Of all the migrant bird species that seasonally grace the Sky Islands region, perhaps the most remarkable one is Lawrence’s goldfinch. Everyone knows, of course, that in the northern hemisphere birds migrate south in autumn and north in spring. Many montane species also execute altitudinal migrations, moving to lower elevations as cold weather and its attendant challenges hit their normal high country habitats.
Then there is Lawrence’s goldfinch. Seemingly breaking the ”rules” of migration, select members of this strikingly beautiful species do a lateral movement—west to east in Autumn, then east to west come spring—from their coastal and valley breeding range in California and northern Baja, Mexico to locales in the southwest. Some of these troubadour flocks somehow make their way to the Santa Cruz River and nearby habitats. This means that they move at least 500 to 700 miles from at or near the west coast to our local haunts. In the process, they traverse some of the most foreboding terrain in North America. Think Death Valley and the Sonoran Desert. Despite these obstacles these diminutive birds indeed show up locally, though only in certain years and then in often highly variable numbers.
Why does this Goldfinch species make such a seemingly bizarre, lateral migration to the Sky Islands when coastal California retains rather amenable temperatures throughout winter? What resources are they seeking in southeast Arizona and how do they know which years might supply those resources?
Enter the North American monsoon season. This profound precipitation pattern largely misses California, which mostly remains parched in Summer. No/little warm season rain equates to few seed resources to rely upon in winter. Meanwhile, the Sky Islands are often blissfully deluged from July through September, spawning many seed-bearing plants – the staple winter food of Lawrence’s goldfinch. Think sunflowers and other members of the Aster family, but especially think Palmer’s amaranth. This member of the Goosefoot family—related to lamb’s quarters and tumbleweed—sometimes has outbreak years when ample rains allow it to proliferate in its preferred habitats—bottomland fields and mesquite woodlands, such as those at Raven’s Nest Nature Sanctuary.
A flock of about ten Lawrence’s Goldfinches recently caught our attention as they foraged for seeds and sang from prominent perches at the preserve. Given that some years they are entirely absent from our region, any sighting is truly a special one. This was indeed an outbreak year for the amaranth, but how do the goldfinches know that? My best guess is that humidity patterns in coastal California are affected by our monsoon patterns in Arizona and southeast California, however subtle those effects may be. If the Goldfinches sense repeated summer upswings in humidity in their otherwise often parched breeding range, then that often equates to multiple Monsoon storms growing their winter food plants in southeast Arizona. It’s as good an hypothesis as any.
Adding to the great charm of this nomadic species is both their appearance and behaviors. Of all the North American Goldfinches—American, Lesser, and even the Pine Siskin in the same genus—to me the most attractive is the Lawrence’s. The female bears a yellow chest above a whitish belly, making her vaguely like a plump Virginia’s Warbler. The male also has a yellow chest, but truly stands out owing to his black forehead and chin, backed by an ungoldfinch-like steel gray—a half-chickadee look. When not feeding, this highly social species—a trait they do share with other Goldfinch species—often can be seen perched high in mesquite or catclaw acacia trees. There they preen and frequently sing to maintain contact with fellow flock members. Their songs are variable and even contain riffs from other bird species that they mimic.
The chitterings of this particular flock caught our attention during a recent Birding and Biodiversity Tour at Raven’s Nest Nature Sanctuary. While observing the flock and nearby groups of wintering sparrows, a ghostly grey male Northern Harrier strafed the lot, sending them willy nilly to cover. Surviving such perils, Lawrence’s Goldfinches somehow must find their way to the Sky Islands, fatten themselves on plant seeds throughout the winter, then trickle back to California come spring. However improbable the feat, they perform it with great alacrity and always leave us wanting for more given the mercurial nature of their Sky Islands presence.