Montana State University

Study shows bat deaths worldwide rising due to human causes

January 20, 2016 -- By Jodi Hausen for the MSU News Service with material from the USGS

Raina Plowright, assistant professor in Montana State University’s Department of Microbiology and Immunology, studies a bat. A new study co-authored by Plowright reports that bat deaths worldwide are markedly rising due to human causes largely unique to the 21st century. Specifically, collisions with wind turbines and the outbreak of white-nose syndrome lead the reported causes of mass death in bats since 2000. Photo courtesy of Shirley Plowright.

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A new study co-authored by Raina Plowright, assistant professor in Montana State University’s Department of Microbiology and Immunology, reports that bat deaths worldwide are markedly rising due to human causes largely unique to the 21st century. Specifically, collisions with wind turbines and the outbreak of white-nose syndrome – a fungal disease that infects the skin of hibernating bats – lead the reported causes of mass death in bats since 2000.

The research, funded by the National Institutes of Health and led by United States Geological Survey scientists, was published this week in Mammal Review.

Plowright was one of five scientists who combed through more than 200 years of scientific literature dating back to 1790 in search of reports of mass mortality events of bats. The researchers found 1,180 such incidents worldwide, more than half caused by humans.

That’s significant, said Plowright, who has degrees in veterinary medicine, epidemiology and ecology.

Plowright said bats are long-lived, slow-breeding mammals that play vital roles in most of Earth’s ecosystems. Bats are important pollinators and seed dispersers in tropical regions, and they serve as the main predators of night-flying insects in most parts of the world. Insect-eating bats are estimated to save farmers billions of dollars each year by providing natural pest control.

But the causes of bat mortality have not been reviewed since 1970. And because bats are well-adapted to survive in their natural habitat, human-caused mortalities can be more devastating than naturally occurring ones, which tend to be more diffuse.

“Many of the 1,300 species of bats are already considered threatened or declining,” said Tom O’Shea, a USGS emeritus research scientist and the study’s lead author. “The new trends in human-related mortality may not be sustainable.”

Researchers found that prior to the year 2000, intentional killing by humans caused the greatest proportion of mortality events in bats globally; the reasons varied with region, but bats were hunted for human consumption, killed as pests, to control vampire bats, and to protect fruit crops. Although the proportion of intentional killing reports declined in recent times, such acts continue in some parts of the world.

Since 2000, however, collisions with wind turbines worldwide and white-nose syndrome in North America are the primary reported causes of mass mortality in bats. In addition, storms, floods, drought and other weather-related factors also historically caused mass mortality, and could increase in the future due to climate change.

Surprisingly, the authors did not find convincing evidence that bats regularly die in large proportion due to infectious diseases caused by viruses or bacteria.  This finding comes at a time when increasing evidence points to bats as natural reservoirs of several viruses that cause disease in humans. Despite often being more social than other animals, bats may somehow avoid deaths from diseases that sweep through dense populations, the researchers said.

Plowright, who hails from Australia, is concerned about the future health of the world’s bat populations.

“Bats cannot easily rebound from mass mortality events, and climate change may create additional stressors on bat populations,” Plowright said.

The researchers conclude that bats could “benefit from policy, education and conservation actions targeting human-caused mortality.”

Plowright, who joined MSU’s faculty in fall 2014, teaches in the WIMU Regional Program in Veterinary Medicine, which is a cooperative program between MSU, Washington State University, the University of Idaho and the Utah State University.

“Raina brings an absolutely unique, internationally recognized infectious disease ecology research program to the department and MSU,” said Professor Mark Jutila, head of the Department of Microbiology and Immunology. “Her research is focused on emerging diseases of wildlife with potential for spillover into livestock and humans, which is of particular relevance in Montana.”

The MSU Department of Microbiology and Immunology is housed in the College of Agriculture and College of Letters and Science.

In addition to Plowright and O’Shea, co-authors of the study were Paul M. Cryan with USGS, David T.S. Hayman with Massey University in New Zealand and Daniel G. Streicker with University of Glasgow in Scotland.    

Contact: Raina Plowright, (406) 994-2939 or raina.plowright@montana.edu