"Up until now, mainly hydrogen isotopes have been used for tracing the natal origin of monarch butterflies and have provided critical information relevant to monarch conservation. Unlike a radio collar which could tell you exactly where an animal travelled, hydrogen isotopes can only tell you the general area where the tissue was formed. In this study, we show that strontium isotopes, particularly when combined with hydrogen isotopes, can help researchers pinpoint where a monarch butterfly hatched to a more precise area ?" about four times better."