August is when a majority of wildlife families dissolve, as the young gradually start to wander from their parent’s care and begin finding food for themselves and developing the strategies for surviving on their own. Among the many maturing creatures achieving independence as summer wanes are the young of the various species of bats that exist within the Park. Regardless of their habitat and the types of bugs on which they prey, all juvenile bats are now capturing their own food and exploring their surroundings without the supervision of their mother.
Prior to the outbreak of white-nose syndrome less than a decade ago, the little brown bat was one of the most prolific small mammals in the Adirondacks. It was common for this small, delicate creature to regularly form maternal colonies from mid spring through mid summer in boathouses, barns, the attics and crawl spaces of year-round homes and seasonal camps as well as in cavities of old or dead trees and crevices on exposed rock faces. Any sizeable enclosure that was isolated from predators, and maintained a high humidity often attracted from a dozen to over a hundred expectant females during mid May. In smaller, more tight-fitting, confine spaces, such as behind the shutters on a house, in cracks between a wall and a chimney, and under a section of loose bark on a tree, solitary males would commonly seek out a summer roost for sleeping during the light of day.
Despite this species’ small size, the little brown bat is extremely tolerant of hot places, as researchers have noted very successful summer colonies in poorly ventilated attics that periodically topped 120 degrees. Because of the harsh thermal conditions in some summer roosts, predators are reluctant to enter. This allows females the opportunity to leave their single newborn unattended for the short periods necessary for her to forage for flying bugs without the likelihood that the baby will be attacked during her absence.
Maternal colonies in cooler places are typically protected from roaming predators by being situated in spots that are inaccessible to most creatures. In such cooler sites, bats are known to huddle together, even during summer, in an attempt to limit heat loss which helps them conserve internal energy. An infant bat, because of its small size and the limited amount of insulation over its skin, can radiate a fair amount of heat. When her mother is out foraging, an infant left behind can still bask in the warmth of nearby individuals in a large colony, rather than having to generate additional internal heat to maintain its core temperature in the cool and damp surrounding. While a single, lone infant bat is able to survive quite well when properly cared for by its mother, it is believed that residing in close proximity with numerous other bats improves the infant’s chance for success, which is one reason why maternal colonies form in spring.
It is not known how many bats have perished since the onset of white-nose syndrome, however, the population of little brown bats is substantially lower now than only a decade ago. Undoubtedly, the number of maternal colonies scattered throughout the Adirondacks this summer was less than the number that existed several years ago, and most of these probably contained far fewer individuals than during the years prior to 2006. It is unknown what impact a low occupancy rate in a maternal colony may have on the chances for success of the babies born in that nursery. Because this species only produces a single offspring each year, the success of every individual is important in helping to restore this species to its former status.
As young animals venture into the wilds on their own, they are confronted with many hazards and challenges, of which acquiring enough to eat is one major hurdle. For young bats, finding their way in another month or two to the entrance to a winter hibernating site is another issue. Years ago, there was an abundance of fellow aerial predators that knew the way to these very select locations. The young are believed to simply follow older bats as they migrate toward these sites during the first weeks of autumn as the population of flying insects decreased. By flying to these sites, the creature learns where to go and what are the preferred routes for travel.
In the months following mid summer, mortality among the young is as high as during any time of the year. Juvenile bats also face the challenge of dealing with white-nose syndrome once they enter their hibernating site and come into contact with the pathogen responsible for causing this ailment.
It has been reported that the population of little brown bats in New York seems to be stabilizing. While white-nose syndrome has decimated the numbers of this common mammal, there are other forces in nature that also harvest a portion of this, and all wildlife populations. As young, inexperienced animals enter into the world on their own many often are unable to cope with the challenges of survival. Considering the low reproductive rate of this delicate creature, it is going to take many years before this population rebounds.
Photos: Above, a thermographic image of a bat using trapped air as insulation (Wikimedia User Arno); and below, a little brown bat with white nose syndrome ().