Butterfly numbers drop 20 percent
In 1993, my wife Marlene and I started conducting butterfly counts in north-central Minnesota. July 2016 marked the 137th count we have held over those 24 summers. Almost 170,000 butterflies—167,082 to be exact—have been tallied.
2016 marks the 22nd consecutive year we've held six counts per summer.
We definitely appreciate the efforts of a small, but dedicated band of counters who year in and year out tromp around us.
Where does 2016 stand?
We had 15,577 butterflies back in the 2001 season. I consider that set a "gold standard" by which other years can be compared. More recently, the three straight years 2012 through 2014 produced new second-place or "silver" seasons. That string was broken last year. Unhappily, this year's 7,515 butterflies were down a further 20 percent from the 9,445 recorded in 2015.
Our two most-western counts did register some gains from 2015: Bluestem (in Clay County, +323) and central Polk County (+250). Those modest gains were more than offset by losses at our closer counts: Nevis (-286), Deep Portage (-970), Itasca State park (-514) and Bemidji (-733).
Though our Itasca count fell into the "loss" column, it could have been much worse. Just five days later, the massive storm hit the state park. The other "arm" of that storm hammered Bemidji only three days before our count there. I'm sure the winds and rains from that storm did have a very negative impact on the butterflies.
I am left wondering: In an Olympic year, what does "half" of the "gold standard" season really represent?
Purpose of counts
Our six butterfly counts are part of a continental effort in North America to gather valuable data on butterfly population trends.
Each year, the North American Butterfly Association (NABA) collects and compiles the citizen-gathered data from over 400 counts held in the U.S., Canada and Mexico.
A 15-mile diameter circle is established for each count. Then on a single day each year, all living butterflies found in that circle are reported to NABA. This year marks the 42nd year these counts have been held.
Ups and downs in 2016
As insects, butterfly populations can rise and fall in as little as a single year. Though some ups and downs should be expected, I feel 10 species were particularly volatile in 2016 versus last year.
One one hand, four species increased a total of 1,384 individuals: Orange Sulphur (+423), Dun Skipper (+393), Common Wood-Nymph (+307) and Meadow Fritillary (+261).
Another six species dropped 3,644 from 2015: Northern Crescent (-1,210), Clouded Sulphur (-797), Compton Tortoiseshell (-654), Monarch (-398), European Skipper (-299) and Northern Broken-Dash Skipper (-286).
The net difference of -2,260 was greater than the overall drop of 1,930 going from 2015 to 2016.
Northern Crescent update
Northern Crescent remains the only species found on all 137 of our summer counts. However, the 685 recorded this summer is down almost 64 percent from the 1,895 we tallied in 2015. Even with two dramatic downturns in the most recent years, Northern Crescents still account for about one of every four butterflies we've recorded since we began the counts in 1993.
Other 2016 tidbits
These 11 species were present on all six counts: Cabbage White, Clouded Sulphur, Orange Sulphur, Summer Azure, Great Spangled Fritillary, Northern Crescent, White Admiral, Eyed Brown, Monarch, European Skipper and Long Dash Skipper. These species accounted for less than 40 percent of the total 7,515 butterflies tallied.
Six species present in 2016 were no-shows in 2015: Dorcas Copper, Regal Fritillary, Milbert's Tortoiseshell, Common Buckeye, Little Glassywing Skipper, and Pepper and Salt Skipper.
Another six species in 2015 were no-shows this year: Greenish Blue, Appalachian Brown, Dreamy Duskywing, Dakota Skipper, Two-Spotted Skipper and Dusted Skipper.
We did have two new species for our summer counts: Western White and Western Tailed-Blue. That brings the 24-year total to 101 species. They represent 70 percent of all Minnesota species found over the entire state over an entire year, not the few weeks we conduct the counts about the same time each year.
The Monarchs decline
Last year, the 534 adult Monarchs tallied were the fifth most common butterfly that season. Only 136 were spotted this year, dropping Monarchs to 16th place. In fact, 79 of them were found on our final summer count in Bemidji. On four of six counts, 10 or fewer Monarchs were present.
The poor showing of Monarchs on the counts was reflected in weekly Monarch monitoring visits. During 15 weeks, a total of 4,162 Common Milkweed host plants were examined for Monarch egg and caterpillar activity. Only 29 eggs and 16 caterpillars were found. That was the poorest showing since 2013.
Adverse weather was a big contributor to the Monarch's plight in 2016. A severe storm in March hit the overwintering sites in Mexico. Then a series of relentless storms and flooding preceded and followed the Monarchs' journey north through Texas, the Midwest, southern Minnesota and finally reaching our neck of the woods with severe weather that began July 7.
Although weather was a major factor this year, for two decades now, Monarchs have been facing a major decline in suitable breeding habitat due to large-scale shifts in agricultural practices in the so-called corn belt.
On a more positive note, I can report having seen a steady stream of migrating Monarchs heading south to Mexico over the past month. In recent days, the stream has decreased to a handful or less per day.
It will be interesting to find out what next February's census will show for the Mexican overwintering sites. In the meantime, wish all Monarchs you see heading south a safe journey.
Also as I write this, numbers of butterflies on the wing for almost all species are rapidly decreasing as the curtain goes down on the 2016 butterfly season.
I did see my last Monarch and butterfly of the season on Oct. 11, 2015. Though I doubt it will be that late in 2016, who knows?