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Climate and species are a-changin’

8 Oct

This summer was a perfect example of environmental changes. In the northern states, some waterfowl species never migrated south last fall, and this spring’s surveys revealed that some birds migrated north earlier than normal. Conversely, milkweed (Asclepias spp.) emerged one to two weeks early and migrating monarch butterflies arrived two to three weeks late in all the northeastern states. Areas in a few northeastern states were stricken with a historic “100-year or more drought.” On the other hand, many areas in the semi-arid southwest experienced historical devastating floods.

Is this a fluke? Or is this the new norm? Perhaps somewhere in the middle, but more likely these weather and climatic changes are the ‘new normal.’  The events and data support that assessment.*

How do living organisms respond?

Published studies by biologists have been documenting the impact of climate change on the environment, especially species that are adapting and not adapting. We can learn about impacts on organisms  by examining changes in cyclic and seasonal natural phenomena of plants and animals in relation to climate. These seasonal changes and cycles are known as phenology. Noting the times of year that specific plants bloom, or when birds migrate are two examples. Comparing the phenology of many species over a period of time can reveal informative clues on how changes in climate may affect them. Many studies along this model of investigation demonstrate that the living environment is indeed impacted.

United Kingdom researcher Stephen Thackeray(1) and his colleagues analyzed the phenology of a wide range of species. They used 10,003 phenological data sets to determine if and how much species’ phenology have changed over a minimum of 20 years. The analysis revealed that phenology has shifted in unequal rates in different species groups. Thus, climate change leads to disruptions of the phenological match between species, which often impacts ecological relationships.

Another question the researchers asked was how sensitive events in their life cycles are to the two most common variables in climatic change: temperature and precipitation. Both variables have changed in an uneven process over the flow of seasons. How does this impact species relationships? Some periods of the year have warmed faster than others, which may affect two interrelated species with equal temperature sensitivities but at different times. This could shift their phenological events at different rates and cause a mismatch in their relationship.

For example, milkweed plants emerging and flowering much earlier than normal resulted in sub-optimal conditions for the late-arriving monarch butterflies to use the plants for breeding. Additionally, the persistent hot and humid weather in the northeast could impact monarch larva (caterpillar) by either accelerating or arresting development.

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Trophic levels

The study authors also discovered a difference of sensitivity to temperature variations at different positions of the food chain (referred to as trophic levels). Species at different levels did not differ in the time of year at which they were sensitive to annual variations in temperature. But they did vary in how sensitive they were.

 

Species in higher levels of the food chain (the secondary consumers) are less sensitive to temperature changes than species at the bottom (the producers and primary consumers). These species are twice as sensitive to temperature changes than upper level species. Secondary consumers are also less sensitive to precipitation variations.

The authors then combined the species sensitivities with a future climate scenarios. They forecast that primary consumers -birds, insects, small mammals, etc- will shift the timing of their phenological events by twice as much as will species at other levels of the food chain. One reason their response varies is because species at different tropic levels respond differently to exactly the same temperature cue. Species respond differently to temperature during various times of the year.

The above example of the milkweed and monarch butterfly mismatch could impact the breeding success and thus population numbers of the butterflies. Both species have different physiological mechanisms that determine their phenological events and use different cues to determine their timing. Although these cues will be correlated to some extent, the cue used by the consumer -in this example, the monarch butterfly- is less reliable than that of the the plant they rely on. This cue unreliability in the consumers may mean that they will evolve with less temperature sensitive phenology than those species at the trophic level they rely on.

Ecologist Marcel Visser (at Netherlands Institute of Ecology) calls attention to moving from conventional two-species interaction research to a more holistic approach: investigating the effects of climatic change on the entire food-web. In a review(2) of the Thackeray, et al. study, Visser additionally proposes that impacts by phenological mismatches could be buffered by other mechanisms in their ecosystems.

To help us understand the consequences of phenological mismatches and thereby form predictions, he proposes questions that should be considered in studying changes in climate changes and relationships:

How are the strengths of the links in a food web affected by phenological mismatches? What happens if the phenology of species at one trophic level shifts more than that of species at another? Does this lead to the loss of some links and the formation of others? Does this destabilize the web? Such analyses would be a stepping stone from studying the phenological shifts of species to understanding the effects of
climate change on ecosystem function.(2)

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Stink bug preys on larva.

An example for a holistic ecosystem approach is field observations (my own and in the literature) that have suggested that as prolonged temperatures increase, depredation and parasitism of monarch larvae and adults increase. Is this a function of differences in phenology of  monarchs and its predators, or changes in all vegetation and species interactions (a complex of one or more phenological overlapping and mismatches)  in the habitat? Do temperature mismatches in other members of the monarch habitat increase risk or rates of depredation?

One research team suggested that migration of monarch butterflies may have evolved as an adaptation to decrease depredation and parasitism in their breeding habitats. If monarch adults were to delay or ignore cues to migrate because of changing climate, how would that impact their overall population?

Adding to the complexity, climate sensitivity in species is not fixed. Phenological mismatches can lead to selection on the timing of phenological events. Resilience to environmental challenges can alter phenology, but over time can also result in genetic changes to sensitivity, thereby fixing phenological changes. Conventional theory on temperature range sensitivity of monarch adults and larvae states that it quite narrow. However, some observations(3) of their coping mechanisms with prolonged high temperatures in the Pacific Northwest sub-population questions if this sensitivity range is more flexible than conventional thought, or if this could be a developing adaptation.

Some researchers are already investigating genetic changes accompanying phenological adaptations to climate change (e.g. genetic alterations in melanin associated with plumage and physiology in European owls that have adapted to changing ecosystems). Such complex studies must be conducted to forecast the impacts of climate change and phenological responses and ecosystem function.

Research by Thackeray, Visser, and other colleagues demonstrates that long-time series of data are essential for such investigations. They also applaud and encourage professional and citizen scientists to continue collecting and submitting observations to add to the data pool. As Visser commented, “The additional advantage is that observing phenological shifts in, sometimes literally, your own backyard drives the message of global climate change home.”


(1) Thackeray, SJ, et al. “Phenological sensitivity to climate across taxa and trophic levels”. Nature 535, 241–245 (14 July 2016)
(2) Visser, ME. “Interactions of climate change and species”. Nature 535, 236–237 (14 July 2016)
(3) Anecdotal observations by Dr. David James, Washington State University entomologist, in central Washington and myself at Malheur National Wildlife Refuge, eastern Oregon.

* The main difference between weather and climate is time. Weather is the atmospheric local events over a short period of time.  Climate is an average of the weather over much longer time in a region or globally. Sure, we can agree that weather and climate is cyclic, with highs and lows historically up and down. Also, a few episodic variances from the average can be expected.  But climate does not vary as greatly as weather. The trends clearly demonstrate that climate is changing. Modern paleoclimate technologies can now add to the 70-year human records of climatic changes, both which confirm that climate change is a reality. Those changes have accelerated, more than any other equal span of time in historical evidence.

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Wings of mimicry

17 Sep

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The early rising sun greeted us with a visitor in the damp grass one morning of a camping trip near New York’s Thousand Islands. As sunlight glistened on the blanketing dew, this large winged visitor rested on the grass waiting for moisture to evaporate off its wings and the sun to warm its body. It reminded me of another large moth, the luna moth (Actia luna), that I knew well during my life in the Maine woods.

The moth found on the wet grass that morning was a polyphemus moth (Antheraea polyphemus). Both moths are of the Giant Silkmoth family (Saturniidae). With a wingspan of up to six inches or more, the polyphemus moth is about the same size as a luna moth. These two species are the largest moths in continental America and may be found from Canada to northern Mexico.

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Male polyphemus moth (antenna are larger than female’s)

Polyphemus moths are generalists, which means they do not require a specific species of plant for the larvae to develop and survive. Females lay flat brown eggs on many species of decidous trees: elm, birch, willow, maple, beech, locust and a variety of Prunus species (cherry, plum, peach, etc). Like many Lepidoptera, polyphemus larvae develop through five stages and molts (instar). Unlike monarch butterflies, of which the instars are very similar in coloration, these moths have slightly different coloration with each instar. The fifth and final instar is an average of four inches long and a bright green color with silver spots on its sides. A caterpillar can devour about 86,000 times its weight from emergence to full development in two months.

From the photos of the adult moth below one can see hair-like body scales, small head and mouth parts, and the eye spots on the wings. Because of their small mouth parts, adults do not eat and only live for a week or less, during which their entire purpose is to avoid depredation and reproduce.

Mimicry

Mimicry throughout the animal kingdom is an example of natural selection in evolution. Ranging from mammals to tiny insects, mimicry may increase survival of individuals in their environment. Or it may reduce survival in another environment.

Lepidoptera are fascinating examples of how mimicry enables survival. One tactic is to mimic another insect that may be undesirable prey. Another tactic is the patterns and structures on butterfly and moth wings that mimic a component of their environment to hide from depredation. These tactics may be adaptive defense mechanisms (or artifacts of other patterns of coloration) in response to threats. Our polyphemus moth will serve as an example of mimicry as a defense mechanism.

Distraction Pattern

Like many saturniids the polyphemus moth has large ‘eye spots’ on its hind wings. These wing eye spots are translucent ‘windows’ which may be surrounded by bright colors. The pair of eye spots on the polyphemus hind wing are bordered by bright colors and, with the entire wing pattern, may resemble eyes of a predator. These are distraction patterns, which is a form of mimicry. They may resemble eyes of a different animal and confuse or deceive potential predators.

Wing eye spots can be a form of self-mimicry and a distraction pattern: to draw a predator’s attention away from the most vulnerable body parts or to appear as an inedible or dangerous animal. When threatened, adult polyphemus moths flash their  wings exposing the large hind wing eye spots to distract, startle, or scare off potential predators.

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The centers of the eye spots lack scales, so they are transparent.

Another example of distraction pattern in mimicry is camouflage which helps avoid detection by predators. Eye spots and wing color patterns on adult polyphemus can serve as blending camouflage (color matching) and pattern camouflage (pattern matching) in their environment.

Unrelated to mimicry, these eye spots may also play a role in mate attraction, but this has not been conclusively confirmed.

dscn1811-sMimicry is also exhibited by the polyphemus caterpillars. They can be protected from predators by their cryptic green coloration (another example of what kind of distraction pattern?). When threatened the caterpillars often raise the front part of the body up in a threatening pose. If attacked, the caterpillars make a clicking noise with the mandibles.  This clicking is associated with a distasteful fluid exuded by the caterpillars which can cause regurgitation by the attacker. Some animals (squirrels, birds, other insects) are deterred by the ingestion and regurgitation and the clicking may serve as a warning.

Mimicry and names

Since one of my interests is the etymology of animal binomial names (simply put, the naming of things), mimicry also plays a part in this moth’s name.

The four silkmoth species in the New World (the Americas) were assigned to either Telea or Metosamia genus. The polyphemus silkmoth in the Americas was first described and named by Dutch naturalist Pieter Cramer in 1776 as Telea polyphemus. Jacob Hübner, a German entomologist (1761-1826), assigned the Old World (endemic to Asia and Europe) silkmoths to the genus Antheraea in 1819.  In 1952, American entomologist Charles Duncan Michener (1918-2015) systematically categorized the Telea and Metosamia in with Antheraea classification. All the silkmoths are now in one genus classification.

The Modern Latin genus name Antheraea likely derives from the Greek anthēros, meaning brightly colored, brilliant, or flowery.  The Lepidoptera Antheraea type species (the species on which the description of a genus is based on, and with which the genus name remains associated during any taxonomic revision) is the beautiful and vibrantly-colored tasar silkworm (Antheraea mylitta, formerly Phalaena mylitta), named and characterized in 1773 by English entomologist Dru Drury. Although not a silkworm like the tasar species, the polyphemus is colorful and has similar eye spots.

Cramer’s choice of the species name was based on Polyphemus, the giant cyclops from Greek mythology who had a single large, round eye in the middle of his forehead. Cramer may have been reminded of the name because of the large eye spots in the middle of the hind wings.

And the commonly used name ‘sphinx’ moth?  It could have arisen because of the behavior of threatened larvae. When they raise their heads and thoraxes up, the pose superficially resembles Egyptian sphinxes. Someone had imagination.

Of course, the family name Saturniidae  also peaked my curiosity.  The consensus is that it was based on the eye spots of some members of the family that contain concentric rings reminiscent of the planet Saturn. I’ll take that, too.

 

Nature in Photography

6 Feb

A week or so ago on FaceBook I was nominated by two friends to participate in the #challengeonnaturephotography meme. Although I rarely participate in these memes, the thought “Why not?” prompted me to give it a try. The protocol is to post a nature-themed photograph, include the hashtag, give kudos to the friend that nominated you, and then nominate another friend in the caption.

I played by the rules for three days. Then life got in the way (long days in the field), and I got lazy. I posted when I had time, dropped the official hashtag, the nominators, and ran out of FB friends to nominate. I keep my FB friends to a relatively small number (up to 50 now!), and friends who are into photography have already participated once or twice.

Now I submit a story with the photograph instead. Why? Because photography to me is a storytelling medium. Today’s photograph is a glimpse into the secret lives on the ‘little people’.

Nearly every day for three months last summer, I was privy to an entire world few of us see in depth and detail. I felt like a giant studying, learning, and enjoying a network of soil, water, plants, and insects……….at their level. Sometimes I was so giddy with childlike delight, I forgot who and what I was. And I was full of anger and intense sadness when part of this magical world was destroyed by humans. That, too, was a lesson I won’t forget.

Revealed below is a monarch butterfly larva and several cobalt blue beetles all ‘doing their thing’. They use milkweed as a common food source. Yet they tolerate each other. I have watched members of both species consume leaf material, side by side without conflict. Here, two beetles are copulating, undisturbed and unfettered. While the monarch voraciously chows down, preparing to form its chrysalis. This, however, is only one tiny window into the lives that live in the ecosystem in which I immersed myself.

Most nature photography depicts landscapes of empty agents and actors. Or portraits of animals, still and silent in pose like a person sitting for a photograph. To me this is an injustice to the inhabitants of the landscape as they live out their drama and narratives in those spaces. Few ‘nature’ photographs reveal the complex interrelationships within the landscapes and with their fellow animals. They fail to show the communities of life in places other than within our own human preconceptions and expectations. As if we strive to capture and show only a snapshot in time and space that suits what we want to see.

In addition to the beauty, the silence and solace depicted in landscape and wildlife portrait photography is a dynamic world of creatures living their lives just like we do. The drama, the beauty, the good and bad, birth and death, at every level; from micro to macro. There are stories out there that are not of our own.

And we can learn from them: About their lives, their interactions with each other and how we interact with them. We can even learn about ourselves.

Think about that the next time you are out in the natural world. Take time to observe before you press on that shutter release button. You never know what you might find.

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Fifth instar monarch larva and cobalt blue beetles on showy milkweed.

To be, or not to be, which species? Why question?

22 Sep

Over the past several years I have participated in the genetic and taxonomic debates over the Red wolf: is it Canis lupus (wolf)? Canis latrans (coyote)?  Canis rufus (current classification)? Or a hybrid?

Depending on which author’s paper you read, the general consensus is that the animal shares more genetic similarity with the coyote than wolf. To complicate the game, a few genetic markers associated with (note my avoidance of ‘unique to’)  the red wolf can be found in a sub-population of the timber  wolf, most notably the Great Lakes or Algonquin wolf.

The typical argument against introgression of the two wild canid species, C. lupus and C. latrans, is behavioral boundaries between them. Under normal circumstances, the two species do not tolerate each other and will not mate to form hybrid offspring. When they are sympatric (when their territories overlap), wolves usually kill coyotes or they just avoid each other.

However, a group of geneticists hypothesize that despite traditional behavioral and geographical boundaries that usually prevent introgression between species, these very boundaries are plastic. In other words, they may fail and individuals of both species may mate and produce viable offspring.

A scenario of this transgression might be in a geographical area that borders territories of both species. If resources are severely limiting, such as during a long drought cycle, a few individuals of each species may mate due to poor mating opportunities within their own species.

Another scenario is more common today: when human land use encroaches upon and shrinks traditional habitats, forcing trespass from one species into territory of the other. This is the primary explanation given for the increase of the current  ‘coywolf’ population in the northeastern US.

As one geneticist posits, such introgression may have occurred more than once, especially in an arid region, such as the southwestern area of the red wolf’s former territory: Texas. After several generations of backcrossing and/or admixture with coyotes, isolation of this growing population could conceivably be on the way to speciation, resulting in the historical  and extant Canis rufus.

Now, here lies the question: is this animal a species? Or a sub-species? Is it ‘wolf’? Is it ‘coyote’? Or is it a hybrid? And this is when the poor animal falls into the vortex of the ‘species concept’ debate. And possibly one of life or death.

Tonight I reread a paper published in 2006 and that was once used as a focal topic paper in a journal club session: “On the failure of modern species concepts”, by Jody Hey (Trends in Ecology and Evolution, vol. 21, No. 8). An excellent paper that stirred a three-hour debate between eight students and monitors. Shame on me for forgetting the final two paragraphs (‘Lessons on the method of multiple concepts’).

“Definitions cannot be forced to serve the arbitration of entities that are truly ambiguous. The fact is that species are hard to identify for a variety of reasons related to the various ways that they can be indistinct and no criterion that presumes to delineate natural boundaries can overcome this.

As scientists we should not confuse our criteria for detecting species with our theoretical understanding of the way species exist. Detection protocols are not concepts. This point would be child’s play if we were talking about electrons or disease agents, but because real species are so difficult to study, and because our best understanding of them includes their often being truly indistinct, we have had trouble separating the detection criteria from our more basic ideas on the existence of species.”

Right now, the fate of the red wolf in large part revolves around whether or not it is classified as a true species, sub-species, or a hybrid. The Endangered Species Act does not recognize and therefore does not include hybrids for protection from extinction. Both government agencies, policy administrators and scientists are still embroiled in the vicious vortex of yea or nay. Nor can the biologists agree on how the species concept applies to a possible animal caught in the cycle of speciation.

I am a victim of my own Trickster antics of playing in the ‘species concept’ debate. Tonight this is resolved and I am absolved: it doesn’t matter which species the red wolf is tagged with. It doesn’t matter if it is a hybrid or not. In fact, as a hybrid it’s protection and conservation is even more important. We have the opportunity to watch and learn what happens during the course of a mammalian hybrid as it continues its course of speciation.

May the Red wolf howl and carry on safe from human impact and intervention other than a helping hand for protection from human-caused anhilation. Perhaps you can teach us humans humility. Especially us scientists.

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.

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.

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