Mid-Atlantic Butterfly Field Forecast 2016 May 21-22

 

2016 May 15 Hobomok Skipper_MO-Benton Co-Big Buffalo Creek Cons Area

Hobomok Skipper is flying now locally, even though this one hails from the Missouri Ozarks from my trip there last week [2016 May 15, Big Buffalo Creek Conservation Area, MO — photo by REB]

Given the forecast (again), I debated whether it was even worthwhile putting together a Forecast for the weekend. It certainly would not have proven worthwhile today, which was a complete washout, and tomorrow looks like the same.

Nevertheless, over the past week there have been a couple of new sightings to watch for in the field. In Howard Co (MD) and in NY, Hobomok Skipper was reported on the wing, complementing Zabulon which has been emerging recently as well. Common Roadside-skipper continues to be reported across the region, and Checkered White is flying in WV (which may already be its second flight, given that it emerged early in the mid-Atlantic this year). FOY Northern Cloudywing also put in an appearance in NJ and WV, so both it and Southern Cloudywing are likely to be seen in the right habitats across the region. Sleepy Orange in flying in VA and the Carolinas, apparently in numbers, so 2016 could be a good irruptive year for them.

Also among skippers, Peck’s, Sachem, Least and Little Glassywing are building in numbers in VA and likely to be seen anywhere in the mid-Atlantic this week. Peck’s was also on the wing in NJ.

No reports of Dusted Skipper have come in, and searches for it specifically have come up short.

A fresh brood of Red Admirals and American Ladies is due to emerge over the next two weeks, progeny of earlier migrants to the mid-Atlantic.

Next weekend’s Forecast is likely to be more robust; our riverine weather systems are predicted to break by Tuesday and give us a mostly warm, sunny week and the possibility of a clear weekend. If in fact this good weather materializes, please let us know what you observe here at  https://leplog.wordpress.com/ and on Google Groups at MDLepsOdes.

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Ozarks, Swallowtails, and Ozark Swallowtails

2016 May 14 Western Wallflower_MO-Benton Co-Truman SP

The iconic Western Wallflower (Erysimum capitatum), for which Truman State Park’s Western Wallflower Glade takes its name. [2016 May 14, REB]

Work took me last week to one of the DOE National Laboratories in Ames, Iowa, and took a few days at the tail end of the trip to drive down into the northwestern Ozarks for a combination of butterflies, birds and botany. I grew up in Missouri and spent many hours birding and snake-hunting in the Ozarks, and spent some of my most memorable botany fields trips on the dolomite glades there with the renowned botanist Julian Steyermark. But I hadn’t been back in three decades and really looked forward to this brief sojourn in and around Lake of the Ozarks.

The drive down to Sedalia, MO – my home base for the three days – is about 5 hours, generously interspersed with stops along the way to check out likely nectar sources. My first find of the trip was a Giant Swallowtail flying across the highway just after I crossed into Missouri from Iowa; it was the first of several of this relatively common species in the Ozarks I would see over the weekend. And it gave me the sense the spring was a little farther advanced, lep-wise, than it is here in the mid-Atlantic.

2016May13 Common Sootywing_MO-Daviess Co-Gallatin_Wabash Access to Grand River

Common Sootywing in Daviess Co MO along the Grand River [2016 May 14, REB]

I stopped shortly after to check out some white clover patches along the Grand River near Gallatin, picking up a couple of FOYs for me including Common Sootywing. But the clouds were already piling up for evening rain, so I continued on to Hotel Bothwell in Sedalia for an early dinner at a local steakhouse.

My plan for Saturday (May 14) was to check out the type locality for the region’s endemic swallowtail, Papilio joanae, described in 1973 by one of my early butterfly mentors, J. Richard Heitzman, and named for his wife Joanie. This cryptic species is practically indistinguishable from its close cousin, the common Black Swallowtail (P. polyxenes) unless you have it in hand. The first clue that this was a different beast altogether came from its habitat – unlike the open fields favored by polyxenes, Ozark Swallowtail is a butterflies of forest clearings and glades. P. joanae doesn’t use Queen Anne’s Lace or domestic carrot family members as caterpillar hosts; it uses a small number of related woodland species instead. I’d scoured all the recent data on P. joanae over the winter while planning this trip, and realized it hasn’t been reported definitively (at least in open literature) for many years. But the scant data available suggested that the species flies at the same time as Black Swallowtail, and mid-May seemed within the range of probable flight dates. I’d corresponded over the past few months with regional natural history mavens Allison Vaughn (check out her excellent website Ozark Highlands of Missouri) and Steve Buback, both of the MO Department of Conservation, who with Paul McKenzie of USFWS and Butterflies of Illinois co-author Jim Wiker will be doing a butterfly and skipper workshop next week in the same area, and it seemed this was as good a time to look for joanae as any.

Saturday dawned overcast and quite cool, and in fact the temperature only flirted with 60 degrees F. by late in the day. But I headed the 25 miles south of Sedalia to Harry Truman State Park, ground zero as type locality for joanae, in the hopes the clouds would burn off. And by the time I reached the park, the sun was showing regularly and eventually would win out. The stiff breezes, however, persisted all day, making butterfly observation and photography difficult. The glade habitat I had identified as my best chance for joanae – the Western Wallflower Glade Trail – was especially windy.

I won’t hold readers in suspense for too long about the search for Ozark Swallowtail; suffice it to say that in the two days I spent traipsing about glades and forest roads in the area I saw no adult swallowtails whatsoever of the polyxenes-joanae persuasion. Spicebush, Pipevine (very common), Giant, and Zebra were all on the wing that weekend, but not Black or Ozark.

2016 May 14 probable Ozark Swallowtail cat 1_MO-Benton Co-Truman SP-Western Wallflower Glade

Probable caterpillar of Ozark Swallowtail, Papilio joanae, in Truman State Park near Waraw, MO, type locality for this endemic swallowtail species [2016 May 14, photo by REB]

However, in my 1.5-mile circuit of the Western Wallflower Glade (whose appellation reflects the fact that the iconic Western Wallflower, an orange spring cress, is common here), I did check out likely host plants for Ozark Swallowtail, and somewhat to my surprise I did locate a handful of caterpillars in about the third instar that are almost certainly joanae, given their presence in an interior glade far from fields and roads and on a host plant seldom utilized by Black Swallowtail. Unfortunately the cats are indistinguishable from polyxenes, so it’s not definitive without rearing out the larvae. But the fact that there were well-grown larvae suggested that I might have been between flights of joanae, and that a repeat visit to this area in mid-June might be more productive.

 

2016 May 14 Southern Cloudywing_MO-Benton Co-Truman SP

Southern Cloudywing on Western Wallflower Glade Trail, Truman State Park, Warsaw MO [2014 May 14, photo by REB]

2016 May 14 Northern Cloudywing_MO-Benton Co-Truman SP

Northern Cloudywing on Western Wallflower Glade Trail, Truman State Park, Warsaw MO [2014 May 14, photo by REB]

There were other butterfly and botanical highlights on the trail, though, including good numbers of both Northern and Southern Cloudywings flying together on the extensive stands of Monarda bradburiana, as well as Common Roadside-skipper. Little Wood-satyrs were everywhere, ranging from relatively “normal” forms to extensively silvered underside specimens of the “viola” form. Botany was the highlight here, with many of the favorite species from my youth – larkspur, sessile trilliums, several uncommon milkweeds, and the spectacular Widow’s Cross sedum – competing for attention with the butterflies. I checked out a number of other trails and back areas, but saw little else of note except an exciting two Hoary Edges, so when the clouds rolled in again late the afternoon I was ready to call it a day.

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Tawny Edge on Hi Lonesome Prairie, Cole Camp MO [2016 May 15, photo by REB]

Day two, Sunday, was predicted to be sunny in the morning and cloudy in the afternoon, so I decided to hit a prairie habitat early for birds and butterflies and an Ozark fen/riverine area for botany in the afternoon. Early morning saw me out on the Hi Lonesome Prairie, a well-preserved tallgrass prairie remnant near Cole Camp MO – under cloudy skies. Butterflies were few and far between, mostly on the abundant blooming brambles, consisting mostly of Tawny Edge and Eastern Tailed-blues in the infrequent sun outbreaks. Birding was better, with Bell’s Vireos, Henslow’s and Grasshopper Sparrows, and dozens of Dickcissels singing all over the prairie. Botanizing was great, too; shooting stars and Cream Wild Indigo (Baptisia bracteata).

Toward the end of the morning, just as I was leaving and just as it was supposed to start clouding over, the sun came out with a vengeance and the temperatures began to climb. By the time I reached my next destination, Big Buffalo Creek Conservation Area, it was a gorgeous butterflying day. I checked the forecast again – it’s sunny, should I drive back another 45 minutes to Truman and check out the glades again? or persevere at Big Buffalo Creek, where I didn’t have much intel on good butterflying? Forecast was grim – cloudy within the hour, and overcast and cool the rest of the day. So Big Buffalo Creek it was.

 

Big Buffalo Creek Conservation Area.jpg

I missed the turnoff for the conservation area on my first pass and ended up on a high

2016 May 15 American Lady cat 1_MO-.Benton Co-Big Buffalo Creek Cons Area

American Lady, final instar caterpillar, on pussytoes [2016 May 15, Big Buffalo Creek Conservation Area, MO; photo by REB]

ridge road well above the creek and associated wet woodlands. Pussytoes, an early spring composite common on dry roadsides all through the area, showed extensive brown, webbed leaves, diagnostic for caterpillars of American Lady (I also saw a number of adults during the weekend) and sure enough, most of the webbed leaves hid a ready-to-pupate American Lady caterpillar.  Farther up the road, around a dilapidated old cabin where a powerline right-of-way crossed the road, I lucked into a bonanza of hilltoppers – lots of black (not Black) swallowtails, mostly Pipevines and a few Spicebush, Zebra Swallowtails (so I knew there would be pawpaw in the lowlands below), and more Giant Swallowtails. And more Hoary Edges than I’ve ever seen in my life – it was the most common butterfly around. I spent a great hour or so here – in brilliant warm sunshine! – before heading back down toward the creek and the designated Natural Area that protects a bluffside fen habitat.

2016 May 15 Hoary Edge_MO-Benton Co-Big Buffalo Creek Cons Area

Hoary Edge, incredibly common along ridge roads around Big Buffalo Creek Conservation Area, MO [2016 May 15, photo by REB]

2016 May 15 Hoary Edge vent_MO-Benton Co-Big Buffalo Creek Cons Area

Hoary Edge, incredibly common along ridge roads around Big Buffalo Creek Conservation Area, MO [2016 May 15, photo by REB]

Along the creek the first thing that popped out was Hobomok Skipper, flying in smaller numbers than ubiquitous Zabulon Skippers – they were simply everywhere. I stood at one trail intersection and counted more than a dozen male Zabs contesting the sunny trailside spots. One of the many Little Wood-satyrs turned out on inspection to be Gemmed Satyr, a real treat and the first time I’d seen this in Missouri. Back out on the road about 4 pm – still sunny and hot! – I picked up Southern Dogface, American Snout, azures (I’m guessing Spring Azure from the size, color of blue, and abundant Flowering Dogwood host plant), and other regulars. By now I’m kicking myself for not going back to Truman, so I hustled back there and pulled up around 5 pm – just as the sun disappeared behind the clouds and it started to rain.  Well, there was nothing for it except to go have barbeque back in Sedalia.

Monday, my last day, was a complete washout. I slept in, headed to my office of convenience at Starbucks, reported back to Allison et al what I’d seen, and worked on plant ID for some of the botanicals I’d seen. Tuesday saw me back on a flight to DC, where this weekend is – you guessed it – wet and dreary, but with memories of hot, dry Ozark glades to keep my spirits up.

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2016 Dates Set for Ft Indiantown Gap Regal Frit Tours

As announced by the PA Department of Military and Veterans Affairs:

>>You have probably heard of our famous “butterfly”…now is your chance to see it up close and personal.  The public is invited to tour Regal Fritillary habitat in an area normally closed to the public and learn how we balance the conservation efforts for this species of concern with military training.

2016 Tour Dates: July 1, 2, 8 and 9

Dates are subject to change depending on military training exercises.

Tour Info: Tours start at 10 a.m. Attendees should arrive a half hour early to attend a required safety briefing and fill out the necessary paperwork to participate. Tours will last approximately 3 hours, but attendees may leave earlier if needed.

Attendees should meet at the Area 12 picnic grove, located at the intersection of Asher Miner Road, Clement Avenue and Route 443. (GPS coordinates in decimal degrees: North 40.431, West 76.591) Participants will park around the Picnic Grove, directly across Clement Avenue from the Recreation Center.

Visitors of all ages are encouraged to bring cameras and binoculars and should wear appropriate clothing and footwear for a nature walk on gravel trails or mowed paths. Visitors may also bring insect repellent, sunscreen and other personal comfort items. Drinking water will be provided. No reservations are required and no rain dates will be scheduled.

Participant Instructions for the Butterfly Tours (PDF)

Butterfly Tour General Release Statement Form (PDF)

Press Release on July 2015 Tours

FACT SHEETS
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Fall Nectar Sources Planting

DSCN9765

Monarch feeding on seaside goldenrod (photo courtesy of the Cape May Monarch Monitoring Project)

As noted in a recent post here and widely discussed on various butterfly listservs, the emerging scientific consensus (especially here in the East) is that milkweed is not and really never has been a limiting factor for Monarch populations, and while it’s never a bad idea to plant milkweed for other pollinators, all the Monarch Waystations in the world are unlikely to improve populations of this iconic species. Partly that’s because Monarchs don’t usually hang around here in the mid-Atlantic during the summer when milkweed is blooming; they mostly pop out an early new generation here and head north.  Our big Monarch surges are in the autumn, especially along the coast, where they take advantage of coastal breezes to float south without expending too much energy and, historically at least, tank up on seaside goldenrod and other fall nectar sources for the remainder of their journey.

It now seems that scarcity of these fall nectar sources on the coastal migration route may be reaching a critical point with East Coast Monarchs, owing to a combination of beach erosion, coastal development, and agricultural pressure.  Denise Gibbs, an indefatigable champion of replenishing fall nectar sources, especially of seaside goldenrod, recently posted this volunteer opportunity:

>>Volunteers are needed to help plant for monarch butterflies and other pollinators at 8 Maryland state parks, WMAs, and NRMAs in key locations along the coastal and mountain migratory corridors.  One planting event has already occurred at Cunningham Falls State Park, where high school students and other volunteers planted 1200 plugs of native fall-blooming nectar sources. 

Assateague State Park, which is a critical stopover for fall coastal-migrating monarchs, is the next planting location.  Seaside goldenrod, the species that fuels the fall monarch migration along the Delmarva coast, will be planted along with other native fall-blooming nectar sources.  Please see the announcement below from MD-DNR invertebrate biologist, Jen Selfridge (formerly Jen Frye).  Please contact Jen at jennifer.selfridge@maryland.gov if you are able to volunteer to help plant. Keep in mind that you would be planting in sand and sandy loam, so digging small holes for plugs is not too strenuous.  Having walked and surveyed these sites, I suggest that volunteers wear long pants and socks/shoes. 

From Jen:

Assateague State Park; Tuesday May 24th:  The Park Manager will be able to have about 4 people from her crew devote the day (8am-4pm) to planting plugs at two sites – a half acre plot on the island near the Nature Center and a one acre plot on the mainland near the bridge in a “Grow, Don’t Mow” area that has a few existing desirable plants but could use a lot of TLC.  This is a big area so our very ambitious plan is to put between 1200 and 2400 plugs in the ground that day.  Needless to say, lots of help will be needed to pull this off. 

Both sites are pretty and I guarantee baked goods and other snacks to share and ice cream on the way home for any interested parties. Volunteers would need to pack a lunch, drinks (I will also have extra drinks on hand), sunscreen, a hat/sunglasses and if desired, work gloves.  We always have some extras on hand.”

Thank you!

Denise Gibbs, Monarch Conservation Specialist, monarchwatch.org <<

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Weekend Lep Field Forecast for 2016 May 14-15

2016 May 8 Cobweb Skipper_MD-Baltimore Co-Soldiers Delight NEA 2

A quite worn Cobweb Skipper hunkered down out of the stiff breezes on the ridge trails at Soldiers Delight NEA near Baltimore last weekend [2016 May 8, photo by REB]

I hope some of you got out into the field today, Friday, the first really good warm sun we’ve had in the mid-Atlantic for weeks. The weekend coming up is so-so; more rain tomorrow in the forecast and a sunny – but very cool – Sunday. Monday would be a good day to skive off work and butterfly.

Needless to say, very little has come in this week, and no FOYs locally to speak of. My foray last weekend to Soldiers Delight failed to turn up Dusted Skipper, although I did photograph one very worn Cobweb Skipper. Other than that, only our two more common sulphurs, Orange and Clouded, a few Eastern Tailed-blues, some American Ladies, a singleton Eastern Tiger Swallowtail, a fading Falcate Orangetip, and a handful of Pearl Crescents. Dick Smith will lead a group there this weekend with what I hope will be better success; details on the LepLog calendar.

In Frederick Co MD, a few late Brown Elfins were still on the wing, and Zabulon Skipper has emerged.

To our south, species continue to pop: In the George Washington National Forest in VA the first Great Spangled Fritillaries are flying, as is Northern Pearly-eye. Least Skipper was a new one for the region in Botetourt Co VA.

I’m off in the Ozarks – where it is also raining cats and dogs and while the weekend will be sunny it will be chilly here, too – in search of the Ozark Swallowtail, Papilio joanae, described by my first butterfly mentor J. Richard Heitzman and named for his wife Joanie. Bonus species will be Ozark Checkerspot (a subspecies of Baltimore Checkerspot, some of the more unusual roadside-skippers (which may or may not be flying yet), and Golden-banded Skipper (I may be early for that one too, but the opportunity to combine this trip with a work trip was too irresistible). Botanizing here is amazing, and I’ll be tromping through cedar glades and oak forest (Ozark Swallowtail habitat) as well as dolomite glades, an Ice Age relict fen, restored and remnant prairies, and spring-fed streams and rills.

If the sun warms local habitats up enough, there should be some leps to see, at least on Sunday and into next week. Readers are asked to please report sightings here at  https://leplog.wordpress.com/ and on Google Groups at MDLepsOdes.

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Weekend Lep Field Forecast for 2016 May 7-8

2014 May 31 Harvester_Indian Springs WMA photo by BAJ

Harvesters puddling in 2014 at Indian Springs WMA in Washington Co MD [2014 May 31 by Beth Johnson]

This is becoming a rather monotonous refrain, but it looks like another week of rain and clouds have put a serious damper (pun intended) on butterfly sightings. As of today, the DC region has had measurable rain for the past 11 consecutive days. And this weekend doesn’t look like too much of a reprieve and could make it 13 for 13, but the weather outlook is so unpredictable with the current set of low-pressure systems that it’s hard to tell. We’ve canceled the LepTrek to Garrett Co (MD) for the weekend, but hope to have some sun on Sunday that might bring out a few new FOY butterflies.

If we do get some sun breaks over the weekend, folks should be looking for Harvesters (which show up this time of year for us and have already been seen at several locations in VA and in southern NY) and American Coppers, for which there are a couple of local sightings already. Dusted Skipper almost certainly is flying (or at least huddled down in the middle of bluestem clumps waiting out the rain) at Soldiers Delight and in other dry habitats where it’s been found.

Appalachian Azures should be flying where black cohosh grows on moist, wooded ravines (which also gives the plant some protection from deer browse); if you check out the population in Frederic (MD) Municipal Watershed be sure to also look for the Pepper-and-Salt Skippers we found there last year. And check out the “tigers” while you’re there – Eastern Tiger Swallowtail is still flying there, but it’s winding down and the brood of Appalachian Tiger Swallowtails should be emerging. In this area, it’s often a dicey proposition telling them apart; Frederick Co. apparently sits in a fairly stable hybrid swarm zone and you can get a range of butterflies that exhibit the gamut of features between Eastern and Appalachian. Here’s a good tutorial.

Most of the elfin populations are on the wane, but Hoary Elfin is being seen in numbers in NJ and there’s always a chance (hope springs eternal!) it could be found in the bog areas of Garrett Co, where it is presumed to feed on trailing arbutus rather than bearberry, its NJ host plant. Frosted Elfin has not yet been reported locally, but is flying in PA, NJ and into New England, so an hour or two of sunshine on MD’s Eastern Shore would make it worth checking out lupine stands on road shoulders of side roads up and down MD 12 from Salisbury to Snow Hill. They won’t venture far from blooming lupine.

There’s a veritable explosion of Question Marks to our south in the Carolinas, so it would be worth watching for increasing numbers of these sometimes irruptive migrants here – so far, they’ve had a rather poor flight locally.

Also south of our region, where it appears they have had a bit more sunshine, a lot of FOY grass skippers have popped that we should be looking for as well – Least, Zabulon, Hobomok, Sachem, Peck’s and Crossline Skippers (Zabulon has also been seen in PA already). Other new for the season leps they’re seeing in VA or the Carolinas that we should keep our eyes peeled for include Common Sootywing and Hayhurst’s Scallopwing.  Carolina Satyr is having a strong flight there already, but hasn’t been reported yet from its expanding locations in MD.

NJ reports the first local Monarchs, Viceroys, and Common Buckeyes this year regionally as well (likely as migrants following the coastline north). Both expected cloudywings, Northern and Southern, could show up now, especially along the ridge roads in Green Ridge State Forest (MD); they’ve already been spotted in NJ. Our chances for rare sightings of Confused Cloudywing increase later in the season.

And lastly, we’re coming close to the season to see the first brood of MD’s State Butterfly, the Baltimore Checkerspot. Palustrine meadows with turtlehead that hasn’t been munched to the ground in the piedmont and mountain counties are the holdout for this beautiful species. As many of you know, the habit of the young caterpillars is to live for the first couple of instars in a communal web, often at the tip-top of the turtlehead plant – right at deer browse level, and the deer don’t seem to mind at all getting a mouthful of web and caterpillar proteins along with tender new growth of turtlehead.

The only listed butterfly field trip of the weekend is May 8 to Lizard Tail Swamp near in Cape May Co NJ; check out the details at https://blogs.stockton.edu/sjbfs/2016/04/19/field-trip-to-lizard-tail-swamp-preserve-may-8/

Ever the optimist, even on weekends like the one coming up, I’ll remind readers to please report sightings here at  https://leplog.wordpress.com/ and on Google Groups at MDLepsOdes.

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Milkweed not the solution for Monarch declines

Monarch nectaring on goldenrod.

Monarch nectaring on goldenrod.

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.

Source:
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.

Journal Reference:
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

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