Monarchs, Redux

monarch2 dreamstime 9812358 Monarchs, ReduxEach fall, volunteers in New Jersey and Michigan keep a careful count of the colorful monarch butterflies they see fluttering south on their annual migration. Now, an analysis of those counts suggests that monarch populations have held steady over the last few decades – in marked contrast to a recent study that documented a worrying decline in wintering colonies in Mexico. The discrepancy has researchers struggling to understand exactly how the species is doing.

“The status of the eastern North American monarch butterfly population is a highly sensitive issue, given that winter and breeding habitats are being lost at an alarming rate each year,” Andrew Davis of the University of Georgia in Athens writes in Insect Conservation and Diversity. “Because of this, most believe the population to be declining, although there has been little empirical data to support this idea.”

In March, however, researchers published a study in the same journal (see Monarch Decline, Conservation Magazine, Summer 2011) reporting that Mexico’s wintering colonies had experienced an overall decline over the past 17 years, including a record low census in 2009-2010. That study, Davis notes, suggested the decline was “the first sign of impending collapse” of Monarch populations.

But Davis wondered how the Mexican numbers compared with the migration counts conducted each fall at monitoring stations in Cape May, New Jersey – which had data for 15 years — and Peninsula Point, Michigan, which had 19 years of numbers. After analyzing the counts, he found no overall decline: “At both locations there was no significant linear trend in average monarch numbers counted over time.” That suggests “the population remains stable for now,” he concluded, “probably because of the high fecundity of the species and its ability to rebound from small winter numbers.”

But why are the U.S. and Mexican numbers so different? It’s surprising, he notes, “that these three data sets are not more consistent. In other words, large numbers of fall migrants should lead to large wintering colonies and vice versa.”

One possibility is that existing data is simply too crude to “estimate the number of individuals in a population that has a massive range and numbers in the millions.” Another is that many of the migrating butterflies die before they reach Mexico – or that they are finding new places to spend the winter. “Indeed, alternative wintering sites are not unheard of for this population, with known areas being in Cuba, southern Florida and increasing reports of locations along the US Gulf coast,” he writes. So far, however, none of these new overwintering sites seem to hold the millions of “missing monarchs” from Mexico.

Another explanation may be that the butterflies have high enough reproductive rates to bounce back from bad years. “Even though the cohort in Mexico may be shrinking, there still could be enough monarchs each year that survive to re-colonize the breeding range in the United States and Canada,” he writes.

The take-home message, he says, is that the monarch “picture seems
more complicated than what is portrayed… So even though the decline in suitable breeding and wintering habitat makes it a foregone conclusion that this unique and well-studied population of monarchs may someday collapse, I contend that it does not appear to be doing so just yet.” David Malakoff | July 9, 2011

Source:
DAVIS, A. (2011). Are migratory monarchs really declining in eastern North America? Examining evidence from two fall census programs. Insect Conservation and Diversity DOI: 10.1111/j.1752-4598.2011.00158.x

Image Copyright Dreamstime.com

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2 Comments

  • Steven Earl Salmony July 10, 2011 at 5:35 am

    Human impact on butterflies is real, I suppose.

    For the past 10 years scientific research from Dr. Russell Hopfenberg has been everywhere avoided by many too many professionals with appropriate expertise in population science. Could someone with appropriate expertise kindly respond to the scientific evidence presented by Russ Hopfenberg? That is to ask, would someone with adequate expertise either report findings regarding extant hypotheses and evidence or else find a top rank colleague with appropriate expertise who will affirm or refute the research? Please note that I am not asking for inexpert opinion pieces of the kind I regularly present. We need something more and different now.
    Hopfenberg’s apparently unforeseen, unfortunately unwelcome and still unchallenged scientific finding regarding the relationship between food supply and human population numbers is being denied by the very experts upon whom the human community relies for guidance and direction. For a decade ‘the brightest and best’ have refused comment on what appears to be the best available science concerning the relationship between food availability and the size of the human population on Earth. Too many experts have ignored certain scientific evidence and failed to report their findings in professional journals, as would be expected. This failure has to be acknowledged and put behind us so that momentum can gather to move the human family in a new direction; so that we can begin making necessary changes toward sustainability.
    Until now what appears so obvious, almost rhetorical to many people, regarding the human population has been rarely acknowledged and seldom reported by experts who have unassumed responsibilities to science and unfulfilled duties to perform for humanity’s sake. Perspectives of many too many professional researchers regarding human population dynamics and overpopulation have not been shared widely and openly. Public discourse of science regarding so vital a topic as human overpopulation has been voided, as it were, into a black hole of silence. Experts in possession of scientific understanding have remained mute about what people see and, in so choosing, have refused to validate what is already alive in the world: vital knowledge of the human population.
    Scientists with expertise in many other fields of inquiry utterly depend on other top notch colleagues to present the best available scientific evidence in each field of study. That is to say, first class scientists who are not expert in matters related to population dynamics and human overpopulation, for example, are dependent upon similarly situated experts in fields of study related to population dynamics and overpopulation for reports of the best scientific evidence. Regrettably, professionals with appropriate expertise in population dynamics and human overpopulation have not been carefully examining and objectively reporting findings regarding certain scientific research from Hopfenberg on the human population. This most problematic situation has to be recognized, addressed and overcome.
    How are human beings to consciously, deliberately and ably respond to the global challenges posed to humanity by human overpopulation of the Earth if experts in population dynamics and overpopulation choose to pose as if they are willfully blind, hysterically deaf and electively mute in the face of scientific evidence? Responding to science with silence, as has been occurring for the past ten years, is woefully inadequate and could contribute to a forbidding result, one in which humankind inadvertently precipitates the ruination of the world as a fit place for children everywhere to inhabit. If the day ever comes when professionals come to regard the best available, uncontested science as meaningless or useless, then I will fear the worst for the children. I cannot see any justification or defense for continuing to consciously and willfully deny what could be true regarding the human population, as science discloses what is real to us.
    On our watch, the human family appears to be unknowingly precipitating a planetary emergency with potentially profound implications for the future of life as we know it on Earth. If a human-driven global emergency is in fact looming before us, it is incumbent upon those leaders inside and outside the community of scientists in my generation of elders to take the measure of the global ecological challenges that are so distinctly human-forced, so rampantly emergent and so rapidly convergent in our time. The extent to which the global predicament already visible on the horizon is derived directly from unbridled overconsumption, overproduction and overpopulation activities of the human species, there can be no doubt that human beings can make such changes in our behavioral repertoire as can humanely alter the dangerous ‘trajectory’ of our current, soon to become patently unsustainable activities. Global threats to human well being and environmental health that are presently induced by humankind can certainly be acknowledged, ameliorated, eventually addressed and ultimately overcome by the family of humanity.

    Steven Earl Salmony
    AWAREness Campaign on the Human Population,
    established 2001
    Chapel Hill, NC
    http://www.panearth.org/

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