According to Reppert : "Coupled with the suspended sexual maturation is what Reppert calls "this incredible urge to fly south." Using the sun as a guidepost, and keeping track of the time of day as their point of reference crosses the sky, the insects head for warmer weather".\n\nMonarchs in the Eastern U.S., that migrate long-distance to the South, in autumn, are undoubtedly attracted to warmth;which is why the direction of their migration is affected by the direction of the sun (though not by any sun-compass). They are also attracted by the odors of the specific type of plants on which they feed, before, as well as during migration. And they are carried by major seasonal winds. \n\nThey do not, however, have any "instinctive" urge to fly South, and they do not "instinctively" plot a flight-route that would lead them to Mexico, or any other "goal" they had never visited, and know nothing about. \n\nHad they lived in the Southern hemisphere, , instead of South, in the Southern autumn. In the Western part of the U.S., e.g. in California, they never migrate to Mexico, and they do not migrate long-distance at all. Instead, in autumn they start gradually migrating further South, through several generations. And in spring they start gradually migrating back North.\n\nThe belief that Monarchs have "instincts' that govern whether they will migrate and to which "goal" they will migrate, is the product of a totally unwarranted and misguided belief in the existence of "instincts". "Instincts" were initially believed to be "heritable" behavior, which, "genetically predetermined" behavior, presumably identifiable by not being learned behavior. Instead, all individual traits (including behavioral traits) of all living organisms, develop ontogenetically (in each individual organism), under inseparable (!) effects of both (!) genes & environment; which means that "instincts" do not exist at all! In fact, by now, even those who still believe in the existence of "instincts", cannot provide any usable definition of "instinct". The term has, thus, become a meaningless word, that not a few scientists still accept as a proper solution to scientific problems.\n\nIf you read the published reports of a years-long project of capturing & tagging migrating Monarchs as they pass through Cape May, you will find that observers once saw a swarm of migrating Monarchs flying South, and shortly afterwards, they saw at the same site another swarm flying in exactly the opposite direction! You can find reports about Monarchs drowning in the Atlantic ocean. And there is even a report about a tagged Monarchs accidentally found in the Bahamas, where no one was looking for tagged Monarchs. Obviously the Northern Monarchs that migrate very long distances, are not heading to Mexico, or any other "genetically predetermined goal". Scientists who believe in the existence of "instincts", however, claim that such cases are due to the Monarchs having made errors. The Monarchs did not make any errors. Instead, it is only those very silly scientists who err!\n\nOf course, you can "prove" any hypothesis, no matter how silly, or crazy it may be, by excluding as "errors" all cases that contradict the hypothesis. Resorting to such practice, however, is outright counter-scientific.\nAs long as many scientists working in the Behavioral field , still remain faithful to their totally misguided, unwarranted faith, in the existence of "instincts", they will continue to inundate the whole field with an ever-growing amount of rubbish. Garbage in, garbage out!