Dr. James Hansen: The monarch butterflies return
Last summer the population of monarch butterflies in the Northeast United States seemed to be greater than it had been in the past decade. This was consistent with the fact that the number of butterflies making it to Mexico for the 2018-19 winter was the highest since 2006-07 (see graph). Unfortunately, only half as many made it to the overwintering forest this past winter, perhaps due to unfavorable weather on the return trip. [1 ha = 2.47 acres is about 50,000,000 monarch butterflies, so more than 100 million butterflies are heading north this year.]
The monarch butterflies are now moving north as shown by the map below, with the long-lived overwintering generation producing the next generation early in the trip. The annual circuit from Mexico to Canada and back takes 4-5 generations.
BTW, it has been found that breeding monarch butterflies indoors does not generally produce healthy monarchs who know where they should be headed. The best way to help monarchs and observe their marvelous transformation from larvae to butterfly is by planting milkweeds, their only food
A remarkable 3-minute film of a ‘hummingbird’ drone spying on the monarch population in Mexico is available. Be sure to watch to the spectacular conclusion at the end!