Friday, April 1, 2011

Batting a Billion

Did you know that 2011-2012 is the Year of the Bat? Thanks to classic literature and popular culture, bats are thought to be nocturnal, creepy, winged rats. Probably every fear people have concerning bats is based on centuries of myths and misinformation. As part of my what-is-becoming-typical subject introduction I thought I'd give some facts and dispell a few of the myths about bats with a little round of True or False. As I plan to present a paper here and not just a bunch of bat facts I'll try to keep to some of the most popular myths and at the end of this post I'll have some links where you can find out more information.

True or False?: Bats are mammals.
Bats are flying mammals belonging to the order Chiroptera. There are more than 1,100 species (that's 1/5 of all mammals!), including the world's smallest mammal, a bat the size of a bumblebee.

True or False?: Bats are blind.
Actually many bats have very good eyesight. However, because many species are nocturnal (active at night) they have an extra sense that helps them to navigate and find food: echolocation. They send out sound which bounces back off of objects and creates a sort of map for the bat.

True or False?: All bats feed on blood.
Well, mostly. Admittedly there are three species of vampire bat: the Common Vampire Bat (Desmodus rotundus), the Hairy-legged Vampire Bat (Diphylla ecaudata), and the White-winged Vampire Bat (Diaemus youngi); all of which are found in Latin America. But don't worry, they don't require much blood and typically like to feed on livestock. More than two-thirds of bat species are primary predators of night-flying insects, this includes agricultural pests and many insects humans find to be particularly disruptive or annoying. A single bat can eat up to 1,000 mosquito-sized insects in a single hour! The other third of bat species feed on the fruit and nectar of plants. As such, they serve as pollinators and seed dispersers for many plant species. A small percentage are also known to eat fish, frogs, mice, birds and/or other small vertebrates.

True or False?: Bats are found everywhere.
Close but no. Bats are a very diverse group that take advantage of a wide variety of habitats, but they do not inhabit extreme desert and polar regions.

True or False?: Bats live in caves.
You can find many bat species living in caves. This is because one of the most basic requirements for bat is a safe roost. As such, bats can be found living in almost any conceivable shelter, from caves to buildings to leaf cavities and even in animal burrows. As their habitats shrink, more and more species, and individuals, can be found living in buildings. Building bat houses, the same concept as a bird house, is a backyard conservation technique that is catching on with the public. (Learn how to build you own bat house here:

The questions that I've listed here are not only some of the most popular concerning bats, they are also directly related to today's topic. A new Policy Forum paper published in Science this week takes a look at bat conservation from the aspect of their economic importance.

It is known that White-nose Syndrome (WNS) and the increased development of wind-power facilities are threatening populations of bats in North America. WNS is a fungus (Geomyces destructans) that infects the skin of cave-dwelling bats while they hibernate, particularly around the nose, ears, and wings. It is associated with a high mortality rate and is estimated to have killed over a million hibernating bats in more than 15 U.S. states and 2 Canadian provinces. Little Brown Bats (Myotis lucifugus) are sustaining the highest mortality rates, showing a 93% decline in 23 caves at the epicenter of the WNS outbreak. Other species affected include the Big Brown Bat (Eptesicus fuscus), Northern Myotis (Myotis septentrionalis), Tri-Colored Bat (or the Eastern Pippistrelle, Pipistrellus subflavus), Eastern Small-Footed Myotis (Myotis leibii), and Indiana Bat (Myotis sodalis).

Our growing concerns about climate change mixed with our desire to break our dependance on oil have resulted in the construction of more wind turbines. As a source of alternative energy wind turbines are a wonderful thing. However, for species of migratory tree-dwelling bats they are a flight, and life, hazard. In North America, these species include the Eastern Red Bat (Lasiurus borealis), the Hoary Bat (Lasiurus cinereus), and the Silver-haired Bat (Lasionycteris noctivagans). Other species that are ssusceptible to wind turbines include the Tri-colored Bat (L. subflavus), the Little Brown Myotis (M. lucifugus), and the Big Brown Bat (E. fuscus), species names that should sound familiar after reading about WNS. Included in this list of affected species includes bats with a relatively small range sizes, the Mexican Free-tailed Bat (Tadarida brasiliensis) and the federally endangered Indiana Myotis (M. sodalis). High numbers fatalities in species with small range sizes has a greater impact on the survivability of the species than the same number of fatalities in populous, large-range species. It is still unclear why these species are so susceptible to wind turbines. There is no continental-scale monitoring programs for assessing wildlife fatalities caused by wind turbines, but it is predicted that by 2020 an estimated 33,000 to 111,000 bats will be killed by wind turbines just in the Mid-Atlantic Highlands of the U.S.

This article focuses on these two sources for declining bat populations, leaving out sources such as habitat degradation. The numbers of bat fatalities are, in and of themselves, pretty staggering, but many people in political and policy making positions still consider it an academic interest rather than an economic problem. That is where this article becomes particularly interesting. In fact, the economic consequences of losing so many bats could be substantial. One example the authors use is the Big Brown Bat (E. fuscus). A single colony of 150 bats in Indiana as been estimated to eat nearly 1.3 million pest insects per year. Think about it: That is one relatively small colony of bats eating a whole lot of insects. Other estimates have a single Little Brown Myotis (M. lucifugus) consuming 4 to 8 grams of insects each night. Doesn't sound like much, but if you extrapolate that from one bat to one million bats that is 660 to 1320 metric tons of insects. This is a huge disruption to the population cycles of agricultural pests, and to say that bats are unimportant is just ignorant. 

The paper goes on to discuss the economic importance of bats in agricultural systems, estimating the value of the pest suppression services provided by bats. Previously published estimates have the value at anywhere from $12 to $173 per acre, with a likely value at $74/acre in a cotton-dominated landscape in south-central Texas. The authors here took these values and extrapolated the estimates to the entire United States. They estimated that the value of bats to the agricultural industry at between $3.7 billion and $53 billion per year with a likely value of approximately $22.9 billion per year. This cost does not include any downstream impacts of bat loss such as the impact of pesticides, secondary predation, and the predator release of insect populations.

A figure describing the worth of bats. Yellow being low cost to red being high cost.
 In terms of policy, the authors suggest that wait-and-see approach to the issue of widespread declines of bat population is unacceptable as the life histories of these mammals suggest that population recovery is unlikely for decades or centuries, if at all. They suggest management actions to restrict the anthropogenic spread of WNS, taking additional steps toward developing improved diagnostics to detect early stage infections and fungal distribution, investigating biological or chemical control of the fungus, increasing disease resistance through habitat modification, potentially culling infected bats, altering wind turbine operations during high-risk periods for bats, and continued research into these problems.

Here's the article:
Justin G. Boyles, Cryan Paul M., McCracken Gary F., and Kunz, Thomas H. (2011) Economic Importance of Bats in Agriculture. Science: 332 (6025), 41. (DOI: 10.1126/science.1201366)

Description of bat species from the Smithsonian National Museum of Natural History:
Info on bats from the Natural Science Research Laboratory at the Museum of Texas Tech University:
The Year of the Bat website:
From Boston University's Bat Lab:
From the Museum of Palentology at UC Berkeley:
A list of academic "bat labs":

From Bat Conservation International:
Bats and Wind Energy Cooperative (BWEC):
Video and information from Boston University about bats interacting with wind turbines:
U.S. Department of Interior, US Fish and Wildlife Wind Turbine Guidelines Advisory Committee:

Buzbee's Bathouse Page:
Info from the U.S. Fish and Wildlife Service:
From the Organization for Bat Conservation:
USGS National Wildlife Health Center WNS Page:
The National Speleological Society's WNS Page:

Bat Conservation International:
Organization for Bat Conservation:
Bat Conservation and Management, Inc.:
Lubee Bat Conservancy:
Bat World Sanctuary:
Bat Conservation Trust (in the UK):
The Warwickshire Bat Group (UK):
The Norfolk Bat Group (UK):

(image from
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