Counting Free-tailed Bats in Bridges

9/10/18
By Merlin Tuttle

Merlin inspects Brazilian free-tailed bats (Tadarida brasiliensis) moments after removing them from their bridge crevice roost for counting.

For many years we’ve wondered just how many Brazilian free-tailed bats (Tadarida brasiliensis) could cram into a single 18-inch-deep bridge crevice. Accurate counts of large colonies are difficult no matter how they’re made. However, when estimating bridge colonies, it would help if we knew the number, using an average horizontal foot of crevice.

The solution seemed easy. Two years ago, Glen Novinger, an MTBC member and I, inserted two, three-quarter-inch-thick wooden frames, each encompassing a square foot of interior space, into bridge crevices of the same width while the bats were out feeding. The idea was to later slowly remove them, forcing those roosting inside to exit into a cloth-lined bag from which we would count them.

However, the bats were full of surprises. The first night we waited patiently till half an hour after we’d seen the last ones leave—or at least that was what we thought! But when we approached to install our devices, roughly half remained inside. I couldn’t help but wonder how many emergence counts had missed those that, for whatever their reasons, didn’t emerge at sundown. (more…)

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Response to Sensational Bat Rabies Stories

Every year around this time there is a spike in needlessly sensational rabies stories featuring exaggerations of truth.  We always encourage others to respond politely to editors, authors, decision makers and media personnel when they see these. Editors’ jobs depend on readership and they do aim to please. They just need to know you like or dislike an article. Responses can be very simple such as, “I don’t appreciate  sensational  headlines or speculation that creates needless fear of bats.”

We work hard to be a source for your personal ambassadorship of bats and wish we could respond to every article, however our resources are limited. We cannot do it alone. We hope that this post will supplement your future responses when you encounter false or exaggerated bat publicity.

 

Response to Beth Skwarecki’s story “If a Bat Was in your Bedroom, You Probably Need a Rabies Shot
By Merlin Tuttle
9/1/18

Unfortunately, this well intended story is a sensational exaggeration of truth. It is correct to say that most human rabies in America comes from bats. However, put in context, it’s just 1-2 cases per year, making it one of the rarest causes of death. By comparison, just by riding one mile in a motorized vehicle, an American exceeds his/her annual risk of rabies from any source.

Because even sick bats almost never bite, except in self-defense if handled, the risk of contracting any disease from one is exceedingly low for anyone who simply leaves them alone. In Austin, Texas, thousands of people gather nightly to observe the spectacular emergences of 1.5 million bats close-up. And in decades of this exceptionally close association, no one has been attacked or contracted a disease.

Post-exposure rabies vaccinations in the United States are outrageously overpriced, currently costing from $10,000 to $22,000 per person treated. With huge profits at stake, and our CDC heavily influenced by drug companies, promotion of exaggerated fear is not surprising. Unprovoked bites are exceedingly rare, so much so that I have yet to experience one despite close association with millions of bats worldwide for more nearly 60 years.

Human rabies cases are often diagnosed post-mortem or after the patient is incoherent. Even in cases in which parents or friends report bites, the U.S. CDC reports “no bite history” unless the patient is able to confirm. Consequently, human cases, regardless of animal origin (i.e. bat, dog, skunk or raccoon) often get reported as having no bite history. Huge misrepresentation occurs when such reports are used to disproportionately frighten people of bats.

Since 1996 the CDC Advisory Committee on Immunization Practices has advised consideration of post-exposure prophylaxis for “persons potentially exposed to bats even where a history of physical contact cannot be elicited,” unless prompt diagnosis excluded rabies. Based on its independent analysis Canada’s National Advisory Committee on Immunization, opted not to follow CDC’s recommended bat policy.  They do not advise vaccination unless there has been direct contact. For detailed documentation, see Rabies in Perspective.

Millions of tourists have watched free-tailed bat emergences from the Congress Avenue Bridge in Austin, Texas over the past 35 years without anyone ever having been harmed.

 

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Bat-Friendly Bridges Help Farmers

Merlin Tuttle
9/12/18

Building bat roosts into highway bridges in farmlands can benefit farmers at little or no cost to taxpayers. Mark Bloschock, a supervising bridge design engineer at the Texas Department of Transportation, discovered the potential for bridges to help bats when he worked on Austin’s now famous Congress Avenue Bridge. As hundreds of thousands of bats unexpectedly moved in, he contacted me for advice. He soon discovered that, by simply making small adjustments in the spacing between box beams, large numbers of bats could be attracted where needed, and where they weren’t wanted, they could be discouraged by simply changing the spacing.

In 1998, when highway US 90 required two new bridges over Seco Creek, near D’Hanis, Texas, he wrote specifications that placed the box beams three quarters to 1.5 inches apart, hoping to attract Brazilian free-tailed bats (Tadarida brasiliensis) to this important agricultural area. The bats quickly moved in and soon exceeded half a million, today as many as two million.

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Our Premiere Member Cruise

At Merlin Tuttle’s Bat Conservation we’re overjoyed to finally launch our membership campaign. Members at the Leadership level or above were given priority invitations to view the famous Congress Avenue Bridge bat emergence with Merlin aboard a chartered Capital Cruises boat. We all gathered at the Hyatt Hotel’s lounge for drinks (and queso) and to meet and get acquainted. The first member to sign up for the cruise was Janell Cannon, the author of the classic children’s book Stellaluna.  Janell graciously signed copies of her book, which is celebrating its 25th anniversary!

Janell Cannon signed Stellaluna for members on the bat cruise. Ingrid Dehn, retired school teacher, had loved reading Stellaluna countless times to her students. The book is celebrating its 25th anniversary!
Bat Slide Scan Project team interns Renee Cornue and Max Gorman with supervisor Teresa Nichta (middle) enjoyed meeting participants on the cruise.

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Texas Department of Transportation Celebrates Bats

8/28/18
By Merlin Tuttle

 

The Texas Department of Transportation (TxDOT) has set world records when it comes to helping bats, and that special help is paying big dividends for Texans and for countless visitors. Thanks to the enthusiastic early leadership of Supervising Bridge Engineer, Mark Bloschock and the continuing efforts of Stirling Robertson, now in charge of Strategic Projects, and John Young, an Environmental Specialist, TxDOT is taking great pride in its accomplishments.

On August 21, Stirling and John organized a special bat evening for 30 of TxDOT’s most important media and public information officers. They each received a copy of Department’s new guide to bat watching at state bridges, attended my 20-minute presentation at TxDOT headquarters, then joined me for a special Congress Avenue Bridge bat watching evening. We were delighted when we learned that Mark, who is now retired, would be able to join us.

Merlin speaking to TxDOT media and public relations staff.
Merlin entertaining TxDOT staff with bat facts while waiting for Congress Ave Bridge bats to emerge.

The bats performed beautifully, and Stirling reported, “There has been overwhelming positive response to your talk and the whole event. Good stuff!” A big thank you to Stirling for making this event possible! We look forward to future collaboration and many more bats in Texas bridges.

 

 

Emerging bats providing America’s most famous urban wildlife spectacle.

 

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Panel Discussion on Vampire Control

Wildlife Disease Association
St. Augustine, Florida
8/10/18
By Merlin Tuttle

The Wildlife Disease Association hosted a panel discussion on vampire bats (Desmodus rotundus), their impact, status, and changing distribution on August 5, 2018. A panel of six speakers from Europe, Mexico, and the U.S. were invited to speak. In the lead-off, tone-setting presentation,

Veterinarian and vampire control officer for Costa Rica, Dr. Hugo Sancho treating vampire bites with a mixture of Vaseline and warfarin to kill vampires that return to feed at the same wounds night after night. This kills only those that are causing problems.

I outlined the global value of bats, with special emphasis on Latin America, then proceeded to discuss my decades of observations on vampire control and the enormous damage done when beneficial species are inadvertently targeted. I favored control limited to the vampires causing problems. However, I emphasized that vampire problems are two-fold. One of course involves feeding on livestock and occasionally humans. The other involves their potential impact in crowding other species out of already declining roosting options. The dramatic expansion of vampire populations due to livestock introduction is likely impacting many other bat species that are essential to healthy ecosystems.

Yanomamo Indians living in remote rain forests of Venezuela.

During my early bat surveys in remote rain forests inhabited only by aboriginal Indians, I rarely encountered vampire bats. In fact, I do not recall ever having seen a Yanomamo Indian bitten, despite their habit of sleeping nude in lean-to shelters without mosquito nets. I first encountered significant numbers of vampire bats where Indians under European influence were keeping chickens, pigs, or other livestock. My anecdotal observations indicated that humans first became substantial targets when they began keeping pigs or chickens. Vampires became accustomed to feeding on these, and when they were slaughtered for feasts, the hungry bats turned to humans. Later when ranchers sold livestock, again suddenly reducing the food supply, vampires whose numbers had grown to depend on their herds, turned to people.

 

Only three species of vampires exist. All live only in Latin America, and only one, the common vampire, poses a significant threat to human interests. More than 350 other species are highly beneficial, keeping insect populations in check, pollinating flowers, and dispersing seeds.

A common vampire bat in Panama.

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Mosquito Eating in Bats

8/9/18
By Merlin Tuttle

For decades, bat biologists have debated the extent to which bats prey on, and potentially reduce mosquito populations. However, recent research suggests bats may be eating far more mosquitoes than yet suspected. Amy Wray and associates (2018) relied on newly refined techniques that provide greater sensitivity. In their paper, titled “Incidence and taxonomic richness of mosquitoes in the diets of little brown and big brown bats,” they reported that these common species eat a greater variety of mosquitoes, and catch them more frequently than previously suspected.

A little brown myotis (Myotis lucifugus) in Wisconsin. Just one of these bats can catch 1,000 mosquito-sized insects in a single hour.

They tested guano samples from 22 locations in a range of habitats, across the State of Wisconsin, from May 17 through July 29. Seventy-two percent of little brown myotis (Myotis lucifugus) samples contained mosquitoes representing 15 species, more than twice as many as big brown bats (Eptesicus fuscus). But even the larger big brown bats, previously thought to feed mostly on beetles and moths evidenced mosquito-eating in 33 percent of samples. Frequency of mosquito-eating remained constant throughout the active season in big brown bats but declined slightly in little browns.

Little brown myotis (Myotis lucifugus) from Tennessee.
A third of big brown bats (Eptesicus fuscus) in Wisconsin fed on mosquitoes.

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Nature Nights: BATS! at the Wildflower Center

Nature Nights at the Lady Bird Johnson Wildflower Center is a free family-fun event held each summer. Merlin Tuttle and Lucas Miller were the main entertainment for Nature Nights: BATS! on June 21st. Merlin’s bat photographs captivated the children and their parents alike. Afterwards, Lucas Miller, “The Singing Zoologist,” performed for the crowd with his “silly songs about serious science.”

Live bats, courtesy of Dianne Odegard and Lee McKenzie from Austin Bat Refuge, were a big hit.

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Bats and Chocolate Production

By Merlin Tuttle
6/6/18

While conducting her Ph.D. thesis research, Bea Maas and her team (Maas et al. 2013) collected data that would surprise even her. When insect-eating bats and birds were excluded from cacao trees in Sulawesi, Indonesia, the crop yield fell by 31 percent. And when she compared losses due to night versus daytime exclusion, bats versus birds, she discovered that bats accounted for 22 percent of the prevented losses.

A control site in the same study (poles without netting).

To obtain such data, Bea selected 15 plantations where she enclosed 120 cacao trees in 60 exclosures (like huge, mesh cages) constructed of nylon mesh. There were four exclosure treatments per plantation, one daytime, one nighttime, one day and night, and one always left open as a control.

A bat/bird exclosure in Sarawak, Indonesia, built with bamboo poles and commercial nylon monofilament netting with a mesh size of 2 x 2 cm. These were opened and closed like curtains daily.

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Thanks to Mongabay for Balanced Nipah Reporting

By Merlin Tuttle
5/31/18

We greatly appreciate Mongabay for its handling of the Nipah virus outbreak in Kerala, India. Its story, “Nipah infection in Kerala: Don’t blame the bats alone; improve public health,” appeared on May 30, authored by Haritha John and Gopikrishna Warrier. Needless alarm was avoided by balanced reporting. As so often is the case, the rarest threats make the biggest news. Fortunately, in this instance, the news was accurate, so did not cause needless panic.

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