Looking back at 25 years of the Petroglyphs Butterfly Count
Peterborough Examiner – August 22, 2025 – by Drew Monkman
Last summer marked a milestone for local butterfly enthusiasts: the 25th Petroglyphs Butterfly Count. The first count was held in 1998, and since 2001 volunteers have gathered every mid-July—peak season for butterfly diversity—to tally numbers and species. Part of a continent-wide initiative organized by the North American Butterfly Association, the count records every butterfly spotted within a 24-km circle. Local organizers Jerry Ball and Martin Parker of the Peterborough Field Naturalists continue to lead the effort.
Centered in Petroglyphs Provincial Park, the count area includes butterfly hotspots such as Jack Lake, Kashabog Lake, and Sandy Lake Road north of Havelock, renowned as one of the province’s top butterfly destinations. Its marshes and groundwater-fed fens host an exceptional variety of skippers—small, fast-flying butterflies often mistaken for moths.
Interest in butterfly-watching surged in the 1990s with the arrival of accessible field guides. Today, equipment like close-focusing binoculars and digital cameras with zoom lenses make observing and identifying easier than ever, with little need for nets.
What the data reveals
As part of her fourth-year Conservation Biology degree at Trent University, Shannon Taylor worked with the Peterborough Field Naturalists to analyze the full 25-year dataset. She set out to understand how butterfly populations and communities have changed, and whether weather patterns—such as temperature, rainfall, and accumulated “degree days”—might play a role.
To make comparisons across years, Taylor adjusted for differences in search effort. Instead of raw counts, she used “butterflies per party hour,” which accounts for the number of people and hours spent counting.
Over a quarter-century, volunteers have tallied an impressive 78 species. Leading the list by a wide margin is the dun skipper, a small purplish-brown butterfly whose caterpillars feed on sedges, dominant plants in the fen wetlands of the count area. An amazing 41,654 dun skippers have been recorded—enough to make the Petroglyphs count the top site for the species in all of North America. In 2018, volunteers set a record with 4,914 individuals in a single day.
Far behind in second place is the European skipper (8,505), a tiny orange butterfly introduced from Europe. Next comes the wetland-loving broad-winged skipper (7,040). Other regulars include the bright northern crescent (6,915) and the iconic monarch (4,988).
Less common, but still well represented, are the dusky-brown columbine duskywing (1,849), the showy Aphrodite fritillary (1,685), and the dainty mulberry wing (1,663), another fen specialist. Rounding out the top ten are the eyed brown (1,614), a sedge meadow species, and the beautiful great spangled fritillary (1,496). At the other extreme, the early hairstreak and Indian skipper have each been recorded only once in 25 years.
Rising, falling, and holding steady
Looking back over two and a half decades, the numbers show clear fluctuations. Butterflies per party hour cycle between high and low years, with only a faint suggestion of overall decline. But numbers don’t tell the whole story. Some species may be shifting the timing of their flight periods, meaning fewer are visible on the count date even if their populations remain stable.
To examine community composition, Taylor grouped the sightings into five families: swallowtails, sulphurs and whites, copper blues, brushfoots (such as fritillaries, crescents, and admirals), and skippers. Skippers have consistently dominated, followed by brushfoots. Copper blues and the sulphurs and whites have held steady over time, while swallowtails—though flashy and beloved—remain the least common group.
Year-to-year fluctuations are natural, shaped by factors like weather on the day of the count – and during the previous winter and spring – and even roadside mowing by the townships. But teasing out the underlying drivers—whether they’re shifts in climate, habitat changes, or other forces—remains the next step in understanding population changes.
This year’s count
The 2025 count took place on July 19, and results were mixed. The 54 species recorded exceeded the 25-year average of 50, suggesting strong overall diversity. Yet the total of 2,798 individuals fell well below the long-term average of 3,800. Only two other years, including 2022, a similarly dry season, recorded fewer butterflies. “However, it was great to see the number of participants at an all-time high,” noted Martin Parker.
The drought this summer meant fewer flowers and less nectar, though wetland edges, rich with milkweed and Joe-Pye weed, still attracted pollinators. Among this year’s totals were dun skipper (1,052), columbine duskywing (272), pearl crescent (204), broad-winged skipper (168), northern crescent (156), monarch (84), gray hairstreak (69), and Aphrodite fritillary (42).
The Petroglyphs Butterfly Count shows how decades of patient observation can reveal the species that define a landscape. Long-term monitoring like this not only celebrates the dedication of volunteers but also provides invaluable insight into how insect populations like butterflies are responding to habitat changes and a shifting climate.
Book launch: The Wild Path Home
Join co-authors Jacob Rodenburg and Cathy Dueck on Friday, September 5, for the launch of their inspiring new book The Wild Path Home. The event runs from 7:00 to 8:30 p.m. at Take Cover Books, 59 Hunter St. East, Peterborough. The book offers practical guidance on raising healthy, resilient, and engaged children who can also become advocates for a thriving planet. It’s an essential read for parents, grandparents, teachers, and anyone working with young people. For my full review, see my July 11 column or visit drewmonkman.com.
Extreme weather conditions
Climate data as of August 15 for Peterborough. Source: https://newsinteractives.cbc.ca/features/2023/climate-dashboard/
- This year has seen 21 days above 30 C. That’s 13 days above average.
- There have been a RECORD 4 days with a nightly temperature above 20 C.
- The average maximum temperature for the 30 day period from July 16 to Aug. 14 was 29.1 C. This is 2.8 C above average.
- The total precipitation for this same period was 25 mm. This is 61.2 mm below average.
- Atmospheric CO2 for August 14 was 425.44 parts per million (ppm) compared to 422.66 ppm a year ago. Source: https://www.co2.earth/daily-co2
