‘Ghost Birds’ and albinism

Naturalist, birder and blogger Marcia Bonta recently posted an excellent examination of the complexity of bird coloration (‘Ghost Bird’). As I have alluded to in many of my animal posts on this blog, coloration in birds and mammals can confuse attempts at accurate identification. Also,  guide books often lack information on the many color morphs of animals during their life cycles, seasons, and between sexes.

Adding to the confusion, the occurrence of white aberrations due to albinism and leucism*, which people often conflate into one term, ‘albino’, usually exacerbates identification. However, the two conditions are phenotypic (observable) traits arising from a variety of genotypic (of or related to genes and gene expression) origins. Nevertheless, gene mutations can result in both leucism and albinism.

Then there is the antithetic trait of a darker coloration than normal, called ‘melanism’, exemplified by the rare totally black cougar, leopard or jaguar. All of these are usually called ‘Black Panthers’. Many people assume that all black variants in these big cats are a single species, but they are not. Again, these observable traits have similar origins with changes in pigmentation, especially complete (or partial) lack of coloration. The commonality originates in changes of melanin production in the body, such as in albinism. Leucism, on the other hand, is more complex.

Albinism is associated with altered production of the pigment melanin, either complete absence or reduced amount. White animals can be the result of an complete absence of melanin production and are considered albinos. ‘Melanistic’ animals are the opposite, with an over-production of melanin. However, depending on the genetic cause, some animals can have a only reduced production of melanin, which may impart a much lighter overall color than the typical dark animal coloration; for example, light brown or beige instead of black.

Albinism is inherited alterations in the genes which result in albinism preventing the body from making the usual amounts of melanin. Thus, altered coloration depends on if an animal inherits either a single trait or set of traits that alter melanin production. A non-albino can carry a recessive mutation in a gene that affects melanin production. If that animal mates with another that also carries the same mutation, a portion of their offspring may be albinos. Very rare cases of albinism result in dominant heredity.

Melanin is the primary pigment that determines the color of a mammal`s (including human’s) skin, fur, and eyes. But albinism also occurs in fish, birds, reptiles, and amphibians. Often confused as a protein, melanin is a group of pigments produced in specialized cells, called melanocytes, in the body. Although the pigments are derivatives of the amino acid tyrosine (an important amino acid used to build proteins), they are actually fine granular polymers. Melanin is strongly associated with coloration of skin and fur in mammals, ranging from black to sandy and reddish-brown.

Animals manufacture their own melanin, which also contributes to coloration of bird skin and feathers. In birds, melanin is associated with ranges of blacks, browns, brownish-reds and pale yellow. However, some albino animals may also have some coloration from pigments that are not derived from melanin production. Melanin is not the only pigment affecting bird coloration.

Leucistic red-winged blackbird.

Two additional pigments influence coloration in birds and plants: carotenoids and porphyrines. Birds acquire carotenoids from eating plants that produce the pigment in specialized cells (such as chloroplasts). Most people are familiar with the orange pigment of carrots, which is conferred by the carotenoid, carotene. Carotenoids can interact with melanins in birds to produce feather colors like the olive-green in several tanagers. The pigments are also physiologically important in animals, such as in their association with Vitamin A. Thus, pigments can serve more functions than just coloration. Even melanin contributes strength to feathers!

Porphyrins, like melanin, are amino acid derivatives but bind to metals and have characteristic light absorption patterns. The best known pigment is heme, which uses iron as a central functional group to form a matrix called hemoglobin that reflects red light. Because of their highly complex aromatic matrix, these pigments have very intense absorption bands in the visible region and may be deeply colored. Hence, they usually impart a brilliant coloration to bird plumage.

An animal, especially birds, with a complete absence of melanin may sometimes show some coloration due to these other pigments in the body that are unaffected by albinism. If the genetic aberration results in only reduced melanin production, referred to as an ‘albinoid’, an animal my exhibit an extremely lighter shade of those colors associated with melanin. Regardless, most albinos have pink eyes. Alternatively, an animal may show an absence of all types of skin pigments, including melanin. Or only pigments that are not melanin!  In both of these latter cases, it is a leucistic animal. An example is the rare white tiger with normal colored eyes.

Leucism, in contrast to albinism, originates more from cell abnormalities, such as in cell differentiation or migration from the neural crest (pool of undifferentiated cells in early fetus) to skin, hair, or feathers during development. A leucistic animal may lack pigmentation in its entire surface if all pigment cells fail to develop. Alternatively, if only patches on its body lack cells capable of making pigmentation, then the animal will display patchy white and color. This patchy lack of color is often referred to as ‘piebald’ and can be passed on to its progeny. Regardless, leucism can reduce all types of pigment production, whereas albinism results in the reduction of only melanin even though the melanocyte is still present.

Another difference between albinism and leucism is in eye color. When production of melanin is lacking in the retina and iris, albinos typically have red eyes due to the underlying blood vessels showing through. In contrast, most leucistic animals have normally colored eyes. With partial albinism, in which a single patch or patches of skin that lack melanin, the animal may still exhibit some coloration because of the presence of other pigments unaffected by albinism (melanin).

These two forms of aberrant coloration can be very difficult to verify in birds and reptiles. With albinistic birds, ruddy and yellow hues or other colors may be present on the entire body or in patches (common among pigeons), due to the presence of other pigments unaffected by albinism. To throw in another contribution to coloration, the structure of feathers adds to the diversity of avian colors. All animal coloration results from the way pigments interact with light. Most of the green and blue colors in birds are created through structural effects of feathers and refracted light. But that’s another future post. 🙂

Reading Bonta’s blog post brought back many memories. Back in the mid-1980′s, I bought acreage in the foothills of the Coastal Range of western Oregon, where I established an sheep and horse ranch. My first spring there, the ranch was inundated by people with binoculars standing on the side of the road pointing at the forest of Doug Fir beyond the pastures. A bit alarmed, I strolled down the driveway to investigate.

I was informed that an ‘albino’ hawk was a regular visitor to this area for several years and known to nest in the forest beyond these pastures. Every spring, local birders drive out with binoculars to view the bird.

As a field and molecular biologist, I was intrigued and watched for the hawk to confirm these reports. Sure enough, it made a showing. It was easily recognizable as a hawk, and the one lone ruddy tail feather suggested it was of the red-tail species. Otherwise, it was pure white. It’s full-colored mate confirmed the identity. This pair hunted and raised their young on the ranch for several years, where I often enjoyed watching and hearing the adults teach the young to fly.

I appropriately named my ranch ‘White Hawk Ranch’, which was also apropos since I raised colored sheep and had an interest in color genetics in both sheep and horses. It was a naturalist’s wild and domestic field lab.

*  Luecism derives from the Greek leuko meaning ‘white.’  Like many terms and words derived from the old classical languages, pronunciation varies with time, country and regional language. Many of the older biologists and ornithologists, especially from Europe, tend to use the older pronunciation lū-kizm.  On the other hand, younger generations, both professional and non, tend to pronounce it lū-sizm. Either is acceptable.
As Billie Holliday sang, “Tomāto, tomahto…”  We don’t have to call the whole thing off!

Tanagers in Texas

Tanagers are a large family (240-300 species) of colorful tropical and semi-tropical birds inhabiting the American continents. Four species of the genus, Piranga, migrate and breed in North America and can be spotted in Texas. Those species are P. rubra, Summer Tanager, P. flava, Hepatic Tanager, P. olivacea, Scarlet Tanager, and P. ludoviciana, Western Tanager. However, individual birds can sometimes be difficult to identify which species they are assigned to.

The variable coloration of these perching songbirds often confuses accurate species and gender identification. Overall coloration of the female and immature North American tanagers varies within and between species, but generally they tend towards gray-green or greenish-yellow plumage.

Probably Western Tanager females and/or males. Views of the wings are helpful in accurate identification.

Western and Scarlet Tanager females both vary from grayish to olive-yellow hues, but the former is larger in overall size and bill. The stubbier Scarlet Tanager has a shorter tail, and, to confuse matters even more, a rare orange morph does occur. Female Summer Tanagers are the most variable, ranging from grayish to orange-red. Likewise, the Hepatic Tanager females and immature males both sport olive or orange yellow coloration, although both sexes have a darker bill than the other species.

Another complication identifying females and males is their molts. Feather molts replace worn feathers, alternate between courtship plumages, and possibly to improve hygiene. Molt timing and frequency are very important and each species has its own pattern. One common pattern consists of a partial body molt before the breeding season and a bird assumes courtship color, then a complete molt of all the feathers, including flight feathers, after breeding and before migration.

Feathers are usually molted in a gradual pattern so its ability to fly or to protect its body from the elements is not compromised. For example, the brilliant red and black Scarlet Tanager males molt to greenish-yellow during the winter months, looking much like females, which further confuses identification.

Because historic migration and habitat patterns are recently changing in many species of birds, we can now add another tanager to the list of those spotted in Texas: Flame-colored Tanager (P. bidentata). A traditional resident of northern Mexico and the Panama area, this species has been increasingly sited in west Texas and southeastern Arizona. Although closely similar to the Western Tanager, both males and females of this species may be the easiest to identify because of their streaked back (yellow and black of females or bright orange and black streaks of males).

Although accurate identification of these colorful Tanagers can be confusing and complicated, this shouldn’t detract from enjoying their presence. A detailed bird guide and binoculars might aid dedicated birdwatchers. Note differences of coloration of the wings, the back, and head. A quick view of beak coloration may help, too. Be aware that the underbody and underwing plumage is not helpful because several species have similar colors. Another warning is that taxonomists recently (~ 2002) moved the genus Piranga from the Tanager family to that of the Cardinals. Keep that in mind during any Internet searches and guidebook pursuits.

(photos courtesy of Rick Ethan; local Terlingua Ranch wildlife enthusiast)

Yellow-headed Blackbirds in ‘disguise’

Yellow-headed blackbirds on an ocotillo.

One morning last mid-May, I heard a cacophony of clacking, clicking and gawking. Practicing my tracker’s ‘stealth walking’, I got close enough to see a small group of birds pecking at the ground near the edge of a dropoff. I remember smiling while watching them; they seemed like little jesters at a jumping contest. Some birds would almost jump on their partner, while the aware victim rapidly jumped away only to jump into another’s space. What struck me was the variation in plumage; few birds looked like each other.

I slowly and carefully stalked away to retrieve my camera. Returning again, I was able to get within only fifty feet. I have found that the very process of bringing a camera up to my eye often scares birds away. (Photographing birds is a lesson in patience and slow movement.)

After uploading the photos to my laptop, it took quite some investigation to identify these birds. They are not well documented as typical of the Big Bend region, neither summer or winter habitat. However, they are noted to occasionally migrate through Texas between their summer and winter habitats.

These birds were finally identified as Yellow-headed blackbird (Xanthocephalus xanthocephalus). Occasional visitors to the southern Big Bend area, they are not always easy to identify. Although they are typical of most blackbirds – fairly large, with stout body, large head, and long, conical bill – this species has several color morphs. In other words, they all don’t have the same color pattern.

Most grown males have a striking yellow head and breast with a black band around the eyes, and white patch on the wing shoulders. And this is what you will see depicted in the guide books. However, the females and juveniles, both male and female – and even immature males! – don’t sport this colorful golden hood and cowl.

Females are often dusky brown with a buffy or faint yellow breast, and a belly streaked with white. Juveniles are dark brown with buffy edging on wings and back, heads often tawny with mixtures of faint yellow, black and white. Immature males often resemble females, but with narrow white bands on the tips of wing feathers.

Typical of most blackbirds, this species is usually found in large groups, even commingling with birds of other types. They may also forage individually, but seldom for too long.  Northbound Yellow-headed blackbirds pass through Texas from March through June, with the largest populations between early April and late May. Their breeding range is historically in the Great Plains area of the North America (N of TX and up into S Canada) and west to the Cascade and Sierra Nevada mountain sides. Their winter range is west of TX and south into Mexico. However, changes in bird migration and habitat are well documented, corresponding with climate change.

This group was photographed in the Solitario area mid-May of last year. They stayed around for several days before heading off to parts unknown.

Color morph representations of the Yellow-headed blackbird.

Blue Grosbeak

I am now contributing to the FaceBook page for the Terlingua Ranch Lodge. Weekly posts focus on wildlife: plants and birds,  in addition to posting photos of recent events around the Lodge area (music in the cafe, etc).

Blue grosbeak. Photo credit Rich Ethan.

Today’s post focused on the Blue Grosbeak, a member of the Cardinal family and the Passerina genus, which also includes buntings. Most birds of this genus are characterized by large or thick conical beaks used for breaking seed. Most of these are usually solitary, but are often found in small groups. On the other hand,  several of the true grosbeaks (evening and pine grosbeaks; Pheucticus genus) are often gregarious and sometimes raucous when clustering at bird feeders. Typical of most members of the Cardinalidae family, the males are brightly colored and the females are generally plain, marked with dull brown and some greenish plumage.

Male blue grosbeaks have similar coloration to indigo and blue buntings. Discerning differences are the bi-colored beak, usually dark upper and light gray lower, and is much more stout than beaks of the buntings. Additionally, the blue grosbeak has a black mask around the eyes and extends only to the base of the beak. The mask of the blue bunting, on the other hand, is minimal and usually extends behind the eyes, curving down to the shoulder of the wings. Also, the blue bunting also has shades of lighter and brighter blue on the forehead, the rump, and the bend of the wing. A deep blue plumage is more consistent on the blue grosbeak except for rust and black banding on the wings.

Both the indigo and blue buntings have predominantly blue wings and tails, interspersed with some black feathering. The wings and tail of the blue grosbeak, however, are predominantly black and the ends of the tail feathers are round with white stripling.

Range: Historically, the summer range of the blue grosbeak has been reported throughout mid-central and southern US and south into Mexico.  Although their winter range usually extends north only as far as south of the Rio Grande near the Gulf, they may be shifting or expanding their winter habitat northward in response to climate change and habitat pressures. The bird photographed was spotted this fall in the Chisos Mountain area of Big Bend.

Nests: The deep, cup-shaped nest of the blue grosbeak are typically found on a branch of a tree or bush 3-8 ft above ground, is made of leaves, plant stems, rootlets, grasses, strips of bark, and sometimes bits of snake skin. Nests are lined with smaller rootlets, grasses and occasionally hair. The inside diameter is 2.4 in and the depth is 2 in. Egg laying in Texas has been documented in late April and young hatchlings reported in early June. Unfortunately, these birds are a favorite target of cowbirds, which are a notorious brood parasite, meaning that they lays their eggs in nests of other species.

Interestingly, the blue grosbeak is one of those species that shares some traits with one genus and another. Their flight call and plumage resemble that of the buntings more than other grosbeaks. Yet their size, both over all and beak size and egg size, are more similar to that of other grosbeaks. Ornithologists concluded that this bird sufficiently resembled other members of the buntings more than the grosbeaks that they were removed from the grosbeak genus and placed in that of the buntings. Some ornithologists even now prefer referring to the blue grosbeak as a bunting instead of a grosbeak. Another case of family and genus shuffling. But all science is about reserving the right to ‘change its mind’ as new facts or classifications surface, especially scientists. 😉

Sharing your space with birds

Since recently selling my house and five acres of northcentral Texas prairie and moving into a 30′ travel trailer while I fulfill my academic position in Dallas, I find myself missing my prairie companions: the coyotes, fox, turkeys, rabbits, songbirds, and, especially, the nesting pair of Great Horned Owls. While spending two weeks in west-central New York visiting family and surrounded by birds that I had forgotten existed, I miss them even more.

A rustic and simple birdhouse sits on a wooden post in the corner of my sister’s deck. A wren family established housekeeping for the third year and we have been watching the male and female feed the hungry chirping chicks inside. Yesterday while we were gone, the chicks ‘flew the coop’, so to speak, and Mom wren has spent most of today cleaning house. She stands inside the next box, pops her head out and drops pieces of dried stems, pine needles and other debris to the deck floor. Periodically she will fly from the next box with a feather in her beak and to the top of a deck post. There, she releases the feather, which is caught by the wind and blown away. Then she sings her melodious song before flying back into the box.

One day last week I captured the adults feeding the chicks and put together a brief movie.

Motivated by a woman in the Austin, TX, area that built a nesting box for a pair of screech owls (see webcam images and photos of the owl family here), I intend to establish native plants that attract local birds and construct a few next boxes around El Punto. However, I am not assuming that all bird houses/nest boxes are created equal.

A few websites and guide books are available to learn about the birds that live and/or migrate through the Big Bend area of SW Texas. Or course, one must also be aware of their own microenvironment. While hundreds of bird species inhabit or visit the nearby national park, one cannot expect those same species to be seen even 25 miles away. Big Bend National Park has a biographical feature known as a ‘sky island’, which is a mountain range with a very different ecozone than that which covers the basin floor below. These raised lands offer habitats for birds, flora and animals that cannot survive on the desert floor. Thus we won’t be finding many of those same species amidst the dry arroyos and cacti that dominate most of the perimeter of the park’s sky island, the Chisos Mountains.

However, as the bird log submitted by Randy in the Big Bend section of this website demonstrates, many bird species do call the deserts of the Big Bend ‘home’, and several more species migrate through. Preserving and/or increasing natural and native habitat will increase opportunities for bird visitation around their dwellings. These birds have different habitat and nesting requirements than those inhabiting western New York and north central Texas. Hopefully, we can learn more about each other and I can help provide them with the nesting they will need.

That, I intend to find out.

Links to bird references for the Big Bend, Texas, region and northern Chihuahuan desert:

1. Birding Checklist for Trans-Pecos Texas region: Birds of El Paso County, Texas and Adjacent Areas
2. Birds of Big Bend National Park
3. Field Guide to Birds of the Big Bend
4. A highly recommended book for building bird nesting boxes and platforms, as well as shelters for other animals.