The song of the Lesser Goldfinch: Another harbinger of a warming climate

As the climate warms, different thresholds are crossed for different species at different times. For the Lesser Goldfinch, that time seems to be now—both in the core and northern edges of its range, where the species is increasing, and in some parts of the southern arid regions, where it is decreasing.

As I prepare to migrate myself from Davis, California to Port Townsend, Washington, I’m serenaded by Lesser Goldfinches every time I step outside. This is a new thing, a warning of coming heat and smoke brought by a beautiful voice. A more open and arid country version of the American Goldfinch, until five or ten years ago, Lesser Goldfinches were sparse breeders in Davis. I would get a few of them mixed with Americans at my feeder in winter, but I’d have to go west to the more arid edges of the Sacramento Valley, or up into the hot dry foothills, to find them in the breeding season.

They arrived in my neighborhood as nesters about five years ago. This year, 2021, they seem to be the most ubiquitous singing bird, setting up terrorities throughout the town. Friends in Sacramento have reported the same. This comes after several years of record heat and lack of rain (only 6″ in all of 2020).

Here’s what the eBird data says. For comparison, Northern Mockingbird, one of the most common birds in town, is reported from about 20 eBird locations in Davis each June (ranging from 16 in 2015 and 14 in 2016 to 18-22 in the more recent years as eBird users and reports increased). Using mockingbird as a metric for Davis, it’d be fair to say that 20 sites represents close to 100% presence throughout the town, and that number was probably 25% lower (i.e. 15 sites) in 2015. Lesser Goldfinches have increased from reports from four sites in June of 2015 (representing about 20% of the town) to 17 sites in June of 2020 (representing 85% of the town). It feels like it will be 100% this year.

They are not the only arid-country species increasing in Davis as a breeder. Nesting Say’s Phoebes have expanded up from the south, with multiple pairs in Woodland each year (and it’s looking like Davis this year as well).

As with so many less-migratory species, Lesser Goldfinches are expanding north into the Pacific Northwest and beyond.  Their colonization of the Columbia River Valley began in the 1950s, with the first state of Washington record in 1951; they are now established around Portland, The Dalles, and in the vicinity of Clarkston on the Idaho border. They remain rare elsewhere, but increases in records have been dramatic in recent years. In the northern Puget Trough region (Chehalis north thru Puget Sound to Canada), June records have increased from 1 in 2015 and 2016 to 10 in 2020 (as reported on eBird). While they have clearly gained a toe-hold in Olympia and Puyallup in the South Sound region, in 2020 they made appearances in Victoria and Vancouver, Canada (not shown in the data because these records were in May, not June).

Lesser Goldfinches in British Columbia were limited to four scattered records until 2007. Since then, they have become nearly annual, with most records between January and June.

This is a pattern seen in other resident and less-migratory species. Many of those that were already growing before detectable climate change (around 1985) have expanded noticeably since then. Anna’s Hummingbird is the most dramatic example.

Further east, Lesser Goldfinches are moving due north from Yakima and Kennewick into the Okanagan Valley. June records in this region have increased from zero in 2015 to eight in 2020.

All this is predicted. The National Audubon climate prediction map for Lesser Goldfinch, under the 2C warming scenario, describes much of what we are witnessing.

In the Mojave Desert, Lesser Goldfinches have declined. Iknayan and Beissinger (2018) reported them from only 43% of 61 study sites, compared to 68% historically. This is part of a massive avian community collapse in the Mojave Desert, as extreme aridity is pushing many species beyond their limits.

Mojave Desert bird populations plummet due to climate change

Two recent papers concluded that many breeding bird species in southern California and Nevada deserts have declined dramatically due to climate change.

In their abstract, Iknayan and Beissinger (2018) summarized, “We evaluated how desert birds have responded to climate and habitat change by resurveying historic sites throughout the Mojave Desert that were originally surveyed for avian diversity during the early 20th century by Joseph Grinnell and colleagues. We found strong evidence of an avian community in collapse.”

They re-surveyed 61 sites originally surveyed by Grinnell teams in the early 20th century (primarily between 1917 and 1947).

Of 135 species assessed (which included some wintering and migrating species, as well as breeding species), 39 had significantly declined; only one (Common Raven) had increased. This was in stark contrast to similar assessments they conducted of Sierra and Central Valley sites, where more species had increased than decreased and there were no overall declines (not to say there weren’t winners, losers, and range shifts within those regions).

Figure 1B from Iknayan and Beissinger (2018). Every study site had fewer species than previously– on average each site had lost 43% of their species.

Detailed analyses suggested less rainfall and less access to water was the primary driver. Habitat change only affected 15% of the study sites and was of secondary importance. They found no evidence of expansion of species from the hotter, drier Sonoran Desert (e.g. Phainopepla, Verdin, Black-throated Sparrow) into the Mojave Desert.

Consistent with a community collapse, declines were greatest among species at the top of food chain — carnivores such as Prairie Falcon, American Kestrel, and Turkey Vulture. Insectivores were the next most impacted, and herbivores the least. But the declines affected both common and rare species, both generalists and specialists.

Figure 1B from Iknayan and Beissinger (2018), which I’ve augmented with species labels from the database available in the supplementary materials. Other significant losers (red dots), in order of degree of decline, included Western Kingbird, Western Meadowlark, Black-chinned Sparrow, Lawrence’s Goldfinch, Bushtit, Ladder-backed Woodpecker, and Canyon Wren. The yellow dots are newly invasive species: Chukar, Eurasian Collared-Dove, Eurasian Starling, and Great-tailed Grackle.

A follow-up study by Riddell et al (2020), also involving Iknayan and Beissinger, focused on the thermoregulatory costs — the water requirements to keep cool — for the declining species. They found that “species’ declines were positively associated with climate-driven increases in water requirements for evaporative cooling and exacerbated by large body size, especially for species with animal-based diets.” Larger species get much of their water from the insects they eat. They estimated larger species would have to double or triple their insect intake to meet their water needs, though insect abundance is lowest July thru September.

American Kestrels were among the biggest losers in the study, struggling to meet their cooling needs.

Intriguingly, they found that 22 species had actually declined in body size over the last century, consistent with Bergmann’s Rule, and had reduced their cooling costs up to 14%. These species fared better. Current climate change, however, is at least ten times more rapid than any previous warming event, during which many species evolved. They estimated cooling costs have already increased 19% and will reach 50% to 78% under most scenarios, far outstripping any species’ ability to evolve through the current rapid warming.

These results stand in stark contrast to the Pacific Northwest, where many of the same bird species (e.g. Anna’s Hummingbird, Turkey Vulture, Northern Mockingbird) are increasing. This is consistent with projections which generally show individual declines along species’ southern edge and expansions at the north edge of their range (see Audubon climate projection maps for individual species).

Iknayan and Beissinger conclude, “Our results provide evidence that bird communities in the Mojave Desert have collapsed to a new, lower baseline. Declines could accelerate with future climate change, as this region is predicted to become drier and hotter by the end of the century.”