Robert Swihart, Purdue University (IMAGE) Purdue University Caption Robert Swihart, professor of forestry and natural resources, found that pine voles, when given a choice, prefer to eat oak roots. Swihart believes voles are part of the reason oak trees are having difficulty regenerating in forests. Credit Purdue Agricultural Communication photo/Tom Campbell Usage Restrictions None License Licensed content 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.