Yosemite Annual Butterfly Count

2023 butterfly count participants
2023 Butterfly Count participants
 
 
Gray Hairstreak on a flower
Gray hairstreak

Julien Ueda

Yosemite National Park held its 12th annual Yosemite Butterfly Count in the Tuolumne Meadows area in summer 2023, thanks to the dedicated scientists and collaborators that make it possible each year. 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. Each of the approximately 450 counts nationwide contributes a tremendous amount of information about the geographical distribution and relative population sizes of butterflies all around the country. Participants spend the day gathering data, raising public awareness toward butterfly conservation, and socializing with other butterfly devotees.

On July 31, 2023, expert lepidopterists and butterfly enthusiasts returned to Tuolumne Meadows in anticipation of finding as many butterflies in a single day as possible. Each group was assigned to a specific zone and were responsible for counting and identifying all the butterflies they detected within that area. The butterfly count area included such hotspots as Dana Bench, Gaylor Lakes, Saddlebag Lake, Gardisky Lake, Mono Lake County Park, Log Cabin Mine Road, Dana Meadows, and Lundy Canyon.

Clear skies greeted everyone as old friends and new faces gathered into their groups and raced into the high country. Participants quickly developed a search-image for target butterfly species, depending on the habitat, elevation, and the presence of specific flowering plants. The leaders enthusiastically shared their knowledge about butterfly identification and ecology, including tips for identifying tricky species. In the early evening, the groups rejoined in Tuolumne Meadows and compiled their findings over pizza.

Since its inception in 2011, the Yosemite Butterfly Count has recorded a remarkable diversity of 100 butterfly species. This diversity is the result of experienced and knowledgeable leaders, a growing number of learned participants, and diverse habitats comprising a 5,000 ft. elevation gradient between the lowest and highest zones. One group can search for butterflies along the shores of Mono Lake at 6,400 feet elevation, while another group can observe butterflies on the Dana Bench at 11,000 feet elevation.

 
Sheridan’s Hairstreak, turquoise butterfly
Sheridan’s hairstreak

Alison Sheehey

This year (2023), 63 participants counted 1582 individual butterflies and found 75 species. While the total butterfly count was just 17 individuals shy of the average (1565), this year’s group found an unusually high number of species. At 75 species, this year found 19 more species than the average (56) and was just one species short of the 2017 high of 76 species. Further, this year’s count and last year’s count had a similar total number of individual butterflies, but this year had many more species (2022 totals: 48 participants, 53 species, 1538 individuals).

The five most frequently detected butterflies in 2023 were the Mexican Cloudywing (206), Sandhill Skipper (101), Shasta Blue (95), Orange Sulfur (80), and Checkered White (74). This year also set the Yosemite Butterfly Count record for an incredible ten species: Becker’s White (4), Western White (9), Behr’s Hairstreak (66), Marine Blue (32), Reakirt’s Blue (31), Lupine Blue (10), Mormon Metalmark (37), California Crescent (14), Satyr Comma (5), and Mexican Cloudywing (206)! The Orange Sulfur, Reakirt’s Blue, and Greenish Blue were some of the most widely observed butterfly species and were found in 7 of the 8 butterfly count areas, but the Painted Lady was the most widespread, and was found in all 8 count areas.

 
Indra Swallowtail black and cream in color on the ground
Indra swallowtail

Alison Sheehey

The top five species in 2022 shared the Shasta Blue and the Sandhill Skipper but differed otherwise [2022 top five: Sandhill Skipper (347), Shasta Blue (196), Mormon Fritillary (109), Sierra Sulfur (82), and Greenish Blue (78)]. Compared to 2022, the 2023 counts for those species were also notably lower: Sandhill Skipper (101), Shasta Blue (95), Mormon Fritillary (6), Sierra Sulfur (1), and Greenish Blue (20). The 2023 count is also the first year that the Small Wood-Nymph and the Mariposa Copper have not been observed since 2013 and 2014 respectively. However, both species usually receive less than ten observations a year.

Many groups of species contributed to the unusually high biodiversity of the 2023 count, but a handful stood out. While the 2022 and 2020 count only documented the Checkered White, four “whites” were documented in 2023. Only two hairstreak species were found in 2022 but 6 species were found this year. Though, the “blues” stood out most of all. While in 2022 and 2020 only 9 “blues” were found, 16 species were found this year (2023), and all additional species this year were not in the more common Plebejus genus. While an incredible 75 species were found this year, no new species were found. With each year of butterfly counting, the species list grows and the chance of observing a new species
diminishes. Though, the difficulty of finding a new species demonstrates the hard work participants have put into more than a decade of Yosemite Butterfly Counts.

 
mating pair of Pacific Dotted Blues on a flower
Mating pair of Pacific dotted blues

Alison Sheehey

In 2023, some of the most notable observations were an Arrowhead Blue and two Pacuvius Duskywings, as both species were only recorded on one other Yosemite Butterfly Count (2019). Every year, the leaders continue to seek rare species to better understand which ones call Yosemite home. Some rare species, like the Sierra Nevada Parnassian (22), Rockslide Checkerspot (16), and Chryxus Arctic (12), are highly specialized alpine butterfly species that make Yosemite National Park and its Butterfly Count unique.

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 has quickly become Center Court/Wimbledom of the California Butterfly Count Season.”

See you at the next Yosemite butterfly Count on Monday, July 29, 2024!

Learn More

Last updated: September 11, 2023

Park footer

Contact Info

Phone:

209/372-0200

Contact Us