A WHITE BLACK BIRD

I look at a lot of birds every year, and I don’t see many that are as cool as this one, a leucistic Black Turnstone (Arenaria melanocephala). This striking bird is wintering at the end of Sandy Point, north of Bellingham, Washington, in a flock of its relatives, and I finally got around to checking it out in February. I found the flock feeding on rocks at the mouth of the marina there.

What a bird! From a distance it looked entirely white, but at close range elements of the pattern became visible, most of them very subdued. The more or less straight line across the breast identified it as a Black rather than a Ruddy Turnstone (Arenaria interpres), which has a bilobed pattern of black there. There was also a Ruddy with the flock.

By comparing the bird with a normal Black Turnstone, I could see how much the melanin pigment was reduced on this bird, yet it wasn’t entirely absent. The darkest areas of normal pigment were on the rump and tail, but tan areas all over the bird, most readily seen in flight, gave me a good hint of typical Black Turnstone pattern.

The bird is definitely leucistic, not albinistic, because it has normally pigmented eyes. Albinism is the complete absence of melanin pigment. Because that pigment is what gives brown eyes their color, when it is lacking in an albino, the blood vessels in the eyes give them a bright red color. Leucism is a reduction of all pigments, but not necessarily their absence.

The bird presumably grew most of its feathers in July and August, the time of fall molt in Black Turnstones, so they were about six months old in February and showing their age. In comparison with nearby normal birds, the primary feathers were distinctly more worn. The tertials, the long feathers that overlie the primaries, were very worn, much more than on the other birds.

The bright orange legs of this bird contrasted with those of normal Black Turnstones, in which they are brown to dull orange. Presumably in normal birds, melanin masks what would be bright orange otherwise. The legs of Ruddy Turnstones are bright orange, and one wonders whether they would remain exactly the same in a leucistic bird.

Its behavior appeared to be the same as that of the other birds, and they must have accepted it as a flock member. However, when the entire flock flew away, startled by a jogger coming down the beach, the white bird flew in the opposite direction with two of the black ones rather than with the flock.

Such birds are extremely rare, and I feel fortunate to have seen this one. One thing special about it is that it could never be mistaken for another turnstone, thus always recognizable. If we could recognize all birds individually, we would know a lot more about them!

The white turnstone’s presence is being monitored closely, so we may know when it has departed for the north, assuming some local falcon doesn’t pick it out of the flock. It is well known that birds of prey will home in on odd-looking birds, as they are easiest to follow in a twisting, turning flock.

If it does persist into spring, local birders will be watching closely for it late next summer, when Black Turnstones return here from their breeding grounds in the Yukon/Kuskokwim River delta. Let’s hope it makes it back.

Dennis Paulson

WATCH OUT, IT STINGS—OR DOES IT?

We all know when yellowjacket season rolls around, with pesky wasps that bother us on every picnic. You can usually chase them away easily, but they come back again and again. They are relatively innocuous when you’re trying to give them the brush-off, but don’t ever disturb one of their nests in the ground!

Western yellowjackets (Vespula pensylvanica) are members of the insect order Hymenoptera, the bees and wasps. Other wasps that are common in our area are bald-faced hornets (Dolichovespula maculata), bigger and fiercer than the yellowjackets and with a big turnip-shaped paper nest up in the trees; and introduced European paper wasps (Polistes dominula), with a much smaller paper nest with chambers open below.

All these species have in common a black and yellow or black and white banded abdomen. That coloration is common in wasps and bees and is thought to be aposematic (Greek ‘away sign’), a word used to denote a warning coloration. “Don’t mess with me” is a loose translation.

Some birds, for example kingbirds, are able to take stinging insects in their stride, catching them in flight and beating them to death, even squeezing out their stinger, but a lot of animals doubtless leave them alone because they pack such a punch at the end of their abdomen. The warning coloration assures that they are safe either because the predator species has a genetic memory of them or has tried to capture one previously and was stung by it, a much more immediate memory!

As these wasps move through our environment, relatively impervious to predation, other insects have benefitted by evolving coloration, shape, and even wing sound that mimic the wasps. Most of them in our area are flies (Diptera), especially hover flies of the family Syrphidae. Here are a few of them. They look very much like the wasps as they fly around, and even seasoned entomologists often have to look closely. I for one have grabbed what I thought was a fly from an insect net and been stung for my mistake.

By mimicking stinging wasps and bees, these so-called Batesian mimics (from Henry Bates, early student of this phenomenon) gain protection from predators, mostly birds, that mistake them for their models and leave them alone. It must work very well, as there are so many kinds of flies that mimic wasps. There are also grasshoppers, beetlees, moths, and other insects that do the same, especially in the tropics, where there are so many more species of insects and so many more birds that eat them.

A study done in Illinois that involved extensive collecting of model Hymenoptera and mimic Diptera showed that the mimics are common in the spring, when adult birds are present as predators, but virtually absent during the period in midsummer when young birds are fledging. Some of them appear again in fall. The authors speculated that the mimic flight seasons were adjusted to miss the time when young, naïve birds were everywhere, birds that wouldn’t know enough not to catch them!

Dennis Paulson 

WHAT'S WITH THE WHITE BIRDS?

We become so used to seeing birds such as robins and chickadees and sparrows that we notice right away when one of them is oddly colored. The abnormal color variations that are seen in birds often are the result of mutations that involve the reduction or lack of melanin pigments. When melanin is reduced, dark feathers become paler, even whitish. When melanin is absent, feathers are pure white.

Albinism involves a complete absence of melanin and usually results in a pure white bird with red eyes. The melanin pigment that gives birds brown eyes is absent, so the red blood is visible through the transparent cornea. This mutation does not affect other pigments, so if a bird has carotenoid pigments coloring it red or yellow, that color may remain.

Leucism is different from albinism in that it may affect all pigment types, reducing their concentration to produce a paler bird or eliminating them entirely to produce a white bird. This can occur in some or all feathers, making some birds a patchwork of normal and white or whitish feathers. A bird that is white with brown eyes is leucistic.

Odd variants are typically seen in the most common birds, so even when such a mutation is rare, we see enough individuals to eventually encounter a funny-looking one. Robins that were pale overall have been reported with some regularity. Dark-eyed Juncos are often reported with scattered white feathers, even a head pattern somewhat like a chickadee; pure white ones are much rarer, perhaps in part because they are very conspicuous to predators and don't last long! You can see why these mutations would remain rare.

Some populations of Black-capped Chickadees in the Seattle area have persistent leucistic genes, and individuals are seen year after year in a neighborhood with different combinations of whitish caps and backs and white outer tail feathers (looking a bit like a junco as they fly away). Apparently chickadees don't have enough visual predators to eliminate these genes entirely.

I know of at least four male Red-winged Blackbirds in Washington that had plumage almost identical to the one shown here. Apparently that leucistic mutation is widespread in the genome of this species, at least in the Pacific Northwest. Is this some basic blackbird color pattern that is suppressed by the males' black pigment?

Leucism can be hard to detect in birds such as gulls that are already gray and white, but a pure white one like this Ring-billed Gull usually indicates this mutation. Remember that egrets and swans aren't leucistic; they just evolved white plumage, obviously advantageous to them.

Dennis Paulson