Outdoors
The BDN outdoors section brings readers into the woods, waters and wild places of Maine. It features stories on hunting, fishing, wildlife, conservation and recreation, told by people who live these experiences. This section emphasizes hands-on knowledge, field reports, issues, trends and the traditions that define life outside in Maine. Read more Outdoors stories here.
Mother Nature loves to experiment. Every creature around us is the survivor of those experiments. In 1859, Charles Darwin called the process “natural selection,” observing that evolution favors survival of the fittest.
Some of those experiments were so successful, the animals have survived virtually unchanged since the dinosaurs. Crocodiles have been around for 95 million years. Sharks have existed for almost twice that long.
Birds are participants in nature’s experiments, all individuals striving to pass on their genes to the next generation. Every species has its own strategy.
Most birds produce young the old-fashioned way. They form pair bonds, and both parents raise the chicks. However, within those bonds, a considerable amount of infidelity occurs. For the species, sexual intermingling stirs up the gene pool in beneficial ways. For individual birds, it’s a certain victory for the female. No matter what happens, she’s sure to pass her genes along. But what about her poor cuckolded mate?
It’s a tradeoff. Males spend a lot of time and energy establishing territories and guarding them against rivals. However, they’re not above slipping next door for a little hanky-panky themselves. Unfortunately, the more they sneak into a rival’s territory, the less they can defend their own. Unfaithful males end up raising the offspring of other unfaithful males, and the gene pool gets a shakeup.
Species deal with this unfaithful canoodling in various ways. One way is to just relax and accept it. About 6% are totally promiscuous. Male grouse and woodcocks establish a breeding spot and invite every female into it, mating indiscriminately with all that are willing. Some even court in groups. Prairie-chickens gather in a field and dance together. Wild turkeys strut their stuff in a flock. In all these species, the females raise the chicks entirely on their own, and each clutch may have multiple fathers.
A tiny percentage of bird species practice polyandry. A single female mates with multiple males and lays multiple clutches. Each male then raises his brood alone. If you see a spotted sandpiper along a Maine shoreline being followed by chicks — which should start happening any day now — those chicks are following Dad, not Mom.
Some species nest in habitats so dense, it’s impossible to enforce fidelity. Birds in marsh and grasslands vocalize a lot, hoping to keep their mates safe from temptation. Their hopes are routinely dashed.
Nelson’s sparrows, nesting in Maine saltmarshes, don’t even try. Males just wander around the grasses, singing to attract a female, coupling whenever they get the chance. With so little certainty about whose kids are whose, the males play no role in raising chicks.
Bicknell’s thrushes reside atop Maine’s taller mountains in a zone of stunted spruce too thick to spot rivals easily. Males assume shared responsibility for raising the next generation. Since their offspring likely inhabit nearby nests, males bring food to multiple mates and chicks.
In some species, the higher the population density, the more likely both mates will cheat and thus maintain genetic diversity. Some colonial nesters, like bank swallows and cliff swallows, commingle their gene pools with reckless abandon.
I wonder about veeries. The veery is a thrush that tends to nest in small clusters. Often, when one starts singing, others join in nearby. They defend their tiny territories against their neighbors, but I suspect their proximity leads them into temptation more often than it does their cousins, the hermit and Swainson’s thrushes. I think my hypothesis would be a good study for a University of Maine grad student. It’s easy to get grant funding for any research project that involves sex.
Birds we hear singing in treetops are fiercely territorial. They chase intruders at the slightest provocation. Some males even follow their mates around to ensure faithfulness, although this strategy may be too exhausting to be effective.
Some species appear to be totally faithful. Larger birds, such as loons and raptors, need to collaborate to feed and nurture their young. This requires strong pair bonds between the parents.
You can observe these family dynamics for yourself. Notice that Canada geese babies are following around two parents. Mallard babies are following only the mother. Female common eiders and mergansers also get no help from Dad. To compensate, they form creches, joining multiple broods into one long flock, tended by mothers and aunts.
Mother Nature seems to be enjoying her gene-mixing experiments. It turns out that infidelity among mated pairs of birds produces a family tree that looks more like a bramble.
