Glacier Natl Park - A Natural History Guide (1995) - Shrews are more primitive than rodents. Smaller brain, and, like reptiles, both genital and urinary tracts merge into a single opening called a cloaca. The pygmy shrew, the smallest mammal at one eight of an ounce, will not take on an earthworm, due to the relative size of the earthworm. The pygmy shrew taking on a grasshopper is similar in relative size as a wolf taking on a moose. Like whales and bats, water shrews, wandering shrews and masked shrews utilize high frequency ultrasonic sounds for hunting, orientation, protection, and communication.

A NATURALIST’S GUIDE TO THE YEAR (SMITH) - Shrew’s small size has pros and cons. Pro in that small size enables small prey to be a meal. Con, in that large ratio of volume to surface area, thus loses a lot of heat-requires more energy input. Shrews cool off faster than all other mammals in fall. Most shrews must eat their approximate weight every day. This means they eat (hunt) all the time. Shrews will attack prey twenty times their size (for example, a mouse). A study of European shrews show that when two males meet, they engage in a squeaking contest. If neither backs away, they will raise up on their hind feet and continue squeaking. If still a stalemate, they will roll over on their backs, with one grabbing the tail of the other and throwing him, judo style. Hence, the winner finally emerges. Shrews utilize echolocation, primarily for communication, but this is not developed to the level found in bats. While most predators of shrews will not eat the shrew, due to the musk glands, the owl, with it’s notably poor olfactory sense, often will, and often does smell of shrew musk. Many shrews die in autumn, not to cold, but to food deprivation.