I’ve talked with a number of you about this recent research from Cornell; I wanted to make you all aware of this paper (that I’ve been aware of for about a year as it worked its way through the peer review process). It’s an in important paper with important implications for how we approach monarch conservation as a public issue. In particular it has relevance on the matter of what actions would be appropriate if the monarch is listed as an endangered species, and what we in Maryland (and the mid-Atlantic in general) could be doing to support monarch populations.
As the Cornell researchers point out, quantity and quality of milkweed is not and has never been an issue in the decline of monarch populations in the East or the Midwest (there is just not enough data on Western monarch populations). Taken literally, all the summer-blooming Monarch Waystations in the world aren’t going to matter much to monarchs. Where they are in trouble is in the increasingly arid final stage of their migrations and at their overwintering sites. So touting garden plantings for monarchs that provide milkweed for caterpillars and summer flowers for the adults is nice, but it isn’t very helpful for monarch recovery and we shouldn’t promote it as such. [note, however, that they could be VERY important for other pollinators in greater trouble than monarchs]
Where monarch is in trouble here in the East in along the coast. Given a preference, monarchs would prefer to save energy and coast along on sea breezes from New England to the South and then cut over (most of them) to Mexico. Doing so means they need high quality nectar along the coastline; historically this has been seaside goldenrod (and a few other fall-blooming composites). But beach development and beach erosion have drastically reduced the available nectar for coastal-migrating monarchs, forcing them to fly inland (expending more energy at a time when they have little to spare) in search of nectar. A number of veteran conservationists in our area have been working tirelessly to replace coastal plantings of seaside goldenrod; if only a fraction of the dollars spent on milkweed were redirected to these efforts it would serve monarchs much, much better than planting the nation to milkweed. Cessation of mowing highway rights of way on the east coast from midsummer on would also help.
There is a great deal of passion and commitment to planting milkweed landscapes to “save” the monarch. This is just one of those cases where the marketing hype does not match the science.
>>Beyond milkweed: Monarchs face habitat, nectar threats (from ScienceDaily)
Date: April 22, 2016
Source: Cornell University
Summary: In the face of scientific dogma that faults the population decline of monarch butterflies on a lack of milkweed, herbicides and genetically modified crops, a new study casts wider blame: sparse autumnal nectar sources, weather and habitat fragmentation.
In the face of scientific dogma that faults the population decline of monarch butterflies on a lack of milkweed, herbicides and genetically modified crops, a new Cornell University study casts wider blame: sparse autumnal nectar sources, weather and habitat fragmentation.
“Thanks to years of data collected by the World Wildlife Fund and citizen-scientists across North America, we have pieced together the monarch life cycle to make inferences about what is impacting the butterflies,” said Anurag Agrawal, Cornell University professor of ecology and evolutionary biology and senior author on the new paper, to be published April 25 in the journal Oikos.
The scientists did not find evidence supporting the “milkweed-limitation hypothesis” during the monarch’s summer breeding season in the midwestern and northeastern United States. Rather, through statistical analyses, the group found problems in the transition from the U.S. and southern Canada to the overwintering grounds in Mexico. Milkweed is only a food source for the caterpillars in summer, but not as the butterflies leave for their epic southern migration in autumn. The study finds that a “lack of milkweed, the only host plant for monarch butterfly caterpillars, is unlikely to be driving the monarch’s population decline, as the problem appears to occur after they take flight in the fall,” said Agrawal.
In any given year, four generations of monarch butterflies traverse much of North America over a 2,000-mile trek beginning in early spring when they leave the Mexican wintering grounds. In the first generation, millions of monarchs flow through Texas and Oklahoma, with the subsequent generations moving into the Midwest and Northeast, until the start of fall, when the fourth generation returns to the mountainous, high-altitude Oyamel fir forests of central Mexico.
Despite the seemingly good news of annual population bounce-back on the return from the south each year, the scientists were clear that the monarch population has been dwindling. Yes, said Agrawal: “The consistent decline at the overwintering sites in Mexico is cause for concern. Nonetheless, the population is six times what it was two years ago, when it was at its all-time low.” Agrawal credits the population rebound to improved weather and release from the severe drought in Texas.
Agrawal said that a persistent decline caused by lack of nectar sources or other threats such as habitat loss or insecticide use can conspire with large annual population fluctuations — mostly due to weather — and may eventually push monarchs to dangerously low numbers.
“Given the intense interest in monarch conservation, the blame being put on herbicide use and the national dialog about potentially listing monarchs under the endangered species act, we have to get the science right,” said Agrawal.
The above post is reprinted from materials provided by Cornell University. The original item was written by Melissa Osgood. Note: Materials may be edited for content and length.
1. Hidetoshi Inamine, Stephen P. Ellner, James P. Springer, Anurag A. Agrawal. Linking the continental migratory cycle of the monarch butterfly to understand its population decline. Oikos, 2016; DOI: 10.1111/oik.03196