The Island Naturalist true stories From catalina's wildlands
The Benefits of Bats
By Alexa Johnson and Calvin Duncan
Conjuring images of plagued vermin, blood-sucking villains, or rock star crucifixions, bats are one of the most misunderstood and fictitiously portrayed animals in modern culture.
Many people associate bats with rabies, and although rabies is reported more often in wildlife such as raccoons, skunks, foxes and bats, human exposure to rabies more commonly occurs through close contact with domestic animals, such as cats and dogs.
And according to the San Diego Zoo, of the nearly 1,000 known species of bats in the world, only three feed on small amounts of blood. All of which are located in Mexico and South America. The majority of bats (over 70%) eat insects, and in doing so, control large numbers of pests that could harm crops or spread disease.
Other items on the menu can include nectar, fruit, or other small animals, such as lizards, fish, birds and rodents.
Bats are effective pollinators that contribute significantly to crop success, particularly for fruit like avocados, bananas, mangoes, figs and peaches. Additionally, they pollinate abundant trees, flowers and cacti and are key players for dispersing seeds.
Sadly many bat species are in decline due to the loss or fragmentation of their habitat, reduced food supply, destruction of roosts, the direct killing of individuals, and disease such as white nose syndrome (WNS).
White nose syndrome is a fungal disease that is devastating bat populations all over the US. It is an emerging disease that is associated with the deaths of millions of bats, which in turn has resulted in the proliferation of many insect pests. Lesions develop on the faces of infected bats and the associated irritation causes bats to rouse too frequently from torpor (light hibernation) and starve to death due to excessive activity. The disease is transferred through physical contact. Initially detected in 2006, WNS has now been confirmed in 25 states and 5 Canadian provinces and is continuing to make its way west. Human’s accessing roosting sites such as mines and caves can facilitate the spread of diseases such as WNS, may cause a bat colony to abandon the roost or may prevent bats from utilizing the site in the first place.
Catalina's Cavernous Creatures
By Calvin Duncan and Julie King
Of the thirteen species of native land mammals documented on Catalina Island, eight (62%) are bats. The power of flight has pre-adapted bats for island colonization, but very specific roosting and foraging habitat must exist in order for bat species to persist.
Catalina Island’s diverse landscape provides bats with abundant natural habitat, including natural caves and rock crevasses, trees and water. Bats utilize human structures as well, and in many cases these human structures can support large colonies.
Very few studies have been conducted on the bats of Catalina Island and very little is known about the abundance and distribution of these fascinating creatures. The largest and most recent survey of bats on Catalina was completed in 2000-2001 by world renowned bat expert Patricia Brown-Berry and her team at Brown-Berry Biological Consulting. The surveys included acoustic detection methods, mist netting, and day searches at bridges and mines, and successfully documented the presence of eight species of bats on the island at the time.
Among the eight species of bats documented on Catalina Island, one has been listed as California Species of Special Concern (Pallid bat) and the other (Townsend’s big-eared bat) is a candidate for state listing as Threatened or Endangered in California. Finalizing its status as endangered should take place within the next year. Four other bat species of Special Concern occur in nearby areas and are expected to utilize Catalina Island, but have not yet been documented here.
Townsend's Big Eared Bats
By Alexa Johnson
Townsend’s big-eared bats (Corynorhinus townsendii) range throughout western North America. On the Channel Islands they’ve been documented on Catalina, Santa Cruz and San Clemente, although their precise distribution is poorly understood.
Townsend’s bats are agile and maneuverable fliers that forage for insects within the protective canopy of trees and shrubs. Moths make up as much as 90% of their diet, but they’ll also eat beetles, flies, bees, and wasps.
Breeding begins in autumn and continues through February. Females form maternity colonies between late spring and early summer, utilizing roost sites for several generations. During this period, males roost alone. Females are pregnant for eight to 14 weeks, before giving birth to a single pup starting in May. Young are born fairly undeveloped, but will grow to adult proportions within a month. They’re capable of flight between two and a half to three weeks and are weaned from their mothers by six weeks. Soon after the pups have weaned, maternity roosts disband, usually around August. Bats are reproductively capable their first autumn, at approximately four months.
Average lifespan for Townsend’s big-eared bats is 16 years; some may live up to 30 years.
Townsend’s bats are considered to be mostly sedentary, usually staying within seven to 20 miles of their roosts. However, some individuals have been found to travel as far as 192 miles from their roost.
Studies have shown a substantial decline of Townsend’s big-eared bats in the western United States over the last 40 years. In a study conducted for the California Department of Fish and Wildlife, Pierson and Rainey identified a 52% loss in the number of maternity colonies, a 32% decline in the average size of remaining colonies, and a 55% decline in total number of animals throughout California.
Townsend’s bats are extremely sensitive to human disturbance. A single disturbance of a maternity roost can cause abandonment. Bats hanging from ceilings and walls are highly susceptible and when roused, are forced to use fat stores necessary for hibernation and may starve to death. Declines have also been tied to agricultural conversion of land that has reduced foraging habitat, the use of pesticides, and issues associated with wind turbines (strikes and changes in pressure).
In an effort to protect Townsend’s big-eared bats on Catalina, the Conservancy is installing bat gates in mines where Townsend's bats have either been previously documented or are potential roosts once human disturbances are eliminated. As mentioned previously, Townsend’s big-eared bats are a candidate for listing as Threatened or Endangered in California. Their continued presence on Catalina will help to ensure that Townsend’s bats persist, despite significant declines elsewhere.
Fact or Fiction?
We’ve all heard the expression “blind as a bat.” But are bats really blind? As it turns out, bats aren’t blind at all. In fact, their vision is as good as just about any other mammal and with the use of echolocation, most bats have the ability detect details as minute as a human hair, even in complete darkness! Echolocation is a biological sonar system where an animal omits a sound wave from their mouth or nose and then processes the echoes that bounce back from the surrounding environment, using their ears as the receivers. From these echoes, a bat can determine the size, location, and texture of object, as well as how fast it is traveling. Since bats are generally active at night, echolocation is an important tool used to navigate and forage for prey.