Wrens are short-winged and round-winged little birds that often do not seem to be accomplished long-distance migrants. Although most species are resident, a few species do cover pretty good distances in migration, including Winter, Pacific, House, Marsh, Sedge, and Rock Wrens. All apparently migrate at night.
The migration patterns of Rock Wren are not something many people think about. Rock Wrens tend to live in inhospitable desert outcroppings, talus slopes in mountains, and ravines as far east as the western Great Plains. Perhaps for these reasons (relatively birdless habitats in which they live), Rock Wrens are reported rather infrequently to eBird despite their large range across the West. The predicted occurrence of the species peaks at 0.06, which may be partly a sign of the habitats in which birders go birding more than the true occurrence levels of the species. With more random checklists from rocky desert areas, where Rock Wren and Common Raven might be the only species, the occurrence metric might go up.
The Rock Wren animation shows some of the variability that we associate with these less common species with STEM. Late summer changes in detectability have some noticeable effects along the edges of the range, and some of this may not be a real reflection of the species’ biology. But the animation does accurately show the broad patterns of occurrence. In breeding season it occurs occurs over much of the west and in winter it is more restricted to the southern areas, including west Texas to southern California and north to Utah and Nevada. Rock Wrens can occur at quite high elevations in the Rocky Mountains and Sierra Nevada, and the northward migration almost seems to follow the thawing patterns. Notice how the Cascades of Washington light up before the Rocky Mountains of Montana; the Pacific Northwest is more temperate and those mountains thaw a bit earlier. Notice also the core winter range in southeastern California and southern Nevada.