Sunday, September 6, 2015

Decline Of The Monarch Butterfly

Nature

Monarch Butterfly WoesEmily DeMarco writes: The results have also put a spotlight on the need to better understand what is happening to monarchs during their fall migration south, researchers say.”
Photo Credit: Fred Habegger; Grant Heilman Photography; Alamay


An article, by Emily DeMarco, in Science Magazine explores the possible reasons for the declining number of monarch butterflies (Danaus plexippu) overwintering in their traditional grounds in Mexico, but there is little scientific consensus on the reasons for this decrease in numbers.

In “Monarch butterfly studies tell a perplexing tale,” (August 5, 2015), DeMarco writes:
Each summer, female monarch butter-flies flutter around their breeding grounds in northern North America in search of nectar, a mate, and a milkweed plant on which to lay eggs. And they have an audience. Thousands of volunteers periodically survey the charismatic black and orange insects, helping scientists track population trends. Others count monarchs as they migrate south each fall to warmer climes. Now, one of the most systematic analyses of these tallies and other data has raised questions about how well researchers understand why monarchs have seen a dramatic decline on their major wintering grounds in Mexico.
The confusing picture emerges from seven monarch studies published this week in the Annals of the Entomological Society of America. One paper suggests that, even as wintering populations of monarchs have plummeted over the past 2 decades, there’s been no similarly steep decline in a key summer breeding area that stretches across the midwestern United States and southern Canada. Others find that some fall migration counts also show no major downward trend. At the same time, the butterflies may be laying fewer eggs overall, concludes one study.
Such findings “present a puzzle,” says ecologist Leslie Ries, now of Georgetown University in Washington, D.C., and an author of one of the studies. They “make me wonder if we really have the strongest evidence to be able to say we know what’s causing the decline that we see in Mexico.” The uncertainty could pose problems for conservationists trying to protect the butterflies.
Although anecdotal sightings is not science, I have noticed a marked decline in monarch butterflies the last few years. I saw a few this summer; one last year, and none the year before. This compares to seeing monarchs as a common sightings decades ago. It is their absence that is noticeable. Such is confirmed by Barbara Kiser in an article in Nature News: “Meanwhile numbers of North America’s Monarchs, whose 5,000-kilometre migration is a wonder of the continent, have dwindled by over 90% since the mid-1990s as their milkweed habitat disappears.” The decline of monarchs is concerning, because they are considered an indicator species, suggesting that something is wrong ecologically. This requires further investigation.

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For more, go to [ScienceMag]

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