Dunlin and Semi-palmated Sandpipers
Dunlin and Semi-palmated Sandpipers
The old saying that birds of a feather flock together is actually true. From nesting activity to emergency escapes from predators, flocking behavior accomplishes several important objectives for bird survival. Examples abound. Colonial nesters, such as the thousands of squabbling Northern Gannets at Bonaventure Island on the Gaspe Peninsula, construct nests within inches of each other. Random bits of seaweed, sticks and assorted flotsam are gathered from the sea surface to erect simple nesting mounds. Mounds are located approximately one neck’s-length reach away from a neighbor. This precise spacing limits serious bodily attacks from neighbors but affords convenient opportunities to pirate pieces of nesting materials from adjacent nests. Gannets returning to the nest are vigorously pummeled, pushed and pecked, leaving some individuals bleeding or occasionally losing an eye. Witnessing such constant aggression between birds, one ponders the biological practicality of the gannet’s colonial existence. Maybe it’s just a matter of “tough love”? We are told, however, that birds do not engage in behavior that does not benefit their survival in some way.

During winter months, groups containing several hundreds of American Crows arrive at secluded night roosting groves. The direct benefits of this flock-joining concept are crows’ shared communal warmth during extreme cold temperatures and ready detection of possible night predators. In the event of a Great Horned Owl raid, the individual odds of becoming an owl’s midnight snack are reduced among members of large congregations.

We are all familiar with “V”-shaped skeins of Canada Geese. In flight, geese position themselves strategically to take advantage of changing wind patterns based on the number of birds in a flock and how each bird’s wings create different currents. These aerodynamic configurations help geese use the surrounding airflow in an energy-efficient way to extend the ranges that such long-distance migrants can fly without rest.

Dramatic aerial maneuvers to flee from winged predators are perhaps the most glaring instance of flocking with a purpose — preserving life itself. Migrant shorebirds are frequent fall targets of Peregrine Falcons and their smaller falcon cousin, the Merlin. At opportune moments, other raptors such as Harriers and Cooper’s Hawks may make brief efforts at sneak attacks.

Now back to the peregrines. For a showcase of pure speed and agility by predator and prey alike, peregrine-shorebird duels are fascinating to watch. The falcon’s best prospect for success is to cull a single bird from the speedy twisting assemblage and focus on an individual attack. While shorebirds maintain tight flock formations, predators have many potential targets to strike. The temporary confusion generated by the flocking factor lowers the danger to any single bird, however. Raptors must also avoid accidental injury through collision with any dense, high-speed flock.

At speeds exceeding 40 miles per hour, how do shorebirds act as a coordinated, unified body of movement? How do they instantly turn on a dime and reverse direction? Some possible answers are provided through modern photography techniques and computer simulation. One researcher explains that a “few birds clump closely together to call the shots. There is no designated team leader. Instead the birds take turns. Once those birds begin to turn, the message spreads fast: about 20 to 40 meters per second, meaning that a flock of 400 birds needs just about a half second to turn.”

Similar research was conducted on swooping intricate flights of European Starlings called murmurations. Some flocks contained hundreds of thousands of birds. Researchers determined that individual starlings took their shift of direction cues from the six or seven birds closest to them. As with all avian behavioral studies, there is always more to learn.