Monarch butterflies suffer population loss (50% - 60% maybe higher)

[OKIsItJustMe]

http://articles.latimes.com/2010/mar/20/nation/la-na-monarchs20-2010mar20

Monarch butterflies suffer population loss

Storms in Mexico devastate an already low population of the migrating butterfly. An advocacy group encourages landowners to plant milkweed to help the survivors travel.

March 20, 2010 | By Bill Hanna

Reporting from Fort Worth, Texas — Monarch butterflies, devastated by storms at their winter home in Mexico, have dwindled to their lowest population levels in decades as they begin to return to the United States and Canada.

The monarch loss is estimated at 50% to 60%, which means the breeding population is expected to be the smallest since the Mexican overwintering colonies were discovered in 1975, said Chip Taylor, a professor of entomology and director of Monarch Watch at the University of Kansas.
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"I think it is very clear that the butterflies lost more than half of the population," Taylor said. "I'm hoping it wasn't as high as 70% or 80%. We've never seen it this bad before."

The butterfly colonies in the Mexican state of Michoacan were hit by torrential rain and mudslides in early February that killed at least 40 people and left thousands homeless. Several towns were devastated by flooding.

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[mike_c]

1. butterfly populations can be extremely resilient to density independent losses....

As long as resources are available, females can lay lots of eggs and reestablish populations quickly. Winter mortality is just a blip on the radar for migrating monarchs. Seriously-- I'll bet that 50-60 percent mortality is within normal variation, or pretty close to it.

[OKIsItJustMe]

2. "I'll bet that 50-60 percent mortality is within normal variation, or pretty close to it."

Except that their population had already been hit.

http://abcnews.go.com/GMA/Weekend/monarch-butterflies-decimated-torrential-rains-mudslides/story?id=10161340

...

According to Taylor, it's the lowest number of monarchs returning to the United States that he has ever seen. Monarch butterflies in the eastern U.S. follow a remarkable migration pattern as winter nears, traveling thousands of miles down to Mexico using a sort of instinctual GPS system. When the weather warms in March, breeding monarchs head back north to repopulate. By summer the butterflies migrate as far north as Canada.

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http://www.physorg.com/news172944025.html

Female monarch butterflies on 30-year decline in eastern North America

September 23, 2009

(PhysOrg.com) -- Female monarch butterflies in eastern North America have significantly declined over the past 30 years, a new study by a University of Georgia researcher reveals.

Andy Davis, a Ph.D. candidate in the Warnell School of Forestry and Natural Resources, analyzed published overwintering and migratory data for the insect from 1976 to the present, discovering that the female to male ratio for the butterflies east of the Rockies has gradually been changing. In the late 1970s, Davis said, females made up around 53 percent of the monarch butterfly population that migrated to Mexico for the winter. Today, that number has dropped to about 43 percent which paints a dire picture for population recruitment. Davis outlines his findings in a new paper co-authored with Eduardo Rendón-Salinas of World Wildlife Fund-Mexico. The paper appears in Biology Letters.

“I nearly fell over when I saw the trend,” said Davis. It was an unintentional but extremely important finding.”

The monarch butterfly, one of the most well-known and widely-recognized insects in the world, is a flagship species for conservation. North American Monarchs can migrate more than 2,000 miles as they fly to Mexico from Canada and the U.S. for the winter. “The implications of this decline are huge,” Davis said. “Female monarchs can lay as many as 400 eggs over their lifetime, which is why the species is so resilient.”

But Davis said that as the monarch population continues to struggle because of breeding habitat loss, widespread pesticide use, and deforestation of the overwintering sites, losing a significant number of females could seriously hinder the population’s ability to rebound after periodic crashes. Davis, who studies monarchs in addition to his doctoral work, said that news of the decline has gone unnoticed until now “because no one’s ever looked at the data like this. For years, scientists have been collecting male and female monarchs at the overwintering sites and during the fall migration. When we compiled the numbers from these collections, along with the year they were made, the trend was obvious.”

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[mike_c]

4. oh I didn't mean to suggest that it isn't a serious population setback....

Especially in light of cumulative threats. But essentially the same thing happened a few years ago when someone cut trees and sprayed insecticide within the overwintering reserve to protest protection of the forest against resource extraction. Mortality was huge, but the populations recovered, or were recovering.

Monarchs are historically at bottleneck risk BECAUSE they migrate and overwinter in concentrations at the very edge of their physiological cold tolerance. It's a delicate balancing act, and one that causes significant mortality most years. By itself, that's just background density independent mortality for monarchs.

I'm MUCH more worried about habitat loss-- both breeding habitat and overwintering habitat-- than I am about winter mortality UNDER THE CURRENT CLIMATE REGIME. That last is important. All bets are off if the climate changes too quickly for the butterflies to adjust their migration patterns, which they might not do in any event. Just a little bit warmer or colder on average and overwintering butterflies will either starve (too warm and metabolically active) or freeze. Those mountains they use for overwintering are right at the temperature/shelter/moisture physiological cusp for monarchs-- there isn't much wiggle room even during good years, so their populations are pretty well adapted to absorbing significant losses, as long as recovery habitat and resources are available. Normal winter mortality is not going to be the cause of monarch extirpation, I don't think.

[arachadillo]

6. Monarch Butterfly Populations

The most recent news reports say, "The monarch loss is estimated at 50% to 60%, which means the breeding population is expected to be the smallest since the Mexican overwintering colonies were discovered in 1975, said Chip Taylor, a professor of entomology and director of Monarch Watch at the University of Kansas."

Mike C says, "As long as resources are available, females can lay lots of eggs and reestablish populations quickly. Winter mortality is just a blip on the radar for migrating monarchs. Seriously-- I'll bet that 50-60 percent mortality is within normal variation, or pretty close to it"

also, "I'm MUCH more worried about habitat loss -- both breeding habitat and overwintering habitat -- than I am about winter mortality UNDER THE CURRENT CLIMATE REGIME. That last is important."

Recent reports also suggest decreases in Monarch populations across Minnesota, close to their northernmost range, due primarily to habitat loss.

OTOH, the existence of a http://www.fs.fed.us/monarchbutterfly/">North American Monarch Butterfly conservation program, and the fact that despite radical population drops, the aggregate monarch population is still sufficiently large (in the millions) to ensure its long term survival.

However, a changing climate poses risks for Monarchs in their wintering grounds because it could mean more storms similar to this past winter's storms (and those of the early 2000s), and/or an ecosystem change that is not conducive to the long term preservation of their forest home. It's still too early to tell.

Could it be that future Monarch migrations will mean population decreases over its entire range, or a decreasing population will reduce its range, or a combination of both?

[mike_c]

9. well, predictions are tough...

...but with monarchs, there is a built in bottleneck potential that makes them particularly susceptible to climate change, i.e. the winter migration and overwintering in Mexican mountains. Their physiological status during overwintering is precarious anyway, and it depends upon just the right balance of cool (but not frigid) temperatures, humidity (but not too much moisture), overhead cover to limit radiative heat losses at night, nutrient storage by the overwintering generation, seclusion in an increasingly crowded world, and so on.

Then the annual population expansion out of the overwintering grounds depends upon prevailing weather patterns to aid dispersal and upon breeding resources along the migration route, both of which are also threatened by climate change.

It's just not a good design for a world undergoing climate alteration. All things considered, I'm not very hopeful about the long term prospects of monarchs.

On the other hand, there are the west coast populations-- they might provide sufficient population refugia to keep the species alive.

[midnight]

3. Here is a beautiful site to view monarch butterflies.

http://www.youtube.com/watch?v=oe1YRC18U7E&feature=player_embedded#

[hatrack]

8. While you still can . . .

.

[TreeHuggingLiberal]

5. Jesus

With our never ending appetite for development being coupled with stochastic events (rising in frequency as we f*** with the climate), we're going to have to be extremely proactive over the course of this century to help alleviate the damage we have already wrought. The migration of the monarchs is truly one of the most amazing spectacles of any species.

[riverwalker]

7. Plant Milkweed for them everywhere

I went here to order.


http://www.livemonarch.com/free-milkweed-seeds.htm