Black-headed grosbeak (IMAGE) University of California - Berkeley Caption In places like Mexico where monarch butterflies overwinter by the thousands to millions, the black-headed grosbeak is one of few birds that can eat them without vomiting. Researchers discovered that the bird has evolved similar genetic mutations as those found in the monarch that allow both to handle milkweed toxins, which accumulate in the butterfly and are deterrents to most predators. Credit Mark Chappell, UC Riverside Usage Restrictions none 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.