Well, it is not a pretty story... about 200 dead crows near Bangor, Maine and there was concern for Avian Flu. They had a Bird Pathologist examine the remains of all the crows and he confirmed the problem was definitely NOT Avian Flu, to everyone's relief. However, he determined that 98% of the crows had been killed by impact with trucks and only 2% were killed by car impact. The State then hired a Ornithological Behaviorist to determine the disproportionate percentages for truck versus car kill.
The Ornithological Behaviorist determined the cause in short order. When crows eat road kill they always post a "look-out crow" in a nearby tree to warn of impending danger.
His conclusion was that the lookout crow could say "Cah" but it could not say "Truck."
Appropriated from another forum.