A Forensic Investigation Into the Etiology of Bat Mortality at a Wind Farm: Barotrauma or Traumatic Injury?

Abstract

Migrating bats have increased mortality near moving turbine blades at wind farms. The authors evaluated competing hypotheses of barotrauma and traumatic injury to determine the cause. They first examined the utility of lungs from salvaged bat carcasses for histopathologic diagnosis of barotrauma and studied laboratory mice as a model system. Postmortem time, environmental temperature, and freezing of carcasses all affected the development of vascular congestion, hemorrhage, and edema. These common tissue artifacts mimicked the diagnostic criteria of pulmonary barotrauma; therefore, lung tissues from salvaged bats should not be used for barotrauma diagnosis. The authors next compared wind farm (WF) bats to building collision (BC) bats collected near downtown Chicago buildings. WF bats had an increased incidence in fracture cases and specific bone fractures and had more external lacerations than BC bats. WF bats had additional features of traumatic injury, including diaphragmatic hernia, subcutaneous hemorrhage, and bone marrow emboli. In summary, 73% (190 of 262) of WF bats had lesions consistent with traumatic injury. The authors then examined for ruptured tympana, a sensitive marker of barotrauma in humans. BC bats had only 1 case (2%, 1 of 42), but this was attributed to concurrent cranial fractures, whereas WF bats had a 20% (16 of 81) incidence. When cases with concurrent traumatic injury were excluded, this yielded a small fraction (6%, 5 of 81) of WF bats with lesions possibly consistent with barotrauma etiology. Forensic pathology examination of the data strongly suggests that traumatic injury is the major cause of bat mortality at wind farms and, at best, barotrauma is a minor etiology.

First Report on Bat Mortalities on Wind Farms in Chile

“…Quantifi cation of bat mortality is based on dead bats numbers by turbine by year and dead bat numbers by energy produced (Cryan & Barclay 2009;Kuvlesky et al 2007). Previous articles reported key diagnostic features from dead bats found in wind energy facilities (Rollins et al 2012;Baerwald et al 2008). Pulmonary damage and signs of traumatic injury have been the most frequent lesions found in dead bats collected near turbines (Rollins et al 2012;Baerwald et al 2008).…”

Bat fatalities at two wind farms in Tasmania, Australia: bat characteristics, and spatial and temporal patterns

“…Studies to date have indicated that bat fatalities occur as a result of traumatic injury following collisions with moving turbines and possibly from barotrauma (Baerwald et al 2008), although the incidence of barotrauma has been recently queried, with collisions thought to be the primary cause of fatality (Grodskey et al 2011;Rollins et al 2012).…”

Reducing Bat Fatalities From Interactions with Operating Wind Turbines (Fact Sheet)

“…While preliminary research [4], [10] suggested that barotrauma was responsible for a significant fraction of turbine-related deaths, more recent research that used advanced forensic pathology [11] and computational fluid dynamics simulations [12] indicate that impact trauma is responsible for the vast majority of turbinerelated bat deaths and that barotrauma is likely a minor etiology.…”

“…Rollins et al [11] used forensic techniques, including autopsy and radiology, and found that while the barotrauma hypothesis could not be dismissed outright, 94% of bat deaths were directly attributable to impact trauma, and only 6% could Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 10% post consumer waste.…”

“…Moreover, Rollins et al [11] found that the methods in previous studies used to diagnose barotrauma could result in the misdiagnosis of barotrauma-due to the degradation of tissue before it was analyzed and because radiology was not used to check for internal signs of impact trauma. In addition, NREL researchers Houck et al [12] used computational fluid dynamics simulations to study the range of pressure variations that bats experience when flying in the vicinity of an operating utility-scale wind turbine.…”