Thursday, March 14, 2024

Coming Back to Earth

 

Purple Sandpiper, landing

Imagine that you could actually take to the air like a bird. Would you be able to come down again accurately and gently?


The sandpiper's dexterity requires intricate coordination of eyes, wings, and legs, all governed by its 'bird brain.'


As these flight calculations are being made the bird slows down, prepares to absorb the impact with its legs, and keeps a balanced posture.



It can reduce its forward speed by swooping up to a near vertical attitude, cupping its wings and fanning out its tail. Flapping in this orientation puts on its air brakes.


A perfectly timed approach lets the sandpiper come to a stall and drop softly onto its landing spot. 




Thursday, March 7, 2024

Merged Minds

Any encounter with a flock of Purple Sandpipers enlivens a winter walk along the shoreline of Halibut Point. Their adaptation to this environment is of course astonishing. If you happen to see them flying in unison your sense of wonder will multiply.

Purple Sandpipers

These birds present a most interesting combination of individual skills and collective cohesion. 


In an instant they can transform their self-oriented foraging pursuits into aerial group dynamics.


Their explosions into collective flight have been measured as occurring in 38 milliseconds, three times faster than a human eye blinks.


Once in the air they form a unit navigating as with one mind.


Their cohesion, seemingly without vocalization or other signals, has always defied human comprehension. Precise observation has measured waves of movement traveling from bird to bird in 15 milliseconds as the flock weaves and reconfigures in flight. 

Explanations leave us more satisfied with the what than the how. The most accepted account was offered by zoologist Wayne Potts in the journal Nature decades ago in 1984. He posited that birds in flocks are able to change direction quickly not because they are following a leader or their neighbors, but because they see a movement far down the line and anticipate what to do next. Potts called this rippling effect the chorus-line hypothesis with reactions propagating through the flock at least three times faster than could be explained by birds just watching their immediate neighbors.


The photograph above shows a lead bird but not, I am assured by a leading naturalist, a flock leader. From a lifetime of shorebird study he is convinced that sandpipers have no decision-making leader even when they're relocating to another feeding ground down the coast and re-settling together at a certain tide line. "They're not deciding it," he says. "It reflects a group ambivalence. The group as a whole knows what it's doing."


Sometimes understanding must be satisfied with going beyond logic, particularly when processes happen quicker than the blink of an eye. The mysteries of these birds enhance rather than diminish our fascination. Purple Sandpipers have earned a niche not only on improbable terrain but in the near-mythic landscape of human wonder.


Thursday, February 29, 2024

Purple Sandpipers

Bird watchers will know this is on the level, even if others suspect hallucinations.

Purple Sandpipers

Purple Sandpipers really do winter on the shoreline of Halibut Point.


They forage at  the tideline, pulling tiny invertebrates from rocks and seaweed.


Are they really purple? Or is that a flight of fancy colored by intrepid, overly entitled observers at the winter shore? It depends on the angle of the light. The orange legs and bill make a nice complement to the plumage.


The Purple Sandpiper has the northernmost winter range of any shorebird on the East Coast. When the season mellows into spring they take off for nesting grounds in the high Arctic tundra.


They manage to grip near-vertical algae-slick rocks with sturdy feet and toenails.



When an especially large wave hits the rocks, the birds flutter up far enough to evade the incoming water.



Having worked out their remarkable adaptations and reflexes, Purple Sandpipers have a niche with few others at Halibut Point, and none so masterful.


Between tides they roost in sunny spots in the open. They keep one eye alert to danger but are surprisingly approachable.


Thursday, February 22, 2024

Mallard Mixes

Duck genetics can get pretty mixed up, and so can nature lovers who try to make sense of what they see. Even though we're used to noticing Mallards in very specific patterns the reality is more complicated than that. Interbreeding among closely related groups is not unique to Mallards nor even just to ducks. It may or may not be a "conservative" occurrence, depending on perspective. Perhaps it "just is."

R to L: Mallard male, American Black Duck male, hybrid female

The Mallard is a common and widespread species in the large, fresh water duck genus Anas. Other species in this genus frequently commingle with Mallards, especially American Black Ducks. They're often seen together at Halibut Point. 

Northern Pintail (f) in foreground

This female Northern Pintail Anas acuta currently in residence at Halibut Point is fairly easy to distinguish from other Mallard-like ducks on the quarry pond. It has 'pure' Pintail characteristics of diminutive size, buffy-brown plumage, and gray legs and bill. But what about the bird to its rear in this picture, with the wing bars of a female Mallard but the drab olive bill of an American Black Duck? Its identity to ornithologists is more ambiguous. There's a blurring at least of the edges.

A typical female American Black Duck Anas rubripes

A typical female Mallard Anas platyrhynchos

A Gadwall female, until recently Anas strepera

Returning to the first photograph we can see that genes of a dark colored heavy-bodied male American Black Duck (center) seem to have influenced the appearance of the female duck standing on the left.

A Mallard x Gadwall x American Black Duck female hybrid?

Enlarging that photo we can take further stock of this bird's bill and plumage. It's possible that it exhibits Gadwall traits as well as Mallard and American Black Duck.

Mallard male

The male Mallard in the group is clearly characteristic of its species and gender.

A male Mallard x American Black Duck cross

Cross-breeding occurrences produce ambivalent plumages among male offspring too.

The hybrid male with a Mallard female

The drake in the photograph above blends American Black Duck and Mallard characteristics, at the expense of the iridescent green head. The female doesn't seem to mind, though it's a loss from our standpoint. Human aesthetics, and taxonomy, do not necessarily enter into matters of natural selection except insofar as they result in successful futures for the species.

Part of the concept of 'species' for both flora and fauna is that it preserves a stable group identity for its members. But as we've seen, birds in the Anas genus sometimes make inter-species pairings that produce viable offspring with mixed characteristics, especially when closely related species flock together.

Favoritism by humans has played a significant role in the increase of Mallards. According to local naturalist Chris Leahy, they "were once uncommon spring and fall migrants in New England. They only began to breed and to become common permanent residents when people began introducing feral or captive-bred  birds to private ponds and public parks. Their superabundance can cause problems for native waterfowl and even human health."

That puts humans in the Mallard mix too.

 

Thursday, February 15, 2024

Mallard Chaperones

 

American Wigeon

At Halibut Point, almost any time you see a dabbling (surface-feeding) duck it either is, or is in the company of Mallards.

Ring-necked Duck, juvenile male

In part that may be because Mallards are more numerous than any other kind of duck, so they have a wing up on the prime habitat.

Green-winged Teal

But they're also not territorial nor competitive by nature. They make room for others.

Black Ducks, lower left

In the case of Black Ducks, Mallards commingle to the point of occasional inter-breeding.

Gadwall pair with Mallard pair

This can also be true of the closely related Gadwalls that stopped for a rest at the quarry this winter.

Female Pintail, foreground

Similarly this Pintail must have felt sufficiently reassured by the flock of Mallards to join them for a couple of days. Ordinarily it would frequent a pond with more vegetation than a deep water granite quarry.

The Pintail at the center of the Mallards

The fact that most of the singular 'guests' are females or juveniles gives further credence to the conclusion that Mallards are a reassuring presence for other ducks.

Juvenile Greater Scaup, in the water

Occasionally even diving ducks like this Scaup find the Mallard contingent companionable.

Female Common Merganser

A visiting Merganser found reassurance on the quarry pond by the escort of a Mallard drake.



Thursday, February 8, 2024

Mallard Iridescence

Mallard Ducks, an everyday sight in public parks, look like nature exaggerated into artistic fantasy.


The males display a peacock-like iridescence about their heads. Both sexes show iridescent blue wing bars in flight.


Most of the Mallard's colorful effect comes from light reflected directly by feather pigments, as it does in a painting. Special brilliance results from light waves passing through iridescent structures, which are microscopic layers of crystals within the feather barbules. Their interspersion with air forms complex surfaces for refraction which, coupled with underlying pigments, create vibrant sheens on the feather.


Contrasted with the plumage array on its body, its yellow bill and orange feet, the male Mallard's iridescent green head makes a splendid sight in courtship and to casual Park visitors.


A couple of weeks ago as ice was beginning to form on the Halibut Point quarry, these Mallard Ducks swam by with the sunlight at a low oblique angle from the rear. Their apparently dark purple heads momentarily confused recognition. What happened to the lustrous green sheen?



Peter Brown, an art professor friend, supplied the answer. "Green light and violet light are complements. This means that when combined they will create white light. The microscopic structure of certain feathers refracts white light like a prism. At certain angles we see one color and as we shift our vantage point we will see the color’s complement. When one color is being absorbed by the feather, its complement is being reflected to our eyes. With iridescence this process flips back and forth."


This duck seems to be resting peacefully with a blend of green and violet iridescence.


Thursday, February 1, 2024

Goldeneye Theaters

 

The quarry wall, Halibut Point

Water and ice have made dramatic cliff pictures (hydroglyphs ?) in the recent cycle of warm and cold weather.

Female Goldeneye

One day a bird normally found at Halibut Point only on the winter shoreline appeared at the base of the quarry's icy cliffs. It's the only time I've seen one on this interior pond.

The swimming hole

It found refuge in the small remaining area of open water that allowed it to fly in and out. Goldeneyes need less patter distance (running on the surface) than do Mallard Ducks for takeoff.

The duck diving, right center

The duck dove repeatedly in search of invertebrate food along the shallow edge.

Female and male Goldeneye pair at sea

When seen at close range it's obvious how these birds come to be named Goldeneyes.

Goldeneyes by coastal cliffs, Folly Cove

Their winter habitats can make as dramatic a sight for shoreline ramblers as the prime actors themselves.