cetacean

—any member of the order Cetacea of aquatic, mostly marine mammals that includes whales, dolphins, porpoises, and related forms; among other attributes they have a long tail that ends in two traverse flukes.

critical band (CB)

—frequency band within which background noise has strong effects on detection of a sound signal at a particular frequency.*

critical ratio (CR)

—difference between sound level for a barely audible tone and the spectrum level of background noise at nearby frequencies.*

echolocation^†

—a physiological process for locating distant or invisible objects (as prey) by means of sound waves reflected back to the emitter (as a bat) by the objects.

ecosystem^†

—the complex of a community of organisms and its environment functioning as an ecological unit.

elasmobranchs^†

—any of a subclass (Elasmobranchii) of cartilaginous fishes that have five to seven lateral to ventral gill openings on each side and that comprise the sharks, rays, skates, and extinct related fishes.

glucocorticoid

—steroids such as cortisol and corticosterone produced by the adrenal cortex and affecting a broad range of metabolic and immunologic processes.

habituation (behavioral)

—gradual waning of behavioral responsiveness over time as animals learn that a repeated or ongoing stimulus lacks significant consequences for the animal (cf. sensitization).*

hair cell

—a special kind of cell that has tiny hairs projecting from its surface into the intercellular space. Movement of the hairs is registered by neurons that contact the hair cell. Hair cells are found in the inner ear of mammals.

haulout

—the act of a seal leaving the ocean and crawling onto land or ice.

homeostasis

—a relatively stable state of equilibrium or a tendency toward such a state among the different but interdependent elements or groups of elements of an organism, population, or group.

hyperplasia

—an abnormal or unusual increase in the elements composing a part (as cells composing a tissue).

hypertrophy

—excessive development of an organ or part; specifically an