The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Sunday, February 25, 2007

Skunks Are on the Trail of Romance in Spring
by Ro Wauer

In spring, like so many other critters, including humans, skunks turn their attention to love. They begin to wander about in search of that one true love of their life or, more truthfully for skunks, their annual affair.

Skunks normally live a solitary existence, only pairing up during the spring breeding season. Consequently, they are far more likely to meet their demise from high-speed vehicles in early spring, usually in February or March, when are searching for a mate, than at any other time of the year.

Our South Texas area has three species of skunks: eastern spotted, hognose, and striped, but only the striped skunk is reported regularly. The smaller less common eastern spotted skunk, identified by numerous white markings, is far more secretive and is rarely seen. It is found throughout eastern and northern Texas, while the very similar western spotted skunk occurs primarily in the Trans-Pecos and a portion of the Hill Country, and westward to the Pacific Coast. The larger hognosed skunk, with a longer snout and an all-white back and tail, is more numerous to the south and west, and is only rarely reported in the Coastal Bend. There is a fifth skunk species in Texas, the hooded skunk, which occurs only the Big Bend region.

The striped skunk is easily identified by its black body and narrow white stripes that runs from the top of its head backward along its back, like an elongated V. About the size of a large house cat, striped skunks can appear almost anywhere, from our fields and woodlands to even our residential areas. Nocturnal in behavior and rarely encountered, they are more often detected by scent than they are seen.

All skunks possess scent glands with an obnoxious odor that they can spray at an antagonist when disturbed. When hit by a vehicle, they usually will spray automatically. Although it may seem that the typical skunk odor is commonplace, they spray only as a last resort. The scent glands, located near the base of the tail, are normally activated only after the animal warns the intruder first. It first will audibly strike the ground with its forefeet and even make short rushes at its enemy before actually using its potent spray. It finally will bring its rear around toward its enemy, with its tail erect, and then discharge fine yellow droplets through small ducts that open just inside the anus. These glands are encased in muscles that can be voluntarily controlled by the animal when the situation demands it. The powerful scent may then be detected miles away during favorable weather.

Skunks are omnivorous, feeding on practically any animal they can find that is small enough to capture. Insects may constitute from 50 to 90 percent of their diet, but snakes, frogs and even freshwater clams that are often dug for in loose sand, are utilized. Skunks also love bird eggs and babies. And their few enemies consist of humans, large dogs, coyotes, bobcats, and great horned owls. Few nighttime predators are large enough and aggressive enough to kill a skunk. The skunk’s powerful defense immunizes them effectively from most potential enemies.

Until recently skunks belonged to only a subfamily of carnivores, along with dogs, cats, raccoons, badgers, weasels, and bears. But, according to David Schmidly's revised book, The Mammals of Texas (Univ. Texas Pres, 1994), they were raised to the family level Mephitidae, based on molecular studies and their truly unique behavior.

Sunday, February 18, 2007

How Fast Do Birds Fly?
By Ro Wauer

On several occasions the last few weeks, a Cooper’s hawk has zoomed through my back yard where I have a number of bird feeders. A second or two before the hawk appears all of the songbirds utilizing my feeders suddenly explode, dashing for cover in the adjacent brush or oak foliage overhead. They are somehow warned of the approaching hawk, probably by a bird chirp at the outer edge that detected the hawk first. But in at least one instance the Cooper's hawk already had a bird in its talons, probably captured just before passing through.

The hawk's swift flight caused me to wonder about its speed. After all, predators of all kinds, rather birds, mammals, or reptiles, depend upon speed, timing and/or surprise for their survival. A Cooper's hawk is one of the pursuit hawks, often referred to as an accipiter, that can quickly accelerate to 60 mph, although it and the closely related sharp-shinned hawk may fly as slow as 16 to 20 mph. The larger and more common full-time resident red-tailed hawk commonly flies at 20 to 40 mph. The American kestrel, a common wintertime falcon, has a flight speed that varies from 22 to 36 mph. And golden and bald eagles fly from 28 to 44 mph.

The fastest of all birds is the peregrine falcon at over 140 mph, and some claim that a diving peregrine can reach more than 200 mph. This large predator can actually chase down swifts that can fly at more than 100 mph. Peregrines reside through the winter along the Texas coast, and occasionally they are seen 30 to 50 miles inland. Waterfowl and shorebirds are favorite prey species that, even in an accelerated escape mode, are in no way able to escape from the much faster peregrine. Ducks have been recorded to fly from 40 to 65 mph, while a spotted sandpiper, a common wintering shorebird, has been clocked at 25 mph.

Hummingbirds seem to be extremely fast, but that is largely due to their relatively small size. Ruby-throated hummingbirds, the common species that we see daily during the summer months, normally fly at 28 mph, although one was clocked at 50 mph with a tailwind. High-speed photography has been used to time their wing beats at about 70 times per second.

Wing beats also vary considerably, from the 70 per second of hummingbirds to as few as two beats per second for the American crow. Chickadee wing beats average 27, mockingbirds 14, American goldfinches 4.9, European starlings 4.3, eastern bluebirds 3.1, domestic pigeons 3, mourning doves 2.45, and American robins 2.3. And the great blue heron, a huge wader that is common along area waterways and wetlands, barely beats its wings at a rate of one per second. Its normal flight speed had been clocked at 28 mph, but it has the ability to speed up to 45 mph.

But what about the flight speed of the average songbird that we see daily in our yards and fields? Most fly at 15 to 25 mph, but they often can accelerate to about twice that speed for short distances when pursued. The crow, among the most common birds in the Golden Crescent, has a flight speed at 16 to 19 mph; the common house sparrow is one of the slowest at 16 to 19 mph; blue jays normally fly at 20 mph; loggerhead shrikes at 28 mph, American robins at 32 mph, and barn swallows at 60 mph.

A bird's relative flight speed is most evident when it is fleeing from a faster bird. But a predator's speed is often only part of its success. I once watched a Cooper's hawk sitting in a tree overlooking a pond at Guadalupe Mountains National Park where white-throated swifts were drinking. The swifts were making passes over the pond, right to left from the hawk's perspective. After considerable time watching the swifts, the hawk took flight just as a swift was approaching the pond, and its timing was so perfect that it picked off the swift, grabbing it at from a side approach, and flew back to its perch to consume its prey.

Sunday, February 11, 2007

It's Time to Get the House in Order for Purple Martins
by Ro Wauer

Still winter and too early to get ready for purple martins? Think again. Some of the first males can arrive in South Texas the first week of February.

Although our first martins usually do not appear until mid- to late February or early March, it’s time to prepare for their arrival. That means cleaning the martin house, getting rid of the spiderwebs and insects that may have taken over since the rightful tenants vacated in midsummer of last year, and hoisting it up the pole so it's ready and waiting.

Martin house preparation may include a fresh cover of white paint, at least for the wood houses. The metal houses require less attention. And in recent years, white plastic gourds have become popular. But all that have been previously used must be properly washed down. The light color helps to reflect the hot Texas sun and also to highlight the entrance holes.

In addition to the above preparations, predator guards may be necessary. Guards fastened on the poles keep raccoons, squirrels, and snakes from climbing to the house. And aerial predators, such as hawks and owls that land on the house and reach in to extract an adult or baby martin, can be controlled with an external owl guard. Although these features can often be purchased at nature stores, such as Wild Bird stores, they also can be purchased from the Purple Martin Conservation Association at www.purplemartin.org or by phone at 814-833-7656.

In case this is your first time at attracting martins, here are some easy rules to follow:
* Houses must contain apartments with at least a 6 x 6-inch floor space and an entrance hole 1 ¾ inch in diameter and 1 inch above the floor.
* Houses must be placed on poles 12 to 20 feet above the ground and should be 40 feet away from taller trees, poles, other structures, as well as vines and shrubs, that might allow predators to better reach the house.
* Houses must be free of nesting materials and other debris that accumulated during the off-season.

Purple martins often are rather finicky at the start but seem to put up with shorter poles and poorly maintained structures once the colony is established. Most bird are repeats, but the majority of the first-year birds (usually last year's youngsters) seek out new sites, usually in the general area of their natal home site. This means that a new martin house, especially if it is in the proximity of an active martin house, is likely to be used early on. Distant houses are not as likely to be selected.

Another way to attract first-year martins is to play a tape or CD of their dawn chorus. Playing purple martin songs at a new martin house will certainly attract their attention. And if they like what you have to offer, they will probably remain and nest. If not, give it time, and sooner or later you will attract martins that will begin a new colony.

An established martin colony is likely to return year after year so long as you maintain the house and environment. They will consume millions of flying insects during the short time they are with us. And they will also provide us with their marvelous songs from long before dawn to throughout the day and evening. By mid- to late July they will leave our neighborhoods and begin their 5,000-mile southward migration to their wintering grounds in South America.

But rather than think about their departure, think first about their arrival. It is now time to prepare. Good luck!

Sunday, February 04, 2007

Where Monarchs Reign
Carol Cullar, Eagle Pass News Guide, week of 2-4-07

Just a few miles due south of here, roughly six hundred fifty, to the Transvolcanic Mountains of Michoacan and some one hundred fifty miles west of Mexico City, there is a tiny region on the globe that is ideal for monarchs.

If this were a fairy tale, then at this point, the children would all know that this was a perfect place and they would chant together that this place was “Not too hot and not too cold!” In fact, it is just right. It has been “just right” for possibly the last ten thousand years—a region of pine and fir-covered peaks between nine and fourteen thousand feet high.

These peaks have their bases firmly set in the tropics and each has a sheltered southwest side where nighttime temperatures rarely go below 32º for any length of time.

On November 19th, 2006, a winter storm began and persisted for two hours. In the morning of Nov. 20th the north sides of the sanctuaries of Sierra Chincua and Sierra Campanario had light snows. The snow persisted only for the morning on the tips of the crowns of the trees where it had accumulated. The rains and the cloudy skies lasted for four days until November 23rd. On the dawn of the 20th and 21st the temperatures fell to 0.78C (33.4 fahrenheit); and during the dawn of November 25th, the temperature descended to -0.38ºC (31.4 fahreneheit.) Fortunately, the massive mortality of monarchs did not occur as was noted on two occasions in the last five years. In 2001 and 2005, freak ice storms cause the death of eighty percent of the population.

Coupled with the dry season currently persisting over Southern Mexico, these mild conditions are sufficient to cool the butterfly’s ardor and serve to keep their metabolism slowed below the temperatures needed for active reproduction. In an bug whose typical lifespan is between fourteen and twenty-eight days, this chill enables the brightly colored insect to hide out from the cold of its typical breeding grounds to the north and survive the lack of flowering plants on which to feed.

The winter’s population is measured each December by figuring the number of hectares covered by their mass, then counting the number of trees within that particular colony. This year researchers located eleven hibernating colonies: seven within and four outside the Monarch Butterfly Biosphere Reserve. Six colonies were located in Michoacan and five in the state of Mexico. The butterflies occupied a forest surface total of 6.67 hectares, which represented an increase of 12.7% with respect to the 5.92 hectares occupied during 2005, and more than three times the area occupied (2.19 hectares) during, 2004.

An exact nose count of the actual number of individual butterflies is impossible, since each tree is estimated to hold between 40-100,000 monarchs. Scientists vary in their estimations of how many monarchs exist per hectare (2.6 acres). Some go as low as 10 million; others as high as 50 million. So this year’s actual population could range between sixty-seven million and 334 million monarchs.

Now they are merely awaiting the mysterious signal that tells them when it is time to return. During the last week of February and the first two weeks of March something happens. Perhaps it is the arrival of the sun at a particular angle in the noon sky, perhaps other unknown factors govern their departure. Whatever the trigger, it is abrupt. Within a matter of days some 140 (or more) million monarchs cascade down the mountains into the warmer tropic regions and began their return journey toward the arriving spring in the north.

All of those survivors will develop adult reproduction and begin to mate as they fly north, searching for their host plant, the lowly milkweed. And where are the first signs of tender milkweed sprouting from the earth? Why, south and southwest Texas, of course!

Fields, pastures, roadsides in the region west and south of San Antionio are absolutely vital to the health and size of the entire monarch population of the United States and Canada for the coming year.

If they meet with breeding success, determined by low fireant counts and rain-fed host plants (hierba de zizotes, antelope horn, green milkweed, and Mexican milkweed in people’s yards), then the monarch populations will multiply and spread across the continent, until the fall brings their grandchildren back to Eagle Pass and their journey south.

Watch for Early Spring Butterflies
by Ro Wauer

After our recent cold and wet weather, I am more than ready for butterflies. Yet I know that it will still be several weeks before butterfly numbers are back to what we can expect during the warmer days in late spring. But that doesn't mean that we can’t start watching now for some of the very early species, especially for the two butterflies, Henry's elfin and falcate orangetip, that fly in early spring that we will not see the remainder of the year.

Henry's elfin can be expected first, in early to mid-February just when agarita shrubs begin to bloom. The yellow flowers of these early flowering plants seem to be a preferred nectar source for these little hairstreaks. They often will remain on the flowers for some time, even allowing for a reasonably close approach to see them well or to get a photo. Others will easily frighten with a close approach, and swiftly fly away. Henry’s elfins are not the easiest of butterflies to locate, however, as they are only quarter-size when perched and their brown, black and gray colors blend in very well with the plant's branches and leaves. Elfins undersides have a very dark base and lighter, almost frosty, margin. A close look will also reveal two tiny white spots at the forward and trailing edges of their hindwings. And really fresh individuals, those that have only recently emerged and not worn, will possess extremely short tails. Larval foodplants for this hairstreak can vary from redbud to Mexican buckeye, to Texas bluebonnets, viburnum and American holly.

The second springtime only butterfly is the falcate orangetip, but very, very different than elfins. This is a gorgeous little creature with a wingspan only a little over one inch. The upperside of this miniature white is all white except for orange wingtips on males and a central black dot on females; females lack the orange wingtips. The forewings are slightly hooked, thus the falcate name. The underside of both sexes is mottled silver and black with greenish edges. When perched they fold their wings so their undersides is visible. Yet they seem to spend most of their time on the wing, flying about searching for either a mate or, in the case of the females, for specific larval foodplants, including rock cress, bitter cress, and a few other mustards, on which to lay eggs. Their flight is swift and constant and usually low to the ground, so following one in anticipation of it landing to allow for a good look is seldom worthwhile; most good observations are the result of serendipity.

Besides the fact that both of these butterflies fly only in early spring, there is another similarity. Their tiny caterpillars hibernate most of the year. Orangetip females, however, lay a single egg on each hostplant; they are able to detect an egg already laid on the host. The tiny caterpillars feed on the hostplant's leaves and flowers before hibernating. But elfins may lay several eggs on a single hostplant. The caterpillars also feed on the hostplant's flowers and leaves before going into the hibernation stage. But by early spring they become active and are soon flying about to the delight of all us butterfly lovers.