In a city nicknamed Butterfly Town, USA – where an annual Butterfly Parade marks the beginning of the monarch overwintering season, and tourists flock to visit the famous Butterfly House – the absence of thousands of orange-and-black-winged annual visitors is something of an identity crisis.

“If Butterfly Town loses its monarchs – not good,” says Pat Herrgott, a long-time volunteer docent at Pacific Grove’s Monarch Grove Sanctuary.

The sanctuary is low on butterflies this year, and some monarch enthusiasts suspect that the city’s heavy-handed trimming of eucalyptus branches is to blame.

“It was obvious to me this amount of pruning will substantially degrade the suitability of the sanctuary as a cluster site,” entomologist Paul Cherubini wrote on a monarch listserv in late October. “The butterfly population is likely to be substantially lower and less stable this year and for years to come.”

P.G. Public Works Director Celia Perez Martinez says the trimming was done for public safety in late September, before the Oct. 1 start of monarch overwintering season. (In 2004 an 85-year-old woman was killed by a falling branch while visiting the sanctuary; the city settled with her family for $1 million.)

“Eucalyptus trees are very vulnerable to limb breakage,” she says. “[But] we would not have trimmed any branches that had butterflies on them.”

City arborist Rick Katen directed a tree service on which branches to cut, Perez Martinez says, but the city didn’t document the work. “In the future we’ll do that, but we’ve never done it in the past,” she says.

This year’s low butterfly numbers could be caused by any number of things, she says, including October’s storms: “They could have gone to Santa Cruz for all we know.”

Dr. Francis Villablanca of Cal Poly is tasked with reviewing the monarch count data. “At the current time we do not know if the P.G. Sanctuary population count is low because of something peculiar to this site (e.g.: tree trimming), or if the populations are low range-wide and across all sites,” he wrote in an e-mail to Perez Martinez.

Villablanca expects to have some findings within the next few weeks. “I would call for calm minds to prevail until we have some data,” he wrote. “The story will make itself evident.”

But Bob Pacelli, who has been filming P.G.’s monarchs for two decades, has a strong hunch that the trimming messed up the particular microclimate – humidity, temperature, precipitation and wind shelter – that makes the P.G. sanctuary a critical overwintering site.

Last year at this time, he says, the monarch clusters were dense. This year he could barely spot any butterflies. “Every single place that the monarchs could hang onto is gone,” he says morosely. “I hope I’m totally wrong, but in my heart I know it’s not true. No more butterflies. Oof.”