A roads meta-analysis found an average wildlife cost—and big uncertainty

A synthesis of 160 studies found a roughly 32% reduction on one effect scale, while other effect metrics were uncertain and site results varied greatly.

Wild Lands Ecological Intelligence Editor
Wild Lands Institute · 14 October 2026

Evidence: Peer-reviewed
Geography: Studies spanning multiple world regions
System: Road corridors; terrestrial wildlife communities

WHAT THE EVIDENCE SAYS

Reviewers fitted three-level models to 643 effect estimates from 160 studies. On the log-response-ratio scale, wildlife outcomes near roads averaged about 32% lower, but the standardized mean difference and correlation estimates had confidence intervals crossing zero. Prediction intervals spanned positive and negative responses; traffic volume was reported for only 91 effects.

WHY IT MATTERS / OUR READ

An average road effect is not an adequate crossing-location or mitigation design. Species, outcome type, traffic exposure and nearby habitat all matter; mixed effect scales should not be silently collapsed into a single universal loss percentage.

CAVEATS / UNCERTAINTY

Effects were heterogeneous and most studies did not supply standardized traffic-volume information. This synthesis is observational across studies and does not prove a single causal road response for all taxa or habitats.

SOURCE

Frontiers in Ecology and Evolution — primary systematic review and meta-analysis
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