Migratory Monarch Butterfly Populations Are in Rapid Decline

The spectacular migratory creatures are under threat.
Jessica Miley

The monarch butterfly migration is an enduring image of nature at its most resilient and beautiful. But over the last few years, the population numbers of the butterflies have been in steady decline.

Loss of habitat and other threats have slowly decreased the monarch butterflies migrating population to a point scientists fear might be too late to turn around. Monarch butterflies are currently under consideration for adding on the endangered species list. New research from the University of Chicago investigates the insect's decline.


Public gets behind the threatened insect

News of the loss of population numbers has spurred huge public support. North Americans have come together to help the butterflies by planting their favorite foods, paying more attention to protecting the butterflies in their pupae stage and even buying monarch pupae from commercial suppliers.

Schools in areas where the monarch butterflies live have taken on raising butterflies as whole school science projects.

Despite the goodwill, scientists are questioning whether raising the butterflies in schools is actually helping the species.

The Chigaco based research group warns that monarch pupae bought from commercial suppliers may not be able to migrate effectively and are possibly only boosting numbers for a short time.

Babies born on the go

Usually, butterflies surf spring winds as they head north, creating new generations along the way. As the weather cools in autumn, the spectacular flutter shuts down reproduction and starts heading south, finding their wintering grounds. During this migration, the butterflies undergo significant behavioral and physiological changes.

Scientists know that the female reproductive system is limited and females carry fewer unfertilized eggs in the autumn.

Butterflies being analyzed in the lab will orient themselves to the south when placed outside. Scientists wondered if butterflies raised in captivity would display the same behaviors.

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Commercial pupae without the instinct to head south

To test their theory, they obtained the butterflies from a commercial breeder and caught others in the wild. Both sets of insects were then raised in an outdoor environment and assessed whether they could pick up any seasonal cues related to migrating.

When each set was placed outside in the autumn, the wild ones were carrying fewer eggs and also showed a prevalence to orient south. Neither of these signs were displayed by the butterflies selected from the commercial supplier.

Lack of Instincts

This lack of migratory instincts can be attributed to one of two reasons.

The first is that the long-term captive breeding over generations. The second reason is that these magnificent butterflies don’t want to head south as they aren’t from a migratory population.

Marcus Kronforst, who is the associate professor of ecology and evolution at UChicago notes that “These monarchs have been brought into captivity and prevented from migrating for many generations, and they have genetically lost migration.”

Monarchs have spread to the Caribbean, South America, and out into the Pacific, reaching as far as Australia. None of these populations outside of North America migrate so it could be possible that the commercial populations were sourced from a nonmigratory population.

Genetics help solve the puzzle

To get to the bottom of this problem, the researchers turned to genetics. It seems that the three known non-migratory populations all independently derived from North American populations.

New analysis suggests the commercial creatures are a fourth non-migratory population.

It’s not all bad news though, early research suggests that the migratory instinct can return after two generations so butterflies obtained early enough in the year could still boost migratory numbers.

But even if this is true, there are concerns about raising the butterflies inside, small scale testing shows that raising the pupae inside reduces their migratory instincts. Further research is needed to more fully develop this theory.

Schools which raise butterflies might not be fully contributing to migratory butterfly populations, but they are still raising awareness of the plight of the creatures which is a crucial effort too.

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