Sargent’s view murder on the sandy point marsh columns newburyportnews.com gas company

#####

Most snowy owls have to hunt both diurnally and nocturnally in order to find enough food to thrive. But this owl had adopted crepuscular behavior, hunting in the low light of both the evening and at dawn. Then she would use her white camouflage, night vision and ability to fly noiselessly to swoop down toward a sleeping duck until it was awakened by pressure waves coming off the owl’s wings.

The duck would jump out of the marsh vertically, then hang stationary for a second before righting itself to attain its maximum flying speed, which was several times faster than that of the owl. But the owl would have already lunged directly at the neck of the terrified bird that had never encountered such a formidable predator. With one quick bite of her powerful beak it would be over. Every time I visited the owl I found the decapitated carcass of a duck or goose that was often twice as large and heavy as the rapacious owl. Good thing for us, she is no longer the size of her distant cousins, the velociraptors.

After eating her fill, the owl would return to the top of the dune where she blended in with the white sand and snow, unseen and unmolested by coyotes and photographers that she probably thought were equally predatory. A snowy owl in Salisbury had adopted the opposite strategy, showing off and becoming friendly with the photographers who flocked to see it atop a light pole every day.

So how had this pioneer bird discovered that her perch was so superior to those selected by other snowy owls? Did she somehow realize that selecting and defending this territory would provide her enough protein to return to the Arctic to raise her own chicks? Was she just luckier, smarter or more adventurous than other snowy owls?

Scientists have long been as intrigued with the evolution of migration as that mystery of mysteries, the evolution of species themselves. Their fascination was perhaps expressed most memorably in Jurassic Park III when Alan Grant sees the pterosaurs flying out of their electrified enclosures and utters something like, “Good God, they really do migrate!”

When scientists first started seriously studying animal migration in the ‘60s, they discovered that animals use specific cues like day length, water temperature, and the earth’s magnetic field to trigger and steer their migrations. They ended up thinking that animals were like driverless cars that automatically followed GPS to their predetermined destinations.

They also didn’t think very much about how such migrations evolved. But the most astute animal behaviorists realized that wasn’t really the whole story. Birds blown off course managed to correct their migrations to end up at the correct destinations, not to belabor the analogy, but remarkably like the human occupants of old-fashioned driver-driven cars.

Other researchers wanted to know why songbirds migrate north when they could have just as easily stay in the tropics where food and nesting sites are abundant. Then they discovered that robins that nested in Alaska could successfully raise more chicks that robins that nested in the Midwest because they had several more hours to feed their chicks because of the longer day length in the north. This enabled the Alaskan robins to shave several days off the amount of time their newly hatched chicks would be most vulnerable because they couldn’t fly. In the crapshoot that is evolution, such advantages are more than enough to drive birds’ migrations farther and farther north.

Bill Sargent is a North Shore science writer and contributing columnist. His most recent book, Plum Island to Palm Beach; Our Sinking Shoreline is available in local bookstores and through http://plumislandoutdoors.org and at www.ingramcontent.com.