Nature Notes: Trick or Treat

There is a lot of exposure accompanying migration

   The great migration south is about to begin. It will include millions of birds, millions of fish, many different bats, and quite a lot of butterflies and dragonflies. Although at the boreal latitudes, many mammals, including two species of caribou, use their legs to march long distances, in the temperate zone where we are, migration is a matter of wings and fins. Shorebirds, terns and ospreys, to name a few, have already started down. Some of them go thousands of miles, deep into South America, a few like the Arctic tern, all the way to Patagonia.
    There is a lot of exposure accompanying migration. Just as driving 1,000 miles on roads and highways in uncharted territory increases the chances of an accident severalfold over compared to driving back and forth around one’s neighborhood, the vulnerability for migrating animals and insects traveling long distances is increased exponentially over that for all-year residents such as house sparrows and blue jays that are mostly stay-at-homes.
    One way to minimize the chance of predator encounters by birds is to migrate at night rather than during the day. While owls are adept nighttime predators — they are usually looking for mice, rats, and small mammals to feed on — bird hawks don’t fly at night. The chief worries for the night migrants are meteorological in nature; however, in 20th century a new obstacle to night migration was created, this one anthropomorphic in origin. Encounters with skyscrapers in large cities across the globe account for thousands of bird deaths during times of migration. Toronto has the distinction of causing the most losses, but New York, Chicago, Philadelphia, D.C., and so on are not far behind.
    Think about it, ever since the end of the last ice age, for at least 10,000 years or more, birds have been migrating north and south annually, mostly at night. One hundred centuries of clear unobstructed sailing back and forth over the same routes and then one year, boom, tall buildings appear out of nowhere and birds start falling like flies. In addition to the hundreds of looming edifices now in the path of any one of the main north-south migratory routes, there are thousands of windmills and cellphone towers making migration through unlighted skies a real problem. It takes many, many generations to change a pattern of instinctive behavior that is thousands of years old!
    So, why not migrate during the day? If you are a small bird or insect, you better be careful, for hawks and other expert avian predators will be waiting for you. Better have some kind of protection or it’s curtains for a lot of you. At least for one species, the monarch butterfly, protection comes from having an unsavory taste. Both males and females are identically bright orange and readily detectable from above or below as they move south toward the overwintering grounds in Mexico’s mountains. Some may be blown off course by stiff winds, but very few are taken by predators. They taste simply awful.
    Monarch butterfly eggs are laid on milkweeds, which contain a sap that is not only acrid tasting but poisonous as well. Almost no herbivorous mammals, such as cottontail rabbits and deer, have use for milkweeds. The larvae of monarch butterflies and milkweed beetles, however, prefer them. As they eat and grow larger, they store those unpalatable chemicals in their body tissue and when they pupate and emerge from their pupae as flying adults, their body tissues still contain them. That is why the milkweed beetle is also spectacularly marked bright red and black. It’s called warning coloration: “I am a monarch butterfly, I am a milkweed beetle, you can see me clearly, come and take a bite.” Predators have learned not to.
    In fact, red is a standard warning color for many diverse creatures. The West Coast newt, Taricha torosa, is a good example. Eat a little bit of this salamander and you’re liable to become deader than a doornail. It’s like eating a death angel mushroom. The velvet ant, in actuality a wingless wasp, has a potent sting. Fortunately, it is bright red and black, and so is usually uncontested. The female black widow spider is another good example. The western species have a red hourglass on the underside of the abdomen, the eastern ones, including the ones on Long Island, have a red rear end or red spot just above it. “Stay away, I’m warning you,” the red mark says for the spider. (The male is much smaller, not poisonous, and nondescript in coloration.).
    Bats are adept at catching flying insects in the dark, so it makes sense that they would migrate at night, nibbling along the way as they fly to their winter quarters in caves hundreds of miles away. One local exception is the red bat, which every year crosses Long Island on its way north in the spring and south in the fall, flying during the day. Its redness is a kind of mimicry. It is not poisonous or bad-tasting itself, but why take a chance? The viceroy butterfly, which occurs farther to the west, is almost identical in coloration to the monarch. It mimics the monarch and is mostly safe from predation. However, viceroys, which stray to areas where monarchs never exist, are another matter. They are easy game. Fortunately for viceroys, monarchs have a very widespread distribution in North America. The lionfish, which strays into our marine waters during the warmer months, is quite red and quite poisonous. In human society, red also serves as a warning color. Which came first: the red warning signs of humans or those of insects, salamanders, fish, and bats?
    The human species is one of the few in which the female is generally more attractive than the male. Female clothing and accouterments such as lipstick and hairdos, bikinis and high heels, jewelry and perfume heighten their attractiveness.
    The opposite is true in songbirds, however. The males are mostly knockouts and the females drab. Moreover, the males sing better than the females, which are mostly silent except for chips and peeps. It’s a simple case of differential survival. It’s easier for a bird predator to spot and catch a prettily clad male than a dull-colored female. In nature just as in human cultures, you can pay a price for too much vanity.
   While the brown recluse spider is an exception, most poisonous animals are vividly colored or advertise their toxic state in other ways. Take the poisonous coral snake of the Southeast. Its red and black banding is quite obvious. The scarlet king snake has the same coloration and is harmless. But unless you’re an expert ophidiologist, I’d avoid both. The gila monster’s yellow and black beading over its body is scary. Bumblebees are bright yellow and black. They don’t want to sting you. They’ll die if they lodge a stinger in you, but they will if cornered.
    On the other hand, some poisonous animals do not possess warning colors; they have other means of saying “beware, beware!” The rattlesnake rattles, the cobra rears up, flattens its collar, and hisses. Long Island’s own eastern hognose snake doesn’t have a rattle, but it hisses and shakes its tail in the sand mimicking the two poisonous snakes. If that doesn’t work, it rolls over and plays dead, an altogether different kind of defense mechanism, which is used by opossums and several other species.
    The blowfish, or northern puffer, blows up when cornered, becoming almost unswallowable to most would-be predators. The squids and octopi secrete a blinding ink.
    There are all sorts of ways of protecting oneself without having to go to war. When I was a young boy, my mother advised me to act stuporously when traveling on subways in New York. Nobody will hit on you if they think you are weird. I wonder if that stills works today?