Like so many species, the Carolina Wren is expanding northward. And, like many of those species, this expansion started decades ago, before any measurable climate change, but has exploded in the past decades with climate change.
The Carolina Wren has been expanding north since the 1800s due to habitat recovery after deforestation (Haggerty and Morton, 2020 – the Birds of North America (BNA) species account). What makes the recent Carolina Wren data so interesting is that we can clearly see, in its expansion into Canada, its battle with winter weather conditions.
The species is known for “decimation… by severe winter conditions” (BNA) at the northern limits of its range. The same account notes that “severe winters have apparently been infrequent enough during the 20th century to allow populations to expand and move northward.” Indeed, one of the key conclusions of an analysis of climate change in southern Ontario was that there has been “a decrease in the frequency of cold temperature extremes”. While the wren is aided against cold snaps by bird feeders, the climate trend, at least in Canada, is in its favor. The report noted an overall average increase of 1.5C.
As the wren expanded, certain record-breaking and persistent cold waves knocked the population back, where it restarted. It’s also clear that it is restarting from a higher position each time, thus building its numbers and continuing its expansion.
The cold snaps denoted on the graph were particularly severe in southern Ontario. A more detailed look at weather data may reveal a more complicated pattern and even greater correlation to warmer winters.
This blog post is merely to provide a visual illustration, by way of a map, of the expansion of the California Scrub-Jay across Washington, British Columbia, eastern Oregon, Idaho, and even Montana (one record so far). It is intended to complement my more detailed article, “Tracking Expansion of the California Scrub-Jay Into the Pacific Northwest”, in the Washington Ornithological Society (WOS) News, August-September 2021 edition.
As becomes clear in the article, these are not hard lines. The jays are advancing gradually, not in a solid wave. Typically, a single jay will appear well outside the known range (e.g. Spokane). Within a year or two, there will be several. Then they’ll be breeding. Then they will begin expanding further. Meanwhile, a wave of jays will be backfilling the new territory, with densities increasing annually. The lines in this map are as much art as science, but are intended to show the primary region were jays were “regular and expected”. There were always outliers, pioneer dispersers expanding the range. Records beyond the 2020 line are shown as pale blue dots.
The jay’s expansion, when considered in the context of timing and trends in other species, is likely a function of a warming climate combined with suitable food sources. For more discussion of this, see the WOS article linked above.
It will be interesting to see where the 2030 scrub-jay “contour line” will be. I predict they’ll be on Vancouver Island from Victoria to Campbell River, as well as up the Sunshine Coast, up the Okanagan Valley to Kelowna and possibly Kamloops, and east to Idaho, from Coeur d’Alene in the north throughout the Snake River Valley in the south.
After that, they face some formidable hurdles. The biggest obstacles to their expansion further north and east will be habitat with limited food sources (e.g. high mountains). That said, they’ve already shown some ability to travel up mountain valleys and potentially cross the Cascades north of Mount Rainier.
Looking at Version 8.0.8 (March 12, 2021) of the ABA Checklist, 116 of the 1,123 species, or a little over 10%, are named after people. Of the 116 in the ABA area, two (Bishop’s Oo and Bachman’s Warbler) are considered extinct, one is an introduced species in Hawaii (Erckel’s Francolin), and 32 others are Codes 3, 4 or 5, meaning they occur rarely in the ABA area. The remaining 80 are all Code 1 or 2 and can be expected to be seen in the ABA area regularly. The following analyses focuses on these 80 familiar species.
The first thing to note is that these 80 species come from a wide array of families and species groupings. As with all birds, Passerines are dominant, making up 49% of the list. Digging deeper, seabirds and Passerines with limited ranges (mostly warblers and sparrows) are over-represented—because they were described relatively late in the European discovery process, when honorific naming became more in vogue.
The AOU (American Ornithological Union, the precursor to the AOS) began proposing English names in its first checklist in 1886, but didn’t complete the effort – and the names were not universally accepted – until the 5th edition in 1957. Meanwhile, the Latin scientific names have always followed a clear rule: the Latin name is set by the first published description of a species. The “bird names for birds” movement is focused on English names only.
Eponymous naming was rare in the 18th century, limited to just four of the 80 species, all emanating from Russian/German and British field work, primarily focused on the far north. The four early birds are Steller’s Eider (1769), Blackburnian Warbler (1776), Steller’s Jay (1788), and Barrow’s Goldeneye (1789).
Then, in 1811, Alexander Wilson named a woodpecker and a nutcracker after Lewis and Clark, and honorific naming was off and running, peaking in the mid-1800s.
Eponyms for the 80 Code 1 and Code 2 species are overwhelmingly honorific. Only six are named after the describer himself (Wilson’s Warbler, Sabine’s Gull, Brandt’s Cormorant, Townsend’s Warbler, Gambel’s Quail, and Cory’s Shearwater), and it’s not clear that even all of them intended for the species to have an eponym; the Latin names for the warbler, cormorant, and shearwater suggest otherwise. Wilson himself called his warbler the Green Black-capped Flycatcher and the western subspecies went by Pileolated Warbler (coined by Pallas) as late as the 1950s.
The namers were widespread – 36 different people provided the 80 names, though four stand out. John James Audubon provided fifteen of the eponymous names, Spencer Baird and John Cassin each provided seven, and Rene Lesson four. Together, these four ornithologists were responsible for 41% (33/80) of the honorific names in this analysis. In addition, many eponymous subspecies were coined by Baird.
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The majority of the namers were connected to each other, with many naming birds after colleagues, who in turn named species after other colleagues. Lesson described Audubon’s Shearwater and Oriole; Audubon described Baird’s Sparrow; Baird described Woodhouse’s Scrub-Jay; Woodhouse described Cassin’s Sparrow; Cassin described Lawrence’s Goldfinch; Lawrence described LeConte’s Thrasher.
There are no examples of a quid pro quo, where two people named birds after each other, unless you count Audubon’s Warbler, described by Townsend in 1837; Audubon returned the favor with Townsend’s Solitaire the following year. Or Coues, who christened a sandpiper after Baird in 1861; four years later, Baird named a warbler after Coues’ sister, Grace.
Despite Audubon’s dominant role in honorific naming, no Americans honored him (excepting Townsend with Audubon’s Warbler); only Lesson, a Frenchman, did.
A third of the species (27 of 80) have Latin names that do not match the honorific English name. In most instances this is because the bird was accidentally described twice. Most often, they were not originally intended to have an honorific name. A person described the species and gave a descriptive Latin name, then later another person described the same species and gave an honorific name. For example, Lichtenstein described A. aestivalis in 1823, then Audubon described it again in 1839, naming it Bachman’s Sparrow. When it was realized the two were the same species, the Latin name provided by the first publication held, but, at least in these instances, the honorific English name was also given—a kind of consolation prize to the second describer. Thus, what was called Pinewoods or Oakwoods Sparrow became Bachman’s Sparrow. It’s apparent that oversight and review of “naming and claiming” was limited.
Among the 80 species in this analysis, this double-describing happened at least 18 times. Curiously, six of these were by Audubon and account for 40% of his honorific bestowments. These are Harris’s Hawk, Bachman’s Sparrow, MacGillivray’s Warbler, Harris’s Sparrow, Brewer’s Blackbird, and Smith’s Longspur. MacGillivray’s Warbler was intended to be Tolmie’s Warbler as described by Townsend; the other five have descriptive Latin names. There is one other double-described species that has a Latin honorific—Scott’s Oriole, Icterus parisorum, originally named after the Paris brothers. Most of the others have descriptive Latin names.
Cassin’s Auklet (P. aleutica) and Cassin’s Kingbird (T. vociferans) were first described, respectively, before Cassin was born and when Cassin was just thirteen. Clearly the original describers did not intend to honor Cassin. However, by the 1886 AOU checklist both carried the Cassin moniker, though there is no record that I could find how or why that came to be (and even a co-author of the auklet’s Birds of North American species account didn’t know the answer).
Interestingly, two species have Latin names derived from indigenous words: pipixcan of Franklin’s Gull is Nahuatl for the gull or possibly the Aztec region in Mexico; sasin of Allen’s Hummingbird is Noo-chah-nulth (Nootka) for hummingbird, a reference to when the species was lumped with Rufous Hummingbird. The gull was described twice, which is how it ended up honoring Franklin. The hummingbird was split, providing an opportunity for another name. Ironically, Allen’s, not Rufous, Hummingbird always bore the Noo-chah-nulth name which emanates from Vancouver Island.
Correlated with the timing, a clear regional pattern emerges. Because the common eastern species had already been described a century earlier, western species with honorific names outnumber eastern ones nearly ten to one. A map plotting the year of description with the core of the species’ range mimics European expansion – and ethnic cleansing of Native Americans – across the continent in the nineteenth century.
As for the honorees, most were naturalists, either doing field work or promoting it (70 of 80), most were Americans (55 of 80) or at least had spent some time in North America (add ten more). French collectors dominated the hummingbirds.
Only six species honor women—or girls. Blackburne is the early outlier, a British naturalist honored by one of the German ornithologists in the late 1700s. Neither spent time in North America; the type specimen comes from South America. Curiously, the eponymic title is not in the possessive form (e.g. Blackburne’s Warbler). For reasons unknown to me, the Latin name was changed from blackburniae to fusca before 1910.
During the surge of honorifics in the mid-1800s, the only females honored were friends or family, and they only got first names. Anna, age 27 when the hummingbird was named in her honor, was the wife of an ornithologist and a lady-in-waiting in the court of Emperor Napoleon III’s wife. She was described by Audubon as a “beautiful young woman, not more than twenty, extremely graceful and polite.” Virginia was the wife of William Anderson, the original collector; she was honored by Baird at Anderson’s request. Grace, also honored by Baird, was Elliot Coues’s sister. Lucy, age 13, honored by James G. Cooper, was Baird’s daughter.
We don’t return to female scientists – and last names – until the 1900s, with Scripps, who was honored in 1939, and her bird didn’t reach species status until 2012.
Most of the honorees have no obvious indications of a checkered past (66 of 80), though most of these were quite comfortable associating with, or honoring with bird names, those who were slaveholders, white supremacists, or actively involved in killing or removing Native Americans, even while these actions were hotly debated and contested at the time among whites—and universally opposed by Blacks and Native Americans. As early as 1920, the entire concept of eponymous bird names was challenged.
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The dominance of western species among honorific names with morally objectionable pasts is no accident. Many of the ornithologists working in the West were attached to US military expeditions or other surveys of colonization, such as railroad surveys or the border survey after the Mexican-American War. They often served as doctors while doing naturalist work on the side. Many were likely looking for a vehicle to get into the field.
Others were active combatants, with the naturalist work coming on the side. William Clark, after the famous 1803 expedition, played a leadership role in the ethnic cleansing of Native Americans for three decades. Abert served as a soldier under John Fremont’s Third Expedition and likely participated in the Sacramento River massacre of Wintu families, deemed horrific by their contemporaries. General Winfield Scott, not a naturalist in any way, was honored by Couch with an oriole precisely for his role as the Commanding General of the US Army, which included overseeing the arrest, detainment, and expulsion of the Cherokee during the Trail of Tears.
But why did they turn to honorific naming when their predecessors did not? Was it the spirit of conquest, of erasing the former occupants of the land, that gave them the presumption and bravado to name even the birds after each other? After all, mountains, rivers, valleys, and large regions of land were all being re-named and claimed as European.
White supremacy permeated the sciences. Crania Americana was published between 1839 and 1849 by Samuel Morton, a colleague of several of the naturalists. Townsend collected skulls for him. During the same era, to support the Indian Removal Act and other similar policies, the Mound Builder Myth, asserting that Native Americans were not actually native, but that North America was originally populated by Europeans, was widely taught in grade schools across the land. The land was originally European, so the story went. This theory was eventually laid to rest thanks to the efforts of John Wesley Powell, but only after most Natives were detained in concentration camps.
In short, the scientific fields were permeated with white supremacy and a sense of white ownership. Ornithological research found itself interlocked with US military endeavors and, on the Western frontier, far from Eastern progressive voices advocating abolition and respect for slaves and Natives. In this climate, honorific naming eventually ran amok, often foundering on the rocky shores of slavery and ethnic cleansing, aka manifest destiny.
Caveat: Researching the origins of species’ names is challenging, especially for those described more than once or subject to taxonomic revisions. Corrections from knowledgeable readers are much appreciated. Regardless of errors, the larger picture, the trends regarding time and place, still hold.
Note: Updated June 2, 2021 to include Blackburnian Warbler.
At the American Ornithological Society (AOS) Congress on English Bird Names on April 16, 2021, a host of prominent organizations and individuals endorsed “bird names for birds”, a widespread effort to rename eponymous or honorific species names with more descriptive names, focusing on their physical or ecological attributes. For example, Wilson’s Warbler could become Black-capped Warbler, Townsend’s Solitaire might become Northern or Juniper Solitaire, and Kittlitz’s Murrelet would probably be re-named Glacier Murrelet.
While specific new names have not yet been chosen, representatives of the American Birding Association (ABA), National Audubon Society, as well as David Sibley and Kenn Kaufmann, all heartily endorsed developing a process to make the changes, noting that new names would engage a larger audience, contribute to greater equity and inclusivity among birders and the interested public, and could aid in public communication and conservation efforts.
The effort has grown out of the national reckoning on racial equality in the aftermath of the George Floyd killing. Movements to change names are underway with regard to parks, mountains, streets, other wildlife, and even rock-climbing routes. Current names generally go back to the eighteenth and nineteenth centuries during European expansion across North America and recall an era of conquest, when species and landforms were “discovered” – and some named after the individual who documented them, or after their friends and colleagues.
Sibley commented that, the more he learns about the names, “the more they cast a shadow over the bird” and “the name doesn’t mean just the bird anymore. They have baggage.” Out of respect for people and the birds, they “should not have to carry a reminder of our own fraught history.” Choosing between stability and respect, Sibley stated “I choose respect.”
Name changes over social justice concerns began last year when McCown’s Longpsur was changed to Thick-billed Longspur, after widespread outcry because McCown was a Confederate general and involved in the ethnic cleansing of Native Americans. A proposal in 2018 for that name change was roundly rejected.
Name changes for these reasons are not new; most birders can probably recall the switch from Oldsquaw to Long-tailed Duck in 2000. At that time, the American Ornithologists’ Union, the precursor to the AOS, asserted that the name change was not for reasons of “political correctness” but merely to conform with usage elsewhere.
Bird Names for Birds, a group of interested birders, was instrumental in reaching out to the larger organizations to participate in the congress. In their words, “Eponyms (a person after whom a discovery, invention, place, etc., is named or thought to be named) and honorific common bird names (a name given to something in honor of a person) are problematic because they perpetuate colonialism and the racism associated with it. The names that these birds currently have—for example, Bachman’s Sparrow—represent and remember people (mainly white men) who often have objectively horrible pasts and do not uphold the morals and standards the bird community should memorialize.” They describe such names as “verbal statues” that should be removed.
Jordan Rutter of Bird Names for Birds argued that, when reaching out to the public to protect an endangered sparrow, Bachman’s Sparrow has much less appeal than an alternative name rooted in local ecology that the public could identify with. Kaufmann pointed out that Bachmann was a pro-slavery white supremacist and that the species was formerly known as the Pinewoods Sparrow.
In the AOS’s own language, “The Community Congress opens the discussion on the complex issues around eponymous English Bird Names…. The specific aim of the Community Congress is to provide an opportunity for a broad range of stakeholders from the birding and ornithological community to share their viewpoints, including challenges and opportunities from their perspectives, to best inform future next steps to address the issue of naming birds after people.”
Keepers of various ornithological databases also participated in the Congress, including representatives for eBird, Christmas Bird Counts, Breeding Bird Surveys, and the Bird Banding Laboratory. While noting potential complications with name changes (and changes in four-letter banding codes), they all agreed the hurdles were not insurmountable. Indeed, name changes, as well as taxonomic lumps and splits, occur every year, with name changes being the simplest of the three to address in data management. eBird currently supports bird names in 47 languages, including 14 different versions of English. Where Americans see Black-bellied Plover, Brits see Grey Plover.
Marshall Iliff of eBird pointed out that the effort is also an opportunity to clean up old taxonomic messes, pointing out that Audubon’s Shearwater has been used for eleven different combinations of nine different taxa. In this case, he said, fresh names for specific taxa will provide clarity, not confusion. He embraced a worldwide effort to “dig into the essence of each species” to “find inspired and appropriate names.”
For now, the effort will be limited to primary eponymous English bird names. The effort will not include secondary names (e.g., American Crow, named after the continent, which was named after Amerigo Vespucci). Other problematic names, such as Flesh-footed Shearwater for a bird with pink feet, were not discussed.
Many suggested using Native names for species, though most stated this could be challenging because 1) names from Native languages may have been lost, or 2) most bird species’ ranges span multiple historic aboriginal territories and languages, creating a conundrum over which indigenous word to use. The exception to this is Hawaii, where indigenous names are already in widespread use. Among mammals, moose, raccoon, and skunk are all derived from Algonquian.
Looking at Version 8.0.8 (March 12, 2021) of the ABA Checklist, 115 of the 1,123 species, or a little over 10%, are named after people. Of these, 2 (Bishop’s Oo and Bachman’s Warbler) are considered extinct, and 20 others are Code 4 or 5, meaning they occur extremely rarely in the ABA area (though three of these are regular in Mexico, within the AOS area). The remaining 93 are all Code 1, 2, or 3, and can be expected to be seen in the ABA area regularly.
Here are the 113 non-extinct species from the ABA Checklist.
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).
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.
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.
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.”
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).
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.
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.
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.”
Birds, because of their mobility, are considered to be fairly adaptable to climate change. They evolved in the aftermath of two of the world’s most catastrophic warming events (the K-T extinction and the Paleocene-Eocene Thermal Maximum), spreading to the Arctic, crossing continents, and evolving along the way. While those warming events took place over tens of thousands of years, the current warming is happening in the space of a couple hundred, with noticeable changes in climate within the lifespan of a single bird.
There will be winners and losers. Generalists, and species that enjoy warmer weather, are likely to be winners. Those with narrow food or habitat requirements, especially those dependent on the ocean or the Arctic/Antarctic, will likely be losers. Although counter-intuitive, it is primarily non-migratory resident species that seem to be more adaptable to a changing climate.
Studies of climate impacts on western North American birds using past data are limited, but some focusing on California were recently published. Iknayan and Beissinger (2018) showed that, over the last 50 years, “bird communities in the Mojave Desert have collapsed to a new, lower baseline” due to climate change, with significant declines in 39 species. Only Common Raven has increased. Furnas (2020) examined data from northern California’s mountains, showing that some species have shifted their breeding areas upslope in recent years. Hampton (myself) (2020) showed increases in many insectivores, both residents and migrants (from House Wrens to Western Tanagers), in winter in part of the Sacramento Valley over the last 45 years. These changes, particularly range shifting north and out of Southwest deserts, is predicted for a wide number of species.
The invasion of the Pacific Northwest
Here I use Christmas Bird Count (CBC) data to illustrate that some of California’s most common resident birds have expanded their ranges hundreds of miles north into Oregon, Washington, and British Columbia in recent years. The increases are dramatic, highly correlated with each other across a wide range of species, and coincide with rapid climate change. They illustrate the ability of some species to respond in real time.
In parts of Oregon and Washington, it is now not unusual to encounter Great Egret, Turkey Vulture, Red-shouldered Hawk, Anna’s Hummingbird, Black Phoebe, and California Scrub-Jay on a single morning—in winter. A few decades ago, this would have been unimaginable. Some short-distance migrants, such as Townsend’s Warbler, are also spending the winter in the Pacific Northwest in larger numbers.
The following graphs, showing the total number of individuals of each species seen on all CBCs in Oregon, Washington, British Columbia, and (in one case) Alaska, illustrate the range expansions. Adjusting for party hours scarcely changes the graphs; thus, actual numbers of individuals are shown to better illustrate the degree of change. The graphs are accompanied by maps showing predicted range expansions by the National Audubon Society, and recent winter observations (Dec-Feb) from eBird for 2015-2020.
These range expansions were predicted, though in some cases the recent trends exceed even projected scenarios under 3.0C increases in temperature.
Average nationwide winter temperatures deviation from average.
Great Egrets on Oregon CBCs have increased from near zero to nearly 900 on the 119th count (December 2018 – January 2019).
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But their expansion, which took off in the early 1990s into Oregon, is now continuing in Washington, with a significant rise beginning in the mid-2000s. Great Egrets occur regularly in southern British Columbia, but so far have eluded all CBCs.
They have not quite fulfilled the full range predicted for a 1.5C increase, but are quickly on their way there.
Turkey Vultures began increasing dramatically in winter in the Sacramento Valley of California in the mid-1980s, correlated with warmer winters and a decrease in fog. Prior to that, they were absent. Now, over 300 are counted on some CBCs. That pattern has been repeated in the Pacific Northwest, though about 20 years later. Both Oregon and British Columbia can now expect 100 Turkey Vultures on their CBCs. Curiously, Puget Sound is apparently still too cloudy for them, who prefer clear skies for soaring, though small numbers are regular in winter on the Columbia Plateau.
Red-shouldered Hawks have increased from zero to over 250 inviduals on Oregon CBCs, taking off in the mid-1990s.
Twenty years later, they began their surge into Washington. It’s a matter of time before the first one is recorded on a British Columbia CBC.
While their expansion in western Washington is less than predicted, their expansion on the east slope, in both Oregon and Washington, is greater than predicted. This latter unanticipated expansion into the drier, colder regions of the Columbia Plateau is occurring with several species.
If this invasion has a poster child, it’s the Anna’s Hummingbird, which, in the last 20 years, have become a common feature of the winter birdlife of the Pacific Northwest. Their numbers are still increasing. While much has been written about their affiliation to human habitation with hummingbird feeders and flowering ornamentals, the timing of their expansion is consistent with climate change and shows no sign of abating. Anna’s Hummingbirds are not expanding similarly in the southern portions of their range. The sudden rate of expansion, which is evidenced in most of the species shown here, exceeds the temperature increases, suggesting thresholds are being crossed and new opportunities rapidly filled.
The expansion of the Anna’s Hummingbird has now reached Alaska, where they can be found reliably in winter in ever-increasing numbers.
The range expansion of the Anna’s Hummingbird has vastly outpaced even predictions under 3.0C. In addition to extensive inland spread into central Oregon and eastern Washington, they now occur across the Gulf of Alaska to Kodiak Island in winter.
Non-migratory insectivores seem to be among the most prevalent species pushing north with warmer winters. The Black Phoebe fits that description perfectly. Oregon has seen an increase from zero to over 500 individuals on their CBCs.
With the same 20-year lag of the Red-shouldered Hawk, the Black Phoebe began its invasion of Washington.
The figure below illustrates two different climate change predictions, using 1.5C and 3.0C warming scenarios. While nearly a third of the Pacific Northwest’s Black Phoebes are in a few locations in southwest Oregon, they are increasingly populating the areas predicted under the 3.0C scenario.
Migrant species tend not to show the dramatic range expansions of more resident species – and short-distance migrants show more range changes than do long-distance migrants. Townsend’s Warblers, which winter in large numbers in southern Mexico and Central America, also winter along the California coast. Increasingly, they are over-wintering in Oregon and, to a lesser degree, Washington. This mirrors evidence from northern California, where House Wren, Cassin’s Vireo, and Western Tanager are over-wintering in increasing numbers. These may be next for Oregon.
Townsend’s Warblers are already filling much of the map under the 1.5C warming scenario, though their numbers on CBCs in Washington and British Columbia have yet to take off.
Due to problems with CBC data-availability, I have no graph for the California Scrub-Jay. Their northward expansion is similar to many of the species above. Their numbers on Washington CBCs have increased from less than 100 in 1998 to 1,125 on the 2018-19 count. eBird data shows they have filled the range predicted under the 3.0C scenario and then some, expanding into eastern Oregon, the Columbia Plateau, and even Idaho.
Other species which can be expected to follow these trends include Northern Mockingbird and Lesser Goldfinch. (See more on the expansion of the Lesser Goldfinch here.) White-tailed Kite showed a marked increased in the mid-1990s before retracting, which seems to be part of a range-wide decline in the past two decades, perhaps related to other factors.
Curiously, three of the Northwest’s most common resident insectivores, Hutton’s Vireo, Bushtit, and Bewick’s Wren, already established in much of the range shown on the maps above, show little sign of northward expansion or increase within these ranges. The wren is moving up the Okanogan River, and the vireo just began making forays onto the Columbia Plateau. Both of these expansions are predicted.
Likewise, some of California’s oak-dependent species, which would otherwise meet the criteria of resident insectivores (e.g. Oak Titmouse), show little sign of expansion. Oaks are slow-growing trees, which probably limits their ability to move north quickly. Similarly, the Wrentit remains constrained by a barrier it cannot cross—the Columbia River.
Call it the invasion of the Northwest. Call it Californication. Call it climate change or global warming. Regardless, the birds of California are moving north, as predicted and, in some cases, more dramatically than predicted.
Pine Siskins in fall 2015 during the “superflight”. Davis, California.
Boreal seed-eating birds are notoriously unpredictable in their winter wanderings. Unlike a certain distinctive Dark-eyed Junco that once returned to my small apartment patio in Davis, California several winters in a row, these birds of the northern forests have no such allegiance to any patch of land. A Pine Siskin once banded in winter in Quebec turned up in California during a subsequent winter; other Pine Siskins banded in winter in New York and Tennessee spent a later winter in British Columbia; an Evening Grosbeak banded in winter in Maryland spent a later winter in Alberta; a Eurasian Siskin banded in winter in Sweden was later found in Iran; a Common Redpoll once wintered in Belgium, and later in China; another Common Redpoll banded in winter in Michigan was found during a later winter in Siberia (Newton 2006). In other winters, they hardly migrate at all. While up to 90% of band recoveries for many winter-banded species are pretty much where they were banded, that rate fall to about 1% for irruptive boreal species (ibid).
There’s a rich literature focusing on cone crop failure and irruptions of crossbills, redpolls, Clark’s Nutcrackers and other species (Reinikainen 1937, Lack 1954, Svardson 1957, Davis and Williams 1957 and 1964, Ulfstrand 1963, Evans 1966, and Eriksson 1970). To quote Newton (2006), “Clear evidence has emerged that major emigrations follow periodic crop failures.” Most recently, Wilson and Brown (2017) confirmed that Red-breasted Nuthatches are not fleeing bad weather nor are they attracted to specific food elsewhere; they are spreading across the land “because of failure of conifer seed production on the breeding grounds.” They are famine refugees. Other research has shown that, “despite the presumed benefits of irruption as an adaptive response to food shortage when population levels are high, negative population consequences can ensue.” Large irruptions are correlated with smaller numbers on Breeding Bird Surveys the following summer; they don’t all make it back (Dunn 2019).
Another factor, however, is high population densities of the birds (Bock and Lepthien 1976). Koenig and Knops (2001) reached some specific conclusions when they examined 30 years of Christmas Bird Count (CBC) data, focusing on multiple species, and compared it with data on cone crops. They found that Red-breasted Nuthatch, Black-capped Chickadee, Evening Grosbeak, Pine Grosbeak, Red Crossbill, Bohemian Waxwing, and Pine Siskin irruptions were “correlated with a combination of large coniferous seed crops in the previous year followed by a poor crop.” In short, a good year causes a pulse in reproduction, followed by a lean year which causes the expanded population to suddenly roam in search of food. There was some variation, with the good year or the bad year playing a more dominant roll for different species, but for most species, it was both. (And for Purple Finch, it seemed to be neither.) They concluded that “seed crops of boreal trees play a pivotal role in causing eruptions for a majority of boreal species, usually through a combination of large seed crop resulting in high population densities followed by a poor seed-crop, rather than seed-crop failure alone.”
Red-breasted Nuthatch, also in Davis in fall 2015.
A year previously, Koenig and Knops (2000) studied just the trees, and concluded that various tree species often boom and bust in sync. They noted that “the large geographic scale on which seed production patterns are often synchronized, both within and between genera, has important implications for wildlife populations dependent on the seeds of forest trees for food. In general, resident populations of birds and mammals dependent on mast are likely to be affected synchronously over large geographic areas by both bumper crops providing abundant food and, perhaps even more dramatically, by crop failures.” Newton (2006) reported synchrony in boreal conifer seed production in forests 1000 km apart. Strong et al (2015) links Pine Siskin irruptions to continent-wide winter climatic patterns.
With synchronized cone crop failures, one would expect synchronized irruptions across bird species. The literature on this is supportive but mixed. Bock and Lepthien (1976) provide nice annual maps by species illustrating “generally synchronous” irruptions in many (but not all) years. Koenig (2001) offers the most comprehensive analysis, exploring synchronous irruptions among all combinations of 15 species, including multi-year lagged effects. (Here it’s important to understand correlation coefficients, or Pearson’s r. For guidance in interpreting r, 1.00 would be a perfect match, 0 would mean no correlation, and -1.00 would mean they do the exact opposite of each other.) Koenig’s highest correlation coefficients between two species were generally between 0.30 and 0.50. He also shreds an earlier assertion from Bock (1999) that there is strong correlation between Common Redpoll and Pinyon Jay irruptions; there was, but it didn’t last long.
Here I examine 49 years of CBC data (1970-2018) for Red-breasted Nuthatch, Pine Siskin, and Red Crossbill from the northern Central Valley of California, centered around Sacramento. I used data from eight CBCs: Caswell-Westley, Folsom, Lincoln, Marysville, Rio Cosumnes, Sacramento, Stockton, and Wallace-Bellota. I didn’t have any data on cone crops, but I assumed they might be correlated with precipitation the previous year, so I looked at snowfall. In short, I find some support for Koenig and Knops, but I wouldn’t bet more than a beer on it in any given year.
Here are the results. CLICK TO ENLARGE.
First, there are no units for the vertical axis. That’s because the units I used for the birds is basically an index. I converted them all to natural log (ln) because the numbers of siskins, which often occur in large flocks, dwarfed the nuthatches and crossbills. Converting to natural logs put them all more on a level playing field. What you’re seeing is the natural log of total individuals across all eight CBCs each year. (In most years, most birds were in the Sacramento CBC.) The blue circles are the water content (in inches) of the deepest observed snowpack from winter snow surveys at Upper Carson Pass from the previous winter. For example, the large irruption (or “superflight”) in 2015 occurred in the fall and winter of 2015-16, and the very low blue circle on that column is associated with the snowpack from the winter of 2014-15. In general, the snow surveys occurred in Jan-Apr and the CBCs in December of the same year.
A few quick observations from the chart:
Red Crossbills only occurred in six of the 49 winters, but 4 of those were during nuthatch/siskin irruptions. The only large crossbill irruption occurred in 2015, on top of the largest combined nuthatch/siskin invasion. The 2015 superflight also coincided with the lowest snowpack the previous winter, which came at the end of a four-year drought. So 2015, as an extreme event, tells us a few things. Previous snowpack is important, and correlation across species does occur.
Most of the other highest irruption years (1981, 1987, 1992, 2012) all came after low snowpack years, and all had higher snowpack the year before that, exactly what Koenig and Knops would predict.
And now for some math:
The correlation coefficient between nuthatches and siskins is 0.32, so they do tend to irrupt together-ish, but not always and certainly not in the same magnitude. Koenig writes, “For Red-breasted Nuthatch and Pine Siskin, synchrony over different 10-year periods varied from a high of 0.82 (1965-1974) to a low of 0.24 (1987-1996).” His sample included eastern North America, which he showed follows different patterns than the West.
I then looked at correlation between the cumulative nuthatch/siskin/crossbill irruptions (in natural log, so the full blue, yellow, and red columns in the graph) and a variety of other parameters. Here are the results:
Correlation with previous winter’s water content from snowpack (the blue circle): -0.44.
Correlation with water content more than 5″ below average: 0.41.
Correlation with multiple years of drought: 0.37.
Correlation with a 10″ drop in water content from the year before that (thus going from a good year to a worse year): 0.38.
Correlation with the same 10″ drop in water content, but only if the recent year was below average (thus, going from a good year to a bad year): 0.40.
So these correlations all lean in the right direction, supporting Koenig and Knops’ notion that bad years are bad, and bad years after good years are even worse. I would also add that bad years after bad years (a drought) are also bad.
These correlations come with some caveats. First, the correlation between snow water content and cone crop is imperfect. Koenig and Knops (1999) state that, while recent precipitation is indeed an important variable, it’s not the only one. Spring and summer temperatures play a role in cone development, as well as previous seasons. After a really good year, trees need a break, regardless of rainfall, and will produce less. An example might be 1984, where there was an irruption after an average snow year, but two really heavy precipitation years preceded that.
Another source of noise in the data is that our birds, especially the siskins, may be coming from much further afield than Tahoe. (I deliberately left out Evening Grosbeak because call types from our last invasion suggested the birds were brooksi from Washington state or somewhere up there.)
Donner Pass without snow. January 20, 2015.
While it may seem that the data on irruptions and snowpack tell a compelling story, let’s not forget the present. It’s fall 2019 and we’re in the midst of a significant Red-breasted Nuthatch irruption (and I’ve seen one siskin as well). This year is not on the graph above, but we do already have the snowpack data from earlier in the year. It was way above average. Thus, we’ve just gone from an average snowpack year in 2018 to above-average in 2019, the opposite of what should prompt an irruption. If you bet me a beer, I’d owe you one.
Bock, C.E. 1999. Synchronous Fluctuations in Christmas Bird Counts of Common Redpolls and Piñon Jays. The Auk 99: 382-383.
Bock, C.E. and L.W. Lepthien. 1976. Synchronous eruptions of boreal seed-eating birds. American Naturalist 110: 559- 571.
Davis, J. and L. Williams. 1957. Irruptions of the Clark nutcracker in California. Condor 59: 297–307.
Davis, J. and L. Williams. 1964. The 1961 irruption of the Clark’s nutcracker in California. Wilson Bulletin 76: 10–18.
Dunn, E.H. 2019. Dynamics and population consequences of irruption in the Red-breasted Nuthatch (Sitta canadensis). The Auk 136.
Eriksson, K. 1970. Ecology of the irruption and wintering of Fennoscandian redpolls (Carduelis flammea coll.). Annals Zoologica Fennici 7: 273–282.
Evans, P.R. 1966. Autumn movements, moult and measurement of the lesser redpoll, Carduelis flammea. Ibis 106: 183–216.
Koenig, W.D. 2001. Synchrony and Periodicity of Eruptions by Boreal Birds. The Condor 103: 725-735
Koenig, W.D. and J.M.H. Knops. 2000. Patterns of annual seed production by Northern hemisphere trees: a global perspective. American Naturalist 155: 59-69.
Koenig, W.D. and J.M.H. Knops. 2001. Seed-crop size and eruptions of North American boreal seed-eating birds. Journal of Animal Ecology 70: 609-620.
Lack, D. 1954. The Natural Regulation of Animal Numbers. Clarendon Press, Oxford.
Larson, D.L. and C.E. Bock. 1986. Eruptions of some North American seed-eating birds. Ibis 128: 137-140.
Newton, I. 2006. Advances in the study of irruptive migration. Ardea -Wageningen 94: 433-460.
Reinikainen, A. 1937. The irregular migrations of the crossbill, Loxia c. curvirostra, and their relation to the cone-crop of the conifers. Ornis Fennica 14: 55-64.
Svardson, G. 1957. The ‘invasion’ type of bird migration. British Birds 50: 314-343.
Ulfstrand, S. 1963. Ecological aspects of irruptive bird migration in Northwestern Europe. Proceedings of the International Ornithological Congress 13: 780–794.
Wilson Jr., W.H. and B. Brown. 2017. Winter Movements of Sitta canadensis L. (Red-breasted Nuthatch) in New England and Beyond: A Multiple-scale Analysis. Northeastern Naturalist 24.
I’ve been asked quite a lot about my fountain and pond (in Davis, California) and why it is so successful in attracting birds. Here are some, I think, key elements:
The first is the sound of falling water. Birds hear this and come to investigate. The pond is rather simple. It all begins with an amoeba-shaped pre-fabbed pond liner, about 18″ deep. A small electric pump and hose carries the water about 3 feet up, where I feed the hose through a knot-hole in a piece of wood. From there, it falls into a plastic garbage can lid, and then pours thru a small cut into another garbage can lid, and finally into the pond itself. Each fall creates more trickling sound. I’ve put a flexible pond liner under the “waterfall” so that any water that wicks under the garbage can lids still ends up in the pond. The two lid pools are 1-2″ deep for bathing. Finally, all this stuff is covered up with rocks and driftwood.
Second, it’s all about context. The pond is essentially in a green grotto with lots of vertical structure above it, meaning that birds can come into a high tree, descend to a medium tree, and descend again to a shrub near the fountain, and then finally into one of the pools. They do serious recon about where they drink and bathe; an individual often takes several minutes to come in. I think the horizontal structure — what’s 15′ away from the pond, matters less than what’s above it; they come down from above.
At the same time, they need some visibility and escape corridors in case a cat or Cooper’s Hawk comes. I’ve trimmed all the bushes around it 18″ off the ground so any stalking cat will be clearly visible. A Cooper’s Hawk is largely thwarted by all the vegetation.
With all this cover, the pond is mostly in the shade. That’s good for controlling algae growth, but bad for taking photos. But in my experience a birdbath out in the open sun attracts only a few species. I have installed a couple iPhone holders so I can do some live video feeds (e.g. Facebook Live) of the birds coming in. I’ve also situated the pond so I get a clear view from my kitchen table, from right here as I type this on my laptop. My binoculars and camera are beside me in case anything interesting comes in.
UPDATE: I moved to Port Townsend, Washington, and quickly built another pond. It has been just as successful. Here’s a pic of it:
For this one, I use a plastic rectangular cement batch mixing basin as the bottom receiving pool. I built this whole pond for less than $75. Here are the basic blueprints for my ponds:
Compared to fall, spring migration is fast and furious. It ramps up thru April, peaks in early May, and then ends abruptly. Birds don’t stay long; they’re in a hurry. Rarities rarely last more than a day. And there are fewer birds than in the fall, winter mortality having taken its toll. But, like this Lazuli Bunting, the birds are in their best dress.
In 2010, after ten years of collecting data on morning “warbler walks” in my local patch in Davis, the Central Valley Bird Club Bulletin published my results. You can read the whole paper here:
I’ve divided it into two graphs, one for more common species (peaking at 1 to 4.5 birds per survey), and another for less common migrants (less than 1 per survey).
CLICK TO ENLARGE.
CLICK TO ENLARGE.
The same caveats apply:
A “survey” here is basically a morning walk lasting about 35 minutes.
This was for my little route in north Davis (where the eBird hotspot is “North Davis Farms Subdivision”). For other locations in the Central Valley, even nearby ones, I would expect the numbers and relative abundance to vary a little. For example, I see a lot more flycatchers at Babel Slough and Grasslands Park than are reflected here.
Putah Creek near Pedrick Rd, a current favorite of birders, generally has more birds than is shown here because it’s a larger area, birders spend more than 35 minutes when they visit, and the habitat is slightly different.
A large portion of the birds in my data are “heard only”.
For additional details, see the full article linked above. I’m happy to provide my Excel spreadsheets of this data to anyone interested.
Some species are more common in spring than fall. These include Hermit Warbler (above), Townsend’s Warbler, and Swainson’s Thrush (with a very narrow migration window in mid-May).
I’ve also linked lots of the bird literature specific to Yolo County at my Yolo County Birding website; see the list of papers in the lower right corner of that page.
On these graphs, I’ve left out the rarer birds, species that occur at a rate of less than 0.2 birds/survey (less than 1 out of every 5 surveys). These include Hammond’s and Dusky Flycatchers. It also includes Willow Flycatcher, House Wren, MacGillivray’s Warbler, Common Yellowthroat, and Chipping Sparrow, all of which are quite regular in the fall but rarely seen in spring migration.