Bats are an important part of our wildlife heritage and are critical for maintaining healthy ecosystems. Most bat species in the continental United States feed exclusively on insects. Voracious predators, some bats can consume as much as 50% of their body weight in insects nightly. A few species that occur in the United States, primarily in the Southwest, forage on nectar or fruit. Most bats species use echolocation to locate prey and orient to their surroundings. These ultrasonic calls generally are above the hearing range of humans. By interpreting the returning echoes, bats can use sound to figuratively “see” the 3 dimensional representation of their immediate environment where they are flying, foraging for food, or searching for roosts.
Bats in temperate zones experience seasonal changes in food availability with the end of the growing season. Their responses to changes such as the onset of winter can be broadly divided into 2 strategies:
1. Some bat species will migrate to another area where food is present, typically to more southern latitudes. Migration distances vary among species. Eastern red bats (Lasiurus borealis) that spend the summer in New England or the upper Midwest may migrate to coastal regions of the Deep South. Millions of Brazilian free-tailed bats (Tadarida brasiliensis) that spend the summer in Texas caves migrate into Mexico and central America during the colder months. As seasons change and food resources are again available, bats make the return trip.
2. Other bat species do not migrate, but rather use caves, mines, or rock outcrops as hibernation sites to survive the winter months. During hibernation, bats conserve energy by dropping their body temperature to near ambient. Bats may arouse periodically and increase their body temperature to near normal for short period of time before re-entering hibernation. The reasons for this energy-expensive action are not fully known, but many hibernating mammals often arouse to help physiologically “reset” their immune systems and biological clocks. Successful conservation efforts for hibernating bats have focused on limiting human entry in cave and disturbance to bats that result in unnecessary arousal and energy expenditure of fat reserves needed for survival until spring-emergence.
Unlike rodents or other small mammals, most bat species produce only 1-2 offspring a year and many species have relatively long life spans. Although the abbreviated time from birth to volancy (being able to fly) to being prepared for their first hibernation results in high juvenile mortality, once bats reach adulthood, annual survival often high. Some species have been documented living 30 years in the wild. However, their low reproductive output means that bats can be very slow in recovering from mortality events and population declines.