Annual Yosemite National Park Butterfly Count
Yosemite National Park held its 8th annual Yosemite Butterfly Count in the Tuolumne Meadows area in summer 2018. Yosemite coordinates this event in association with the North American Butterfly Association (NABA), an organization that conducts long-term monitoring of butterfly populations all over North America. The purpose of the NABA counts is to determine how many species and individual butterflies can be observed within a 15-mile diameter circle, during a 24-hour period, within the same date-span year after year. Participants spend the day gathering data toward long-term monitoring, raising public awareness toward butterfly conservation, and socializing and having fun with other butterfly devotees.
On July 30, 2018, butterfly experts and enthusiasts convened in Tuolumne Meadows in anticipation of finding as many butterflies in a single day as possible. Expert lepidopterists came from around the state to lead their groups in butterfly quests and to share their knowledge and intense appreciation for butterflies and natural history.
Following introductions, the larger group divided up into six smaller groups, each led by one or two butterfly experts. Each group was responsible for counting and identifying butterflies in their respective zone. The butterfly count area included such hotspots as Dana Meadows, Gaylor Lakes, Saddlebag Lake, Ellery Bowl, Warren Canyon, Lower Lee Vining Canyon, Mono Lake County Park, and Lundy Lake.
In spite of less than optimal butterfly viewing conditions amidst a hazy smoke-filled sky and late afternoon scattered rain showers, butterflies still made their appearances. Each participant learned to conjure a particular search image for target butterfly species, depending on the habitat, elevation, and the presence of certain flowering plants. The leaders enthusiastically taught the participants all facets of butterfly identification and ecology, including tips for identifying tricky species.
At the end of the day, the group reconvened back in Tuolumne Meadows to share highlights, report count results, and enjoy pizza. The best part of every compilation is the lively discussions concerning difficult species identifications.
This year (2018), forty-one participants counted 58 butterfly species composed of 1,504 individuals, which is significantly lower than the past two years (70 and 76 species in 2016 and 2017, respectively). The four most frequently detected butterflies were California Tortoiseshell (356 individuals), Sierra Sulphur (182), Mormon Fritillary (144), and Edith’s Copper (81). As in past years, Orange Sulphur was the most wide-spread butterfly and was the only species observed by all six groups.
2018 was the year of the California Tortoiseshell! This butterfly species made up approximately 24% of the total count, which is an unusually high proportion considering the species is absent in some years. This is the first time during a Yosemite Butterfly Count that participants observed this species undergoing a population irruption. Unusually high counts also occurred for Behr's Hairstreak (29), Northern Blue (80), Mormon Fritillary (144), and Great Basin Wood-Nymph (75).
No new species were observed this year, in contrast to last year when 10 new species were observed. Twenty-four butterfly species were not detected compared to last year. The four most surprising misses included Lupine Blue (first time ever missed), Rockslide Checkerspot (missed in only one other year – 2012), Chryxus Arctic (missed in only one other year – 2014), and Heather Blue (hasn’t been missed since 2012). While never common, these species are sought after by the leaders and are part of what makes this Yosemite count so unique. Consistent with past years, the lower elevation groups observed higher butterfly species diversity, due in large part to a greater diversity of host plants.
The combination of the butterflies themselves, people brimming over with natural history knowledge and passion, and beautiful scenery makes this one day very special. As Liam O’Brien put it, “the Yosemite Butterfly Count quickly has become Center Court/Wimbledon of the California Butterfly Count Season”. See you at next year’s count on Monday, July 29, 2019!
Last updated: August 10, 2018