Convergent Evolution

Bird #1

Bird Number 1: Sitting by my river, I watched him working the opposite bank, teetering and bobbing as he went from stone to stone. He is a brownish bird, with a white breast and prominent dark spots on his breast. He is seldom found far from water, but it can be a river bank, a tiny creek, a lake, or a muddy pond. I remember seeing him one time when I was walking a friend’s farm in Pennsylvania. He stood ankle deep in a muddy puddle surrounded by dense brush and shaded by the forest canopy, bobbing his tail with each step. The one I was watching from my chair by the river suddenly took flight, his “peet-weet, peet-weet” giving me the signal to follow as he flew upstream to the next big rock where bowed repeatedly in my direction.

Bird #2

Bird Number 2 bobs and teeters, just like Bird Number 1. Bird Number 2 is larger than Bird Number 1: 8.5 inches verses 7:5 inches. Instead of the prominent spots, Bird Number 2 has a faint brown band around the neck and a white breast. It also is a bobber and teeterer. Both of these birds are tail waggers. The tail moves busily up and down as these birds perform their bowing gait. I see Bird Number 2 in puddles and ponds during May. It only stops in our neighborhoods very briefly before continuing its migration to the northern reaches of our continent to breed.

Bird #3

I saw Bird Number 3 was on the edge of a beaver pond in Stratton town. At 6 inches, this bird is smaller than the other two. But, it looked remarkably similar. Its back was dark olive-brown, its breast streaked and its sides buffy. The stripe above its eye was also buffy. The source of its folkname is obvious as I watched it move along a prone log: this was the “water wagtail.” However, the difference between this bird and the first two is most apparent when it sings: a loud, ringing, “twit twit twit sweet sweet sweet chew chew chew” carries through the forest, rivaling the winter wren for the power and clarity of its song.

Bird #4

Bird Number 4 is a Vermont breeding bird, like Number 1 and 3. In our neighborhoods it likes flowing streams, leaving the standing or sluggish waters to Bird Number 3. Bird Number 4 is almost identical to the Bird Number 3, except the sides and the eye stripe are whiter. Like the previous birds it wags its tail incessantly as it walks along the damp stream edges. Its folk names is also “water wagtail.” When he finds a singing perch he lets loose with three clear slurred whistles and a jumble of twittering notes.

So what are these four similar looking birds who have similar habits (tail wagging and bobbing), and very similar habitats?

Bird #2 - Spotted Sandpiper

Birds 1 and 2 are sandpipers, the Spotted Sandpiper and Solitary Sandpiper, respectively. They belong to the order, Charadriiformes, which includes the sandpipers, plovers, phalaropes, gulls, terns, alcids, and other birds closely associated with the water.

Birds 3 and 4 are waterthrushes - the Northern Waterthrush and Louisiana Waterthrush, respectively. They belong to the order “Passeriformes” - the perching birds. If you are able to watch either waterthrush for a period of time, you may occasionally see him leave the downed log or the damp pondside and sing his resounding, musical notes while perching on a low tree branch.

Bird #4 - Louisiana Waterthrush (J.J.Audubon)

Given their appearance, you might then conclude that the Northern and Louisiana Waterthrushes are related to the other thrushes, like the Wood Thrush or Hermit Thrush. Their names certainly suggest such a relationship. Alas, that is not the case. They are wood warblers, disguised as thrushes and with an extreme fondness for water, like sandpipers.

Confused? Don’t be. Classifying species is an art form masquerading as science, although in fairness to the biologists who try to do the classifying, DNA testing is making species classification much more scientific that it use to be.

Though not related, these two sandpipers and two waterthrushes occupy similar habitat, have similar habits, and are similar in appearance. “Convergent evolution” is the term used when unrelated species have, through time, come to look alike, think alike, and live alike.

In a very broad sense, the development of the forearm into a wing in bats and birds is an example of convergent evolution. In the Northern Hemisphere there is the auk family (e.g. Atlantic Puffin) while in the Southern Hemisphere there are the penguins with a similar life style and similar habitats - another example of convergent evolution.

Along our streamsides and ponds we may be able to see convergent evolution up close in the resident Spotted Sandpiper and the transient Solitary Sandpiper, and in the warblers which don’t look like warblers: Northern Waterthrush and Louisiana Waterthrush.

Bird #3 - Northern Waterthrush (Belize)

Edward Forbush, the early twentieth century Massachusetts ornithologist, provides this description of the northern waterthrush: “Watch him now, and see how prettily he walks, rustling among the fallen leaves where he threads his way like a mouse, or wading even up to his knees in the shallow miniature lakes, like a Sandpiper by the sea-shore, all intent in quest of the aquatic insects, worms, and tiny molluscs and crustaceans that form his varied food. But as he rambles on in this gliding course, the mincing steps are constantly arrested, and the dainty stroller poises in a curious way to see-saw on his legs, quite like a Spotted Sandpiper.”

Bird #1 - Spotted Sandpiper (non-breeding)

But lest we think that the Northern Waterthrush and Spotted Sandpiper are just imitations of one another, Forbush writes about the latter: “The Spotted Sandpiper swims and dives readily. It can dive from the surface of the water or from full flight, at need. Under water it progresses by using its wings, which it spreads quite widely, and in shallow water it can go to the bottom and run a short distance with head held low and tail raised like a Water Ouzel or Dipper.”  Spotty and the American Dipper is yet another example of convergent evolution.

Learning about the habits and relationships of the birds can be very illuminating. Watch the closely and see what you notice. Start with the birds at your feeders. Good Birding!

Vacationing Birds

Just like humans, when birds go on vacation they often behave very differently from when they are engaged in domestic duties. Two weeks ago I wrote about the Wood Thrush on its wintering grounds in Belize where its behavior is positively robin like. The thrush’s behavior is a sharp contrast to its behavior on its breeding grounds in Vermont where it is shy, secretive, and elusive.

Here are a few more examples of bird behavior on wintering grounds that is different from behavior on breeding grounds.

Northern Waterthrush (Belize)

When I was surveying for the Vermont Breeding Bird Atlas, I found a Northern Waterthrush in a beaver pond in Stratton. It was singing, and I listed it as a probable breeding bird. I have returned to the beaver pond during June every year since. I have circled through the forest to the back end of the pond where the water is shallow and still, the favored habitat for the Northern Waterthrush. By contrast, it cousin, the Louisiana Waterthrush, likes fast moving mountain streams. Both waterthrushes are are warblers which look like thrushes (Wood, or Hermit) - brown birds with spotted white breasts. They bob their tails, like a Spotted Sandpiper, as they walk along the ground.

One June, I saw the Northern Waterthrush in the beaver pond for an extended time. At the the shallow end of the pond, I sat on a log and fed the mosquitos. While the male sang somewhere in the swampy pond, the female bobbed along the muddy edges a couple dozen feet from me, feeding. Then I suppose she gathered nesting material, because she flew off with something in her beak.

Every quest I have made for this warbler during June has required patience and luck. In our  swampy forest neighborhoods, the Northern Waterthrush is shy, secretive, and elusive, like the Wood Thrush. It carefully balances the need to advertise its presence in order to attract a mate and warn off rivals against the need to protect its nest, eggs, and young from dangers.

Along the shallow edges of a small pond in Belize, I watched a pair of Northern Waterthrushes as they foraged through leaf debris. It was the dry season, and many trees dropped their leaves. Large brown leaves covered the forest floor and the muddy pond edge. The waterthrushes walked along, tails bobbing. Systematically they flipped over the large leaves looking for food. Walk, bob, flip, feed ... walk, bob, flip, feed. They were cautious about any movement in their direction on my part. After all, I was a huge intrusive presence. But they were not the shy and elusive birds I knew in Vermont.

Hooded Warbler (male - Belize)

For many years I lived in Delaware Water Gap, Pennsylvania. The sides of the mountain ridges were covered with rhododendron, prime nesting habitat for the Hooded Warbler. On many occasions, I sat along the trail for long periods trying to get a good look at the male. He is a bright yellow bird with a bold and striking black hood. A good look is worth the wait. He often chose a mid-level branch as his singing perch. Picking that tiny spot of yellow out of filtered sunlight in a forest always included a dollop of luck. If a second male sang nearby, fast flights in defense of territory might provide a glimpse.

The first day we were in Belize, I caught my breath and said, “Oh my, a Hooded Warbler.” Then it happened again ... and again ... and again. The Hooded Warbler’s frequent appearance never became humdrum, but it was not the breath-catching experience that I had been accustomed to.

Botanical gardens adjoined our jungle lodge in Belize. One morning in an open orchard section, I watched a male Hooded Warbler feeding. He went from tree to tree, working the branches and gleaning the leaves. While he never allowed me to get too close, he did not hide in thick foliage where he was a mere flitting and fleeting presence. Back and forth he went, pausing from time to time to pose and allow me to marvel at the black cowl framing his yellow face.

The Hooded Warblers I saw were all males. The females, which lack the prominent black hood, were absent. That typified the experience with the “northern” birds which I saw on their wintering grounds.

Black-throated Green Warbler (female - Belize)

Magnolia Warbler (female - Belize)

Where we were staying in Belize, I saw lots of Black-throated Green Warblers - all female. In a much different location, I saw males. The Black-and-White Warblers were male. The Magnolia Warblers were female.

Parenthetically, last year I struggled to get reasonable pictures of the Magnolia Warbler. They were high in tree branches, moved rapidly, and rarely presented a good photo opportunity. I had several good opportunities to photograph the female Magnolia Warbler in Belize and the male in Tikal, Guatemala.

Continuing. I saw lots of American Redstarts with the black and orange plumage of the male and the gray and yellow plumage of the female. But, one year old male redstarts look like the female; they do not acquire the adult male’s black and orange plumage until they are two years old. I suspect that the American Redstarts were all male.

You see the pattern. In addition to very different behavior from what we see when these birds are in our neighborhoods during their breeding season, the sexes also vacation separately. With many species, males and females occupy different habitats during the winter.

Another striking behavioral difference in these wintering birds was the lack of song. They did not sing. Bird song is such a key component to knowing what birds are present, but singing is an activity largely confined to the breeding season. Local guides relied on voice for identification, but that voice was not song, it was call - the chip notes that birds use to communicate with one another.

On the wintering grounds, there is no singing, no displaying, and no rivalry among the males. There is no need for such behavior until the birds begin their journey northward when they are driven by hormonal changes and the urgency of species propagation.

Gray Catbird (Belize)

The Gray Catbird presented something of an exception. I heard some catbird mimicry, though not nearly as much as I hear during the summer in my yard. Otherwise, the catbird on vacation behaved like the catbird I see in Vermont. It came to the feeder on the veranda for fruit. It picked berries from the ground and off branches. It hoped about with friendly curiosity, cocking its head when listening to my silly sounds or when some other movement caught its attention.

In summary, it was fun seeing old friends on vacation.

Local Birding

I've been fortunate to get out for some local birding the last few days, including birding with my favorite companion, whatever the occasion might be. Up in the Green Mountains we bushwacked into a beaver pond, then just sat still and enjoyed the setting (made possible, in part, by heavy applications of toxic substances).

Highlight at this pond was the Northern Waterthrush, which is why we bushwacked in the first place; we heard it singing. Finally it showed itself feeding in the muddy edge. The rest of the time the pair were busy moving about, seldom staying still.

The highlight this morning was finding a pair of Blue-headed Vireos building their nest. What appears to be a white glob beneath the bird in the very delicate beginning of their hanging nest.

I can't tell the male from the female, but we can assume that they know the difference. To the left of the visible vireo is the mate working on the nest. It is a joint project.

Nothing more needs to be said about this Scarlet Tanager.

Nor does much need to be said about this Blackburnian Warbler.

Eastern Tiger Swallowtails seem to be everywhere.

And finally, while waiting for the Swamp Sparrow and Alder Flycatcher to come close in yet another marshy beaver pond (they never did), I was joined by this moose cow, and that's no bull!

Moose are fairly common, but shy and secretive. I often see signs of moose, but do not often see them. Always a treat!

Sometimes a morning of good birding includes things that don't have feathers.