The number of monarch butterflies spending the winter in the western United States has dropped to its second-lowest mark in nearly three decades as pesticides, diminishing habitat and climate change take their toll on the beloved pollinator. Here’s what to know: The survey began in 1997 Monarch butterflies, known for their distinctive orange-and-black wings, are found across North America . Monarchs in the eastern United States spend their winters in Mexico and are counted by the World Wildlife Fund , which has yet to release data for this year. Monarchs west of the Rocky Mountains typically overwinter along the…..