighbor’s ornamental crab apple (highly susceptible!) will get infected. But I’m not sure this has any real effect on the local prevalence of the fungus.

Such dual-host life cycles, called “complex” or “indirect” by biologists, may seem implausible but are actually pretty common in the parasite world. Indirect life cycles evolve to help a parasite get past a difficulty posed by its primary host. I’m just speculating here, but in the case of cedar-apple rust, the fungus may essentially be a disease of apple leaves which evolved the ability to use cedar as a refuge in winter, when the deciduous apple trees have no leaves on them for the fungus to inhabit.

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Duskywings look like moths, but they are in fact butterflies.

I’ve always had a fondness for groups of organisms that are closely related and similar to each other. There’s a certain elegance in the way nature improvises on the theme of a good idea, with a common ancestor rapidly (by evolutionary standards) diversifying into a cluster of species, resembling each other but each occupying its own niche.

The duskywings are hard to tell apart, but "hyaline" spots – like little translucent windows on their wings – distinguish one species from another.

Photo by Matt Pelikan

The duskywings are hard to tell apart, but “hyaline” spots – like little translucent windows on their wings – distinguish one species from another.

The duskywings are a perfect example. These are butterflies in a particular genus, Erynnis, five species of which inhabit the Vineyard. Drab and only about an inch in wingspan, they don’t really fit the popular notion of a butterfly, and the untrained observer, encountering two different species of duskywings, might not even notice a difference. But butterflies they are, and to my mind they present a fascinating mix of similarities and individuality.

As is the way with butterflies, our duskywings differ in what type of plant their caterpillars feed on. Three of our species feed on oaks of various kinds; a fourth feeds on aspen; and the fifth, on a common wildflower of dry, sandy areas called wild indigo. Oaks, of course, are nearly inescapable on the Island, and it’s easy to find places where wild indigo overlaps with oak. There are even a few spots — the northwestern corner of Correllus State Forest is one — where these plants occur along with aspen, meaning that all five duskywings can occur in the same spot. I’ve found all of our duskywings along the fire lane that heads east from County Road along the northern edge of the State Forest.

As is also the case with related butterflies, the duskywings differ at least a little in the timing of when their adults are on the wing. But right about now, sometime during the second half of May, the flight periods of all five species overlap. So, in theory anyway, you could find all five in the same place at the same time! The most I’ve managed in a day is four species, but trying for a clean sweep is one of those pointless but amusing exercises that makes insect-hunting so much fun.

The similarity of duskywings makes identifying these butterflies a challenge, though it’s a challenge that eases rapidly once you learn a few tricks. Rapid, bouncing flight and a strong territorial tendency are behavioral traits that help one spot duskywings in general. But beyond that, these are basically dark brown insects with mottled patterns that are difficult to describe or remember.

Happily, one unambiguous trait divides our duskywings into two groups: the presence of so-called hyaline spots — little translucent windows in the wing — distinguishes three of our species, while the other two lack these details. And of the three with hyaline spots, two species feature large spots while on the third, the spots are tiny. So these spots are a critical aid for identification. Duskywings often perch, helpfully, with their wings spread wide, making it easy to look for hyaline spots.

Named after Roman poets, Juvenal’s and Horace’s duskywings are the ones with the big hyaline spots. Juvenal’s is invariably the first duskywing to fly each spring, usually by the third week of April, and is among our most common butterflies. Horace’s is rare and, unlike Juvenal’s has flight periods in both spring and summer (so a “big-spotted” duskywing in late July is surely a Horace’s). Otherwise, these two are hard to tell apart: a pair of pale spots on the underside, present on Juvenal’s but absent on Horace’s, is the most helpful field mark.

The “small-spotted” species, wild indigo duskywing, also has spring and summer flights but is fairly easy to identify because its distinctive hyaline markings. Also, this butterfly is rarely found more than a few feet from its host plant, so location offers a useful cue.

Of the “spotless” duskywings, the sleepy duskywing, an oak-feeding species, is by far the more common, usually on the wing in respectable numbers from late April through the end of May. It is a small and dark species, and after years of watching duskywings, I can often pick this species out even in flight by these characteristics.

Even smaller is the final duskywing, dreamy, which has the aspen-feeding caterpillars. Flying in late May and early June, it features extensive grayish frosting on the outer part of its wings. It’s the prettiest duskywing (which isn’t saying much), but sadly it’s also the least common on the Vineyard; I’ve only encountered it here a handful of times and have only managed one decent photograph of it, years ago in my pre-digital, slide-shooting days.

In the grand scheme of things, these are not particularly important insects. They’re neither helpful nor harmful from the human perspective, and their disappearance would likely have little ecological effect. But I value my acquaintance with them: knowing these insects, I feel like I have a secret perspective on the Vineyard landscape. And the season’s first Juvenal’s duskywing, bopping across a path or clearing, is always a welcome sign that spring is here to stay.

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The insect is probably Nomotettix cristatus, northern crested pygmy grasshopper, but the author does not know for sure, and may not be able to find out.

Times have never been better for the amateur naturalist. Excellent field guides keep coming out, addressing harder and harder groups of organisms. Internet sources like Bugguide.net provide vast catalogs of indentified photos to compare a subject to. Digital photography has greatly simplified the process of capturing a good image of what you find. And a vast network of helpful experts is getting steadily easier to tap into.

But the study of natural history remains endlessly challenging. Sometimes you bang up against a genuine gap in knowledge — nobody may know, for example, how to tell the members of a fly genus apart without dissecting specimens. Other times, the knowledge is out there, but the subject is so obscure that you can’t find it. But most often, your own ignorance and wrong assumptions lead you astray. The study of nature has a built-in measure of frustration.

I’m wrangling with a good example of this, and the history of my relationship with the organism in question illustrates how the study of nature often goes (or doesn’t go). The story starts about a dozen years ago, when I first noticed some type of tiny hopping insect along the fire lanes of Manuel F. Correllus State Forest in early spring. Perhaps three-eighths of an inch long at most, these grayish mystery critters were perfectly camouflaged against the sand: I usually noticed them only when they jumped, and then my eyes simply couldn’t follow them. Unable to get a decent look, I had no idea what they might be.

Over time, after catching glimpses of dozens of these mystery insects, a vague impression of their appearance evolved. Stout and seemingly arched along the center line of their backs, they aligned most readily with my mental image of a leaf-hopper. So I perused photos of leaf-hoppers, hoping in vain for a match that might at least be close enough to point me to toward some subset of this vast family (it has more than 20,000 members worldwide).

Barking up this very wrong tree might have been the end of the story if one of these critters hadn’t landed, coincidentally, almost under my nose as I was photographing something else. Finally getting a decent look, and even a poor but possibly helpful photograph, I realized I was actually seeing a grasshopper, wholly unrelated to the leaf-hopper I had surmised. Grasshoppers I know at least a little about, so this seemed like progress!

But again, I bungled. Such a tiny grasshopper must be an immature nymph, right? And to be active early in mid-April, such a nymph would have to belong to a species that either overwinters as nymph, or hatches very early in the season, right? These seemingly reasonable assumptions had me searching for a match among photos of band-winged grasshoppers, a large grasshopper family that contains all the species I know of that are active in early spring on the Vineyard.

Meanwhile, I posted my bad photo on various websites and Facebook groups, seeking assistance putting a name to the beast. Shortly, I received a response that didn’t provide an identification, but at least revealed the flaws of my thinking: the insect wasn’t a nymph at all, but rather an adult member of a group called the pygmy grasshoppers. Aptly named, these tiny grasshoppers overwinter in their adult stage, a behavior I had never heard of among grasshoppers and therefore hadn’t even considered. And it had never occurred to me that there might be pygmy grasshoppers on the Vineyard.

With a gradually developing sense of what to look for and where to look for it, I finally managed to spot a few of these insects before they disappeared, and then, stealthily, I closed in for some better pictures of one in the moments before it bounded away, its powerful legs making an audible “snap” as it took off. The photos revealed an odd but distinctive design: as on most pygmy grasshoppers, the exoskeleton of the thorax extends backward to the insect’s tail end (the beast lacks visible wings). And along the center line of this extension of the thorax runs a raised and serrated ridge.

At present, I think these traits narrow this insect down to the genus Nomotettix. It’s probably the species cristatus, sometimes known as the northern crested pygmy grasshopper. I’ve sent my photos out to a couple of experts hoping to either confirm this, or else correct my latest error! But I’m prepared to learn that my photos aren’t sufficient to tell what species it is. In any case, the experience has been a useful reminder of how much patience matters to a naturalist, as you navigate a winding path through incomplete knowledge and false assumptions.

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Bombylius major belongs to a family known familiarly as the “bee-flies,” due to their uncanny resemblance to bees.

If you run into Bombylius major — and it’s easy to do, since this species is common on Martha’s Vineyard — you might find yourself puzzling over what, exactly, you’re looking at. About a half-inch long, plump and fuzzy with an almost spherical abdomen, Bombylius sure looks like a bee. But a closer look, if you manage one, tells a different story: this species has stubby antennae and only one pair of wings, physical traits that land Bombylius squarely in the fly department.

It’s not too surprising, then, that Bombylius major belongs to a family known familiarly as the “bee-flies,” due to their uncanny resemblance to bees. (The genus name “Bombylius” echoes “Bombus,” the genus to which our true bumble-bees belong). Bee-flies are a diverse and hugely successful division within the flies, with many thousands of species known (just the single genus Bombylius has more than 250 members). There are surely scores, and maybe hundreds, of bee-fly species on the Vineyard alone, but like so many groups of insects, our bee-flies have never been seriously studied.

Known commonly as the big bee-fly or greater bee-fly (despite the fact that its of middling size for this family), Bombylius major occurs naturally across much of the world. In addition to the traits I’ve already mentioned, this insect sports distinctly two-toned wings, with a dark leading half sharply distinguished from a transparent trailing half. The legs of Bombylius are long and delicate, and protruding from the front end is a fearsome-looking spike that might suggest a blood-sucking habit.

But don’t be alarmed: adult greater bee-flies are not the least bit aggressive, and they limit their diet to pollen and nectar taken from flowers. Given their early spring flight season on the Vineyard, these foods are often taken from blueberry and mayflower blossoms (about all that’s in bloom when Bombylius is at its peak of activity). The long proboscis, effectively just a straw, allows this fly to drink nectar from the deep, bell-like flowers of these plants.

If adults are benign, the larvae of the greater bee-fly are tough customers. Like most members of its large family, Bombylius is a parasite of ground-nesting bees. Female flies lay their eggs near or even in the burrow of a ground-nesting bee. I’ve never seen this behavior, but some accounts suggest that the eggs are flicked toward the bee burrow while the fly is airborne, aiming for the burrow like pilots releasing aerial bombs. The bee-like appearance of Bombylius may help it approach bee burrows without alarming the bees, and of course it may also deter would-be predators from attacking the fly.

Upon hatching, the fly larva bides its time while the bee industriously lays her own egg and provisions the burrow with pollen for the young bee to eat. As the larval bee nears maturity, the fly larva attaches to it, gradually devouring it as an external parasite. The maturing fly then overwinters in the bee burrow, tunneling its way to the surface in the spring before emerging as a fuzzy adult, ready to repeat the cycle.

Pollination is a beneficial role played by insects, of course, and it would be easy to frown on Bombylius because it preys on bees. But the greater bee-fly is itself a pretty fair pollinator, with its hairy body carrying pollen effectively from one flower to another. And there is presumably competition among bee species for pollen and suitable nest sites; bee parasites like Bombylius help keep bee populations in balance, ensuring that no single bee species grows so common that it squeezes out its relatives.

Greater bee-flies occur quite widely around the Island. But given their close association with ground-nesting bees, these flies are most common in areas with the dry, sandy soils that bees find most congenial for burrow construction. Fire lanes in Correllus State Forest are the easiest place to find Bombylius, and on a warm, sunny day in late April, I encounter one of these excellent flies every few yards.

Their small size and unobtrusive coloration make them a bit hard to spot, as does their active flight pattern: hover, dart, hover, nearly always within a foot or so of the ground. From time to time, you’ll spot a bee-fly visiting a flower, perching delicately on the flower’s rim and sometimes even continuing to beat its bicolored wings while that long proboscis probes the flower like a hypodermic needle.

Equipped, like other flies, with compound eyes that wrap around a good portion of the head, the greater bee-fly has remarkable vision and is very wary of moving objects (like people). When disturbed, they don’t usually move very far, but it is next to impossible to sneak up on one, and a pair of binoculars is almost essential if you hope to get a good look at this species. It took some crawling, but a high point of this past weekend was finally getting within camera range of one of my favorite flies!

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Even with frosty nights still lingering, ground beetles like this gnarly black Meloe are out and about, doing their thing.

The earliest days that feel like spring rather than late winter are among my favorite days of the year — after the last of the snow has melted, and plants are just starting to break out of dormancy. It’s a time when the world still looks dead and it’s hard to imagine any insects stirring, until you look more closely and see that, in fact, a surprising variety of hardy bugs are on the move.

Following a crummy winter, it was not until this past weekend that it felt like spring had taken charge on the Vineyard. Sunday was not quite as warm as the bright sun suggested — our thermometer read 42 around noon. But the ground was thawing, and I inevitably ended up in Correllus State Forest, where sun-warmed soil along the fire lanes yields interesting early-season arthropods, as early as mid-March in some years.

It takes a certain amount of audacity for a cold-blooded insect to be out and about at this point in the season. A week ago, there was snow on the ground, and temperature at night still drops regularly below freezing. But the sun, shining stronger and longer with every day, can easily heat an insect up to operating temperature. For the relatively few insects that have mastered the problem of freezing while they’re in an active state, early spring is perfectly workable.

While there are plenty of dull-looking examples, beetles as a group include a lot of striking insects. An excellent example would be the so-called “oil beetle” I ran into on Sunday. More formally it’s a species (I can’t tell which one) in the genus Meloe. The six or eight species that seem possible on the Vineyard differ only in very subtle ways, but the odd qualities they share go well beyond the bloated, almost wingless, glossy black form these inch-long beetles take as adults. I find what I assume is the same species more springs than not on the same stretch of fire lane, and it makes me happy that I know a place where I can reliably find such a creature.

The name “oil beetle” (or “blister beetle,” a more general name for the entire family) derives from a bizarre defensive trait these insects have evolved. By and large, they’re sluggish insects, and you can tell by its looks that they are flightless and about as agile as a washing machine. But don’t mess with them. When disturbed, they’re said to exude a caustic chemical from their joints, a juice gnarly enough to raise blisters. This is not something I’ve felt it necessary to confirm by personal experience!

The life cycle of Meloe is bizarre as well, at least to human sensibilities, though it’s actually pretty tame by insect standards. Like most blister beetles, the members of this genus are known to be parasites of ground-nesting, solitary bees. Living as individuals rather than in colonies, such bees lay their eggs in burrows they’ve provisioned with pollen or other food for their offspring to eat while developing. In effect, a bee nest is a little cache of resources, and blister beetles, like a surprising number of other insects, have found a way to purloin it.

Blister beetles exploit the frugal provisioning habits of the bee by laying their eggs on flowers that the bees are likely to shop at. The larval beetle — which are even homelier than the adults if that’s possible — simply latch onto a bee’s body hair and hitch a ride to a burrow that’s being provisioned. There, the beetle grub lives on whatever the adult bee provides, and occasionally on the eggs or larvae she has produced.

At least some blister beetles reportedly locate areas rich in the appropriate kind of bee, whether by detecting the bees themselves or perhaps just by having an instinctive love of the same habitat the bees prefer. And while the associations of parasites and hosts is a vast subject that we know very little about, at least some blister beetle species are known to successfully parasitize only very specific bee species. Again, such tight and obligatory relationships aren’t unusual in the insect world.

Oddly, a second blister beetle species was on the move on Sunday, one that I had never encountered before. Tricrania sanguinipennis (it seems to have no common name) is smaller and has a more conventional shape than its cousin Meloe, with a prettier orange-and-black color scheme. But it shares much of the same biology. The females of both these species will mate and lay eggs in carefully selected sites as the spring progresses. The resulting larvae will waylay the requisite bees and, after maturing underground during the course of the summer, overwinter until the earliest spring days next year.

When I’ll be looking for them.

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Unimpeded in its upper reaches, Mill Brook winds its way through the Land Bank's Waskosim's Rock preserve.

Matt-PelikanMatt Pelikan has been writing the Wild Side column since 2008. He is a restoration ecologist for The Nature Conservancy, and he lives in Oak Bluffs.

Native brook trout cling to survival in the brook’s upper reaches where cold water temperatures prevail.

Aside from a few brilliant seasons catching frogs when I was about nine years old, I haven’t spent much time exploring freshwater habitats. So I was happy to have the opportunity to learn from an expert last weekend, when I attended a presentation by Steve Hurley, Southeast District Fisheries Manager for the Massachusetts Department of Fish and Game.

The presentation, Sunday afternoon at the West Tisbury Public Safety Building, was attended by about 60 interested Islanders. Mr. Hurley discussed the results of two important studies of the Mill Brook, the Vineyard’s most significant stream system, which winds from Chilmark through West Tisbury to empty into the Tisbury Great Pond at the head of Town Cove. The Mill Brook is currently a subject of much study and debate as the Town of West Tisbury contemplates the future of the Mill Pond, an artificial impoundment on this stream just northeast of the town center and adjacent to the Edgartown-West Tisbury Road.

Streams, like any other ecological system, feature astonishing complexity. But as a practical matter, a few simple principles often suffice to explain a great deal about a stream. Drawing on a recent survey of the Mill Brook’s fish and a season-long effort to track water temperature at multiple points in the stream, Mr. Hurley developed an elegantly simple explanation for the distribution of various fish species.

The Island’s streams have always struck me as a bit incongruous in the Vineyard landscape: cold, gravel-bottomed, and often flowing quickly down fairly steep gradients, they seem like bits of Vermont transplanted to the coast. I learned from Mr. Hurley that this impression isn’t so far off. Fed mainly by groundwater, Island streams tend to be cold, and they support some cold-water fish species that one would also find in a northern New England river. The most notable of these is the brook trout, essentially a northern or high-elevation species that approaches the southern and lower limit of its distribution in cold groundwater streams of coastal Massachusetts.

Unlike cold streams in Vermont, though, our streams flow to the sea rather than into lakes or larger river systems. Some brook trout populations have developed a fascinating strategy to take advantage of this: during spring and summer, they descend their streams and enter saltwater, feeding in the rich waters of estuaries before returning to freshwater streams to spawn. In our coastal streams, in fact, such journeys are not unusual: many so-called “diadromous” fish split their time between freshwater and oceanic life. River herring, shad, smelt, salmon, and the American eel are among the diadromous species native to our region and requiring access from salt to fresh water.

Brook trout, wherever they are, require cold water, with about 70 degrees being the upper limit at which they can survive and temperatures below 60 needed for healthy growth. Historically, Mr. Hurley reports, sea-run or “salter” brook trout were abundant in the Mill Brook system. In the 2013 fish survey led by Mr. Hurley, a solid population of native brook trout – both adults and young fish – was documented in the upper reaches of the Mill Brook. But the species was virtually absent from the lower stretches of the stream, which were dominated by fish species that prefer warmer water, and there was no clear evidence of a sea-run brookie population.

An explanation for this pattern came from water temperature data from a survey supported by the Edey Foundation and the Sea-run Brook Trout Coalition. An array of data loggers placed at various points in the stream recorded water temperatures, and the results as presented by Mr. Hurley were startling. Predictably, upper reaches of the brook featured temperatures congenial to brookies. But at each artificial impoundment surveyed lower down in the stream, sun-warmed water from the pond crossed the spillway to heat the stream below. Above and below dams on the Mill Brook, sustained temperatures last summer reached well into the 80s, a level that produces brook trout chowder.

In addition to altering the temperature regime of the stream, Mr. Hurley pointed out, the half-dozen or so major dams on the Mill Brook form impassable physical barriers to brookies and other diadromous fish that might otherwise use the stream. Good numbers of eels were detected in the stream; but generally, the fish survey suggests, the Mill Brook functions poorly if at all as a resource for diadromous fish.

In considering whether to dredge the Mill Pond, remove the dam and restore the stream, or take some other course of action, West Tisbury will need to balance factors including ecology, recreation, scenery, and tradition. But Mr. Hurley’s presentation made it clear that, however natural one may think the Mill Brook is, in fact it’s a system that is vastly altered from its original state. Town leaders and residents should know that however familiar the stream’s artificial impoundments seem, they are recent developments in the overall history of the Mill Brook. And they are features that dramatically interfere with the life cycles of many fish that once flourished here, and could do so again.

For a complete report on the Sunday presentation, click here.

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The gray kingbird spends most of its time in the southeast U.S. and the Caribbean, but may take a wrong turn.

Matt-PelikanMatt Pelikan has been writing the Wild Side column since 2008. He is a restoration ecologist for The Nature Conservancy, and he lives in Oak Bluffs.

Some birders focus on “listing” — tallying as many species as they can in a state, a country, or the world. Others drift in the direction of “citizen science,” participating in organized survey projects or simply orienting their leisure birding to close observation and detailed record-keeping. But the one thing that will get virtually any birder excited is finding a rare vagrant — that is, a misdirected bird making an unusual appearance far from where it belongs.

Because birds are so mobile, vagrancy is a routine fact of life in the bird world. And although any particular vagrant may be a rare occurrence in a given location, there are lots of species in the world; so encountering a vagrant of one kind or another isn’t all that rare. But as you gain experience in the field and become more familiar with the vast and ever-growing body of bird records, you begin to realize that vagrancy is less random than you might expect.

Avian species vary widely in how prone they are to wander, and vagrancy for a particular species — or for birds generally — is often associated with seasonality and weather. Very little is truly impossible when it comes to avian vagrants, but experienced observers develop a finely tuned sense of how plausible a particular report is.

One factor shared by most vagrants is a migratory life history. It’s much more likely for a migratory bird, which routinely covers large distances, to turn up out of its normal range than it is for a non-migratory species. And the more strongly migratory a species, in general, the more prone it is to wandering. The point is well illustrated by pairs of closely related species that differ in their migratory habits. Allen’s and rufous hummingbirds, for example, are so closely related as to be nearly identical in appearance, and they are both species of the West Coast of North America. But rufous hummers follow, in general, a much longer migration route than Allen’s, and in consequence, rufous turn up many times more often in the East than does its very close relative.

This is why many so-called Neotropical migrants, breeding in the boreal forest and wintering in Central and South America, are prone to vagrancy. With such a long migration route, all it takes is minor navigational error to take an individual someplace unexpected. Migration also governs the seasonality of vagrancy. Many migratory species spend the vast majority of each year in one of two places — their nesting territory in the north, or their wintering grounds in the south. They have no inclination to wander once they are in either of the locations, until the season prompts them, and they rarely start to move until the correct time. So finding a vagrant during the height of summer or an early arrival in late February is much less likely than finding one during the relatively narrow migration windows in spring and fall.

Moreover, during fall migration, the numbers of any species are augmented by the many “birds of the year” that recently hatched, and these birds, never having migrated before, are especially prone to taking wrong turns. Because of both the inflated numbers and inexperience, vagrants of many species are far more likely in fall than in spring.

Weather is also a major factor in bird vagrancy, with storm systems or high winds capable of driving birds far off course. Tropical storms, for example, are notorious for bringing southern seabirds to northern latitudes or pushing them many hundreds of miles inland. And weather may interact with normal migratory behavior to produce clear patterns in avian vagrancy. The best examples are so-called “overshoot” vagrants — usually Neotropical songbirds that can get caught in storm systems when they’re beginning to move north through the United States. The result can be remarkable waves of southern birds, like hooded or prothonotary warblers that can appear far north of their usual range in early spring, or of more northern species like indigo bunting appearing in the north weeks before their usual May arrival.

There’s still more to it. Some groups, like flycatchers, seem to be especially prone to vagrancy, but for no obvious reason. And some groups, like gulls, seem to show a nearly random pattern of vagrancy. An individual, or even more than one, evidently just decides to go exploring, sometimes all the way to a different hemisphere. And it’s important to remember that our picture of avian vagrancy is imperfect: many, probably most, vagrants are overlooked, and our expectations of what vagrants are likely where may influence how we bird or how we identify what we see.

But finding a bird that has wandered across thousands of miles of ocean, plains, or mountains provides a thrill that doesn’t depend on having a full explanation. The Vineyard’s situation — a last stop for birds wandering east, and a welcome first stop for the occasional vagrant from Europe — ensures that we get far more than our share of vagrants. As the weather warms and bird populations once more go into motion, Island birders will be out in force, looking for the southern, western, or even Eurasian bird that took a wrong turn.

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With a wing span reaching six feet and a broad tail, turkey vultures can ride thermal up-drafts indefinitely, using their primary feathers to make minute adjustments

A rarity on the Vineyard not so long ago, the turkey vulture has grown steadily in numbers here over the last couple of decades, and we now have a smallish but conspicuous year-round population. While its personal habits win few admirers, this massive carrion-eater is a marvel of ornithological engineering, perfectly designed for its manner of living. And its status here presents enough mystery to make this bird worthy of more attention.

They’re hard to miss, here or indeed anywhere else in their vast geographical range, which extends from southern Canada to the farthest tip of South America. Like all vultures, these are big birds, weighing about four pounds and having broad wings that span about six feet when fully spread. Turkey vultures are typically seen overhead, soaring on motionless wings that are slightly raised into a shallow vee, a profile recognizable from a vast distance. The primary feathers — the large ones at the tip of the wing — are likewise broad and solid. Watch a vulture carefully in flight and you can see it making constant, precise motions with these feathers — little aerodynamic tweaks for maximum efficiency.

These birds are splendidly designed for soaring, able to ride updrafts for hours. But for all their grace in a thermal, on take-off they labor to flap their wings in slow, rolling strokes, almost painful to watch and totally different from the snappier wing-beats of a red-tailed hawk or even an eagle. From a distance, “TVs” appear all black with slightly paler flight feathers on their wings; with a better look, you’ll note an unfeathered head, dark brown on young birds but bright red on adults.

That bare head is probably a good place to start in discussing the habits of the turkey vulture. Though generally grouped with hawks and eagles, vultures lack the powerful feet and sharp talons of those feathered assassins, and vultures seldom or ever kill their own food. But they’ll eat nearly anything that something else has killed. For Vineyard vultures, this probably means road kill of any kind, gut piles during deer-hunting season, and a side-order of garbage. The bare head — an adaption shared by vultures generally — is simply designed to stay clean while its possessor is poking around for good bits inside a well-ripened body cavity.

Once carrion heads down the hatch, it encounters a vulture’s industrial-strength digestive system. The intestinal secretions of a turkey vulture make short work of nearly anything, but the contents of a vulture’s digestive tract serve a couple of functions that you might not expect. Self-defense, for one: corner a vulture and it will vomit its latest meal, mixed with highly acidic digestive juices, all over you. I bet you’ll back off. And thermal regulation, for another: when overheated, vultures defecate on their bare legs, and the cooling effect as the droppings evaporate lets the legs dissipate heat like a car radiator.

Happily, turkey vultures are bashful birds, and getting close enough to witness these unappealing habits is difficult. These are hard birds to study: while their numbers and year-round presence suggest that turkey vultures are nesting here regularly, only a few nests have ever been found on the Vineyard, and the questions of where on the Island they’re nesting and where their nests are placed remains largely unanswered.

Life for a vulture takes place largely in the air, and it isn’t just their soaring abilities that help them out. Vultures have keen eyesight and, unusual among birds, a sharp sense of smell (they reportedly are particularly sensitive to the scent of certain chemicals produced by the onset of decay in animal flesh). A vulture goes shopping, then, in prolonged soaring flight with constant scrutiny of the land below for anything dead, or looking to become that way soon. These are patient birds, and if a potential meal isn’t quite holding still yet, a vulture will wait.

Turkey vultures were once rare in Massachusetts, occurring regularly in the state only over the last 50 years or so as their range gradually extended northward. They were slow to get established on the Vineyard, probably because, like many other soaring birds, they dislike flying across large bodies of water (which don’t tend to produce the warm updrafts that lift a soaring hawk or vulture). But once established here, they rapidly settled into year-round life on the Island; though most vultures at our latitude migrate south for the winter, ours, again probably deterred by the surrounding water, spend the winter here, and I’ve seen little indication of any vulture traffic at all between here and the mainland.

Birds, of course, evolve for survival and not to gratify the sensibilities of human beings. It’s not fair to blame these birds for their habits, and indeed, the removal of carrion can be considered a public service. You needn’t think too hard about the specifics of what vultures do, if you don’t want to. But keep an eye out for their graceful soaring and give these odd birds some respect for the remarkable ways they’ve evolved to do their job.