Niwot migrations: Birds of a feather fly great distances together

Hundreds of Canada geese take off from the mowed fields around Dodd Reservoir where they have spent the day browsing for food. The evening sky is going purple after a clear day. Some of these geese make a fuss, honking as they take off. Others silently glide away, the turmoil of a disordered flock resolving into a giant V-formation that disappears into the distance. But where are they going?

According to the Audubon Society, in North America, seven out of 10 bird species participate in either a long or short distance bi-annual migration. This twice-a-year feat often has birds flying upwards of several thousand miles to reach their summer or winter destination.

While the Canada goose is one notable species that passes through the Niwot area, they are not the only bird on a migration mission with a stopover on the Front Range. A closer look at the geese bobbing on Dodd Reservoir might reveal Cackling, Snow, Ross's, or Greater White-fronted geese--not to be mistaken for the American White Pelican, a large, predominantly white bird with ink-black tipped wings that typically migrates south in September or October and can be spotted at Dodd or circling around the Boulder Reservoir.

And though we often associate the autumn months with migration, thanks to well-known and easily observed bird species like the Canada goose, migrating birds are actually passing through the area, heading south, as early as July. One example, the Rufous hummingbird, makes a staggering journey from their breeding grounds in Alaska and northwest Canada to their overwintering spots in Mexico--pretty impressive for a bird that weighs less than two pennies.

But if you've never spotted a Rufous hummingbird here in the summer or, for that matter, any other birds passing through the area in the fall, you might not be staying out late enough. Eighty percent of bird species in North America migrate at night. These birds can also be spotted during the day if you keep an eye open as they will rest and forage during the sunlight hours before their next overnight haul.

According to the Audubon Society, birds prefer night time navigation, because the atmospheric conditions are more stable, temperatures are cooler, and certain daytime predators aren't out looking for a tasty meal.

But that doesn't mean that nocturnal travel is without risks. Artificial light pollution, especially in densely populated cities with tall buildings, can confuse or disorient migrating birds. One way to help migratory birds is to turn off unnecessary lights during peak migration nights.

Colorado State University's Aeroeco Labs creates real-time maps that show intensities of bird migration based on the U.S. weather radar network. And though historical data shows that Sept.1 - 27 tends to be the timeframe when 50% of migrants pass through Longmont (the closest city on record with Aeroeco), an estimated 310,500 birds were slated to pass over Colorado on the night of Nov. 7.

Not all bird species participate in stealthy, nocturnal migrations, as attested to by the thousands of European starlings that can often be found perched in the cottonwoods. These iridescent black birds are short-distance migrators and can be raucous in the morning; you will often hear them before you see them. But what makes them most memorable is their flight pattern. Thousands of starlings will take off together to form a great mass of birds moving like a shape-shifting school of fish or pouring like a river across the morning sky.

Known as a murmuration, this phenomenon is both beautiful and perplexing to witness, a mystery of coordinated crowd movement and mass communication that scientists are still unraveling. In 2010, a study using advanced computational modeling and video analysis found that starling flocks model a complex physical phenomenon known as scale-free correlation.

Scale-free correlation is rarely observed in physical and biological systems, making it even more remarkable in starlings. To boil it down to the basics, the Cornell Lab of Ornithology sums it up like this:

"When one starling changes direction or speed, each of the other birds in the flock responds to the change, and they do so nearly simultaneously regardless of the size of the flock. In essence, information moves across the flock very quickly and with nearly no degradation."

But how does a single bird keep track of thousands of very noisy neighbors? Another study on starlings found that individual starlings within large flocks respond to a fixed number of their nearest neighbors-specifically the seven closest birds around them.

No bird flock is led by a single individual, even ones that appear to have a designated leader, like geese flying in a V pattern. When flying together, the flight pattern of a flock is determined by all flock members' movements.

Something to think about the next time you see a V of Canada geese winging away at the blue hour. Depending on the flock, they might be on their way south to Arizona, Texas or Mexico. Or, thanks to the proliferation of lawns and easy grass foraging, they might be headed to the nearest golf course to hunker down for the winter here in Colorado.