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The advancing role of Global Positioning System (GPS) technology in ecology has made studies of animal movement possible for larger and more vagile species. A simple field test revealed that lengths of GPS‐based movement data were strongly biased (P < 0.001) by effects of forest canopy. Global Positioning System error added an average of 27.5% additional length to tracks recorded under high canopy, while adding only 8.5% to open‐canopy tracks, thus biasing comparisons of track length or tortuosity among habitat types. Other studies may incur different levels of bias depending on GPS sampling rates. Ninety‐nine percent of track errors under high canopy were ≤7.98 m of the true path; this value can be used to set the scale‐threshold at which movements are attributed to error and not biologically interpreted. This bias should be considered before interpreting GPS‐based animal movement data.