When Their Owners Are Coming Home, and Other Unexplained Powers of Animals. Cockrell, Barbara J., Stephen B. Malcolm, and Lincoln P. Brower, Time, temperature, and latitudinal constraints on the annual recolonization of eastern North America by the monarch butterfly, pp. Grace, Eric S., The World of the Monarch Butterfly. Sierra Club Books, 1997. Paths of fall migrations.
Eastern colonies fly a longer route to Mexico.
A histomap showing 8 months in the life of an eastern colony of monarch butterflies. Dashed lines indicate the caterpillar phase, and solid lines the butterfly stage, of each generation. Numbers count the generations. Time runs along the horizontal axis to the right, for 8 months, beginning in mid-March. Bifurcation diagram showing attractors of the morphic field as a function of time.