Sunday, September 28, 2014

Hummingbird Highway

Ruby-throated Hummingbirds, Archilochus colubris

Some of the most abundant jewels in Texas, black-chinned and ruby-throated hummingbirds may be small, but their fall migration is a feat of gigantic proportions! 

Measuring a mere three and one-half inches long with a three and three-quarter-inch wing span, the black-chinned hummingbird weighs only three to three and one-half grams, which is about equivalent to the weight of a dime plus a dollar bill. The male is dull metallic green above, gray below, black on the chin and upper throat, with an iridescent violet lower throat known as a gorget (pronounced gore-jet). The female lacks the characteristic coloring on the chin, upper throat, and lower throat.  Ruby-throated hummingbirds are also only about three and one-half inches long with the adult male having a black upper chin and ruby-red gorget, and they are a more eastern species with Austin being the westernmost border of their range. 

Like all hummingbirds, nectar serves as its main food source, fueling the tiny bird’s extreme metabolism.  These hummingbirds feed on several species of plants, most notably native penstemons, agaves, salvias, sages, and honeysuckles.  While artificial feeders supplement their diet, they also prey on insects and spiders, particularly during nesting season, which gives them the dietary fat and protein necessary to breed.

Black-chinned Hummingbird, Archilochus alexandri

The hummingbird’s unique skeletal structure allows them to fly forwards, backwards, sideways, and even on their backs!  This requires a wingbeat frequency of about 50 beats per second, and massive muscles that make up a third of their tiny body weight.  While the males perform an elaborate flight display during courtship, no pair bond is formed between the males and females.  Females build the tiny nest (out of spider webs, mosses, and various plant fibers), incubate the eggs, and raise the young, while the males are feeding and off chasing other females.  This is unusual among birds as a whole, since this class of animals exhibits the greatest amount of monogamy among vertebrates (animals with a backbone or spinal column). 

Ruby-throated Hummingbird (Female), Archilochus colubris
While most biologists believe that the shortening length of daylight hours triggers fall migration, black-chinned and ruby-throated hummingbirds begins their long journey south from Texas in September, to spend the winter mainly in western and southern Mexico.  The number of birds migrating south may be twice that of the northward trip in the spring, since it includes all immature birds that hatched during the summer, as well as surviving adults.
Amazingly, for a newly hatched hummingbird, there is no memory of past migrations, only an urge to put on a lot of weight, fly in a particular direction for a certain amount of time and hundreds of miles, and look for a good place to over-winter.  Once it learns such a route, a bird may retrace it every year as long as it lives!  There is evidence that fall and spring migration routes differ, with the hummingbirds following the Texas coast back into Mexico in the fall and crossing non-stop over the Gulf of Mexico on their way north in the spring.  Perhaps the hurricane season is a factor, and these birds have developed an innate sense to avoid the Gulf during its most precarious weather season. 

The timing of the fall hummingbird migration occurs when their natural food is most abundant.  However, you can enjoy this amazing spectacle up-close by keeping your feeders full of clear, fresh sugar water through at least the end of October, and enjoying the company of these enchanting little gems as they make a rest stop in your yard!

Monday, August 4, 2014

Red and Yellow Fellow

Many of us have heard the sayings “Red on black, friend of Jack, red on yellow, kill a fellow” or “Red against black, venom lack” as a way for us to distinguish between non-venomous lookalike snakes, and the venomous coral snake.  Over 65 species of coral snakes are recognized in the New World, but in Texas we have our own version.  The Texas Coral Snake (Micrurus tener), actually ranges from the south central US (Texas, Louisiana, Arkansas) south to northeastern and central Mexico.

Texas coral snakes have the traditional black, yellow, and coral red banding coloration encircling the body that is associated with all coral snakes. They are slender snakes with smooth scales, eyes with round pupils, and average two feet in length.  Males are typically smaller than females, but both are shy and secretive, typically nocturnal and spending most of their time hiding under logs, in leaf litter, or in ground burrows.  Fairly common in the Austin area, they typically feed on other smaller snakes and occasionally lizards, and are often attracted to suburban yards and gardens where they can more easily find their prey.

While no deaths have occurred in Texas from a coral snake bite, their venom is a powerful neurotoxin that causes neuromuscular dysfunction.  Usually encountered by people when weeding or gardening, coral snakes do have a hard time injecting venom into a human because of their small, blunt head and short, fixed fangs.  Bites usually occur on the hand or in between fingers, and the snake has to chew in order to inject the venom.  Most people don’t allow them to hang on long enough to do much serious damage, but anyone bitten by a coral snake should seek medical attention immediately.

Much debate has ensured about whether or not the Texas Coral Snake’s bold coloration in and of itself acts as a warning signal to potential predators, but recent studies have shown that this coloration is only effective when combined with the coral snake’s distinctive threat behavior.  When confronted, they will raise their yellow- and black-banded tail tip and slowly wag it at the threat (presumably mimicking a strike with their similarly colored head), all while keeping their head safely and neatly tucked under a body coil.  

If you are lucky enough to run across this native red & yellow fellow, remember that Texas Coral Snakes are an integral part of our ecosystem, and enjoy their striking colors and distinctive pattern from a distance!

Tuesday, July 8, 2014

Two Heads Are Better Than One

Juniper Hairstreak, Callophrys gryneus 

Hairstreaks are mainly small butterflies, most with threadlike tails on their hindwings.  They typically fly rapidly, fitting from side to side or in circles, before sticking a landing.  Most perch with their wings closed, and reveal their upper surface only in flight.  Males and females can look quite similar, but the males will often be the more vibrantly colored of the two.  

In central Texas we have three common hairstreak butterflies.  The largest, as indicated by its name, is the Great Purple Hairstreak (Atlides halesus).  Dusky purplish-black below and brilliant blue above with red spots near the base of the wings and a bright orange abdomen, this butterfly flies spring through fall.  It tends to stay well above the ground, and males will sit on trees on hill summits or flat plains to await females, mostly in the afternoon.  Its larval foodplant, or plant upon which the female lays her eggs, is mistletoe species in the genus Phoradendron.  

Great Purple Hairstreak, Atlides halesus 

Another commonly encountered hairstreak is the Gray Hairstreak (Strymon melinus).  It has only one tail on the hindwing and an upperside that is blue-gray with a large reddish-orange spot near the tail.  The male's abdomen is orange and the female's is gray.  In the spring and fall its underside is dark gray, and paler gray in the summer, but it always has a dashed white line, parallel and inset from the wing's edge, bordered with orange.  It flies from February to November and is the most widespread hairstreak in North America.  Males perch all afternoon and into evening on small trees and shrubs to seek receptive females, who lay eggs one at a time on a wide variety of plants including peas, mallows, beans, clovers, and cotton.  

Gray Hairstreak, Strymon melinus

One of our most beautiful hairstreaks is the Juniper Hairstreak (Callophrys gryneus), belonging to a group called Evergreen Hairstreaks, which are widespread and variable.  The upperside of the male is dark brown with an olive-colored sheen, and the female is blackish brown.  Their underside is a vibrant green with two white spots near the base of the forewing and an irregular white line edged inwardly with a reddish-brown.  Males perch on host trees, those in the genus Juniperus like our native Ashe Juniper, awaiting females.  They perch with their wings closed and blend into the junipers so well that they may not be noticed until moving branches cause them to fly.   

Juniper Hairstreak, Callophrys gryneus 

When it comes to survival, hairstreaks have developed an interesting adaptation, much of which has to do with their tails.  Often having distinct markings or spots near these tails, together they form what is known as a 'false head' with the tails looking like antennae.  The illusion is carried further when the hairstreak performs a back-and-forth 'sawing' motion with the hindwings when resting. This motion can distract would be predators such as spiders, causing them to attack the wrong end of the butterfly, leaving the vital structures intact.  

Missing tails and part of the lower portion of the hindwings does not hinder flight, and the butterfly lives to carry on another day.  So it really is true that two heads are better than one!  

Friday, June 20, 2014

Dancing Damselflies

Desert Firetail, Telebasis salva

Often overlooked but in the same Order (Odonata) as dragonflies, damselflies are a group of insects that differ from dragonflies by wing shape, wing position, and eye separation.  Damselflies have similarly shaped fore and hind wings, typically hold their wings together over their abdomen when perched, and their eyes are widely separated but never touching.  In comparison, the hind wings of dragonflies are broader basally than their fore wings, they hold their wings spread out and away from their body, and their eyes are much larger and usually touch at least at a single point. 

Amethyst Dancer, Argia pallens

While damselflies are less robust fliers than dragonflies, they are still quite agile in flight.  They can move each of their four wings independently, and can not only beat them up and down, but also rotate them on their own axes.  Most damselflies fly by alternating the two pairs of wings, and while one is moving down to propel them forward, the other is moving up.  In spite of their fast wing beats, damselflies have relatively short, narrow wings that don’t allow them fast flight, and they move at an average speed of about 2 meters per second.  

Rambur's Forktail, Ischnura ramburii

Over 75 species of damselflies occur in Texas, more than half of the known species in North America.  These species represent members of all families of damselflies, which include broad-winged damsels (jewelwings and rubyspots), spreadwings, threadtails, and pond damsels (dancers, bluets, yellowfaces, wedgetails, damsels, forktails, swampdamsels, sprites, and firetails).  Like most dragonflies, the males are usually the most colorful and the easiest to identify.

American Rubyspot, Hetaerina americana

Springwater Dancer, Argia plana

Usually inhabiting small seepages and springs, the Springwater Dancer (Argia plana) is one of the most common pond damsels in our area, and has a blue head, face, and eyes, and a blue thorax with a black dorsal (top) and shoulder stripe.  Its abdomen is also predominately blue, with black rings on most middle segments.  It can often be found along roadsides, away from water.  The Great Spreadwing (Archilestes grandis) is the largest damselfly in Texas and the US, and is recognized by its blue eyes, the metallic green stripes on the top of its thorax, and bright yellow stripes on its sides.  Its wings are clear to slightly smoky, often with darker tips.  Found around bodies of standing water, it perches in a distinct manner on vertical stems with its body hanging downward and its wings partly spread.  Common around open streams and rivers, the American Rubyspot (Hetaerina americana) is a broad-winged damsel that has a metallic red thorax, a metallic green abdomen, and a vivid red patch at the base of its wings that grows larger with age.    

Great Spreadwing, Archilestes grandis

Observed throughout the summer at almost any body of freshwater, damselflies are slender and delicate.  They seem to dance around and about the water, marked with colors of the rainbow, delighting all those who take the time to get to know and admire them!

Monday, June 9, 2014

Wild Woodland Orchids

Spiked Crested Coralroot, Hexalectris spicata var. spicata

A colorful group of native orchids called Hexalectris or coralroots are found mainly in the mountains of northern Mexico and West Texas, but we are fortunate enough to have at least two species that grow in our area.  The name Hexalectris literally means ‘six cock’s combs,’ referring to the six prominent ridges that were thought to run down the length of the flower’s lower lip.  Despite this name, most flowers have only five or seven ridges.  

These orchids are micro-heterotrophic, which describes a plant that gets some or all of its food from parasitism on fungi rather than from photosynthesis.  Most Hexalectris orchids have only been discovered and studied in the last fifty years.  They depend heavily on an extremely delicate balance of environmental factors, which means they are not always observed every year, and it makes them impossible to transplant from the wild.

In our area, April through August is the best time to spot the Spiked Crested Coralroot (Hexalectris spicata var. spicata).  An uncommon orchid, it is most often found in the leaf litter on the wooded limestone hillsides and canyon slopes in oak-juniper habitats of the Edwards Plateau.  Also called cock’s comb or brunetta, the blooms of the Spiked Crested Coralroot grow on a tall, leafless, fleshy-pink stalk.  Each bloom has creamy yellow petals and sepals striped with brownish-purple, and the central white lip is adorned with five to seven wavy crests of deep, royal purple. 

Giant Crested Coralroot, Hexalectris grandiflora

Recently, the first record of the Giant or Largeflower Crested Coralroot (Hexalectris grandiflora) was discovered in the Balcones Canyonlands Preserve in Travis County.  Previously thought only to grow in the Davis and Chisos Mountains of West Texas, the bright pink, leafless stalk of this species grows from 10 to 24 inches tall.  Along the stalk, vivid pink flowers bloom with a white mark in the center of an elaborately shaped, three-lobed lip.  This coralroot also flourishes in our oak-juniper woodlands, and is thought to bloom from June to September.  Other common names for this beautiful wild orchid include Greenman’s hexalectris or Greenman’s cock’s comb.

These unique wild woodland orchids are uncommon to rare in our area, and together they help define the true nature of the Texas Hill Country.  Monitoring and preserving them is not only good for the sake of maintaining biological diversity and understanding changing environmental conditions, but for the future beauty of our ecoregion as well.  

Wednesday, May 14, 2014

Butterfly Buffet

Crimson Patch ovipositing on Flame Acanthus

The very nature of a healthy ecosystem is defined by the interrelationships and dependencies one species has on another, and nowhere is this depicted better than in the world of butterflies and their host plants.

Gulf Fritillary caterpillar on Purple Passionflower

For butterflies, life begins as a tiny round, oval, or cylindrical egg laid on the stem or leaf of a plant. From the egg, a caterpillar or larva emerges, feeding at a steady pace, often shedding its skin several times from its rapidly growing body.  The mature caterpillar then pupates, or encloses its body by forming a chrysalis, in which its tissues are broken down and the adult insect’s structures are formed, transforming itself into a butterfly.

Pipevine Swallowtail chrysalis

While most butterflies nectar or feed on a wide variety of blooming plants, when in their larval stage they are much more restricted.  They are considered to be ‘oligophagous’, or feeding on an especially limited range of typically related food plants, sometimes only one particular species.  Often called host plants, these plants are sought out by female butterflies needing to lay their eggs on or near the plant.  

Giant Swallowtail ovipositing on Wafer Ash

While scientists are still learning how butterflies locate their host plants, many believe it is a combination of chemical smells and taste cues that determine a plant’s appeal to an insect. Butterflies have chemoreceptors at the ends of their antennae and on the bottoms of their feet, which enable them to taste or smell.  They use this sense to locate both nectar and host plants, find mates, identify rivals, and avoid predators.

The dependency of butterflies on specific host plants is among the key factors in restricting the range or distribution of a particular butterfly species, although many species are widespread.  In fact, host plants of certain species may vary across different geographical butterfly populations, and there is still much to learn about these relationships.
In Texas, the astounding diversity of ecological habitats and associated native plants support a wide variety of butterfly species, more than any other state.  In addition, regional specialties can occur, where a species is very limited in range and not typically found in other parts of Texas or sometimes not even elsewhere in the United States.

Malachite, Siproeta stelenes, found in South Texas

Taking the time to learn about host and nectar plants and the butterflies that love them gives us yet another glimpse into the fascinating, ever changing web of life.  It transcends the information we have gathered at the species level and raises it to the inter-species level, providing us with a more connected view of the inner workings of a functional ecosystem.  By applying this knowledge, not only can we more fully appreciate the intricacies of nature, we can create, restore, and nourish the very places where they take place.    

Thursday, April 17, 2014

Ghosts in the Graveyard

Twistleaf Yucca, Yucca rupicola

Commonly found growing in rural areas including graveyards, Twistleaf Yucca (Yucca rupicola) is sometimes called ‘ghosts in the graveyard’, for when in bloom the clusters of white flowers on thin stalks appear as floating apparitions.  But this common plant, which is widespread in our area, has a much more uncommon, mysterious association with a rarely seen butterfly called the Yucca Giant-Skipper (Megathymus yuccae). 

Flying in the spring, the Yucca Giant-Skipper is a medium-sized, robust-bodied butterfly with a fast, powerful flight.  Above, its dark forewings are elongated with a variable pale yellow outer band, and a yellow marginal border can be seen on the hindwings.  Below, the hindwings are a dark blackish brown with a violet-white frosting and prominent triangular white spot along the leading margin. Males and females are similar, but females are generally larger and males have wider, more rounded forewings.  Although fairly common, this species is like a ghost in the butterfly world, as sightings of adults are rare.

Tent formed by larva of Yucca Giant-Skipper

The most fascinating aspect of these butterflies is how they depend on the Twistleaf Yucca to carry out their life cycle.  Males perch on low vegetation or on the ground near twistleaf yuccas, awaiting passing females.  Producing only one generation per year from February to May depending on location, the cycle begins when the female butterfly lays a single egg on the leaf of a Twistleaf Yucca.  The young larvae (or caterpillar) feeds on the leaves of this plant and constructs small, individual silken shelters to protect itself as it grows.

Once larger, older larvae bore deep into the plant crown and feed within the root, constructing a prominent silk tent at the opening of the burrow.  Active tents can be discovered by looking for larvae excrement (called ‘frass’) that is pushed out of the tent opening before the larvae pupates.  In the spring, the adult butterfly emerges from the tent opening and allows its wings to dry before it takes flight and begins the search for a mate.  Adult yucca giant-skippers do not visit flowers to feed, and it is unknown how long they live, or if they utilize other food sources.

Yucca Giant-Skipper, Megathymus yuccae
Look closely and take care when performing your winter landscape cleanup, so as not to unwittingly destroy the tents that may be present on your Twistleaf Yucca plants.  These ghosts of the graveyard may just be harboring ghosts of their own!