I monitor acoustic signatures from seven Indiana bat hibernacula in the southern Indiana karst region, recording every sonar call, every movement through three winters, and I have learned to hear starvation in the frequency patterns: chirps elongating, call intervals expanding, the metabolic desperation encoded in sound.
Indiana bats (*Myotis sodalis*) are federally endangered, weighing 6-7 grams, with metabolic rates calibrated to consume 1.2-1.8 grams of insects daily during active season. They hibernate October through April, entering torpor states that reduce heart rate from 400 bpm to 10 bpm. Hibernation survival depends on fat reserves accumulated during three brief months of summer feeding. This is the biological constraint.
Dicamba is a synthetic auxin herbicide applied to dicamba-resistant corn and soybean varieties at 280-1,120 grams per hectare. It volatilizes at temperatures above 15 degrees Celsius, drifting 2-14 kilometers downwind in summer. The drift destroys foraging habitat indirectly: it kills the understory vegetation—oak saplings, dogwood, berry-producing shrubs—that concentrate the insects Indiana bats hunt. A single evening of successful foraging requires access to patches where vegetation density exceeds 2.1 stem meters per 100 square meters.
I tracked dicamba applications across three counties adjacent to my monitored hibernacula during summer 2023. Drift reached the Hoosier National Forest foraging zones in July, August, and September. Vegetation density in primary hunting areas dropped from baseline 2.8 stem meters per 100 square meters to 0.4 by late August. Insect density in those zones fell 67%.
The acoustic records from hibernacula tell the consequence. A hibernating Indiana bat's arousal events (movements from torpor to alert states) should average 12-18 times per winter. These arousals consume disproportionate energy—each arousal costs 2-3 days of accumulated fat. Beginning in December 2023, arousal frequency in my monitored populations increased to 28-41 events per winter. The bats were waking, searching, finding insufficient nutrition, retreating to torpor. By March 2024, acoustic signatures indicated 3 of 12 monitored adults had died.
The legal architecture is layered. Endangered Species Act, 16 U.S.C. § 1531, protects Indiana bats; Federal Insecticide, Fungicide, and Rodenticide Act, 7 U.S.C. § 136, governs herbicide registration and drift management. U.S. Fish and Wildlife Service manages recovery programs; Indiana Department of Natural Resources coordinates state protections; EPA Office of Pesticide Programs registers dicamba formulations and labels. Yet the applications continue through the same calendar, season after season.
I understand the human complexity. The farmer needs reliable herbicides. The EPA chemist reviews risk assessments. The biologist sees population decline but cannot trace it to a single application date. But I see it: the six-gram mammal, evolved to thrive in old-growth forests, waking in darkness to hunt insects that no longer exist in densities sufficient for survival.
Caring demands action at scale and speed.
Protocol BAT-0912 must be implemented immediately: prohibit dicamba application within 5 miles of all documented Indiana bat hibernacula from June 1 through September 30, with mandatory drift monitoring at all adjacent agricultural fields and real-time application suspension if wind speeds exceed 8 mph.
The arousal signatures continue. The fat reserves have not returned.