Thursday, February 27, 2014

Good scents

It’s the middle of the night. You are sound asleep until, suddenly, your nose drags you out of your dreams and into the world of reeking romance.

In February and March, skunks go a-courting. But admiration isn’t always mutual, so a female may decide to send off an overly aggressive male with a shot of her perfume; hence, the sudden burst of scent seeping into the house on a late winter night.
Despite their occasional odors, however, skunks are wonderful animals – gentle, shy, and rarely disposed to using their defenses. People have accidentally caught skunks in Havahart traps aimed at woodchucks, and were not sprayed or even threatened as they let the captives loose.
What’s more, skunks eat many rodents and pest insects – even digging up yellow jacket nests to get the larvae. Savvy farmers love skunks for just that reason. One farmer who had a skunk living in a barn for five years said, “My skunk never sprayed in or near the barn, although he did occasionally have residual stink from an argument elsewhere!”
So putting up with some bad scents can make good sense.

Wednesday, February 26, 2014

Survival of a bright red beacon

A male cardinal is the most common, North American “animal” of size that is virtually all red, a color used by few wildlife species hereabouts. We have a few small red beetles and salamanders plus several birds, like tanagers, that mix bright red with other others, but what else is almost all-red?

Cardinals don't seem to need camouflage.
Ornithologists say male cardinals have probably evolved their bright, distinctive color to attract female cardinals. However, how do they survive so well in the wild with such a rare, flashy outfit that, even among the fully leaved trees of summer, seems to stand out like a sore thumb?

Hawks see red. Why, then, don’t they decimate the population of male cardinals, which seem to do little to hide themselves, especially in winter when the deciduous trees have no leaves for cover.

The answer probably lies in our own perception of color vs. a bird’s perception.
“Birds see very differently from the way that we do,” says Chris Elphick, assistant professor of ecology and evolutionary biology at the University of Connecticut.

“They see into the ultraviolet ranges and have different types of receptor cells in their eyes, so a bird that seems the brightest to us is not necessarily the brightest to another bird — such as a hawk.

“How a hawk sees a cardinal — or anything else — is thus hard for us to conceive,” he adds.

An evolutionary biologist named John Endler found that how a color looks can depend on surrounding colors because of the wavelengths of light that are absorbed by the environment. Thus, in the forest full of green, red light tends to be absorbed, so red objects would not stand out the way they would against, for instance, a snowy background. “This phenomenon helps explain why scarlet tanagers — or any number of warblers — can be so hard to pick out even when there are not leaves obscuring them,” Professor Elphick observes.

He adds: “It’s important to remember that evolution always involves a balance between benefits and costs. Being conspicuous has potential costs — e.g., increased predation risk — but if those risks are balanced by greater benefits — e.g., more/better reproductive opportunities — then maybe that’s OK, evolutionarily speaking.

“Also, hawks are rare relative to cardinals, so even though a cardinal may be vulnerable when it encounters a hawk, there may be enough cardinals that do not have such encounters that the selection pressure to be less conspicuous is not as great as it might seem. And, of course, just because a cardinal is seen by a hawk doesn’t mean it will get caught.”

Laura Erickson, science editor at the Cornell Lab of Ornithology, reports that hawks can definitely see red. “But they can see a whole spectrum of colors, and much of their favored prey is more muted in color, so there is no good reason for hawks to focus on cardinals.

“Cardinals, like Scarlet Tanagers, spend much of their time hidden in foliage, and it’s very difficult for even accipiters [bird hawks] to grasp prey from the branches that cardinals favor.

“Goldfinch or Prothonotary Warbler yellow, Blue Jay blue, and oriole orange are almost certainly at least as vivid to a hawk’s eyes.

“The brilliant colors of many birds, especially when found on males only, tend to be territorial and sex signals. Of course, birds do tend to be safer when not noticeable to anything, so many of the most brilliant birds do molt out of those bright colors during the non-breeding season. New feathers on male Northern Cardinals are edged with brown, and the tips wear away to reveal the brightest red at the end of winter/early spring. But Baltimore Orioles and Blue Jays stay in their bright feathers year round.”

Laura adds, no doubt with a smile, “You know what color is even rarer than red in the bird world? Pink. Apparently, birds shun Mary Kay cosmetics, too.”