sweeter, and mellow with rising and falling passages that make the song much longer than the robin's. The note is a sharp ik or eek. Both the male and female sing, but have different songs. Diet The black-headed grosbeak eats pine and other seeds, berries, insects and spiders, and fruit. During the summer, it mostly eats spiders, snails, and insects. It is one of the few birds, along with the black-backed oriole, that can safely eat the poisonous monarch butterfly. In their wintering grounds, this grosbeak consumes many monarch butterflies, perhaps over one million per year in the overwintering colonies in Mexico. However, only the black-headed grosbeak is physiologically insensitive to the cardiac glycoside heart poisons in the monarchs, which monarch caterpillars sequester from their milkweed host plants and are retained by adults even after metamorphosis, which protects them from most predaceous birds. The same genetic changes that confer resistance to the poisons in the monarch and its relatives were found to have evolved in the black-headed grosbeak in a case of convergent evolution. The cellular target of the heart poisons is the first extracellular loop of the sodium pump, a critical ion pump needed for nerve cells to fire and heart cells to contract. Two of the grosbeak's four copies of the gene encoding this protein have changes that are also found in insects adapted to feeding on plants producing the cardiac glycosides. In one of the copies, it has the same genetic changes at position 111 and 119 as in the common grow and other Euploea butterflies closely related to the monarch, and in another copy, position 111 has the same change as Largus bugs, which feed on dogbane plants that produce cardiac glycosides The mutations at positions 111 and 119 have been shown together, but not alone, to confer resistance to the heart poisons in insects through positive, intramolecular epistasis. In the breeding season, the black-headed grosbeak comes to bird feeders for sunflower and other types of seed, and fruit, and also joins northern orioles at feeders with grape jelly. Range and migration Black-headed grosbeaks range from the Pacific Coast to the middle of the US Great Plains and from southwestern Canada to the mountains of Mexico. US and Canadian birds are highly migratory, wintering in Mexico. In the Great Plains, the range of the black-headed grosbeak and the rose-breasted grosbeak overlap and they have interbred somewhat.