The number of monarch butterflies across North America has long been thought to be declining. Previously, scientists have thoroughly researched the winter behavior of these insects which led to this unfortunate conclusion. Therefore, even though no studies have been carried out on monarch populations and breeding patterns in the summer, they were assumed to also be negative.
A new paper, published in Global Change Biology, has just uncovered what really happens to this species in the heat, revealing a surprising upward trend in population levels. “The whole reason that we did this research is that monarch colonies have been declining,” said Micheal Crossley from the University of Delaware who led the research team. “Up until now, there were real fears that the monarch is in trouble.”
The team examined trends in the breeding patterns of monarchs across the continent. “Our question was, ‘Are monarchs declining across their breeding range?’ The key take-home message was yes, monarchs are declining in some places, but increasing in other locations,” stated Crossley. “There is no consistent, long-term trend.”
The data revealed location-specific patterns in the populations. Sections of the U.S. Northeast and Midwest revealed population declines, while the U.S. Southeast and Northwest numbers were unchanged or increasing, especially in Florida. Overall, this resulted in a slight overall increase in the abundance of the species.
The team hypothesized that this is due to the population compensating for losses during the winter time. This decline comes from struggles during monarchs’ grueling winter migration to Mexico, where parasites, increasingly hot conditions, traffic, and decreasing habitat all have a role to play in declining species numbers. Though the team’s results show that despite all this, monarchs are extremely resilient, being able to bounce right back in a surprising manner.
This information can help conservationists understand how environmental variables impact death and reproduction levels in the population. From this, plans to protect the species can be put into action.
Source study: Global Change Biology – Opposing global change drivers counterbalance trends in breeding North American monarch butterflies