Saturday, August 25, 2007

When the Swallows Gather

I make periodic trips to Plum Island and the New England coast because I can see numbers and varieties of birds that can’t be seen in southern Vermont - shore birds and waders in Spring and Fall, gulls, diving ducks, and pelagics in the winter.

But mid-August is not a good time to go to Plum Island. The mosquitos are voracious. The green headed flies are at a vicious peak. The sun is baking hot. Parking is a premium as beach goers pursue their melanomas.

Nevertheless, I make a trip to Plum Island in mid-August anyway, because that is when nature has a show - one of her great shows. It’s a show that rivals the arctic migrations of the caribou, or the movement of the herds across the Serengeti. It is a winged show. The swallows are gathering - by the thousands and, at their peak, by the tens of thousands. They are predominantly Tree Swallows, but the purpose is not to pick out different species. The purpose is to stand in the midst of the abundant life.

Some years I have been early, or late, and have missed the show. I don’t think I was there at the peak numbers last week, but there was never a moment during the day when there were not hundreds of swallows on the wing, and any bush might be alive with swallows resting, but restless.

Entering the Parker River Refuge, there was a sign cautioning motorists about swallows in the road. Within yards, we had to pause, creeping slowly forward until two hundred swallows took flight.

Along the refuge road there were gatherings that numbered in the thousands. We stood on the road in the middle of one roost. Trees and bushes were covered with swallows, resting a moment, bursting into flight, darkening the sky, coming back to roost - restless, swirling life - a conclave and convention meeting to prepare for the great journey ahead.

Tree Swallows do not make the epic migration that many of our summer birds make. They winter predominantly along the southern Atlantic and Gulf coasts, and in the West in Baja California and the coast of Mexico. 170 years ago, Audubon saw huge flocks wintering in Louisiana, and still today flocks are often estimated in the hundreds of thousands. As sub-tropical winters have moved northward, so also have wintering swallows. I have seen Tree Swallows throughout the winter in Cape May, NJ, and it is not uncommon to find them wintering even further north. Seventy years ago, an observer studied a small flock of swallows which stayed the entire winter on Long Island, NY; most survived.

Tree Swallows can winter as far north as they do, because, unlike most other American swallows, they eat a substantial amount of vegetable matter. One study found that 20% of their food was vegetable - a variety of seeds and berries, but with a strong preference for the fruit of the bayberry.

Because Tree Swallows winter along the southern North American coasts, they return early to their northern breeding areas. Last year I saw Tree Swallows on Lake Champlain on March 28. By early-April, they are regularly reported in our neighborhoods, and by mid-April (barring a late winter storm which may cause them to withdraw) they are here to stay. By late April they are staking their claim to nest sites, often competing - successfully - with bluebirds, starlings, and House Sparrows for those boxes and holes.

Tree Swallows nest early, and raise their young. Unusual among our swallows, they undergo a complete molt before migrating. They gather in huge flocks and migrate late.

Arthur Bent summarizes this annual convocation: “Fall is a season of drama in the tree swallows’ yearly cycle. A single idea, or an urge, seems to grip every swallow in the land. The nesting season with its quarrels over, the swallows draw together with a common interest in preparation for their next step, the long migration they will take in companies of hundreds or thousands. In August and September we see them gathering in the great marshes by the sea, where they linger for many days in ever-increasing numbers, young and old.”

Last week on the barrier Plum Island, the swallows were gathering. Hundreds mingled restlessly in the bushes along the road. Some swallow hiccup sent them into the air, their mass creating a shadow across the road, before they settled again, briefly.

This annual Fall massing of swallows among the marshes of our seacoast seems to have survived, to some degree, the coastal development which has decimated the numbers of so many other species. In the 1830s, J.J. Audubon’s friend, Dr. Bachman, wrote that he “saw such an immense quantity of this species of birds that the air was positively darkened. As far as the eye could reach, there were Swallows crowded thickly together, and winging their way southward; there must have been many millions!”

These early naturalists observed North American fauna before it was drastically altered by the explosion of the human population. The line runs from a primeval past through these naturalists to the gathering of swallows today. The continuity in this line sets the swallows apart from other huge numbers of birds which we may commonly see and whose numbers may be as great, or greater, than that of the swallows.

For example - blackbirds. Huge flocks of blackbirds can be seen in Fall and Winter. They are often mixed flocks with starlings, a non-native species, and cowbirds, a Great Plains native which has colonized the opened lands of the continent. Or pigeons - the urban flocks all derive from feral birds brought over by settlers. Or Canada Geese - these adaptable birds winter by the thousands in the Connecticut River’s open water, and many travel but a few miles from their wintering fields to their breeding ponds. Most of these large geese flocks are very different from what the early naturalists observed; then the Canada Geese were almost all Arctic nesting birds which wintered in the deep south and whose New England presence was limited to a stopover on their journey.

But as nearly as we can tell, the gathering of the swallows from the vast continental interior to the marshes, grasses and dunes along the sea coast in the Fall, has been an annual event since the glaciers receded and tundra became forest. This glimpse of a primeval past draws me to the New England coast at this time of the year. Thousands of swirling and swooping swallows tell me that the natural order is highly prejudiced in favor of profligate life. It is a system that has served earth’s many life forms exceptionally well - until very recently when one of those life forms, in its profligacy, has gone dangerously amok.

The swallows, at least, seem to be maintaining their balance. I doubt that they are gathering to celebrate, but I celebrate their gathering, and thank them for it.

Saturday, August 11, 2007

The Differences among the Woodpeckers

Six woodpeckers breed in southeastern Vermont. All six have been in my backyard. The Pileated Woodpecker, a species of mature forests, has made a couple of brief stops. The Northern Flicker occasionally forages in robin like fashion on the grass. The Red-bellied Woodpecker, a relatively new breeding species in Vermont, has made a few Spring visits, perhaps in search of a potential breeding territory.

The remaining three breeding woodpeckers are regulars in my backyard. Downy and Hairy Woodpeckers are present throughout the year; the Yellow-bellied Sapsucker forages throughout the summer in our willow tree.

Nearly all woodpeckers are sexually dimorphic. This means, simply, that males and females have two different forms. This difference is most observable when the dimorphism is dichromatic; that is, when there are color differences in the plumage for males and females. For many species of birds, distinguishing between the sexes is almost impossible. The plumage of Blue Jays and chickadees is the same for both sexes; during the breeding season an experienced bird bander may be able to see physiological evidence which will identify the sex of a bird in the hand. Outside of the breeding season, dissection may be only the sure way of distinguishing the sexes, but this technique is a bit difficult on the bird.

Females usually incubate the eggs; if we observe a Blue Jay sitting in the nest, we may be able to conclude that we are seeing the female, and we may be right most of the time. Such a conclusion, however, is based on probability, not on verifiable evidence, unless we are somehow able to examine the bird in hand. Most of the time, we must simply be content with knowing that the birds know who is what. In general, birds which are not sexually dimorphic are two parent families, with both parents taking an active part in raising their young.

By contrast, many of our favorite summer songbirds are markedly dimorphic. Think of the stunningly beautiful male Indigo Bunting and the plain jane female - likewise with the Purple Finch, and the Rose-breasted Grosbeak. The plumage differences are less dramatic but very evident with birds such as the Northern Cardinal, American Goldfinch, Baltimore Oriole, and nearly all of the warblers. In general (but with lots of exceptions) the handsome male keeps singing, protecting his territory, and mating as often as possible, while the female does the parenting duties without much help.

Our six resident woodpeckers are all sexually dimorphic, and distinguishable by plumage differences between the male and the female. These differences in plumage are slight, but clearly observable. For example, the male Yellow-bellied Sapsucker has a bright red cap and a bright red throat. The female’s throat is white. The male Northern Flicker has a black mustache; the female does not have the mustache. The male Red-bellied Woodpecker has a bright red stripe over the top and back of his head; the female has less red, usually only on the back of the head. Both the Downy and Hairy males have a bright red spot on the back of their heads; the females do not have the red spot.

In my backyard there is lots of opportunity to watch woodpeckers, and much opportunity to observe the differences. The Downy and Hairy are the two most common. Their plumage pattern is almost identical. The Hairy is larger (9 inches verses 6.5 inches); the Hairy’s bill is much longer and larger. The Downy’s bill is short, almost petite. The juveniles of both species appear to be smaller than their parents when they have first fledged, with the result that the sizes between the two species almost overlap. Juvenile Downy and Hairy males have a rusty red crown rather than the red spot on the back of the head of the adult males; juvenile females do not have any distinctive plumage differences but can usually be identified, as so many young, by their cluelessness.

The Downy and Hairy both have a large white patch on their backs. The similarly sized Yellow-bellied Sapsucker has a long white stripe on its folded wing. This white side stripe makes it possible to identify the sapsucker as it works its way along a tree trunk, even when no other field marks can be seen. The juvenile sapsucker also has this white wing strip, but its head is mostly brown.

Year round, all woodpeckers forage for insects hidden in bark, but they also eat fruit, berries, and seeds. The Downy and Hairy are especially fond of suet, but will also take seeds from a feeder. As with most species, woodpeckers may have a preferred diet, but when times are lean, they will include in their diet whatever food is available.

Insects are the principle component in the diet of all of our woodpeckers, including the sapsucker. The sapsucker does drink tree sap (the little round holes on a tree trunk are evidence of its activity), but like all animals, it needs protein. On several occasions, I have seen a sapsucker carrying a beak full of insects back to its nest hole. On the other hand, the Downy Woodpecker will also drink tree sap on occasion, especially maple sap in the early spring; this led to its folk name, Little Sapsucker. The Hairy Woodpecker was similarly named, Big Sapsucker.

The common names of our most common woodpeckers make little sense. The Downy and Hairy were named by naturalists with the bird in hand. They apparently felt that the feathers of the Downy were soft and downy, and that the feathers of the Hairy were shaggy, rough, and hairy. But in the field, the Downy does not look downy and the Hairy does not look hairy. Likewise, the less common Red-bellied Woodpecker seldom shows its red belly except in the hand.

On the other hand, the Yellow-bellied Sapsucker does have a yellowish belly, and the eastern “yellow-shafted” race of the Northern Flicker clearly shows yellow feather shafts under its wings when it flies. At least the Pileated Woodpecker, with its prominent red crest, is named for a field mark which we can all see. “Pileated” derives from the Latin for “crest,” although with few us having studied Latin, we would only know this if our curiosity sends us to a dictionary. Curiosity sent me to the dictionary, and a bunch of other resources. And I’m glad to share with you.

In the heat of the summer, I don’t do a lot of birding. But I do a lot of sitting still and bird watching. And the bird watching has been good!

Saturday, August 04, 2007

The Hammering Life-style of Woodpeckers

“Banging your head against a brick wall” - it’s a phrase that conveys futility and uselessness. For example: Trying to make sense out of the administration is like banging your head against a brick wall. Unless you are a masochist who thrives on pain, you don’t want to do it, and you certainly don’t enjoy it.

Unless ... you are a woodpecker. Then you make your living by banging your head against hard surfaces. If you are a woodpecker, you bang your head (in a manner of speaking) when you are hungry, when you need a place to stay, and when you want sex. But unlike the rest of us who get headaches when we bang our heads, woodpeckers are equipped for such activity. The brain case is larger than would be expected and frontal bones are heavier and folded at the base of the bill, enabling them to absorb the shock of the hammering. Heavier muscles behind the bill also act as shock absorbers.

Woodpeckers dine primarily on insects. They search for them in bark and wood, and sometimes in nuts, or crops such as corn. Their tapping may be heard throughout the year as they excavate insects from crevices with their bill and lap them with their long tongue.

Woodpeckers are cavity nesters, but they’re picky about their cavities. They make their own, usually spending about two weeks on the excavation. They make a new cavity for breeding purposes each year. Often they make a second hole for roosting during fall and winter.

Foraging and cavity excavation involve beating on wood, but the beating is slow and deliberate. During the spring and early summer, however, the beating on wood takes on a different character. Then it is likely to be fast and is the primary means by which woodpeckers communicate.

Both males and females drum. Their drumming establishes territory, and attracts a mate. It is the equivalent of a songbird’s song. During the spring rituals, woodpeckers will drum on wood which has good acoustic qualities, a branch or trunk that is hollow and which amplifies and reverberates their drumming. A pipe or rain gutter may serve the same purpose. The key is that the sound carry over a distance. I remember one spring when I was awakened early every morning by a sapsucker drumming on a neighbor’s metal mailbox.

Some astute listeners claim they can identify local woodpecker species by the way they drum, but in most cases I am skeptical. What a woodpecker chooses to drum on and how far away the drummer may be effect how a listener is going to hear the drummer. A Downy Woodpecker drumming on a hollow branch overhead may make one think that a much larger Hairy Woodpecker is doing the drumming. The pattern of drumming among many species (locally the Northern Flicker, and Downy and Hairy Woodpeckers) is so similar that visual identification is the only reliable way of knowing which species is doing the drumming.

Among our local woodpeckers, the exception is the Yellow-bellied Sapsucker. The sapsucker’s drumming begins fast, then slows down, as though it were running out of steam.

When woodpeckers are foraging or drumming, their hammering only involves the head and neck muscles. Then the head banging is relatively benign. But when they are excavating a cavity, they put their whole body into the effort. I once spent about twenty minutes sitting on a hillside in a hemlock forest watching a Pileated Woodpecker making a cavity. Every time it hammered, it was a full body strike, and the force was so great that the chips went flying. What I could not see were other adaptations that allowed for such activity. Woodpeckers which do a lot of excavating (Downy, Hairy, and Pileated) protect their nostrils from flying sawdust with feathers or by hiding them beneath a ridge. Just before their bill strikes, they close their eyes.

The woodpecker bill is also adapted to their hammering lifestyle. Think of the pointed tools in your shop, and how they tend to get stuck in the wood. The same would happen with a pointed bird bill. However, the woodpecker’s bill is chisel-shaped and exceptionally sturdy. The Pileated Woodpecker prefers to forage on hard wood trees; as you might expect, it has the stoutest and straightest bill to allow it to hammer without damaging the bill.

Most woodpeckers have two toes forward and two back to enable them to cling in their characteristic horizontal position. When climbing, one of the back toes can rotate to the side. Their upright position is assisted by relatively short and very stiff tail feathers. When molting, those tail feathers are replaced gradually so that the bird is never lacking in the tail support which it requires. By contrast, in late summer it is not uncommon to see a tailless songbird, one which has molted all of its tail feathers. I’ve seen tailless cardinals and sparrows this past week.

In southeastern Vermont, we have six species of woodpeckers, four of which are year round residents. The Downy Woodpecker is the smallest woodpecker and is common almost anyplace that has trees. The Hairy Woodpecker is fairly common; it looks like the Downy, but is half again as big, and requires bigger trees. The Pileated Woodpecker is our largest North American woodpecker (except for the Ivory-billed Woodpecker). As New England forests have recovered and mature, the Pileated Woodpecker has also recovered, but must still be called uncommon. Mainly a bird of mature forests, it will appear in town if there are big trees. The Red-bellied Woodpecker is a new arrival. The first confirmed nesting in Vermont occurred in Brattleboro in 2001. Its numbers have been increasing steadily, but it is still uncommon.

We have two migrant woodpeckers. The Yellow-bellied Sapsucker winters in the south and comes north to our northern forests to breed. It is common in our deciduous and mixed forests during the spring and summer. The Northern Flicker generally withdraws from its northern range during the winter, but may be found year round in nearby Massachusetts and Connecticut. It is occasionally reported on the Brattleboro Christmas Count. It is fairly common from deep woods to town lawns, although there is some evidence that its numbers are declining. The flicker is the least woodpecker-like of the woodpeckers; it often forages in robin-like fashion on the ground, or hops along in search of its favorite food - ants.

Red-headed Woodpeckers are reported about once a year in southeastern Vermont. Black-backed Woodpeckers are uncommon in the Northeast Kingdom and on rare occasions have been reported in the southern Green Mountains.

More about woodpeckers will have to wait until next week. I’m hearing a lot of woodpecker chatter through my study window. The Downy family is complaining that I haven’t put out the suet feeder this morning. So I’d best do that before they start hammering on the shutters.


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