Sky Dance

A pair of red-shouldered hawks came over the back yard this morning in full courtship mode. Screeching like gulls (red-shouldered hawks are among the most vocal of all the raptors), with translucent wingtips back lit against the sky in bright crescents, they spiraled about a common center, higher and higher until they were barely visible. At the apex of the spiral, the smaller male broke off and, with wings in the classic "M" bird configuration (think first graders' drawings), dropped like a hammer. He leveled off at tree-top level, searched out the female to make sure she was paying attention, and started the whole sequence anew. They spiraled up one last time and flew off with deep wing beats. All the squirrels in the yard had frozen against the boles of trees until the hawks were out of sight. They needn't have worried; dalliance, not lunch was uppermost in the hawks' minds.

Spring Tide

In the mid 1950's, the naturalist Edwin Way Teal wrote "The seasons, like the greater tides, ebb and flow across the continents. Spring advances up the United States at the average rate of about fifteen miles a day." So, late in February, Teal and his wife loaded up their Buick Roadmaster, drove from Long Island to Everglades City, Florida and commenced a 17,ooo mile drive north, zig-zagging across the continent and keeping pace with Spring until they hit the Canadian timberline. This odyssey produced a delightful book, North With the Spring and lay the foundations for a companion piece Autumn Across America. Back in pre-Interstate Highway days, a trip the breadth of North America was practically Homeric in its scope and execution.

Some of us, me included, while admiring the Teals in their adventures, prefer just to sit at home, a barnacle on a rock, and let Spring wash over us. For one thing, driving, even 17,000 miles to experience Spring still gives, at best, a series of snapshots. Sitting still lets you watch the whole movie from opening credits of skunk cabbage melting its way through the snow in February to goldfinches fledging their young in June for the fade out.

For one thing, once the leading edge of Spring creeps past you at fifteen miles a day, it's still Spring. And will be until the heat and humidity of Summer set in, usually way before the official calendar date. For another, Spring is probably the only season with nuance. There is early Spring, frequently confused with late Winter, mid-Spring, and late Spring where it blends into Summer, and innumerable shades of Spring within each piece. In the 1940's Edwin Halle wrote in Spring in Washington:"Our summers are tropical, our winter are arctic but our Spring and Fall are like nothing else on the planet."

Since Winter has decided to put in a farewell encore with night temperatures below freezing, Spring is temporarily on hold right now. This give me the chance to catch up on some items that otherwise would have passed by in the rush.

Two weeks ago, Spring was American toads in full trill, sounding like a fleet alien spacecraft on final approach. One toad sounds plaintive, but a whole marsh full of singers can be heard from a mile away, rising on the scale until you half expect the lenses in your eyeglasses to shatter. I always think of Ella Fitzgerald in the Memorex commercial bursting a champagne flute with her voice. The toads are drawn from the surrounding acres of woods to the marsh, the males singing and jousting for their ladies. A male will find a good place to trill his love song, and as soon as he hits the climax, like Pavarotti hitting the final high C in Nessun Dorma, another male will push him out of the spot and pretend his was the voice that drew the ladies. Tussles ensue. A pair of snapping turtles, the size of garbage can lids roam through the singers snapping them up like Godzilla rampaging through Tokyo. The toads in the direct paths of these behemoths leap out of the way. The rest just keep singing.

A week later, the marsh is silent save of the honking and hissing of nesting geese and the gabbling of ducks. Toad spawn lies across the surface and toad tadpoles sport in the shallows like herds of miniature hippos.

Froggie Went A Courtin

For weeks I've been telling Pat that spring is coming. She just laughs at me, explaining that if and when winter reappears, I will blame her. She is probably right. But as Bullwinkle the Moose used to say when trying to pull a rabbit out of his hat: "This time for sure". Of course, he always got a rhinoceros, but that's beside the point. This time for sure. The signs are getting too obvious: the front yard down the street is full of pale crocuses; the skunk cabbage is fragrantly blooming in wet places, using its perfume of cadaverine and other assorted rotted meat stinks to attract scavenging flies to pollinate it and to lay their eggs which hatch into hopeful maggots, only to starve in the warm depths of the spadix.

Today, spring manifested itself beyond doubt. Long skeins of Canada Geese are headed north. Aldo Leopold in Sand County Almanac, described the "March goose who is staking two hundred miles of black night on the chance of finding a hole in the lake with the conviction of an Old Testament prophet who has burned his bridges." Leopold lived in Wisconsin, on the edges of the frozen tundra; just a hop, skip and jump from Hudson Bay, the main breeding ground of most of the migratory geese east of the Rockies. The lines of geese I saw this morning, undulating and shifting like some aerial version of crack-the-whip, will probably move north until they find the last open water and wait out the next part of the thaw, leapfrogging until they get to ice-free territory.

The thing that clinched it for me, though, was the chorus of spring peepers and wood frogs I heard last night at a low swampy area a few minutes from home. The peepers were making their sleigh bells racket at full blast but underneath you could hear the lower, almost conversational duck-like quacking of the wood frogs. Wood frogs are one of the joys of backyard biology (although as E.O. Wilson, one of the prominent ecologists of our day, said: "Even the most humble roadside weed has a fascinating ecological history"). Wood frogs are one of those creatures that, if found only in Borneo or Tierra del Fuego, would rate an hour on Animal Planet. As it is, they are all over North America, from Georgia to the Arctic Circle and beyond. And that is what makes them so cool (in more ways than one). When winter comes, wood frogs can freeze solid, turning into little froggy Popsicles. As long as the temperature drops slowly enough, wood frogs can pull water out of their organs and muscles, sequestering it in their stomach and bladder where it can expand (water expands as it freezes, thus potholes in pavements) without rupturing cell walls and killing them. Slow chilling also allows the frog to produce anti-freeze glucose and other sugars helping to keep ice crystals from forming within their cells. Breathing stops, heart beat ceases, and the beast basically solidifies. Come the thaw, the frog reabsorbs the water, rises from its cocoon of ice, comes back to life, and starts looking for love.

Wood frogs breed in vernal pools. In fact, they are what ecologists call "obligate vernal pool species", meaning they breed nowhere else. Vernal pools are temporary snow melt and rain pools, forming in late winter and early spring. They may last for a few weeks to several months but they all eventually dry out. For wood frogs and other obligate vernal pool species, such as spotted and Jefferson salamanders, this is good and bad. Temporary water means no fish predators but it also means eggs must develop and hatch into larvae, larvae turn to adults, and adults get the hell out of Dodge before the whole shebang turns into cracked drying mud.

Wood frogs are "explosive breeders" meaning all the frogs in an area move to the pools and engage in a mating orgy. Since females may spend up to forty percent of their body weight making eggs, they need an additional year to build up body fat to make the next clutch - males outnumber females in a pool by two or more to one. Males lay on the surface, making their duck calls (the lower frequencies of which may propagate underwater) and attract interested females. When a female responds, the male climbs on her back and holds on, a behavior called amplexus. When the female releases her eggs, he fertilizes them as they come out. Eggs are covered in jelly, absorbing water until the egg mass forms a tight golf ball- sized mass. Fights break out as additional males try to dislodge the breeder or just pile on, hoping to add their sperm to the mix when the females drops her eggs. Males will attempt to mate with anything floating: females, sticks, and other males until they kick them off. Enough males piling on to a female will drown her, but even that won't stop them. Wood frogs make the old Roman Bacchanals look like a Sunday ice cream social.

Assuming everyone survives intact, females tend to clump their eggs with existing egg masses. The trick is to get your eggs out as early as possible so your clump is near the middle of the blob. The jelly-covered egg masses do hold moisture but those on the outside are at higher risk of drying out if and when water levels fall. The jelly acts as a solar panel, focusing and concentrating warmth towards the center, so eggs in the middle develop faster and turn into tadpoles earlier. Once a tadpole makes it that far, its troubles are just beginning. Here you are, stuck in a rapidly shrinking pool, with a gazillion other tadpoles, all trying to eat enough, fast enough to get out before the hammer falls. Even though there are no fish, a whole host of predators inhabit vernal pools and like nothing better than tadpole du jeur. Voracious dragonfly larvae stalk the bottom, slurping down anything that won't eat them first. In addition, carnivorous Spotted and Jefferson salamander larvae patrol the pools like tiny sharks. Even more fearsome are the larvae of Marbled Salamanders. Marbleds get a big head start on the other predatory salamander species by breeding in the same pools in late September on a wet night and placing their eggs under damp leaves. The eggs remain throughout the winter in stasis until the pool fills. They hatch in less than two days, becoming the alpha predator, the Great White Shark, in the vernal pool food chain. And don't forget, while the tadpoles are trying not to become lunch, the pool is steadily drying out. If the rate of drying hits a threshold level known only to the tadpoles, they change from happy little algae grazers and filter feeders into cannibals, chowing down on anything smaller, including brother and sister tadpoles and small larval salamanders, that crosses their path. Big eaters develop faster and get out sooner.

Animals living in vernal pools tend to share certain characteristics. They tend to be long-lived. Wood frogs live three to five years and salamanders up to twenty. Long life spans are conducive to "boom and bust" reproductive strategies - the pool may dry out early one year, dooming all the tadpoles, but next year it may last longer than usual and more frogs than average emerge. If you are an adult, all you need is two eggs to make it to breeding adults to have moved your chromosomes to the next generation (Darwin's definition of "fitness"). Vernal pool animals tend to be explosive breeders with everyone mating with everyone. Once the eggs are in the water, the adults quickly return to the forest and go back to whatever it is they do for the rest of the year. In the case of wood frogs, living in the leaf litter and eating small invertebrates, in the case of salamanders, going back into their burrows and doing who knows what for the next fifty weeks. But that is another story.

Tiny Dancers

Yesterday was warmish and sunny. I was on my deck, checking out the bird feeders, when I noticed movement like drifting dust motes in the long afternoon shadows over the azaleas. The motes were tiny mosquito-sized insects, bobbing up and down as if on invisible foot-long yo yo strings. The first question that popped into my mind was What are they?, followed by Why are they here? and Why are they here now? and finally, What the heck are they doing? I consulted my library and did some research on the net. That, plus a couple of calls to entomologist acquaintances, gave me an answer as to identity. They were Winter Crane Flies (family Trichoceridae for those keeping score), one of about 30 species in North America. My entomology text says "Usually seen in the fall or early spring, and some may be seen on mild days in winter. Adults form swarms, consisting mostly of males, over bushes or high places. The larvae occur in decaying vegetable matter". That was pretty much it. Okay, I thought, I know a little about what; maybe I can guess the rest, or at least make a reasonable inference.

They are here due to the abundance of larval habitat; dead rotting leaves. Larvae chomp their way through compost and damp leaf piles, pupating when the temperatures go below freezing and come out as reproductive adults as soon as it gets warmer. Adults do not eat. They are here to find a mate and reproduce, living on stored nutrients, like animated batteries.

They are here now because, duh, it's winter. Although most insects spend the winter as immatures (egg, larva, pupa) or hibernating adults (some butterflies), a few species can be seen on all but the most bitter days if you know where to look. If you can manage not to freeze, being a winter adult insect has advantages. One being few predators; birds are foraging for calories, not protein for their chicks, and insect predators like dragonflies are hiding out as the above mentioned immatures and not on the wing. Small size is an advantage as well; you are not worth the energy expenditure for a warm blooded predator such as a chickadee to bother with.

What they are doing pretty much all boils down to sex. The clue being the "Adults form swarms, consisting mostly of males, over bushes or high places" part. Although I haven't found anything in the literature, I'm reasonably sure the swarms consist mostly of lekking males. Leks are aggregations of males gathering for the sole purpose of attracting a mate. Leks are very efficient if your species is spread thinly on the ground. Males of many species form leks -Peacocks, Birds of Paradise, and Prairie Chickens lek, as do some bats and a few other insects such as solitary bees. Great Hammerhead Sharks gather over submerged mountains, coming from hundreds of miles around to form "breeding aggregations" which are probably leks. A lek is nature's equivalent of a singles bar, where (mostly) males congregate and do their damnedest to impress a female into choosing them for a partner. Males compete for females by showing off. Gaudy plumage, loud hoots, or, in the case of Winter Crane Flies, dancing. "Look at me" they are saying to cruising females, "I can bounce higher than the rest of the guys here, pick me." The advantage is that the female can pick and choose the best dancer with the best genes (he's the one bouncing highest, or at least the most enthusiastically), and mate with him. She doesn't even have to go home with him. Females are attracted to groups of males rather than to a single male, so swarming together, or hooting together, or shaking your gaudy plumage together, or trying to look your coolest in the same bar together increases your chances a female will seek you out. Or at least choose someone. Since most males in a lek are related and share at least some genes (except in most bars), even if you don't get picked, you can still get some of your genes out to the next generation just by being there.

Spring, or in this case, mild winter days, and a young Winter Crane Fly's fancy turns to thoughts of love. So get on your dancing shoes, all six, and join a lek. Who knows, you might get lucky.