Thursday, September 24, 2015

A New Monarch Highway Through Arizona

Monarch at Buffalo Park, Flagstaff in early July
The clues were there in spring. Sightings of monarch butterflies were reported in late April and May in Sedona followed by early sightings in Flagstaff. At the time we were thrilled to have new eyes looking for monarchs and larvae in those areas. But as I mentioned in the last post, monarchs were scarce along the east-central portion of Arizona, most notably near the Little Colorado River where the population flourishes especially during August and early September when orange wings are usually everywhere you look. Not this year. Instead a new monarch highway developed.

In general monarch sightings were unusually low throughout the state while the population appeared higher than earlier years in New Mexico, Nevada, even Utah. Reports from the state of Washington also seemed robust. So what happened here? It's unclear. Maybe a late freeze in the last days of May and early June in the higher elevation eliminated the spring migrants in the area. The cooler than normal spring as well as rain could have slowed reproduction and milkweed availability. Or strong monsoon winds could have shifted movements.

Grand Canyon Butterfly Count
While numbers were lower than usual in early August, there was an uptick in numbers as the premigrants moved south through the state in mid August and early September. This movement is a precursor to the main monarch migration appearing about 30 days prior to the peak migration by latitude. Usually this southward moving pulse of monarchs are breeders laying eggs as they move through and their offspring will mature in time to join the main migration. That is exactly what happened as more and more people began reporting monarchs throughout the state beginning in the Grand Canyon where we easily counted 35 monarchs each day three weeks ago with at least six females laying eggs in eye view. Last week they reported more large fifth instar monarch larvae than they've seen all summer.

Steve Plath, Signature Botanica, Sept 23, 2015
So where are the monarchs in Arizona? The pattern appeared in August with numerous sightings in the Grand Canyon, Sedona, followed by increasing numbers in Prescott as the month progressed. Yesterday, Steve Plath of Signature Botanica in Wickenburg was excited to report a monarch in his shade house on Arizona Milkweed, Asclepias angustifolia. But he didn't just have a monarch visit - she was laying eggs. This year it looks like the main thrust of monarchs is in west-central Arizona. Everyone living along this monarch highway may likely see more monarchs than usual, so get your tags ready!

Canelo July 2015
Yes, there are monarchs now throughout the state of Arizona. A monarch and larvae were reported in Mesa the second week of September and Adriane Grimaldi found monarch larvae on Desert Milkweed, Asclepias subulata, in north Scottsdale. A week later Mary Klinkel reported a monarch in the Tucson area followed by a report of another at Tohono Chul that was promptly tagged by Andy Hogan. There are more monarchs in southeast Arizona as well, although the numbers are still lower than recent years. But, so far, the largest density is following the west-central route through Prescott.

The main migration this year seems late. Strong southerly winds could have easily caused a bottle-up in southerly movement. We are watching the skies and reports that filter in. Last year the monarch migration was also two weeks late. Warm temperatures in the southern deserts this weekend could also have slowed their progress. Our paper, Status of Danaus plexippus in Arizona published last June showed that we had the most recoveries (sightings in another location) when upper level winds blow from the northwest to the southeast or from the northeast to the southwest. This was a statistically significant finding.

Enjoy this special time of year as temperatures eventually ease and monarchs move in. Don't forget to report sightings to the Southwest Monarch Study Facebook page and if you are interested in tagging in the southwest there is still time to get tags before the main migration moves through.

Note:  Three monarchs were sighted at Boyce Thompson Arboretum in Superior recently. If we see any monarchs we will tag them as part of this Saturday's Butterfly Walk at Boyce Thompson Arboretum near Superior beginning at 9 a.m.