Why Pacific Grove's Monarchs Gather on the Grove's Sunny South Edge

When the first monarchs reach Monarch Grove Sanctuary this fall, which trees will they choose? For two winters in a row, the answer has been very consistent. The city's 2026 review found that after the butterflies arrived in 2025, they gathered in the sunny areas along the grove's South and Southwest edges, and they stayed there all season. Of all observations, 94% were on eucalyptus, 5% on Monterey pine and 2% on Monterey cypress.

From those numbers you might guess the monarchs like eucalyptus. The report that produced them explains the pattern differently. It ties where the butterflies settle to sunlight and shelter from wind, and in years when they move to the pines and cypress, it credits the sheltered interior where those trees grow rather than any preference for the species. What the 2025–26 season shows is how the grove works.

The edge that held all winter

The city's assessment is titled "Assessment and proposed management activities Monarch Grove Sanctuary and George Washington Park for 2026." It is written for Pacific Grove's public works staff, and it reads like a field notebook. It describes the 2025–26 season zone by zone. The monarchs stayed on the South Edge, mostly on eucalyptus, and on the Southwest Edge for the whole season. Only a few moved into the South Interior, just north of the main trail, and those were on pines.

The 2024–25 season looked almost the same. The season before that did not. In 2023–24, the clusters began on eucalyptus and then moved mostly to pines and finally to cypress. They left the South Edge for the South Interior by mid-November, reached the Interior in early January and ended up along the Driveway in February. In 2022–23, one strong storm after another pushed the butterflies deeper still, into the North Interior. At the end of that season they regrouped along the Driveway.

The review ties these moves into the interior to wind. It names exposure to higher winds as the usual immediate cause of a cluster shifting, and in 2022–23 the push came from successive strong storms.

Sun and wind choose the branch

The city's 2026 Monarch Grove Sanctuary review describes how monarchs choose a site:

They "crowdsource the microclimate" – leaving sites when conditions are too warm or too cool, too sunny, or too shady, and especially too windy (if conditions are suitable for flight). They tend to land where other monarchs are clustered, because the best indicator of good conditions for monarchs is the presence of other butterflies.

According to the review, the season often starts on the sunny South Edge. The clusters move into the interior after southerly storm winds. The interior is mostly pine and cypress, so in stormier years the butterflies seem to favor those trees. The report says plainly that this comes from where the sheltered interior happens to be, and that the species themselves are not the attraction. The Xerces Society's 2016 assessment of California overwintering sites makes the broader point. South-, southwest- and west-facing slopes get the most sun, and a good grove also needs dappled light, humidity, fresh water and protection from freezing and high winds.

The eucalyptus still matter for one more reason. The review notes that blue-gum eucalyptus flowers give the butterflies plenty of nectar in January, and it recommends keeping the grove's existing eucalyptus structure while adding native nectar plants and shrubs where there is room. It also mentions a detail that's easy to miss on a walk. The monarchs have often clustered just outside the sanctuary to the south, on a single Monterey pine.

What one windstorm did to last winter's count

The sanctuary's weekly counts from 2025–26 show how quickly wind can scatter a cluster. The Pacific Grove Museum of Natural History has run these weekly counts since 2013.

The drop to three butterflies on Dec. 26 looked like the season was over. It wasn't. When the count climbed back to 131 a week later, it showed the monarchs had scattered rather than left. The review also warns that small, spread-out clusters are hard to spot, so counts after a windstorm probably run low. The report's executive summary dates last fall's arrival to early October, and another section lists a Jan. 17 count of 209. The weekly season account gives mid-October and 203, and the table follows that account.

Statewide numbers help put the local count in context. The Xerces Society's 2025 Thanksgiving count found about 12,260 monarchs at 249 sites across California, the third-lowest total since the count began in 1997. The Xerces Society released those results on Jan. 29, 2026. That was about 33% more than the 9,119 counted in 2024, but the city's review says the population is still at perilously low numbers. The late-season survey ended Jan. 11, 2026, with 6,464 monarchs at 193 sites statewide.

The sunny edge is also where the fire fuel collects

The South Edge holds the most butterflies, and it also holds the most fuel. The review's top recommendation for 2026 was to remove and spread out the downed bark, branches and leaves along the South Edge in September, especially where eucalyptus debris has piled up against the trunks. Some debris would stay on the ground, broken up by fuel breaks several feet wide, so a monarch that falls has something to climb back up. The report calls a continuous layer of fine fuel on the forest floor too great a risk, and it points to the grove's March 2023 fire. The cover of the report shows an eucalyptus trunk scorched in another small fire on March 31, 2024.

The 2025 recommendation to rearrange the forest-floor debris and remove the hanging litter around the large eucalyptus was not carried out. Crews did remove dead small trees in the southeast corner, stakes and wires from saplings that no longer needed them, and the leftover pine trunk along the main path. The 2026 list also calls for a pause on new tree plantings with one exception, a double row of cypress along the hotel boundary in the northeast corner. It adds thinning of the dense planted cypress northeast of the nectar beds, deer cages for the oaks along the west boundary and a review of the irrigation schedule. These are recommendations. Nothing published so far confirms how much of the September work was done before the butterflies returned.

The other grove, four-tenths of a mile away

Pacific Grove once had a second overwintering site. George Washington Park, in the stretch between Pine and Spruce avenues about 0.4 mile southeast of the sanctuary, is the only other documented historic cluster site in town. There the monarchs used Monterey pines, some coast live oaks and California lilac. The park counted 11,795 butterflies in 2006 and 61 in 2011. None have clustered there since. The city's Thanksgiving-count table shows a single monarch at the park in 2013 and zero in every other year from 2012 through 2025.

The park's recent pine plantings are being watered by volunteers. The review recommends deeper, less frequent watering so the trees grow deeper roots, followed by a gradual move to rainfall alone. It suggests that a wet 2026–27 winter, if it comes, could help with that. Beyond that, it recommends no major work at the park other than dealing with hazard trees until a fuller assessment is done. The park can show what a grove looks like decades before it has butterflies. The trees need to grow tall enough, in the right places, to create the shelter the monarchs look for.

The 2026–27 season so far

• Arrival status. On Sept. 19, 2026, the museum's monarch page said the butterflies had not yet arrived and that they typically begin arriving in mid-October.
• Hours. The sanctuary is open daily from sunrise to sunset and closes only in extreme weather. Museum docents are usually there from 11 a.m. to 3 p.m., weather permitting.
• Count windows. The Western Monarch Count runs its early-season survey from Oct. 17 to Nov. 1, 2026, its mid-season survey from Nov. 14 to Dec. 6, and its late-season survey from Dec. 26, 2026, to Jan. 10, 2027.
• Museum program. The museum's free Science Saturday: Monarch Magic! runs Nov. 28, 2026, from 10 a.m. to 3 p.m.
• Already past. The Butterfly Parade went off on Saturday, Oct. 3, followed by the Butterfly Bazaar at Robert Down Elementary.

If this winter follows the last two, the first clusters will form on the sunlit eucalyptus along the South Edge. A strong southerly storm would be the first sign they may move toward the pines in the interior.

Michelle Hammons has followed how the Peninsula's groves, gardens and old stands of trees shape the homes around them. If you would like to talk about a Pacific Grove property near the sanctuary or anywhere else in town, request a private consultation.