Saturday, October 29, 2005

Screech Owl Fly-out

Photo by Cal Vornberger -- October 28, 2005

The little red-phase screech owl that has been roosting in a tree in the Ramble for the last three or so weeks left its daytime roost-hole for its night hunting at 6:08 p.m. today. A little crowd of people, including two photographers, were there to watch his/her exit. The owl, in turn, seemed to survey the audience with some curiosity, or so it seemed to us.

Owl etiquette does not allow me to be specific about the bird's location -- the Central Park "nature community" is very protective of its owls, and rightly so. Since owls are predictible and often sleep in the same location day after day, it's important to make sure that owl locations are not transmitted to anyone who might want to harm them in any way. If you are a birder who has come to Central Park in search of a known owl roost, your binoculars are usually your best credentials: other birders in the know will lead you to the owl.

Grackle update

The huge number of Common Grackles and Starlings[more than a thousand] that have been spending the night in the ten pear trees surrounding the Pulitzer Fountain [pictured above] are still streaming into their night roost trees every evening. As sunset gets earlier so too does the birds' arrival time. Nowadays they begin arriving a little after 5 pm, with peak numbers at about 5:40. The trees are beginning to lose leaves. The flock will move on sometime soon, to spend the winter in gigantic evergreen roosts in the south --- roosts that may include 50,000 birds. Every day now I'm prepared to come and find them gone. And every day, as they start flying in I breathe a little sigh of relief: reprieve...for one more day.

Friday, October 28, 2005

Winter Wren Influx

Among the large number of
late fall migrants in Central Park this week were Winter Wrens. While we don't share many species of birds with Great Britain, and while birds the British call by names similar to ours are usually different species altogether -- for instance, the bird the English call a robin is quite different from the American Robin, the Winter Wren we find in Central Park this week is the same species as the one found in Europe, the one British fondly call Jenny Wren.

Lloyd Spitalnik, a frequent contributor to this web site, writes:

Since there has been so much talk about the very large influx of Winter Wrens, I thought I'd send you a photo taken yesterday 10/27/05.[See above] There were at least 5 different birds hanging around the reeds on the north side of Turtle Pond. Here is one of them.

Thursday, October 27, 2005

Two great photos from Lloyd

Lloyd Spitalnik who among many other things is the organizing spirit behind the Central Park birdfeeding squad [the feeders went up a week ago!] writes:


Here is a photo of a Rusty Blackbird that's been hanging around the entire length of the Gill for the last few days. Also a White-breasted Nuthatch with what appears to be some kind of cocoon.

See you,


White-breasted Nuthatch with Cocoon
So that's where all our future moths go!]

Rusty Blackbird at Azalea Pond

Blakeman on food and pigment

JB and Savannah

I should have mentioned that the soft parts of hawks are decidedly colored by their food. Feathers, no. But the intensity of the yellow of the feet and the cere, the soft band of skin around the bill, are markedly influenced by the hawk's food.
Birds of prey kept in captivity, either by falconers, zoos, nature centers, and the educational display birds of rehabilitators, seldom have the intense yellow exposed skin color of hawks that hunt exclusively in the wild. Wild food doesn't change the color from yellow. It merely intensifies it.
The color is probably caused by carotenoids, plant pigments that prey birds and mice have in their GI tracts from plant food they were digesting when caught. The intense yellow color on the soft parts of wild hawks is always impressive, compared to the unsaturated hints of yellow on our captive birds.
I didn't mean to imply that food provides no body pigmentation for hawks, only that food doesn't change feather colors.
Commercial pen-raised chickens are fed marigold extracts to give the fat and flesh a slightly yellow color. Without these food amendments, pen-raised chicken flesh would appear bleached. The color intensity of the flesh and eggs of free-ranging chickens is noteworthy.
On the picture of Savanna II, my falconry red-tail, viewers can see the soft cere directly between the eyes. It's only slightly yellow, not nearly as intense as in wild red-tails. Savanna is copiously fed with turkey necks, occasional pigeons and sparrows, and a vole or mouse every now and again. She's very healthy, but because she's not eating three to five wild-caught voles each day, she's not getting large amounts of plant pigments found in the rodents' stomach and intestines in the plant foods they consumed. Savanna gets veterinary vitamins, minerals, and trace elements I give her to supplement the raw proteins and lipids of her diet. She's in superb health, should anyone be concerned.
The photo also shows her tan breast, which I alluded to a day or so ago. In the Midwest and East, most adult red-tails have a rather white breast, and the neck area beneath the chin is also white. This bird, and a few others from Ohio, are genetically dark-breasted, as I mentioned. Expert viewers from the West would say that this bird is colored very much like typical Western red-tails, but it was hatched here in Ohio. When I go to a falconry event in Indiana or Illinois, just one or two states to the west, I note the very different color patterns of the red-tails from those states. Across the continent, red-tail colorations vary in minor ways within populations. Feather colors are all genetic and can help identify individual birds and variant local populations, such as the red-tails of Central Park.

John A. Blakeman

Wednesday, October 26, 2005

The great Mars Show

Charlie Ridgway, one of the regular Central Park sky watchers, just sent a reminder about the great Mars show now playing in your local... firmament.


This Saturday night, October 29th, Mars passes its closest to Earth for the next 13 years. But for all practical purposes it's already just as close and will remain so for another two or three weeks. See our article:

Take advantage of every clear night to get your telescope on Mars! It's
well up in the east by late evening, far outshining any other point of
light in the sky. An observing guide to Mars, with maps to identify
surface features, is in the September SKY & TELESCOPE, page 67.

You can also try for the planet's two tiny moons, Phobos and Deimos; see
the October issue, page 59.

The last word?

More on the red chests of Pale Male's dynasty. I guess I'm convinced. And apologetic for saying that Blakeman's redtails lived in Illinois, not Ohio.


I'm in Ohio, two states further east than Illinois -- but that's really immaterial. (And I'm not sure where Queens or Staten Island are, either.)

I'm absolutely certain that the breast colors of the Central Park eyasses and immatures are not caused by anything they are fed or capture. The details supporting this contention are far too detailed to go into here, but they derive from both feeding trials of both American kestrels and red-tailed hawks that I conducted using a wide variety of foods.

But here, perhaps, is the clincher. If a particular Central Park prey animal causes the eyasses and first-year hawks to have pigmented breasts, why doesn't this persist through adulthood? The eyasses and first-summer birds are eating essentially the same prey as the adults. What would keep the accumulation of some prey-borne pigment from continuing to persist in new molted feathers each year? Lola appeared to have a rather typical white breast, and she was eating the same food that her eyasses were. She should have had a darker, pigmented breast, if food was the source of the pigmentation of the eyasses.

Savanna, my falconry red-tail, has a slightly darker, somewhat atypical breast coloration, approximating the beige or brownish hues of the Western race of the red-tail, Buteo jamaicensis calurus. I've worked with one of these dark-feathered birds trapped in the area 30 years ago, and two or three others have been seen. Many astute birdwatchers have noted these in Ohio, wondering if they are displaced, wondering Western birds. They are not. They are like the erythismal birds of Central Park, a local population with an atypical coloration gene. Western red-tails are noted for being smaller than our much larger Eastern birds. These dark Ohio birds have the bold shape and strength of our Eastern race, B. j. borealis. They are merely slightly darker forms of the local race, not wanderers in from the West.

All of this supports the notion that pigmentation in red-tails is entirely genetic, not dietary. The powerful protein-digesting enzymes of the red-tail's GI tract do a real number on flesh-borne pigments and most everything else, too (except fur and feathers, which get cast back out in the daily pellet). There is no way that food-borne chemical pigments can enter the hawk's circulatory system in a chemically undiminished form and then get chemically inserted in the new feathers being synthesized in the feather follicle.

It's a fun thought, however, and worthy of consideration. Good thinking by all.


John A. Blakeman

Tuesday, October 25, 2005

Fairway too much for Warbler

Photo by Cal Vornberger
Black-throated Blue Warbler [male]

Ardith Bondi, Central Park birder and photographer reports: 

My sister-in-law, Rebecca Osborn, reported a Black-throated Blue female hopping on the fruit on the outside stand at Fairway* today (Tuesday, October 25, 2005). She said it seemed a bit disoriented as it hopped from one fruit to another.

* Fairway is a huge and often jam-packed fruit, vegetable and grocery store on Broadway and 74th St.

Donna to the defense

 Yesterday I went out on a limb and suggested that the etiology of the reddish chest coloration of Pale Male's progeny might be environmental rather than genetic. I proposed food as a possible cause. Blakeman replied with a resounding and confident No Way.

Today I received a letter for the defense from Donna Browne. I have a feeling she knows that the odds are strongly against anything other than a genetic cause for the young hawks' erythrismal chest coloring,and that she was writing out of friendly hawkwatcher solidarity.
Still it was delightful to have her support. Her letter follows [in part]:

I never would have thought about the red chests
coming from food. But I don't dismiss it because even though the theory goes against RT "common knowledge" and RT's aren't known to have that sort of food/looks affinity, the fact that wild caught pigeons have been fed to hawks in another geographic area doesn't refute the possibility (okay,
probably slight possibility) that something could be happening here. Different ecosystem, different adaptive birds, different soil, different diet.

Not long ago they discovered that what was being taken for a genetic color morph in one of the big cats had to do with diet. They started tracking it because the females preferred one coloration far above the other. It turns out the color variation the girls liked was sported by the males that had the better diet. Whatever "better diet" meant in the article.

PS from Marie

Hmmm. I like the idea that a "better diet" [surely that means more food consumed] changed the lion or leopard or jaguar [or whatever the big cat was] coloration. John Blakeman has often commented about the abundance of food available for our Central Park redtails when compared with the hard-to-catch voles his Illinois redtails depend on. When he was talking about starving Illinois fledglings, ours had bulging crops in every photo. Maybe my food hypothesis was not as absurd as even I was beginning to believe.

Monday, October 24, 2005

Blakeman's response

The pronunciation "erythrismal" is, I think, dismal -- but it's correct.

Blakeman: Pale Male's kids: red. Grandkids: white or red. And nix on diet

Photo by Bruce Yolton
Trump-Parc nestlings, July, 2005
From John Blakeman:

If all the Central Park eyasses are direct descendants from Pale Male, and he's homozygous dominant (2 dominant erythrism genes), all of his first generation offspring must necessarily be erythritic.
The greater question arises in his grandchildren, who are most likely to be heterozygous, having both a gene for erythrism coming down from Pale Male and a white-breastedness gene from a normally-colored mother. These birds will all be erythritic, but can pass on some hidden white-breasted genes. Therefore, depending if the mother was Ee or ee, we ought to start seeing either 25% or 50% of the grandchildren with white breasts. At the beginning, in the first generation of offspring, all will be erythritic. But in the second generation, the grandchildren, about either a half or a fourth should be white-breasted, depending on if the mother had a single erythritic gene or not.
But there haven't been many grandchildren yet, perhaps just the two Trump Parc eyasses this year. Therefore, the universal predominance of erythritic birds is still very probable and understandable.
Again, all of this points very strongly towards Pale Male's genetic primacy. He's apparently the Man, the patriarch of all the nesting Central Park red-tails.
It will be interesting to attempt to determine the genetic line of the first white-breasted eyass. I think we've got a pretty good handle on it now, awaiting such an appearance.

About there being dietary explanation for the marked breast coloration of the Central Park eyasses and immatures. I'm certain that this is not a factor. First, the birds aren't being fed or capturing anything other red-tails don't take elsewhere. Yes, the CP hawks have learned to take pigeons with greater frequency (and success) than any other red-tail population I know of. But I've fed wild-caught pigeons to multiple red-tails, including eyasses in my research, and I'm certain they don't change feather colors. Rats and squirrels don't change feather colors at all, either.

The breast feathes of most red-tails tend to whiten as they age, even in the first year. I think this is plain environmental bleaching, the effects of sunlight and being out in the weather. With a wild red-tail in hand during the molt, we can easily tell feathers that are newly descended and older, unmolted ones. The old ones are a bit bleached. This can happen to lighter-colored breast feathers.

The dark color of Central Park eyass breast feathers is genetics, not a pigment in the food. Yes, in flamingoes feathers are colored by pigments consumed in food. Not so in red-tails, I'm certain.
John A. Blakeman

PS from Marie
If the noun is erythrism, is the adjective erythritic [JB's preferred version] or erythristic
[mine]? Actually, the American Heritage Dictionary gives the adjectival form as erythismal!

Sunday, October 23, 2005

A genetics lesson by Blakeman and a PS [with a bold new theory] from Marie

photo by Cal Vornberger
May 29, 2004


About Punnett Squares:

If you remember back in either high school or college freshman biology, when you learned that genetic traits are stored on matching pairs of chromosomes, you did some genetic probability problems, just like
the ones that will have to be done when we
see a white-breasted Central Park eyass, perhaps next spring.
It goes like this. Pale Male, Sr. appears to be homozygous dominant for the erythrism trait. He's got a gene for this trait on each of the pair of chromosomes with the trait.
(And red-tail chromosomes are an extremely interesting story itself, as they have, as I recall, a hundred or more chromosome pairs or fragments, far more than most vertebrates. And I believe this can vary from bird to bird, as the chromosome fragments don't always uniformly reconstruct for mitosis, cell division. In the non-mitotic state, the chromosomes are in a somewhat dissolved state as chromatin, not as physically condensed chromosomes that could be stained and seen microscopically. Someone with more genetic experience with red-tails will know more about this cellular curiosity.)
Back to the Punnett Square stuff. During meiosis, when Pale Male is making sperm (quite continuously in February and March, as Central Park hawk watchers have noted) each sperm cell will get only one of the two matched chromosomes. This keeps the chromosome number from doubling in each generation. Same happened for us, as we got about half our genes from our mothers and half from our fathers. Standard stuff for sexually reproducing species on the planet.
Therefore, Pale Male could only donate a dominant gene for breast color. For convenience (the Punnett Square stuff from way back in school will come back), we'll let a big E represent the gene for erythrism. The white-breasted gene is apparently recessive, which means for it to get expressed (to show up), both of the chromosomes have to have the recessive trait. In Punnett Square problems, we let the lower case letter of the dominant trait represent the recessive trait. So for our problem, little e will represent normal (but recessive) white-breastedness.
Pale Male's genotype is almost surely EE, homozygous dominant, with two copies of the trait. Each of his sperm cells are going to have a single E. As an adult, Lola is white-breasted. Let's presume she was white-breasted as an eyass. If so, her genotype is ee. Her chromosome pair with the breast color trait has an "e" on each one. In meiosis, when Lola makes an egg, she donates one of her e genes. When the egg is fertilized by Pale Male, the new egg will have a dominant E and a recessive e. The genotype will be Ee, said to be heterozygous. The eyass that grows from this egg must necessarily have a colored breast, as the E gene is dominant. If it's there, it gets expressed, no matter what the other gene is. In order for a red-tail to have a white breast, both of its breast color genes must be e.
Let's presume that Pale Male is homozygous dominant, with a genotype of EE. Let's likewise presume that Lola is homozygous recessive, ee. If so, all of their progeny must be Ee, heterozygous for the trait. Genetically, the kids will all be half-and-half, while Dad is "pure." But all the kids will have erythric breasts, indistinguishable from Dad's. What is seen is known as the phenotype. The phenotypes of Pale Male and his progeny are identical. Their genotypes, the actual genes, aren't.
To keep track of all of that, we make (finally) Punnett Squares. Let's do one of those problems, just the one I mentioned above. First, draw a 4-cell grid (Remember?). Above the top, let's put Pale Male's possible genes. Above the upper left cell write "E." Because he has nothing else, put the other "E" above the cell on the right.
Lola's got only a pair of little e's, so put an e to the left of each of the two cells on the left edge of the grid. Now, just drop the letters into the cells down and across, which represent the probabilities and possibilities of all of the offspring. In this Punnett Square problem, 100% of the offspring will have Ee genotypes, with erythritic breasts. Real simple.
But what happens if two of Pale Male's eyasses, each with an Ee genotype, mate (not at all improbable)? In this case, a big E and a little e go along the top and the side of the square. The offspring predicted by the upper left cell is EE. The lower left and upper right cells are both Ee. The lower right cell got an e from both parents, and will be the only hawk with a white breast from this pair.
But of course, our red-tails don't produce four eyasses each year. And even if they did, they wouldn't always produce three red-breasted and one white-breasted eyasses. It's all chance. All of the offspring could be white-breasted. All could have colored breasts. The Punnett Square allows us to easily parse the probabilities, not the number of offspring.
So far, no little e's have been observed in the phenotypes of Junior's offspring. The prevalence of erythrism in all the Central Park eyasses now strongly suggests that the birds are descendants from Pale Male, as I originally surmised.
Len Soucy's observations are definitive. There appears to be a narrow genetic base in the Manhattan red-tails. But it's not yet an inbreeding problem, as the several mothers are from external genetic lines. All of them have had white breasts. Genetically, it's been extremely helpful that Pale Male has had multiple mates. Romantically, it would have been nice for the original female to still be mated and producing Pale Male offspring. But inbreeding problems down the line might have presented themselves. Not so likely now.
Next March and April, we have the good chance to make out two Punnett Squares, one for the offspring at 927, and the other for new eyasses at Trump Parc. Pale Male can only sire more red-breasted birds. But Junior probably possesses a little e from his mother. On Friday's quiz, everyone reading will have to tell the various probabilities of Junior producing both white-breasted and red-breasted eyasses next spring. Show your Punnett Squares to substantiate your probabilities.
(It's been hard leaving the biology classroom. Nice to have such good students here.)
John A. Blakeman

PS from Marie

Somehow I'm having trouble understanding this. What doesn't hang together for me is this: We have seen 23 chicks emerge from eggs in the Fifth Avenue nest since the first successful brood in 1995. Every single one of them has had an orange-red breast. According to John Blakeman's explanation, this seems highly improbable! [Oh yes, now add the two chicks in the Trump Parc nest. That's 25 erythristic chicks.] So maybe it's not a matter of genetics. Here's an audacious idea: How about diet? When the Fifth Ave. and the Trump-Parc babies hatch they are pure white. The orange chests seem to develop a few weeks later. So maybe there's some pigment in CP rats or pigeons? Don't flamingos get their red-orange color entirely from something they eat? Another clue in this direction is Len Soucy's report that the young red-tails he keeps at the Raptor Trust, having started white-chested, turn orange-chested after a year or two. Doesn't that sound more like the effects of diet than genetics?

PPS. I have no idea when that reddish-orange chest coloration of the nestlings and fledglings changes to white. In the last photographs of the Trump-Parc chicks, taken in the first week of September, the breast coloring is still conspicuously reddish. And all the photos of fledglings of past years seem to show that orangy color. [I'll have to check this with some of the park's reliable hawk observers like Ann Shanahan.] But Pale Male Junior has a white breast. If indeed he is a descendent of Pale Male, when did his breast color change?

PPPS. In some of Lincoln's photos of Pale Male taken in previous years I've seen some reddish glints in his chest feathers. I always thought that was a matter of how the sun was hitting his feathers as the picture was taken. Now I'm wondering... But certainly in most photos of PM and Junior they look white-chested.

Black Swallowtail update

Black Swallowtail caterpillar attached to fence at Shakespeare Garden
October 3, 2005 -- photo by M. Winn

Black Swallowtail shortly after pupation - Oct. 6, 2005
Photo by Lloyd Spitalnik

Pupa on Oct 19 2005
Photo M.Winn

I first photographed it as a caterpillar on October 3 when it had just attached itself to a bamboo fence in the Shakespeare Garden. I posted a series of photos taken during the process of pupation on October 5. The next day I posted a picture of the pupa in its final form. Last Wednesday I photographed it again, as I will be doing periodically until the butterfly emerges next spring.

Though the two chrysalid pictures seem to be differently colored, that is certainly a function of the different times of day the photos were taken. The proof is the relative color in each photo of the pupa and the bamboo fencing-- almost the same. Perfect camouflage. Though I know exactly where the little butterfly-to-be is located and have visited it many times, I still have trouble finding it every time I come to the spot. Without a map or a guide I doubt you'd ever find it.

When I think back to the days the caterpillar spent in that location, first crawling back and forth looking for the perfect spot to spend the winter, and then the four days it spent attached by its "girdle" strings prior to its transformation into a pupa, [see first picture above] I shudder to think of how conspicuous it was -- bright green, yellow and black, just calling out "eat me eat me" to every passing songbird. Fortunately [for it and for us] it survived that perilous phase. In its present dull, woody-looking form, no self-respecting bird or bat would give it a second glance. Just a lump on a fence.