Different barn swallows (IMAGE) University of Colorado at Boulder Caption Hirundo rustica rustica (left) and Hirundo rustica tytleri (right) have different sexually selected traits, so they prefer to mate within their own group. Credit Matt Wilkins Usage Restrictions Use with credit License Original 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.