How do you tell whether a bat population is shrinking? A study in nine national parks around the Great Lakes found that the answer can depend on what you measure. Researchers tracked four species of bats with two kinds of model — one based on bat activity, the other on occurrence, or where bats use the landscape — and found that, though the two are related, they can give different answers.
A scientist programs an acoustic bat detector in a Great Lakes area national park. Credit: National Park Service.
Why it matters
Bats have a bad reputation at Halloween, but they help keep insects from overrunning us — a single nursing mother bat can eat more than 4,000 insects in a night — and they are important pollinators. Despite efforts to protect them, these small, furry, nocturnal mammals are disappearing from North America because of disease and other factors. Managers need reliable ways to see which way populations are heading.
What the study found
| Parks | nine U.S. national parks in the Great Lakes area |
| Species | four |
| Methods compared | activity-based trends and occurrence-based (space use) trends |
| Result | related, but they could lead to different conclusions |
A manager who relied on only one of the two measures might reach a different conclusion than one who relied on the other. The authors argue that activity and occurrence are complementary but not interchangeable. Knowing how they differ helps managers choose the right method for what they need to know.
Sources
Based on "Different Ways of Measuring Bat Populations Could Lead to Different Conclusions," by the editors of Park Science magazine, National Park Service (Research Roundup, Volume 39, Number 1, Winter 2024–25), a work of the United States government in the public domain. The study: Goodwin and others, 2024, "Comparing Occupancy and Activity Metrics for Assessing Temporal Trends in Vulnerable Bat Populations," Biological Conservation 298: 110773.
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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