GPS collar on a cow (IMAGE) American Geophysical Union Caption The cows in the study wear virtual fence collars that give signals when they are approaching the programmed grazing boundary. Virtual fences may help improve vegetation variety in grazed areas. Credit Timothy Olsen Usage Restrictions Credit must be given to the creator. No derivatives or adaptations of the work are permitted. License CC BY-ND Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.