- https://www.usgs.gov/media/images/historical-and-current-grizzly-bear-range-north-america
- https://www.vitalground.org/wildlife-crossings-new-federal-funding/
- https://www.fhwa.dot.gov/publications/research/safety/08034/08034.pdf
- https://www.pew.org/en/research-and-analysis/articles/2024/11/05/wildlife-crossings-save-lives-money-and-improve-the-environment
- https://pmc.ncbi.nlm.nih.gov/articles/PMC1559960/