The Nature Writers of Texas

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

Thursday, August 27, 2009

Spiders, Up-close and Personal
by Ro Wauer

Spiders have always been fascinating creatures to me! A bit alien, a little scary, but always fascinating. So a recent experience of watching a jumping spider stalk a skipper butterfly truly got my attention. I was first attracted to the skipper that turned out to be a Carus skipper, a new county record, as it feed on gold lantana. Half way through photographing the skipper, I realized that it was being stalked by a jumping spider, a potent predator of butterflies. My attention then shifted to the spider and I watched it edge ever closer to its prey. But apparently I didn’t give the skipper enough credit, because it suddenly flew away to another part of the lantana, and the spider retreated from view.

Jumping spiders are commonplace in Texas. I find them in all sorts of places from flowers and shrubs to various human-made structures, including the deck of my house. They can be tiny, less than a quarter of an inch, to those that reach almost an inch in length. All are rather squat with a head containing mouthparts and eight eyes, a thorax, a thin waist, and an abdomen with eight long hairy legs. All spiders are predators that feed on a huge variety of insects, especially flies and other invertebrates, including other spiders.

Although most spiders are nocturnal in behavior, jumping spiders are daytime hunters. They capture their prey by a stalking and jumping attack; some species can jump twenty times their own length. When sufficiently close, the spider lowers its body, fastens a dragline to the surface, and then leaps onto its prey. A jumping spider detects prey with any of its eight eyes, but it will then zero in with its larger central pair of eyes that are based on long tubes that work like miniature telephoto systems.

Most of the 4500 species of jumping spiders live in the tropics, but North America also has its share. Of the more than 35,000 species of spiders of 105 families, the jumping spider family is the largest. But the cobweb weavers may be more obvious. And the crab spiders may be more noticeable to those of us interested in butterflies. Crab spiders hide among the flowers and grab many an unsuspected butterfly. Although most crab spiders are only about an inch in length, they capture surprisingly large insects, including monarch butterflies.

All North American spiders are venomous, although very few possess venom that can seriously harm humans. The black widow accounts for 50 percent of all recorded spider bites. Black widow and recluse spider venom is neurotoxic, affecting the nervous system, but other spider venom is cytotoxic causing damage primarily to the tissues. Spider venom has been studied for their values of dispersal of blood clots that cause heart attacks and also for use in developing safer kinds of insecticides.

When spider specialist John Comstock of Cornell University was asked “What good are spiders:” he replied “They are damned interesting!” And Paul Hillyard, in “The Book of Spiders,” wrote: “One can find spiders that catch their prey with a sticky globule on the end of a silk line. There are spider architects that construct impressive webs overnight and then take them down again in the morning. One can find caring, responsible spiders that build nursery webs for their families while others carry the whole brood of their back. There are spider engineers, which tunnel into the ground and make secret passages for escape in case of intruders. There is even a unique spider “frogman” which takes down an air supply to breathe underwater. Many species preserve and store food for a rainy day when no flies are about, but some crafty little types have turned to a life of crime and do nothing more than steal food from the webs of their bigger brethren. Still, there is actually one that knocks at the door of another spider’s home and waits for an answer before entering.” But my favorite is the jumping spiders.

Thursday, August 13, 2009

Fall Bird Migration is Well Underway
by Ro Wauer

Fall in South Texas is an exciting time of year! For birders and other nature lovers who spend time in the outdoors, it is next to impossible not to notice our south bound migrants. They include birds of every color and shape, many of which we might have seen on their way north in spring. It only makes sense to be filled with wonder. And many folks ask about bird migration. Here are answers to a few of the more common questions.

Where are the migrants going? Most of our passing birds are Neotropical migrants, species that spend their winters in the Tropics, from central Mexico to South America, and nest in North America, from Texas to Alaska. Some Arctic shorebirds that winter in southern South America and nest in northern Alaska travel a round-trip distance of well over 13,000 miles.
Most of the springtime songbirds passing through South Texas are Trans-Gulf migrants that leave Mexico’s Yucatan Peninsula in early evening and arrive along the Texas Gulf Coast the following day (depending upon weather conditions), a distance of about 550 miles. A smaller number of those same songbirds also take a Trans-Gulf route in fall. Songbirds are able to fly nonstop for eighty to ninety hours.

Do all birds migrate at night? Most do, but many others, such as hummingbirds that feed on nectar and swallows and flycatchers that are insect-eaters feed in flight, usually migrate during the daylight hours. We see many of these birds flying south over the fields and woodlands during the months of August, September and October.

How fast do birds fly? Most long-distance migrants travel between 25 and 40 mph. Flight speeds vary with their activity. For instance, purple martins fly at 27 mph, shorebirds fly between 45 and 55 mph, hummingbirds may fly up to 55 mph, but peregrine falcons, our fastest known bird, can stoop at over 125 mph.

How high do birds fly? It varies with the topography, but 90 percent of all migrating birds fly between 5,000 feet above ground level. Many fly much lower so we are able to hear clips on a calm day or night. They tend to fly higher at night when flying over land.

Do birds migrate in mixed flocks? Mixed flocks of songbirds, ducks, and shorebirds are normal, but some other species, such as nighthawks and chimney swifts, usually stick with their own species. In fall, several raptor species can often be found within one area, but most hawks also stay with their own kind.

How do birds prepare themselves for migration? Most accumulate great quantities of fat as fuel for their long-distance flights. Many double their weight. The tiny ruby-throated hummingbird, weighing 4.5 grams, uses 2 grams of fat to fly nonstop for twenty-six hours. A typical bird will lose almost one percent of its body weight per hour while migrating.

What is a bird’s signal to migrate? Although the answer is complicated, a simple answer is the increasing or decreasing hours of daylight in spring and/or fall. Arctic birds can raise a family in only a few short weeks, due to the long daylight hours, and often are some of the earliest fall migrants found in South Texas. Most of the earliest fall arrivals are males, while the females remain on their nesting grounds a bit longer to care for the nestlings.