Bat Averages

Wordwide numbers of bats are on the decline

Bat populations, in the United States and worldwide, are in decline. While this may not be of great concern to people who see bats as pests or threatening, it can have a significant impact on tropical ecosystems and on human populations here in the United States. Far from being threatening or pests, bats are an amazing species and serve some very important functions that sustain human and other natural populations.

Bats are the only true flying mammal. There are nearly 1,000 species of bats worldwide, which accounts for almost one quarter of all mammal species. More than 50 percent of American bat species are in decline or already listed as endangered. The largest bat, the Indonesian giant flying fox, can have a wingspan of up to six feet. The smallest bat, the bumble bee bat, which lives in Thailand weighs less than a penny. Bats can live quite a long time for their size. For example, the little brown bat that lives in our area can live up to 32 years.

Mexican free-tailed bats, during feeding or migration, can fly to heights of up to two miles, allowing them to catch tail winds and reach speeds up to 60 miles an hour.

There is a myth that bats are blind, but bats actually have excellent eyesight as well as hearing. African heart-nosed bats can hear the footsteps of a beetle walking on sand from a distance of six feet or more.

Despite very good hearing and sight, bats also use echolocation to identify prey in flight and to help find their way around at night. While echolocation is used in a number of different animals including whales, dolphins, and shrews, scientists don't completely understand how it works with bats. We know that bats send out a signal or an echolocating call (that is why bats usually fly with their mouths open) and process and respond to the calls or signals that bounce back. What scientists do not understand is how all this input, from a system far more advanced than anything man has created, is processed in the bat's sensory organs and brain.

Bats can also hibernate whenever the need arises. Changes in weather or food shortages can prompt bats to shut down their metabolism for extended periods of time. Unfortunately, disturbing hibernating bats can have serious impacts. A disturbed bat will raise its body temperature in anticipation of fleeing, which can use 10 days to a month's worth of stored fat.

Declining bat populations in the tropics can have a devastating impact on the variety of plants that require bats for pollination or seed dispersal. Many trees have evolved specifically for bat pollination, with large, usually white flowers with a strong odor. Often the bat is coming in to feed on the nectar of the flower. The long stamen of these flowers spread pollen on the wings of the bat. The pollen will be transferred to another flower at the next feeding stop.

There are also a number of plants, including peaches, plantains, bananas, mangoes, figs, avacadoes, cloves, carobs, cashews and chicle (used to make gum) that are dependent on bats for pollination. Agave plants, which are used to make tequila and mescal, will see seed production will drop 3000 percent of normal without bat pollination. If that's not a call for bat conservation, I don't know what is.

Here in Maryland, bats help human populations in two important ways. Bats are the biggest consumer of nighttime insects in our area. While bats feed on a number of different insects, mosquitoes make up a large part of their diet. A little brown bat in Maryland can eat up to 1200 mosquitoes in an hour. The reduction in mosquito population not only makes Maryland residents more comfortable, but bats can also reduce risks of West Nile Virus by keeping mosquito populations in check.

Bat houses can be used to attract bats to one's yard or neighborhood. Houses can be bought at area nurseries and wildlife stores or plans for building a bat house can be found at the Bat Conservation International web site, www.batcon.org.

The needs for bat habitat are not complicated, but bats are finicky about where they live so it may take a while for a bat to move into even a well constructed, well placed bat house. A key element of bats taking roost in a house is temperature. Placing the house in an area that will receive 5 to 7 hours of sunlight a day is ideal. It is also recommended to put two bat houses side by side, one of which is painted a light color and another painted a dark color. The dark-colored house would be used in early spring and the light-colored house would be used in the summer months.

Height is also important. The higher up a bat house is placed, the more likely it is to be inhabited. Twelve feet would be the minimum height, but 15 feet or higher is preferred, as is a large house that can accommodate many bats. The more bats that can live in a house, the more likely the house will be inhabited.

Many of the small houses sold are not really suited for bat populations in our area. If possible, houses should be constructed near water, within a quarter-mile of a stream or pond. For entering and exiting the house, bats prefer to have clearance in their flight, so an open area is preferred, but the side of a house or barn is adequate.

The bats most likely to inhabit houses in our area are the little brown bat, the big brown bat, the Northern long-eared bat, the Eastern pipistrelle, and the evening bat. Other bats found in Maryland include the hoary bat, the red bat, the silver-haired bat, the small-footed bat and the Indianan bat. The Bat Conservation International web site also has a listing of bat species state by state–click on "Maryland" and you can learn all about these little creatures.

The other benefit bats provide to human populations here in Maryland is to help farmers control insect pests that can wreak havoc on crops. A colony of big brown bats, with a population can eat 33 million root worms each summer. Bats also eat June beetles, cucumber beetles, cut worm and corn ear worm moths.

Over and over again, across the planet, we have seen a serious drop in bat populations followed by dramatic increases in pesticide use. So, on the basis of an unfounded fear, bat populations are eradicated only to create real problems associated with chemical use and mosquito born diseases.

If you go to any park in our area around dusk and patiently watch the sky, you will likely see bats flying around, hunting insects—and providing an irreplaceable service for us.