GPS Collars Reveal When Bighorn Sheep Give Birth

Researchers have shown that the movements of a bighorn sheep, recorded by her GPS collar, can reveal when she gives birth—without a single human observer approaching the animal. In a case report published in Animal Biotelemetry, a team working on Antelope Island, Utah, USA, tested whether an analysis of parturition indicators (API) approach, which examines velocity, turning angle, and seasonal range size, could estimate parturition timing in Rocky Mountain bighorn sheep (Ovis canadensis canadensis). Traditional methods for pinning down birth timing and the habitat information that follows can be costly, time-consuming, or can potentially disturb parturient females, so a movement-based alternative has clear practical appeal.

The study relied on unusually direct ground truth. From 2020 to 2022, the researchers determined the birthdates of young bighorn sheep through consistent visual monitoring of collared females on the island. That observational record gave them 19 birthing events from 13 females for which parturition had been observed within 72 hours. Against this known timing, they compared data collected from the GPS collars: step length, velocity, turning angle, and the size of each female’s seasonal range.

The analysis produced a specific movement signature of lambing. Parturition of the 13 female bighorn sheep was identified when step length fell below 95 meters, velocity dropped under 0.05 kilometers per hour, turning angle exceeded 1.8 radians, and the seasonal range shrank to less than 8 hectares. In other words, in the days around birth, females moved short distances, slowly, with frequent direction changes, and confined themselves to a small area—a pattern consistent with a mother staying close to a newborn lamb.

The team then applied those metrics to verify 34 birthdates across all the collared female bighorn sheep in the study. The method therefore does not always pinpoint the exact day, but in this dataset it captured every observed birth within a four-day window.

The authors conclude that the API method, used in combination with step length, can estimate birthdates in bighorn sheep. That capability matters for conservation, because knowing when and roughly where births occur allows managers to delineate and protect birthing habitat for these ungulates. As a case report based on a single population on Antelope Island over three years, the findings describe one tested application of the approach rather than a broad multi-herd validation, and the authors note that such movement-based methods can be used to accurately detect parturition in this setting.

Subject of Research: Using GPS collar movement data to estimate the timing of parturition in Rocky Mountain bighorn sheep.

Article Title: Case report: a movement-based method using GPS data to estimate timing of parturition in bighorn sheep

Article References: Cotcher, E., Bates, S. B., Whiting, J. C., & Larsen, R. T. (2026). Case report: a movement-based method using GPS data to estimate timing of parturition in bighorn sheep. Animal Biotelemetry. https://doi.org/10.1186/s40317-026-00491-z

Image Credits: AI Generated

DOI: 10.1186/s40317-026-00491-z

Keywords: bighorn sheep, GPS collars, parturition, movement ecology, API method, Antelope Island, Utah, ungulates, birthing habitat, wildlife telemetry, step length, seasonal range size