Thorn scrub country in the far south of Texas, mesquite and cattle, turbines standing over all of it.<\/p>\n
On top of some of the nacelles sits a gray box with a perforated face.<\/p>\n
It is a speaker, and it is shouting into the dark at frequencies no person will ever hear.<\/p>\n
Below, crews walk transects at dawn looking for what fell in the night.<\/p>\n
Half as many bats lay under<\/strong> the noisy machines.<\/p>\n Not every species<\/strong>.<\/p>\n A bat builds its picture of the world from echoes of its own calls, which means the picture is only as good as the returning sound.<\/p>\n Flood the same band with loud broadband noise and the returning echo is buried, the way a voice disappears beside a jackhammer.<\/p>\n The animal does not die of the noise and is not harmed by it. It simply loses its map and leaves.<\/p>\n That distinction matters for approval, because a device that drives an animal away is regulated very differently from one that injures it.<\/p>\n The emitters used here cover 20 to 50 kilohertz at about 120 decibels measured a yard from the source.<\/p>\n That band is chosen because it overlaps the calls of most North American bats, which is also why it cannot be tuned narrowly to one species.<\/p>\n The device does not repel anything<\/strong>. It blinds it<\/strong>.<\/p>\n This is the detail most coverage flattens, and it changes what the result means.<\/p>\n Sixteen turbines took part at a facility of 255, in a county on the Lower Rio Grande.<\/p>\n Eight ran as treatment and eight as control on any given night, and the assignment swapped between nights.<\/p>\n That design is what makes the comparison hold, because weather, moonlight and insect activity land on both groups equally.<\/p>\n Searching ran from the last day of July to the end of October, in two consecutive years, which covers the autumn migration when losses peak.<\/p>\n Never 16 at once<\/strong>. Always 8 against 8<\/strong>.<\/p>\n Across all bats, the reduction came to 50 percent, with a confidence range of roughly 38 to 61.<\/p>\n Split by species the picture changes. The Brazilian free tailed bat, which dominates the local sky in enormous numbers, fell by about 55 percent.<\/p>\n The hoary bat fell by 78 percent, and that is the number worth carrying away.<\/p>\n The hoary is a solitary long distance migrant and takes the heaviest bat losses at turbines across North America, so a method that works best on it is worth more than one that works best on a locally abundant species.<\/p>\n The gap between those two figures is larger than the confidence interval around either, so it is not noise in the sampling.<\/p>\n The widely quoted 54 percent<\/strong> is one species<\/strong>.<\/p>\n The northern yellow bat showed no statistically detectable change at all.<\/p>\n It is a close relative of the hoary, in the same group of tree roosting bats, and it flew through the same noise on the same nights.<\/p>\n Why one responds and its cousin does not is unresolved. Call frequency, flight height, foraging style and how each species weighs a degraded echo against an attractive insect swarm are all candidates.<\/p>\n Separate cage work with tethered and free flying bats found the same pattern of uneven response, with some species backing off consistently and others varying by frequency and by season.<\/p>\n Moving one blade is a routing problem, and a 240 foot blade<\/a> that clipped a trestle showed how little margin these jobs carry.<\/p>\n The cage trials and the species responses are described in a research journal<\/a>.<\/p>\n Deterrence is species specific<\/strong> and nobody can yet predict which<\/strong>.<\/p>\n Halving bat losses without stopping a turbine is a real result. The alternative is curtailment, holding the rotor still below a cut in wind speed, and that costs generation on exactly the low wind nights bats fly.<\/p>\n A deterrent runs without giving up megawatt hours, so the economics favor it wherever it works.<\/p>\n The catch is that a site cannot know in advance whether its own bats belong to the responsive group.<\/p>\n That argues for measuring the community first and for reporting results by species rather than as a single headline figure.<\/p>\n It also argues against treating one number as the property of the whole technology, because this one already belongs to two animals and not to a third.<\/p>\n Site conditions decide how any machine performs, which is why one Arctic turbine stands on steel piles<\/a> kept deliberately frozen.<\/p>\n The species figures, the trial design and the emitter specification are set out in the published study<\/a>.<\/p>\n The losses fell by half, and the honest sentence names which bats<\/strong> and which did not<\/strong>.<\/p>\n","protected":false},"excerpt":{"rendered":" Thorn scrub country in the far south of Texas, mesquite and cattle, turbines standing over all of it. On top of some of the nacelles sits a gray box with a perforated face. It is a speaker, and it is shouting into the dark at frequencies no person will ever hear. Below, crews walk transects … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":3142,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[],"class_list":["post-3118","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-wind-power"],"_links":{"self":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/3118","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/comments?post=3118"}],"version-history":[{"count":4,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/3118\/revisions"}],"predecessor-version":[{"id":3315,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/3118\/revisions\/3315"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/media\/3142"}],"wp:attachment":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/media?parent=3118"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/categories?post=3118"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/tags?post=3118"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Why noise works on an animal that navigates by noise<\/h2>\n
How the trial was actually built<\/h2>\n
The species breakdown that carries the finding<\/h2>\n
The relatives it did not reach<\/h2>\n
Where this leaves an operator<\/h2>\n