Heading south for winter, more birds are choosing the Pacific Northwest

Posted on October 7, 2022 by Stephen Carr Hampton

Many papers predict that bird ranges will shift northward with a warming climate (Wu et al 2018, Langham et al 2015).

Many studies have already documented that this is happening (Illán et al. 2014, Virkkala, R. and A. Lehikoinen 2014, Hitch and Leberg 2007, and La Sorte and Thompson 2007).

And some have documented poleward range shifts specifically for wintering ranges (Saunders et al 2022, Hampton 2019, Paprocki et al 2017, Prince and Zuckerberg 2016, and Paprocki et al 2014).

I’ve previously written about an increase in insectivore bird species in winter associated with a warming climate in the Sacramento Valley. As the Putah Creek Christmas Bird Count (CBC) compiler, it was hard not to notice the trends. Cassin’s Vireo, Black-throated Gray and Townsend’s Warblers, and Western Tanagers were becoming more expected in winter. We had crossed a threshold; we didn’t get freezes anymore. My bougainvillea and cape honeysuckle, which previously clung to life in winter, were now growing and blooming year-round. Fruit and insects were available to these birds.

Now in Port Townsend, Washington, we set a local CBC record for Yellow-rumped Warblers last year. This caused me to take a closer look at the data, focusing on Passerines that are rare or uncommon, and at the northern edge of their wintering range. They are: Hermit Thrush, Cedar Waxwing, Lincoln’s Sparrow, White-crowned Sparrow, Orange-crowned Warbler, and Yellow-rumped Warbler. For each of these, the PNW is at the northern limits of their wintering range.

I looked at their numbers and trends on the Portland, Olympia, Seattle, Bellingham, and Vancouver BC CBCs since the 76^th CBC (winter 1975-76). I’ve got more notes on my methodology at the end.

Results

All have increased since 1975, generally with the uptick beginning in the 1990s. Here are the results of my inquiry.

The range maps are from eBird’s Abundance Maps. Red=summer; blue=winter; purple=year-round; yellow=migration. The graphs show the birds per party hour across the five CBCs, taking the total number of birds and dividing by the total number of hours across all five counts.

Hermit Thrush

Hermit Thrush has been increasing at a rate of 4.2% per year across all the CBCs. It has been increasing across all five of the counts, most strongly in Vancouver (4.1% annual growth) and most tepid in Seattle (0.6%). It is most common on the Portland count, which has averaged 26 Hermit Thrushes per count since 2009.

Cedar Waxwing

Of the six species I focused on, Cedar Waxwing showed some of the most erratic growth, averaging only 2.5% per year. That said, it has been above average 8 of the last 9 years. To illustrate the unpredictable nature of waxwings, they have actually been declining on the Olympia (-2.3%/yr) and Vancouver (-4.1%/yr) counts. They are increasing the most on the Portland count (3.0%/yr).

Lincoln’s Sparrow

Lincoln’s Sparrow has been increasing steadily, from near zero, at an overall rate of 3.6% per year. To put this in perspective, these five CBCs tallied 5 or fewer individuals, summed across all counts, in each of the first five years of this analysis. In each of the last five years, these counts, in aggregate, tallied between 34 and 52 individuals. Growth has been strongest on the Olympia count (4.6%/yr) and weakest on the Bellingham count (1.7%/yr).

White-crowned Sparrow

Despite the eBird map, White-crowned Sparrow is a regular overwintering species in the PNW. The five counts, in aggregate, tally between 100 and 750 individuals each year. They’ve been increasing at a rate of 1.8% per year, strongest in Seattle (3.1%/yr) and weakest in Vancouver (-2.5%/yr, the only count with declining numbers).

Orange-crowned Warbler

Orange-crowned Warbler has seen dramatic increases, averaging 5.0% per year, highest in Olympia (7.2%/yr) and lowest in Bellingham (3.2%/yr). The numbers, however, are still small. Aggregate numbers across all counts were zero five of the first eleven years of this analysis (easily seen on the graph). Double digits were not reached until 1999. The last ten years, however, have averaged 15 individuals across all the counts, making this an expected species in winter now.

Yellow-rumped Warbler

Yellow-rumped Warbler wins the award for poster child of species increasing in winter at the northern edge of their wintering range. They’ve been increasing at a rate of 5.3% per year. Interestingly, this growth is concentrated in the south. Portland (3.7%/yr), Olympia (3.4%/yr), and Seattle (6.1%/yr) have seen the most growth, while Bellingham (-0.5%) and Vancouver (-5.0%) have seen declines. Perhaps those Fraser River winds are too cold for warblers.

Methodology

The data includes bird per party hour for the Portland, Olympia, Seattle, Bellingham, and Vancouver BC Christmas Bird Counts from the 75^th count (winter 1975-76) to the 120^th count (winter 2019-20). The 121^st count was impacted by the pandemic.

CBC (and Breeding Bird Survey) data is uniquely advantageous for looking at long-term trends such as climate change, as they both go back many decades with generally similar effort over time (for certain well-established counts). Nevertheless, there were some issues with this data:

I did not use the Portland data from the 76^th thru the 82^nd count, due to aberrantly low party hours relative to later counts.
The following data was missing entirely from the Audubon CBC database: Olympia 76^th, 77^th, 78^th, 84^th, 104^th, and 110^th counts; and Seattle 91^st count.
The following counts had no (or obviously incorrect) data for party hours: Portland 104^th count; Bellingham 111^th, 112^th, and 119^th counts. Because they did have bird numbers, I approximated the party hours based on their counts in nearby years. I used 230 party hours for the Portland count and 200 party hours for the Bellingham counts.

Other climate-related bird changes in the Pacific Northwest

I’ve previously blogged about climate change and birds in the Pacific Northwest:

The invasion of the Pacific Northwest: California’s birds expand north with warmer winters looks at northward range expansions of Great Egret, Turkey Vulture, Red-shouldered Hawk, Anna’s Hummingbird, Black Phoebe, Townsend’s Warbler, and California Scrub-Jay, with some discussion of others as well. Note that Townsend’s Warbler, as a migrant that winters rarely in the PNW, fits with the group of birds described in this post.

The song of the Lesser Goldfinch: Another harbinger of a warming climate looks at increasing records in the PNW in summer.

Mapping the expansion of the California Scrub-Jay into the Pacific Northwest looks at the steady range expansion of this non-migratory species.

References

Hampton, S. 2019. Avian responses to rapid climate change: Examples from the Putah Creek Christmas Bird Count. Central Valley Birds 22(4): 77-89.

Hitch and Leberg. 2007. Breeding distributions of North American bird species moving north as a result of climate change. Conservation Biology 21(2): 534-9.

Illán et al. 2014. Precipitation and winter temperature predict long-term range-scale abundance changes in Western North American birds. Global Change Biology, 20 (11), 3351–3364.

Langham et al 2015. Conservation status of North American birds in the face of future climate change. PLoS ONE 10(9): e0135350.

La Sorte, F.A., and F.R. Thompson III. 2007. Poleward shifts in winter ranges of North American birds. Ecology 88(7):1803–1812.

Paprocki et al. 2014. Regional Distribution Shifts Help Explain Local Changes in Wintering Raptor Abundance: Implications for Interpreting Population Trends. PLoS ONE 9(1): e86814.

Paprocki et al. 2017. Combining migration and wintering counts to enhance understanding of population change in a generalist raptor species, the North American Red-tailed Hawk. The Condor, 119 (1): 98–107.

Prince, K. and B. Zuckerberg. 2016. Climate change in our backyards: the reshuffling of North America’s winter bird communities. Global Change Biology 21(2): 572-585.

Saunders et al. 2022. Unraveling a century of global change impacts on winter bird distributions in the eastern United States. Global Change Biology

Virkkala, R. and A. Lehikoinen 2014. Patterns of climate-induced density shifts of species: poleward shifts faster in northern boreal birds than in southern birds. Global Change Biology 20: 2995–3003.

Wu et al. 2018. Projected avifaunal responses to climate change across the U.S. National Park System. PLOS ONE 13(3): e0190557.

I try to maintain an updated list of references at the Birds and Climate Change Facebook group. At that page, click on Files to find the list.

Mapping the expansion of the California Scrub-Jay into the Pacific Northwest

Posted on October 28, 2021 by Stephen Carr Hampton

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.

California Scrub-Jays are often first detected at bird feeders in suburban areas. As aggressive nest predators, jays should not be subsidized by anthropogenic food sources. In short, please don’t feed the corvids. Port Townsend, WA. April 2021.

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.

CLICK MAP TO ENLARGE

The expansion of the California Scrub-Jay mimics that of several other species, mostly non-migratory or short-distance migrants, rapidly expanding from California and Oregon into the Pacific Northwest.

The jay’s expansion has already surpassed that predicted by the Audubon Society’s climate model under a 3.0 degree Celsius scenario, shown here.

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.

They seem to be particularly taking advantage of warmer winters in the lower Columbia River Basin.

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.

Like most corvids, California Scrub-Jays are big time cachers, storing extra food for future use. I took this photo in southern California, October 2017, when a family of jays were repeatedly stripping an oak, two acorns at a time, flying over a nearby ridge to cache them, and then returning again and again throughout the morning.

Goodbye California: Reminiscences of a climate refugee

Posted on April 4, 2021 by Stephen Carr Hampton

There are a lot of reasons why I’m moving from California to Washington, including family and other personal considerations. But one reason, one big reason, is California’s rapidly changing climate.

It was late February in the Coast Range of northern California when I was wearing shorts and a t-shirt. Dust swirled around my car in the dirt parking lot at Cold Canyon. The car thermometer, warmed by a sun that felt imported from Palm Springs, said 87 degrees; it was actually only 77. A hint of ash, omnipresent since The Fire last summer, remained in the air.

Its oaks torched with little hope of return, Putah Creek Canyon is quickly resembling a sun-scorched canyon in Arizona. Until 2018, only one fire in the area had burned more than 15 square miles. Then the County Fire burned 140 square miles. In 2020, the LNU Complex Fire burned 570 square miles.

The hillsides were green with the new growth of non-native grass, which was responding to a recent heavy rain. That was deceptive. More than half the rain we’d had in the previous eight months came in that single event. We had six inches of rain in all of 2020. Looking beyond the grass, nearly every tree – blue oaks and gray pines – on the hillsides was dead, burnt black and orange monuments to a previous era. For our local blue oak woodland, that era ended last year and, given that recruitment of saplings is unlikely due to heat, fire, and cattle, it was an era that will never return.

Massive die-offs are eliminating blue oaks from the southern third of their range. Black oaks are marching up the Sierra, displacing Ponderosa pine, which are marching up, displacing firs. Everyone is on the move. Oak woodlands are becoming oak savannahs, oak savannahs are becoming grasslands, grasslands are becoming rocky high deserts. Arizonification is happening quickly, thru heat, drought, and ultimately, thru fire.

Virtually all of the east slopes of the Coast Range between San Francisco Bay and the Trinity Alps has burned in the past ten years. In the Sierra, one can practically predict where the next fire catastrophe will happen, because it hasn’t burned yet (hint: Lake Almanor, Placerville, Arnold).

The Fire, the LNU Complex Fire, was part of 2020’s 4.3 million acres of scorched earth. The LNU Fire exceeded the total acreage of all previous fires that impacted my county over the last 50 years combined.

It was a beautiful day—for April. But February has become April, April has become May, and June, July, August, September, and even October and November have become unrecognizable. Every year more heat records are broken. Hottest summer, hottest month, most days over 100, most days over 90. The list goes on, each year breaking the records set the previous year. Weather data is normally highly variable; now it is a straight line—warmer and warmer. And smokier.

My cape honeysuckle and bougainvillea, both planted with a degree of optimism outside their recommended zone, used to die back so badly in the winter that each spring I was tempted to declare them dead and pull them out. Now they bloom year-round, looking like they’re in a courtyard at a hotel in the tropics. We haven’t had a real freeze in seven winters.

The songs of lesser goldfinches on my street are a depressing warning. I can’t take two steps outside without seeing or hearing a bird that reminds me that our climate has seriously changed. Western tanagers, house wrens, and turkey vultures are regular in winter now. The lesser goldfinches have come out of the arid hills and are quickly becoming one of the most ubiquitous nesting birds in Davis. (I know this definitively because one included an imitation of a canyon wren in its song.) What’s more, at least four Say’s phoebes, essentially a high desert species, are scouting for nests in town now. A fifth arrived on my block last week, singing as if on territory. They’ve been doing this for a few years and their numbers are growing.

The graphs of acres burned in California (and in other western states) and the expansion of some bird species into the Pacific Northwest (in this case, Anna’s hummingbirds in winter), are strikingly similar.

I’m leaving. I’ve lived in California fifty-five years but it’s no longer the state I grew up in.

We’re headed to the Olympic Peninsula in Washington. We are fortunate to be able to do so.

Besides the cooler summers, one of the best things about moving to a new place is that I won’t be reminded of climate change on a daily experiential basis. Because the ecosystem will be new to me, I won’t know what’s different, what is changing, except maybe for the brown boobies, a tropical seabird, that are now showing up in Puget Sound each year. Or the family of California scrub-jays that have just established residence on my new street. Like Anna’s hummingbirds, black phoebes, great egrets, red-shouldered hawks, and people like me, scrub-jays are moving north. I expect more of California’s birds to follow me, just as I follow some of them. Yes, lesser goldfinches are coming north too; they’re already established southeast of Tacoma.

I feel like a frog in a boiling pot. I’m getting out. I’m saying goodbye to California, but I feel it has left all of us without saying goodbye to anyone.

The view from Point Wilson, a mile from my new home in Port Townsend, which has had only a few nights below freezing all winter. Climate change is occurring there too, but remains well within temperate ranges.

I do believe that Homo sapiens may ultimately win the climate battle and bring atmospheric CO2 back down to 300 ppm or something. But that’s a hundred years off. And there’s no guarantee we can stop the tide of Greenland and Antarctic ice melt to prevent sea level rise. In the meantime, in the next 50 to 100 years, it’s going to get a lot warmer. And we may ultimately lose New York City, Singapore, Mumbai, and every other low-lying coastal city. My new home is fifty feet above sea level. Well, probably forty-nine and a half now.

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

Posted on March 15, 2021 by Stephen Carr Hampton

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.

UPDATE NOV 2022: eBird released its Trends maps, which illustrate where species have been increasing (blue dots) and decreasing (red dots) between 2007 and 2021. The map for Lesser Goldfinch show exactly what I’ve described above: increasing in around Sacramento and Davis, decreasing in the western foothills (probably due to fires), increasing in Washington, particularly in the Columbia River Basin, and decreasing in the desert Southwest.

The invasion of the Pacific Northwest: California’s birds expand north with warmer winters

Posted on March 9, 2020 by Stephen Carr Hampton

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.

Recent studies

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.

Let’s begin with the climate. Canada as a whole has experienced 3.0C in temperature increases in winter. British Columbia has experienced an average of 3.7C increase in Dec-Feb temperatures since 1948. The greatest increases have been in the far north; increases in southern British Columbia, Washington and Oregon have been closer to 1.5C.

Average nationwide winter temperatures deviation from average.

Great Egret

Great Egrets on Oregon CBCs have increased from near zero to nearly 900 on the 119^th count (December 2018 – January 2019).

CLICK ON GRAPHS TO ENLARGE

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 Vulture

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 Hawk

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.

Anna’s Hummingbird

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.

Black Phoebe

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.

Townsend’s Warbler

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.

California Scrub-Jay

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

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.

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