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Happy Anniversary Plate Tectonics!

5 Dec

Fifty years ago, the ideas of plate tectonics crashed into the earth science arena. First proposed in the early 1900’s by Alfred Wegener, the hypothesis that continents drifted around the planet like floating icebergs was naysayed. He could not explain how or why.

In 1967, while many of us were wearing flowers in our hair and inciting a revolution, Dan McKenzie and his colleague Bob Parker at Scripps Institute in California (and independently, Jason Morgan at Princeton Univsersity) put together pieces of the puzzle and described how plates move and continents drift. They started their own revolution.

Geology was changed, like a volcano erupting in the field. Not only does geological evidence confirm plate tectonics, but also biological. Fossils of some species of plants and animals are located within specific areas on continents where they adjoined each other. Those continents are now separated by thousands of miles of ocean.

Plate tectonics and continental drift have awed me since I was a child. I have no idea why, except that they are like a memory of deep time. And seeing examples and remnants of plate tectonics and continental drift is like looking at old family photos. I’m captivated.

In honor of the anniversary of plate tectonics theory, follow the link to a poem I wrote years ago. Ode to Plate Tectonics.  Meanwhile, enjoy your daily ride on your continental plate.


Sagebrush Galls: Medusa!

16 May

“How galling!! The audacity of this insect making a home in me!”

True; no matter how one organism looks at it, it’s annoying. The word ‘gall’ originates from Middle English (~ 900 A.D) and refers to bile, the bitter fluid from the gall bladder. The figurative word ‘galling’ refers to irritating, offensive, audacity and very annoying behavior.  But how did an abnormal plant growth acquire the same name, gall?

We may never know.

As a child roaming the woods and wild fields, I would often collect tree and shrub leaves and twigs that had protruding bumps in a variety of shapes.  I wondered what these odd shapes were, but it never occurred to me that they might be injurious to the plant, or even malicious at all. Nor did I know then how they were formed.

One day while wandering in the field I found a particularly large growth on the stem of a shrub. Pulling out my magic little ‘looking glass’ (pocket magnifier), I watched half a dozen little translucent bugs crawl out of the ball-shaped growth. In a short time, these bugs acquired color and their wings unfolded away from their bodies. I wondered if the abnormal-looking ball of green was a home for these bugs, and only much later did I learn they were called ‘galls’. And from then on, anytime a person uses the word ‘gall’ or ‘galling’, all I can think of are these appropriated plant cells that serve as a home for small insects.

Five decades later and I’m still fascinated by galls!

Here in the high desert of the Great Basin, galls are common on sagebrush, the most dominant plant. What surprises me is the morphological variety of these galls: the colors, shapes and sizes. So, like the child I was (and probably still am), I have been collecting samples to take back with me, as well as photographing them.

What are galls, anyway?

Galls are an abnormal plant growth induced by various parasitic organisms (1), usually insects. These latter galls will be the focus of a series of posts here as I find examples.

Galls serve as ‘incubators’ for developing insects where they gain nutrition and protection from environmental conditions and predators. Some galls are colorful and easily distinguished from the other plant material. Some are wooly, some round and colorful like tiny plums, some are lobed, and others have spiky protuberances.

Gall-inducing insects are usually species-specific and sometimes tissue-specific on the plants they parasitize. Galls can be found on leaves, stems, shoots, flowers and roots. Combined with gall morphology, these traits will often help to identify which insect is associated with them. However, identifying the insects inside will be the confirmation.

These insects manipulate and exploit the chemistry and physiology of plant tissue to their own benefit and development. Accordingly, galls act as physiological sinks for mobilized plant resources, mostly as nutrition for larvae. Fungi sometimes grow on the interior of the gall surface on which the larvae feed.

Like little houses, galls physically serve as protection from the sun, wind, rain and snow. In fact, because the gall-forming insects control gall formation so well, galls are commonly referred to as their extended phenotype. However, several predatory insects have also adapted to this system by inserting their own larvae inside galls. Then a battle for who eats whom ensues until maturation of one or both species. It’s not uncommon to have more than one species of insect emerge from a gall, but only one of those species induces galls.

Protection is one explanation for the high levels of compounds, such as phenolics and tanins, found in many galls. This is considered a defensive gall trait, protecting the gall against natural enemies outside. Thus, in addition to serving as a nutrition sink and physical protection, some galls have a natural chemical defense.

Sagebrush gall midges

Like any plant, it’s an insect-eat-leaf world out there for sagebrush. Of the 237 species of insects that are associates of sagebrush, 42 are gall-forming insects. Of those, the most predominant are Cecidomiidae, or gall midges. They are a small family of tiny flies that are associated with gall induction.

The most abundant gall midges found on sagebrush are of the Rhopalomyia genus. Although there are 32 species, not all may be present in the same location and area. A recent study suggests that land use or local abiotic conditions may greatly influence the diversity of gall midges.

The adult midges lay eggs in the sagebrush stem tissue. The eggs hatch and the larva secrete saliva into the plant. Compounds in the saliva alter the growth of the injured plant cells and the tissue produces a swelling, or gall, around the young insects. However, the size, shape and color of the developing gall are typically specific to the gall midge species. On the other hand, one species unusually induces a wide range of gall morphologies.

Medusa Galls

During a recent camping trip on Steens Mountain in SE Oregon (and bordering the Refuge), I found many specimens of Medusa galls (Rhopalomyia medusa) on Big Sagebrush (Artemesia tridentate). As seen in the photograph, these galls are composed of numerous leaf-like structures. Looking at the long miniature leafy structures, it’s easy to see how this gall was called “Medusa”.

Medusa Gall on Big sagebrush

The galls develop in October and rest during the winter. They reach full size in the following spring and adult midge flies emerge in April or May. When I was there, May 9-11, the galls were intact with no sign of emergent flies. Considering the elevation (7,300 feet) where I was hiking, patches of snow were common and the climate was barely spring-like.

Authors of a study (2) sampled arthropod diversity on sagebrush in two ecosystems, one surrounded by dryland agriculture and the other area protected from agriculture and significant human use. Their data suggests that diversity of gall midges is highly variable with the dynamics of arthropod-sagebrush interactions and the sagebrush ecosystem. Interestingly, R. medusa was one of a few species that served as an indicator species in low human impact sagebrush habitats. A good description of where I found the many specimens on Steens Mnt.

So, do these galls negatively affect the sagebrush? We will examine that question in a later post!

1. Some bacteria species can also cause galls. This was my first introduction to galls in undergraduate university. Crown gall (Rhizobium radiobacter, formerly known as Agrobacterium tumefaciens) is the textbook and lab example used in plant pathology and lab classes. It is also a common tool to teach Koch’s Postulates. Soil bacterium inserts a small segment of DNA (T-DNA) from a plasmid and into the plant cell. This DNA encodes for genes that produce a plant hormone, auxin (indole-3-acetic acid), via a special pathway that is not used in most plants. Thus the plant has no molecular means of regulating the production of the exocrine hormone. The T-DNA also signals extra production of a group of plant hormones called cytokines, which are involved in cell division. These hormones are responsible for the tumor-like growth of plant tissue and form the galls.

2. Sanford, M.P., Huntly, N.J. 2010. Seasonal patterns of arthropod diversity and abundance on Big sagebrush, Artemisia tridentata.  Western North American Naturalist, 70(1): 67-76.

It depends!!

19 Mar

funny-owl-i-have-no-idea-whats-going-onShould burns take place in spring
Or wait for autumn rain?
Would baiting help or hinder?
Can owl chicks live through flame?

‘I dunno,’ we had to answer.
‘Not sure, can’t really say.
Needs further replication
Might vary day-to-day.’

PhDs require devotion,
Long days with no weekends
But the ultimate conclusion seems
‘Umm, well, it depends.’

– excerpt from post, ‘My Grand Conclusion‘, on zoologist Bron’s blog, Working on the Wild Side


The two of us answered in unision….. “It depends.” And looked at each other with a knowing smile.

A retired couple asked for information on where to go to see this bird and that bird. Husband asked for specific details: what species, what location, what time. He was dissatisfied with my answers, including “They were seen here yesterday morning, and there yesterday afternoon, and at this location this morning, but they may be anywhere. They don’t send us memos on when or where they go.”

When asking for exact details on how to get to ‘Point A’ from ‘Point B’ (a distance of 125 miles), my explanation of various options of traveling from Point A to Point B resulted in visible upset. His wife gently reminded him that they aren’t in a hurry and he might enjoy experiencing different things along the way. Her comment was met with a hand wave, pointing at a map, and listing what he expected to see, do, encounter, etc. He wanted no surprises.

“If something changes, if we stray from the map, it will be an adventure!”, said Wife.

“No! No surprises, and I don’t like adventures. Adventures mean poor planning,” Husband responded. “How long will it take to get to ‘Point B’?”

Wife and I replied simultaneously, “It depends!”

I looked at them both and then asked Husband, “Are you a mathematician?”  Eyebrows went up and he said, “Why, yes! How did you know?”.

“A strong aversion of risk and uncertainty,” I responded. Wife  returned my smile.

“Oh my God, are you a biologist, too?!” Husband asked with raised eyebrows and looking like he was stuck in between two conspirators.  By that time, all three of us were laughing.

Third Law: It Depends!

My First Law, apologetically borrowed from The First Law of Thermodynamics (aka ‘You can’t win’), states that where there’s a positive, there is a negative. And this is related to My Second Law: ‘Everything is relative’. ‘Positive’ and ‘negative’ are relative to the perspective of that which observes or experiences the action/reaction, which depends on time, place and being. (Note that the Second Law of Thermodynamics is ‘You can’t break even’. See blog post linked above.)

I think you can see where I’m going.

My Third Law is ‘It Depends’. If anything I have learned in biology and ecology remains constant, it is ‘It depends.’ For the person who demands or insists on a life or reality of ‘Yes’ or ‘No’, you will either be disappointed or live in perpetual denial. For life is not simply black and white. A vast area of gray reside in between.
Further reading:
The typical ecological answer – it depends“, blog post by oikosasa. Website: Oikos: Synthesizing Ecology.
“Which species is best for their host marsh cordgrass? Fiddler crab or mussel? The answer is – it depends”



A Bald eagle adapts to a handicap

16 Jan

A handicapped Bald eagle on the Bosque del Apache NWR has been reported by a few individuals the last three days. A visiting photographer*  shared with me his magnificent photographs and observations capturing how this bird has adapted to daily life. How the injury occurred and when is unknown to us. But the animal appears to have adapted quite well to flying, landing, perching and even obtaining its own food.

Our one-legged Bald eagle. Photo courtesy of Mike Endres.

How does this handicap affect an eagle’s ability to perform its life functions? As this individual demonstrates, missing half a leg and one taloned foot probably does not significantly impair its ability to fly, perch and eat. However, depending on its sex, could it affect its ability to reproduce? That is a good question, especially for a female. Although no obvious impairments might directly affect courtship and nesting, we won’t know conclusively unless the bird is observed during breeding, nesting and fledgling time.

All eagles are sexually monomorphic, which means both sexes look alike. Thus determining the gender of an individual Bald eagle is difficult. Although the female may sometimes be slightly larger than the male, this difference is often subtle and only determined if a pair are together, such as at a nest. The only other differentiating characteristics, measurements of the bill depth and length of the rear talon, can only be discerned with the birds ‘in hand’.

How can we know if the bird is a male or female? We won’t unless it is seen with its mate, if it is paired, to compare size. The only other recourse is using molecular biology. For this, biologists rely on blood samples, which is an invasive and stressful experience for animals, or collecting feathers, which is the preferred non-invasive approach.

Feathers are processed and analyzed by techniques that are sometimes referred to as ‘molecular sexing’. DNA is extracted from feather segments using a common laboratory kit. Small aliquots are then prepared and run through a polymerase chain reaction (PCR) with molecular primers that ‘bind’ to a specific portion of a gene that is associated with either the male or the female. The ‘bound’ segment(s) of DNA is then amplified many times. Aliquots of the amplified PCR products are then digested into smaller segments and run on an electrophoretic gel. The resultant banding patterns, which indicate the sizes of  all the products, are then matched with what is expected with the male or the female gene segment.

The entire process may take from 3-5 hours in a well-equipped lab. With many sexually monomorphic birds, this is often the only way to determine their gender, but it is non-invasive with little stress (if any) for the birds. When we banded American pelican juveniles (pre-fledge) last summer, the final step (after attaching two leg bands and weighing) was plucking a feather and putting it in a plastic bag with a corresponding code. The sex of each of the seventy-five birds was molecularly determined back in the lab at a later time.

What might be the prognosis for a normal life for this bird? Perhaps we may be bold enough to predict it will survive and live normally. Bald eagles tend to have nearly equal contribution to mated life. During courtship, they fly and lock talons together. Paired bald eagles share duties in nest building, incubating eggs, and providing food for the hatchlings. Consequently, the bird’s life as a mated pair may not be jeopardized. In fact, compared with other raptor species, Bald eagles share nesting duties between the sexes more than many other birds of prey.

However, as the number of hatchlings increase, the female’s role of providing food increases because the male tends to range further for food. Thus, if this bird is a female and her ability to catch and provide food for herself and a large brood is compromised, the probability of higher chick mortality may increase.

Another factor is defending the nest and caught food. The loss of one taloned foot might be decisive in a battle with another bird, especially if it is a large challenger such as a Great Horned owl. But as we have seen demonstrated by this bird here at the Refuge, it seems to have adapted well thus far.

Let’s hope his or her future is bright and fruitful.

The eagle has landed.  Photo courtesy of Mike Endres.

* I gratefully acknowledge and thank Mike Endres of Little Wing Photography  for sharing his photographs and observations of this eagle on the Refuge. I hope readers will visit his website (follow link above), and view his other excellent photographs. Thank you again, Mike. I enjoyed your visit and our chat.

What color are we today?

3 Jan

Male & female Mallard ducks in winter plumage

Since immersing myself in the observation and science of birds, I’ve learned that they might outdo humans in levels of complexity. I must admit, however, that birds are a tad easier to understand simply because they lack the capability to think in abstracts. Unless you watch Loony Tunes’ Wiley and Roadrunner cartoons.

Regardless, one of the many aspects about birds that incites my curiosity is the vast and complex diversity of coloration. This is also a source of understandable but frustrating confusion for many people when attempting to identify birds. Most guidebooks may describe and illustrate only one or two of the color variations that a bird species might show. On the other hand, many bird species may exhibit variations of colored plumage throughout the year depending on the season, their age, and their sex. This often befuddles attempts to identify a bird people see, especially if the bird in question might be a vagrant to their local area, in between-seasonal plumage, or an intermediate between two subspecies.

Understanding the basis for individual variations in a bird species can enhance observers’ identification skills. Consequently, I will address some of the topics that directly and indirectly contribute to bird plumage variations in a series of posts. Additionally, because of my interests in evolutionary biology and genetics, side topics touching on some of the fun things (in my opinion) will also appear. I do this simply because of the ‘why’ and ‘how’ questions that often arise in conversation with other people, which indicate to me that even non-scientists are curious.

Birds of the same feather don’t always flock together

The most direct difference between males and females (sexual dimorphism) is sexual organs. However, examples of secondary differences, those most obvious to our eyes, include body size, behavior, ornamentation and coloration.

For many animals, it’s all about appearances. One of the basic concepts that all of us are aware of, whether we are cognizant of it or not, is what we see. Humans take appearances for granted. Why? Simply because appearances communicate information that we might not be cognizant of when we receive and process it in our brains. That applies to nearly all animals that have and rely on sight.

But humans also communicate in a myriad of other ways: sound, touch, and smell. Although most other animals also possess these senses, humans rely more on one: language.

Sure, birds and other animals might have their own vocal communications that could be described as rudimentary language. Bird songs and other vocalizations communicate basic intent and even distress, etc. Conversely, human kind has a developed a complex network of language rich with abstract meaning, all which we can hear and see (read). This coincides with our species’ capability of abstract thinking and ability to reason. I doubt that a duck could read and recite the Old English Beowulf and understand it.

Not to be outdone, many animals have evolved complex ways to communicate with their own kind. One example is how they look: different colors or different sizes. Although a few explanations can be posited for differences between the sexes, the most prevalent is mate selection. And the most common expression in birds is differences in coloration between the sexes, called sexual dichromatism. With most birds, but not all, the male is usually the most colorful because they compete for attraction to the females. Thus, sexual selection drives the evolution of chromatic variability.

But how does this work in different species? This is where it gets complicated. Birds can’t write love poems or dress up in fancy clothes, but they can look very appealing with their feathers!

Birds can be sexually monochromatic (same color), where the males and females within a species are the same color year round.

Male & female sandhill cranes.

Familiar examples are most eagles, Canada geese, and sandhill cranes. Most of our bird species in North America are sexually dichromatic; the sexes are divided into two basic appearances. In the latter case, the male is usually more colorful. In some species, especially the shorebirds, the female may be the contrasting sex, called reverse sexual dichromatism (e.g. Wilson’s phalarope).

Some species are extreme in colored plumage. The male may have several very bright and contrasting colors, whereas the female may be drab. These two differences are what most guidebooks depict. Sometimes all the females in an entire genus may look very similar making it difficult to identify which species they belong to.

Male & female Northern flicker


But not all mono- and dichromatic species are complete or dramatically colored. Sometimes differences in coloration may be very subtle to our eyes. The male and female red-shafted Northern Flicker look nearly alike except for the absence of the red malar on the female’s face. Similarly, with a monochromatic species, such as the Western bluebirds, both male and female may have the same colors but different saturation. The female’s colors are less saturated than the male’s.


Size does matter sometimes.

Size differences between males and females are more present in monochromatic bird species. In larger birds, such as many eagles, hawks and owls, the female is often larger than the male. Size differences can also be subtle, and unless the two sexes are near each other, one may not easily identify an individual as male or female. In other species, such as the sandhill crane and American pelican, there is hardly any difference in size or color and sexing the birds is difficult. But those birds have evolved other ways to communicate between the sexes!

Secondary sexual traits of birds – coloration and size – are varied and most have evolved to communicate attraction and selection. Some traits, however, are driven more by reproduction demands (physiology) than sexual mate selection. Regardless, birds are much more complex than us simply because of need. Perhaps if we never developed a language to communicate, we may have evolved with more extreme sexual differences. Instead, we create our own 😉

Of course, all this is relatively basic and does not tell the entire story about bird coloration. Anyone familiar with ducks knows that most males have more than one coloration plumage during the year. Observers seeing a flock of red-winged blackbirds in the winter might be confused at all the different color combinations exhibited by the birds, thinking more than one species were mixed in together. And then there is the issue of interbreeding subspecies (and even species hybrids!) resulting in a mix of colors imparted by both parents. It can all get very complicated!

My next post will be about the changing of the guard: molting.

Meanwhile, do you have any additional examples of bird coloration?

Birds are chameleons ?

6 Dec

Of all animals, birds can be especially baffling (other than Homo sapiens). Although each bird species has typical behavior, they sometimes will ‘change their minds’ on how they look. And even where they will be. Nor do they send out memos informing avid avian paparazzi. You know, the ones with multiple field books in their hands, spotting scopes slung over their shoulders, and the gigantic camera lenses that almost require their own wheelchair. I don’t fault passionate birders at all. I’m one, too (albeit not an expert). The bird portraits that adorn photographers’ websites are all very nice, too.

Perhaps my years in field biology explain my preferences for watching and learning about animal behavior (including birds) rather than  obsessing on finding the perfect bird in its guidebook color and within  the human-made boundaries of habitat. Why else would one of my favorite personal photos be one of a Canada goose blowing bubbles in the water?

“Well, the ______ (fill in the blank with bird name) were NOT at the _____  (fill in a specific location on the Refuge) on/at _____ (fill in with time/date reference). We didn’t see them! Are they not here? Where are they?”

We volunteers are often asked about where the birds are when they are not in their expected place at the expected time. We often respond with “They didn’t send us a memo on where they were going!” or “Birds have wings and they fly wherever they want, whenever they want.” I’ll often resort to “You know when they say about people, ‘Follow the money’? With birds, it’s ‘Follow the food.”

Well, it’s true!

Pair of mated sandhill cranes fly over the wildlife refuge.

Birds are fortunate that they can migrate over thousands of miles from one territory to another. Plants and most other animals do not. Most birds nest and brood in a specific habitat, one that provides the food they need to lay eggs and fledge their young. The right habitat must also provide cover and protection from predators. As the young birds grow, they are taught to fly and hunt for food. They also learn how to socialize outside of their family units. As the seasons change, they are encouraged to exercise and train for long daily flights, just like an athlete trains for a marathon. By the time they are ready to migrate elsewhere, they are almost adults.

Migration still perplexes biologists in many respects. What are the signals informing them when to leave one area and go to another? Do they always return to the same place they were born (called natal philopatry)? Do they always migrate to the same wintering location? What determines their migratory route? Do they ever veer away from their traditional route? We’re still investigating these questions. And often times, the answers raise more questions.

Some bird species demonstrate very strong natal philopatry. Sandhill cranes are one of these species. I have known some humans who have demonstrated this, too. 😉 Other bird species are not as tied to their birth place and may choose other nesting locations far from their original place. Likewise, not all birds exactly follow a map with planned stops on their migrations. Only humans do that.

Some of the factors that influence their seasonal locations (nesting and overwintering) are those that also influence humans. Weather, temperature, food availability, water sources, cover for protection, and even topography. High mountain ranges are a barrier to many migrating birds. Although larger birds can often migrate at high altitudes and fly over occasional obstructions, bad weather is often associated with long ranges of high mountains. Birds have learned through their evolutionary history what to avoid to conserve energy. They have also learned from their parents, and those before them, where food and water sources are during their long migrations. Thus, most of the continental flyways can be traced like a hopscotch board from one habitat to another where food and water are readily available for large flocks of migrating bird species.

They follow the food and water!

Of course, there are exceptions to everything. Life is not black and white, but mostly a large expanse of gray area in between.  Many scientists have documented that some birds are changing their traditional migratory routes, nesting grounds, and/or their wintering locations. Two major factors impacting these are loss of habitat and climate change.

Here we go back to the same source: food and water. As temperatures change, plants are becoming rare in one location, but might be increasing in population in another location. For example, some trees and other plants that grew near the base of mountains are now becoming less available or even rare. However, some of these same species are thriving higher up on mountainsides, where they were at one time rarely seen.

Likewise, many birds that nested in some of those plants, or were sustained by the plant seeds or other plant parts, are following the plants further up the mountain. The same applies on larger scales of land: some birds are being seen and documented in areas they were never, or rarely, seen before because their water and food sources have changed.

Additionally, some of their historic and preferred habitats have disappeared due to urban expansion. While some birds can adapt to mutually living with humans in their metropolitan areas, others cannot. With urbanization comes destruction of wildlife habitat. Their food source may no longer be adequate, or there is less available for them to nest and raise their young. Even loss of natural cover from predators may severely reduce bird populations.

Their only memo to us humans is “We’ve gone to find food and water!”.

In addition to the ability to migrate between far distance places, birds change their color throughout the year. All the time. Now, that is what has me stumped in accurate identification many times. But I like a challenge! And as one expert bird guide and author assures us, it’s alright to say, “I don’t know!!!”

Next post, we will look at how, and why, birds change color throughout the year. And why some bird species have a wider variation in colors than other species.

Until then, what are these two birds? 😉

Mystery Bird 2

Mystery Bird 1

Raptor-Wannabes, Kestrel Chic Day, and Walkabout

29 Nov

“I think I see a hawk in the tree at 2 0’clock!”
“No; that’s a Raptor-Wannabe!”

Four of us piled into the Refuge van for the weekly Raptor Survey. Jac, one of the Nature Store staff, joined us for the first time. Between four pairs of eyes and varying levels of experience in locating and ID’ing our intended targets, we all learned something new or refreshed memories. The foursome also made for entertaining jokes, especially when the van wouldn’t start while out on the Refuge loop.

Informally lumped into the popular category, ‘raptors’, not all birds of prey are technically raptors. Eagles, vultures, hawks, and falcons share similar structures and functions. They all have powerful feet (raptorial) with sharped curved talons for catching and holding their prey. They also have strong hooked beaks for tearing their catch into pieces. Other ‘birds of prey’ that are not considered raptors are owls and osprey. Although they also have powerful feet and toes, they are arranged differently; hence they are classified differently. Our Raptor Surveys do not include the two latter species (the osprey is very rare here and owls are typically not active during daylight).

Raptors are commonly subclassified into informal taxonomical groups: the New World vultures, eagles, hawks, and falcons. Most all falcons are of the same genus (Falco sp.) , whereas most of the hawks in North America are of two genus: Accipiter and Buteo sp.

Identifying birds in the field is very similar to ID’ing plants: start with the obvious and the basics. Then dive into the details. The first field cues are size, flight pattern, and shape. With plants, it would be size, shape and growth habit (plants can’t fly ;).

Size: Birds of prey are generally larger than songbirds, although there are exceptions. The American Kestrel, a member of the falcon family, is the smallest with 10 1/2″ length and a 23″ wingspan. Not much bigger than a meadowlark. But like all falcons, a kestrel’s flight style and shape are similar to other birds of prey because of their food source. Yet, because of their body size, they fly differently compared to larger hawks and eagles.

At the other end of the spectrum, eagles are relatively easier to ID because of their large size and there are so few species. Hawks are the biggest challenge. Regardless, judging size in the field can be difficult and unreliable, especially at a distance. Flight styles and shape are field traits to consider next.

Flight: Typically, the smaller raptors fly closer to the ground. Marsh hawks (also known as Northern Harriers) tend to swoop close and parallel the ground, especially over shallow riparian areas, with wings upraised. They hunt for birds, frogs, rodents, and reptiles. Because of the small size and V-shaped wings, they are truly acrobats, turning on a mushroom.

Flight in birds is a function of their size and wing structure. The smaller raptors are quick and flap their wings more in flight than the larger birds. Eagles and the large hawks are more gliders than wing-flappers. Because of their large body size and weight, flapping their wings is very energetically expensive. Their wing beats are typically more deliberate and slow. They also use prevailing wind currents and thermals to take flight and glide. You will often see eagles and large hawks circling on thermal winds.

Shape: The overall shape and proportion of a perched bird or one in flight may reveal much information. Our favorite cue for a perched red-tailed hawk is its football shape. Kestrels are relatively easy to spot. Despite their diminutive size, the shape of the wings, squat head, and curved beak often reveal their identity.

Raptors in flight are a perfect opportunity to observe their tail length, shape and color, as well as their wing shape. Head size and neck length of perched raptors are another field trait that can differentiate them.

Occasionally a non-raptor plays the Trickster and fools us for a few moments. Several of the larger falcons and mid-sized hawks are nearly the same size and shape as the Common Raven. One of us might spot a dark form perching in a tree in the distance and call attention to it. Up go the binoculars and we all realize that dark perching bird is none other than a black raven: a Raptor-Wannabe! Such is what we call the ravens when doing our raptor surveys. (Ravens are not as easily confused as a raptor when in flight; their proportions and flight style are vastly different)

Chic Kestrels

Our raptor counts can significantly vary each week, and from day to day. Our last survey revealed six Northern Harriers, which are common on the Refuge, and five kestrels. Today we spotted only three harriers, but eight kestrels! Only one of the colorful males was spotted, but with a brown mouse in its talons. The other seven were females, which typically hunt solo in the open fields. We were presented with three females hunting together in one field today!! It was like a finely choreographed ballet.

We reported to the others that this morning must have been a Kestrel Chic Day.

Our final count for just 1/2 of the sampling area this morning was as follows:

  1. Red-tailed hawks: 14 non-sexed adults (1 was a dark morph, 1 a rufus-morph) + 3 juveniles = 17 total
  2. American kestrel: 7 females, 1 male = 8 total adults
  3. Northern harrier: 3 non-sexed = 3 total adults
  4. Bald eagles: 1 non-sexed adult, 2 juveniles = 3 total
  5. Cooper’s hawk: 1 juvenile
  6. Merlin: 1 non-sexed adult
  7. Ferruginous hawk: 1 juvenile
  8. Sharp-shined hawk: 1 non-sexed adult

Marsh with ducks and snow geese at Bosque del Apache NWR


Because it was a warm day, and energized by the excitement of today’s raptor survey, I went for a walkabout on the Lagoon Trail. The wide and open trail wanders between two riparian canals on the side of the Refuge Auto Tour route, and across from the expansive marsh where ducks dabble and dive.

The two-mile plus walk was quiet and lovely, with tall grasses on one side and mowed native grasses on the other. I heard two hawks flying over the Chihuahuan desert brush land on one side. And heard the occasional quacks of mallards on the other side. Two scattered V-lines of snow geese flew overheard and I could hear the whoosh of their wings with their constant high-pitched honks.

Glancing down frequently in the gravel under my feet, mammal tracks showed big heavy mule deer, racoons in the dried mud, and one other string of human boots. A large deposit of fresh coyote scat revealed a partially digested diet of juniper berries, and even a small juniper sprig. In one line of big feline scat, I found a small white femur and other tiny tidbits of white broken bone encased in short light gray fur. Another tiny pile of scat further on suggested a young bobcat. Also discovered were two pieces of dried hide with long orange and beige fur! My guess was coyote or possibly red fox. Regardless which species, it was definitely from a wild canid.

Watching the raptors, spotting the tracks and scat, they all told stories of some of the wildlife that call this Refuge ‘Home’. I am perfectly happy sharing their Home with them. I couldn’t ask for anything more.

Color, color on the feathers… Who’s the fairest of them all?

28 Nov

“Look at that beautiful whooping crane! What’s with the gray feathers on it?”

A partly white Sandhill crane  is an overwintering resident here on the Refuge this year. Louie*, as affectionately called by the Refuge volunteers, has caused a great amount of confusion amongst visitors. “Is that a whooping crane?” “Is this an albino bird?” Luckily for Louie, it is totally unaware of its celebratory status and lives a normal life with its mate.

The confusion is understandable. Coloration in bird feathers and skin may result from one of several pigments or their combinations. Thus, a mutation in their production can result in aberrations of color.  Correctly classifying and identifying the color mutations requires knowing what changes cause differences from the original pigmentation, then understanding which pigments produce the typical colors of that bird.

The most common pigment in all animals is melanin, of which there are two types: eumelanin and phaeomelanin. The former imparts black, gray and dark brown feathers. Brick-red and light brown colors are conferred by phaeomelanin. All melanin pigments are granules synthesized in special cells called melanocytes. These granules are deposited in feathers, skin, scales of the feet, and the covering of the bill. A difference in the melanistic colors depends on the amount of pigment deposition as well as the size of the granules. Additionally, combinations of melanin and other pigments, such as those produced from carotenoids, may influence shades of colors.

Both forms of melanin are synthesized from the amino acid, tyrosine, by the enzyme tyrosinase. A bird with a genetic mutation that influences the amount of tyrosine or production of the enzyme, will affect melanin synthesis. Such a bird may exhibit a complete absence of coloration associated with melanin (complete, or 100% albino) or a significant reduction in melanin pigments (an albinoid). Luecism, an incomplete loss of coloration, is more complicated.

In addition to melanin, another important pigment involved in bird coloration is produced from carotenoids. These compounds are usually derived from foods that birds eat, which are then transformed into color pigments by enzymes and deposited in feathers.  Associated colors are pale yellows to scarlet reds. Although the molecular genetics associated with carotenoid coloration are not well known, variations of carotenoid bird coloration are apparently linked with sensitivity to environmental conditions, such as food availability. Additionally, not all red-based coloration is a result of carotenoid pigments. Depending on the bird species, it can be linked with one or more of the melanins, carotenoids, or a combination of both!

Although discrepancies are prevalent, most of the scientific literature defines bird albinism as “a total lack of both melanins in feathers, eyes and skin as a result of an inherited absence of tyrosinase” (van Grouw). The abnormality is caused by mutations in the gene(s) responsible for synthesis of the pigment melanin throughout the animal’s entire body. Carotenoid pigmentation is usually unaffected. Therefore, an albino bird of a species that typically produces colors from carotenoids may be mostly white but still exhibit yellow or red feathers.

On the other hand, leucism (or leukism) is defined as a partial or total lack of the melanins, eumelanin and/or phaeomelanin, in the feathers as a result of a disorder in the deposition of these pigments in the feathers. Both disorders, albinism and leucism, are inherited. However, the enzyme tyrosinase is normally present in leucism, but transformation of color into feathers is disrupted. For instance, all cells or patchy groups of cells that produce or transfer pigments may fail to develop properly. Leucism is the most common color aberration in birds, but frequently confused with albinism.

Degrees of leucism** can range from totally white individuals (100%) to only a few white feathers (less than 25%). In some leucistic forms, skin and scaly parts may also lack color or reduced normal coloration. Regardless, leucistic birds have colored eyes, whereas albino birds exhibit pink eyes.

Photo courtesy by volunteer & photographer John Olson at Bosque del Apache NWR. 11/2014

Photo courtesy of volunteer & photographer John Olson at Bosque del Apache NWR. 11/2014

Unlike an albino, our sandhill crane Louie has some patchy normal gray colored feathers amongst the mostly white body. It also has the typical red cap on its forehead, normal orange eye color and a slightly lighter shade of dark-colored legs. The presence of the red skin cap, patches of gray feathers, orange color in the eyes, and color on the legs indicates that the condition in this bird is related to abnormal production of melanin in specific groups of cells on its body. It is a leucistic bird.

Keep in mind that albinism is associated only with the production of a single pigment, melanin. If Louie bird was an albino, it would likely have all white feathers, pink eyes, and pinkish legs. In other words, it would be almost all white with some pinkish flesh and eyes. “What about the red cap?” you may ask. Well, it depends on what pigments impart the red skin patch on its forehead. Melanin? Carotenoids? Or is it a combination? No one knows!

As for mistaking Louie for a whooping crane, the patches of gray feathers, shorter height, and the red crown on top of its head distinguishes it from the tall white-bodied whooping crane. Whooping cranes have a red malar on the underside of their chin in addition to a red crown on top of their head. Louie does not.

Conversely, hunters should not mistakenly assume that a whooping crane is an albino sandhill crane. Complete albinism in cranes is rare, and the probabilities of finding an albino sandhill crane is extremely low. Although hunting sandhill cranes is legal in several states, shooting a whooping crane is a federal offense everywhere; they are a protected species under the Migratory Bird Treaty Act. One hunter in Wisconsin discovered the hard way that not knowing how to tell the difference between sandhill and whooping cranes, especially  suspected albino or leucistic crane, could be very costly.

Addedum: The motivation for writing this post was the prevalent confusion and misinformation about albinism and leucism. This is not unreasonable. It is a complex biological topic, where even definitions in the literature disagree. However, the presence of a leucistic celebrated bird here at the Refuge is fostering mistaken identities of many bird species here and elsewhere. For instance, two visitors asked me about the ‘leucistic’ snow geese. After described and pointed out in person, some people mistake the dark-morph snow goose, commonly referred to as a ‘blue goose’, as a ‘leucistic’ snow goose.

On the other hand, a ‘leucistic’ Canada goose was also spotted on the Refuge during Festival week. Two independent photographs do suggest that the individual bird is a ‘leucistic’ Canada goose: the body feathers of the bird were all white, but the neck and head were completely typical Canada goose coloration and shape. Compared to the normal Canada geese surrounding it, this goose was the same size, hence much larger than a snow goose. Phenotyptically, and as seen in the photographs, these observations strongly suggest a leucistic individual. However, hybridization with another species or subspecies cannot be discounted without closer examination of the individual bird.

Interspecies hybridization is more common in birds than in mammals, in which sterility is more often the result when it does occur. So always keep that in mind when seeing the odd-ball bird that does not fit the classic descriptions! In fact, the red-tailed hawk as a species not only has several color morphs, but individuals have been documented as hybrids between a Swainson’s hawk, and a Sharp-shinned hawk.

Animal hybridization is of special interest to me as a biologist; it often challenges even biologists as well as wildlife lovers. A good example in mammals is the mule x horse, which, although extremely rare, can result in a viable offspring. Then there’s my obsession: the controversial case of the red wolf, currently classified as Canis rufus, but whose genetic analyses suggest it might be more coyote than wolf! So, don’t be so quick to discount an observed bird just because it does not exactly ‘fit’ the ‘mold’ of traditional identification traits or historical habitats.

While molecular technology increases our knowledge and answers many questions, it also tends to raise more questions. 🙂 I think that’s why I love it and am thankful for my work in the molecular biology field the last 10 years.

* Photograph will be included soon!! I promise    Photo inserted! Thanks to fellow volunteer and photographer here at Bosque del Apache NWR. Thanks, John!

** For those that are interested in more details about leucism, there are many types. They all are associated with different genes and inheritance. An absence of only one type of melanin is called schizochroism. Non-eumelanin schizochroism is defined as a complete reduction of eumelanin, which results in only reddish-brown coloration in the feathers. Non-phaeomelanin schizochroism is defined as the complete reduction of phaeomelanin. In this mutation, feathers contain only black/gray and brown coloration. These single mutations are rare.

References for further reading:

Nesbitt, SA, and Schwikert, ST.  1998. Maturation and Variation of Head Characteristics in Sandhill Cranes. Wilson Bull., 110(2): 285-288.

Price, TD. 2006. Phenotypic plasticity, sexual selection and the evolution of colour patterns. J Exp Biol, 209(Pt 12):2368-76.

Roulin, A, and Ducres AL.  2013. Genetics of colouration in birds. Semin Cell Dev Biol., Jun-Jul (6-7): 594-608.

Sibley, David. “Abnormal coloration in birds: Melanin reduction.”; Web Retrieved 11.27.2014.

US Fish and Wildlife Service. “Foster a Land Ethic That Would Make Aldo Leopold Proud”.; Web Retrieved 11.27.2014.

van Grouw, H. 2006. Not every white bird is an albino: sense and nonsense about colour aberrations in birds. Dutch Birding, 28: 79-89.

Western Tanagers are here!

12 May

No strangers to the Big Bend area, tanagers are some of the most colorful birds in the spring and into late summer here. And one of the favorites for both color and song is the Western Tanager.

Western Tanager. Photo courtesy of Anne Theil.

Western Tanager. Photo courtesy of Anne Theil.

The breeding range of these birds extends from southeastern Alaska to south through the western states and West Texas. Most Western Tanagers arrive in the Trans-Pecos and High Plains regions during spring from early April to late May. They usually breed in Texas from late April to mid-August. In the fall, they migrate south to central Mexico for the winter.

Big Bend National Park is on the migratory flyway of several tanagers as they migrate north and south. Thus, several species of tanagers can be found, especially in the Chisos Mtns., but also in the neighboring area. I enjoyed watching and listening to these colorful birds last May around Cedar Springs area on Terlingua Ranch. A local resident recently photographed a Western Tanager hunting for insects in a clutch of creosote.

Most red birds owe their colors of red, yellow and green to a variety of plant pigments known as carotenoids, which are deposited in their feathers. The Western Tanager gets its scarlet head feathers from a rare pigment called rhodoxanthin. Unable to make this substance in their own bodies, Western Tanagers probably obtain it from their diet of insects that feed on conifer (pine, fir, yew, and cedar) needles, and small fruit (especially of the honeysuckle) which contain the pigment. These pigments are stored specifically in their crown feathers to give them their red appearance.

Another related species of interest is the Flame-colored Tanager. Historically common only to central Mexico, their range has increased north over the last decade. They have become more common in the Sky Islands of Arizona with a few documented sightings in the Chisos Mtns. of BBNP. Interestingly, because their DNA are closely matched, more than of other tanagers, the Western and Flame-colored Tanagers are quick to mate and hybridize. Increasing documented sightings of hybrid birds are reported in Arizona the last several years. It is not unusual for closely related species to hybridize when their border habitats overlap.

Photo courtesy of Anne Theil.

Photo courtesy of Anne Theil.

Hoo’s that?

12 May

The Great Horned Owl (Bubo virginianus) is our largest and most widespread raptor in North America. It is also our second heaviest owl in North America, (Snowy owl is heavier). It ranges in length from 17–25 inches and has a wingspan of 36–60 inches, with the females somewhat larger than males. Although the body shape of the Great Horned owl is consistent throughout its wide range, there is considerable variation in plumage coloration. The facial disks might be gray, brown or reddish colored. Also, the white patch on the throat may vary in size and the ear tufts may have some reddish feathers.

great_horned_owl_reidbarclayAdult birds have large ear tufts, which are just clusters of tall feathers, and the Great Horned owl is the only very large bird in its range with these features. The eyes of this bird are nearly as large as those of a human being and are immobile within their circular bone sockets. As a result, they can’t move their eyes up or down or side to side – the owl has to move its whole head to compensate for the fixed eyes. Thanks to extra vertebrae in their necks, they can rotate their head a full 270 degrees in order to see in various directions without moving their entire body.

The year-round range of the Great Horned owl extends from Central America all the way to just south of the Yukon territories in northern North America. They are known to occupy nests of other large birds and it is the earliest nesting bird in many parts of its range. They will also nest on cliff ledges or even on the ground. No matter where they nest, people are advised not to go near them. They will attack any animal that threatens their nests.

Like most owls the Great Horned is generally nocturnal. However, it can often be seen or heard hunting during dusk and twilight, especially on cloudy days. This owl can hoot, bark, chuckle, growl, hiss, screech, scream, and clack its beak. Because the male has a larger voice box, its hoot is deeper than the female’s. I’ve also noticed that the males tend to range farther for their hunting whereas the females prefer to stay in or near the shelter of trees or brush, possibly close to their nest.

great_horned_owl_donaldthompson Having a nesting pair on my former place on the high prairies for eight years, the male and I established a respectful relationship. Often times I would answer his hoots in the early mornings or evenings. He would fly near my sitting spot and land on a utility pole or fence post and we would have conversations. Even in the middle of the summer nights when he was perched outside my open bedroom window. Although I often heard the female return his calls, I never did see her but once or twice when she flew out of the thick woods bordering my property.

Once in awhile I would lose my Internet connection via the satellite dish mounted on my roof. I discovered when I went outside to check the weather conditions that Mr. Horned Owl was proudly perching on top of the satellite dish and hooting at me underneath him. I smiled and sat down on the bench to pick up the conversation with him. I am tickled happy that there is a nesting pair near where I live now here in the desert.


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