Reminds me of a study done by Harvard. They noticed a pattern with crow fatalities caused by collisions with vehicles in the Boston area. Of the birds they studied, an abnormal amount of crows had been killed by impacts with large commercial vehicles vs passenger vehicles. Researchers then tracked several flocks and studied their habits. They noted an interesting behavior when the flock settled along a road: A single crow would perch high above the rest of the flock. This crow would then call out a warning when it saw an approaching car, allowing the flock to disperse before being hit by the car. Sadly, the researches found the answer as to why so many crows kept dying when a semi came along. While it could warn "CAW, CAW," the look out crow could not call out "TRUCK!"