Migration on Wild About Utah

Sep 27, 2018

Migration has begun, or did it ever end? Even in our little N. Utah valley its happening. We normally think of migration during the great flocks of birds that pass through during swing months of fall and spring, or the deer and elk coming down for the winter, or swarms of salmon swimming to their death when spawning. But that’s only a small part of the story.

A high elevation trek in our Bear River range in July where cloudbursts of lovely California tortoiseshell butterflies surrounded me provided testimony as they worked their way to unknown destinations. With the iconic monarch butterfly populations plummeting, it’s comforting to have other species holding their own- most likely due to their lives being spent in high elevation wild lands, well away from farms and lawns where pesticides and habitat loss present major challenges to monarch survival.

The California tortoiseshell overwinters as an adult and can sometimes be seen sunning itself in midwinter on mild days.  It is generally common in lower canyons in early spring, ovipositing on the young, tender growth of Ceanothus shrubs. The spiny, black-marked-with-yellow larvae feed gregariously, without a web, and in big years can defoliate whole stands of these plants. They often pupate on the bare, leafless stems en masse, the grayish-violet pupae looking like some strange kind of leaf and twitching in unison when disturbed. Adults emerge in late May to early June and almost immediately emigrate, going north and upslope. Breeding localities in summer vary widely from year to year.

In late July they migrate to estivating grounds often in the high country. Estivating tortoiseshells do little but "hang out," and many high-altitude hikers have described their encounters with millions of them in mystical terms. In late September these butterflies scatter downslope to hibernate--they are the late-winter butterflies of the new year, living 9 or 10 months as adults.

They visit flowers of many kinds, aphid and scale honeydew, damaged fruit, sap--and mud: a mud puddle in a mass migration is a memorable sight, often with hundreds or thousands packed side-by-side on the damp surface.

Close to home the yellow warbler is yet singing- one of the last of our neotropical birds to hang it up. These tiny warblers will soon head south to Central and South America.

Even our native people would migrate to follow the plant and animal populations spending time in high mountains during summer months for camas lily, mountain sheep, and berries, then retreating to low elevations as the winter season approached for milder weather and more available food. And here in Logan, we have a swarm of “Summer Citizens” who show up in May to occupy the nests vacated by USU students, who will soon migrate south as our student return.

And I retreat to our canyons for skiing once the snow is on.