Acoustic Irritation Threshold of Ringbilled Gulls

Abstract

When exposed to high-intensity sound, ringbilled gulls do not, to any extent, show the head-shaking reaction that was previously observed for ducks. They do, however, show a great tendency to cringe or crouch and are also subject to a temporary change in the rate of heart beat. These reactions are used to define and measure an acoustic “irritation threshold” at different frequencies between 100 and 3000 cps. The threshold determined with reference to the cringing reaction is remarkably reproducible over a period of weeks (having an average minimum value of about 85 db at 400 to 500 cps) but rises considerably during the first eleven months of the bird's life.