May 20, 2019
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Birds have evolved to excel at certain skills

Bob Duchesne | BDN
Bob Duchesne | BDN
The northern shrike is a predatory songbird, able to chase down small birds.

Evolution is nature’s way of ensuring survival of the fittest. “Evolution” is also the name of a board game from North Star Games. I played it several times with family members over the holidays. It’s a hoot.

“Evolution” is a simple game, yet not simplistic. In short, it mimics evolution. Each round, prehistoric critters must find ways to survive. There’s not enough food for everybody. Sometimes they eat each other. Every round, cards are dealt to each species that augment its ability to feed itself. Some cards help the species defend itself. Some cards help the predators overcome these defenses. The strong prey on the weak. Just like nature.

For instance, some critters are dealt long necks, so they can eat the leaves higher in the tree. Some gain more food by cooperating. Some are better at foraging; some are better at scavenging. Some use their greater intelligence to find food.

Likewise, some critters can hide safely underground. Some critters develop hard shells or protective horns. Some engage in defensive herding. Predators overcome this defense by hunting in packs. Some small animals can climb to safety, but some predators can also climb. And so it goes.

I am deeply amused by the game, because it reminds me of how often I see this same game played out in the real world. Long fangs on a saber-toothed tiger may have made sense when the prey was a mastodon. Tigers didn’t need such long canines when they switched to eating people. Maine’s bird world is full of such evolutionary amusement.

Picture the great blue heron. It has long legs, so it can wade more deeply than any competitor. But then it needs a longer neck to reach the food. Despite its size, it nests colonially in trees, where it is safe from coyotes and bobcats — but vulnerable to eagles and great-horned owls.

Fish school. This mimics the defensive herd instinct in the “Evolution” board game. But some birds attack in packs. I’ve watched up to 15 loons dive together as a unit, concentrating the fish into a convenient feast. I’ve seen flocks of up to 300 common mergansers do the same thing in front of my house. At the ocean, I’ve witnessed hundreds of black scoters diving simultaneously.

I’ve often wondered what keeps blue jays alive. They are big, slow, colorful and tasty. They should be easy pickings for a marauding hawk. But they are also very vocal, raising the alarm whenever trouble approaches. As it happens, “Warning Cry” is also one of the defenses in “Evolution.” Only a predator with “Ambush” ability can overcome that defense. And that is exactly how a successful hawk catches a blue jay. Sharp-shinned and Cooper’s hawks flash in from trees around the perimeter, unseen until it’s too late.

Last week, I saw a northern shrike in the distance. This winter visitor from Canada was hundreds of yards away — too far for me to spot field marks — but I recognized it right away, because of evolution. It has developed a distinctive flight. The shrike is a predatory songbird, able to chase down small birds. It only needs speed for a brief distance, so it has evolved short wings that allow it to accelerate quickly. But turbulence builds up behind short wings, inhibiting flight. Birds overcome this disadvantage by gliding for a short distance between bursts of flapping. This flutter flight, interrupted by brief pauses, is particularly obvious with shrikes.

Evolution gifted birds with flight. Some birds returned the gift. For seabirds that must dive deeply and swim underwater, wings are an encumbrance. Penguin wings are short and stubby, suitable only for underwater propulsion. Some Maine birds are headed that way. Puffins can barely fly. They have to flap their tiny wings so quickly that they resemble bumblebees. One puffin cousin, the thick-billed murre, is predicted to be the next species that will sacrifice flight. They are poor flyers, but extraordinary divers. The nearest breeders are in Newfoundland, but they do venture into Maine waters in winter.

Think of the weirdest-looking birds, such as woodcocks, pelicans, vultures and hummingbirds. Whatever it is that makes them weird is also what gives them an advantage. Think of normal-looking birds. Each has its own advantage. The robin may not look weird, but its bill is perfectly designed for plucking worms from the lawn. As you’re watching birds in 2019, think about why birds look the way they do.

Each must follow two rules: Eat. Don’t get eaten.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.

 



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