Heart rates of white-tailed deer fawns in response to recorded wolf howls.

Abstract

Weekly measurements of heart rate responses of a hand-reared white-tailed deer fawn to recorded wolf howls were completed through the age of 87 days, with occasional measurements of the responses of three other fawns. Alarm bradycardia was a very predictable initial response to the first howl through 45 days of age. Increased heart rates were observed in response to a chorus of howls 35 s into the 62-s sequence. A most interesting characteristic of the response was a highly significant (sign test) relationship between the direction of the heart rate response at 1-s intervals from one test to another, and from one week to the next, until the fawn was 45 days old. Heart rates varied from 86 to 225 beats per minute during the tests, within the ranges observed for transient stimuli such as horses, rain, machines, and other deer. The fawn remained bedded during the tests. A hiding response and alarm bradycardia in the first few weeks of life seems to be good adaptive strategy as the neonate has little chance to escape from a predator by running.