72 Microseasons of the Pacific Northwest

From mid-September through early October, monarch butterflies (Danaus plexippus) of the western North American population pass through Oregon and Washington on their way to overwintering groves of Monterey cypress and eucalyptus on the California coast. Pacific Northwest monarchs summer on showy milkweed (Asclepias speciosa) in the dry valleys east of the Cascades — the Willamette Valley, the Columbia Basin, and the Klamath Basin in southern Oregon support the largest breeding populations. The September migrants are a special generation: reproductively dormant "super-generation" individuals that can live 6–9 months, compared with 2–6 weeks for their summer parents, built by evolution to complete the long overwintering migration. While monarchs are not abundant in the Pacific Northwest relative to the Midwest, southern Oregon is the region's hot spot for observing migration. The area around Ashland, Medford, and the Applegate Valley in the Rogue River watershed regularly produces sightings of nectaring monarchs on late-blooming wildflowers — particularly on goldenrod (Solidago spp.), asters, and Indian hemp (Apocynum cannabinum). The Native Plant Society of Oregon and the Xerces Society's Western Monarch Milkweed Mapper citizen-science program document late-summer monarch presence and can help identify active sites in any given year. Scientists have documented that PNW monarchs migrate west and south along the Coast Range, staging at the Oregon coast before moving down to California wintering sites. Research using tiny radio transmitters and population genetics has confirmed direct movement from Pacific Northwest summering sites to the California coast — a journey averaging nearly 500 miles. Because western monarch populations have declined more than 95% since the 1980s, seeing a migrating monarch in September is now a notable event. The best chance comes from walking flower-rich habitat — meadow edges, roadside wildflower patches, and remnant milkweed patches — on warm, still September mornings in the Willamette Valley, Rogue Valley, or Klamath Basin.