Threats to Bats

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Bats are threatened by many things, but probably most of all by the lack of knowledge and misinformation about them. That leads to bad things happening to these important predators of the night. Here are some specific threats:

White nose syndrome – This is a foreign disease introduced accidentally into bat hibernation caves in the Eastern U.S. and has spread from there. It was first identified in New York state in 2006, so it has not been around a long time, yet it has already killed millions of bats. It has spread throughout New England and into the Midwest, devastating hibernating bat colonies.

White nose syndrome does not do the actual killing of bats. It is an irritant, like a cold might irritate us, but it irritates and awakens bats during hibernation. Every time a bat wakes, it uses its stored energy, which is limited for a small, flying mammal. The bats then cannot make it through the winter without getting more energy, but when they awaken hungry, it is still winter, not spring, so no food is available. They die in masses.

Bats that have been found with white nose syndrome (from WhiteNoseSyndrome.org):

  • Big brown bat
  • Eastern small-footed bat
  • Gray bat (endangered)
  • Indiana bat (endangered)
  • Little brown bat
  • Northern long-eared bat (threatened)
  • Tricolored bat

These are all cave bats. Tree bats have not been affected.

Much research is being done to try to find a cure for the disease. Plus a lot of effort is being made to prevent the spread of the disease to new hibernating colonies.

You can learn much more about white nose syndrome at WhiteNoseSyndrome.org.

Habitat loss – most of nature is threatened by habitat loss. Conversion of native habitats to farm fields, houses, industrial areas can all reduce the feeding and roosting areas available for bats.

Tree dwellers lose their homes when forests are clearcut, and especially when snags are removed. Bats often use hollow trees for roosts. Plus, forests where bats live generally have larger ecological effects on bats than simply the loss of trees, including loss of insect prey, damaged streams for water, and so on.

Caves – Many bat species concentrate in limited locations during hibernation and when mothers have their young. For cave dwellers, each species often has very specific requirements for survival. Gray bats, for example, are limited to a very specific number of known caves for summer and winter residence in the South. Many caves have been protected with gates to limit access to bats so that they are not disturbed during hibernation or when raising young. While bats are not deliberately killed in caves like they used to be, cave vandalism is still a problem, too.

Mine reclamation – With the loss of caves, bats have found that many mines provide good substitutes. However, when mines are closed and reclaimed, they are often shut up without checking to see if bats used them. At the least, this reduces their roosting habitat but that can also kill bats inside and destroy their home. Mines can be reconsidered as bat habitat with appropriate protection. Bat Conservation International publishes a nice booklet on bats and abandoned mines that you can download.

Bridge replacement – When bridges are repaired and rebuilt, bats can be the losers if they have used those bridges for roosting. Now highway engineers are required to do bat surveys before knocking down a bridge. Bats use bridges for maternity colonies and summer roosting, so often the work can be delayed until they are gone for the year.

Wind turbines – Wind power has become an important generator of electricity in many areas. The turbines used are known to kill thousands of birds and bats. Researchers are not sure what draws bats to the turbines, but when they get close, the sudden air pressure change as the blade goes by causes severe lung damage which kills these small mammals. Work is being done to find bat deterrents, such as sound they don’t like, as well as adjusting when turbines are running and at what speeds. A lot of information about this can be found on the Bats and Wind Energy Cooperative website.

Climate Change – As the climate changes, getting warmer overall, bats are affected in a number of ways. First, this affects hibernation timing. Bats may go into hibernation later and leave that state earlier, yet both times may be off timing for insects. Second, climate change can affect the ability of caves to maintain the precise conditions bats need for hibernation. Third, climate change can be a disruptive factor in all ecosystems which can change relationships of bats to where they live.

Insecticides – Pesticides used on farms are mainly used to control insects, bats’ food. Overzealous use of insecticides can reduce insect populations that have no effect on crops but reduce food available for bats. In addition, bats that could control crop pests are then driven away because there is less food, meaning that crop pests can get worse and more pesticides used. In addition, DDT is a direct threat to bat health. Although it is not used in the U.S. anymore, it is used in Mexico which can affect Mexican free-tailed bats that migrate there in winter from the South and Southwest.

Pest control in buildings – Buildings provide good habitat for many bats that like protected spaces like those found there. A few bats roosting in a building will cause little problem, though uninformed public health officials may warn of rabies. Rabies is not a significant concern for bats roosting in buildings (see the rabies section for more information). In many areas, bats roost in small numbers in houses and residents are not aware of it. However, large colonies of bats in buildings can cause problems with noise, smell and piles of guano. To remove bats from a building, they need to be excluded from returning after they leave at night. Bats should never be killed in buildings (that is illegal in many areas anyway), nor should mothers be excluded from young in maternity roosts – both will create a big mess and smell, besides the ethical issues. You can learn more about this from Bat Conservation International.