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.”

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

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.

winter temps in Canada.jpg

Average nationwide winter temperatures deviation from average.

Great Egret

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


GREG OR graph.jpg

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.

GREG WA graph.jpg

They have not quite fulfilled the full range predicted for a 1.5C increase, but are quickly on their way there.

GREG maps.jpg

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.

TUVU CBC graph.jpg

TUVU maps.jpg

Red-shouldered Hawk

Red-shouldered Hawks have increased from zero to over 250 inviduals on Oregon CBCs, taking off in the mid-1990s.

RSHA OR graph.jpgTwenty 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.

RSHA WA graph.jpg

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.

RSHA maps.jpg

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.

ANHU CBC graph.jpg

The expansion of the Anna’s Hummingbird has now reached Alaska, where they can be found reliably in winter in ever-increasing numbers.

ANHU AK graph.jpg

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.

ANHU maps.jpg

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.

BLPH OR graph.jpg

With the same 20-year lag of the Red-shouldered Hawk, the Black Phoebe began its invasion of Washington.

BLPH WA graph.jpg

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.

BLPH maps.jpg

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.

TOWA WA OR graph.jpg

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.

TOWA maps.jpg

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.

CASJ maps.jpg

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.

ANHU CBC graph.jpg

Predicting winter irruptions: Correlating Red-breasted Nuthatch, Pine Siskin, and Red Crossbill winter invasions with previous years’ snowfall

I can almost do it; I’m just wrong this year.


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.”

RBNU Davis 10-12-15

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 Jan20-2015

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.

My backyard fountain and the birds that come to it

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: pt-pond

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:


Finally, there is the issue of my house in Davis, which has windows that birds sometimes fly into. See this post about how to prevent birds from flying into your windows. 

I’ve recorded over 40 species using the pond in Davis. Here are some of them.


Wilson’s Warblers


Audubon’s Yellow-rumped Warblers


Myrtle Yellow-rumped Warbler


Nashville Warbler with a Western Tanager


MacGillivray’s Warbler


Black-throated Gray Warbler


Yellow Warbler


Orange-crowned Warbler


Tennessee Warbler– this bird appeared while I was working from home on a conference call. Needless to say, I managed a photo.


Western Tanager


Black-headed Grosbeak with Wilson’s Warbler


Varied Thrush


An unusual strawberry blond Purple Finch in front of a regular one


Hooded Oriole


A White-crowned Sparrow defends a bathing spot from a Western Tanager


Hermit Thrush, typically the last visitor of any winter evening


American Robin and Cedar Waxwing


intergrade Northern Flicker


Spotted Towhee


Slate-colored Junco


Sooty Fox Sparrow in front of a Yellow-rumped Warbler


One more Western Tanager

Not shown: Anna’s Hummingbird, Wild Turkey, Willow Flycatcher, Pacific-slope Flycatcher, California Scrub-Jay, Warbling Vireo, Cassin’s Vireo, Northern Mockingbird, Red-breasted Nuthatch, Ruby-crowned Kinglet, Bushtit, Townsend’s Warbler, Hermit Warbler, House Finch, Cassin’s Finch, American Goldfinch, Lesser Goldfinch, Pine Siskin, California Towhee, Golden-crowned Sparrow, Lincoln’s Sparrow, Song Sparrow, House Sparrow… and probably some others.

Spring Migration in the Central Valley


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:

Hampton, S. 2010. Passerine migration patterns in Davis, Yolo County—2000-2010. Central Valley Bird Club Bulletin 13(3): 45-61.

Last fall, I posted a re-visualization of the data from that paper with regard to fall migration. Here is the spring version.

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).




DavisMigrants2springThe 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.

Two of the nation’s top birding spots threatened by the wall

Of the top 20 birding sites in the entire United States, based on the number of species reported on eBird, six of them are in south Texas. Two of them, Bentsen-Rio Grande Valley State Park and Santa Ana National Wildlife Refuge, are threatened by Trump’s proposed wall.


RG border map

The map above, taken from an excellent article illustrating all of the natural resources at risk from California to Texas, includes the bird totals for the eBird hotspots associated with the at-risk parks and wildlife refuges. The wall is often constructed hundreds of yards north of the actual border (the Rio Grande River). It typically includes a swath of cleared land on each side of it.  At Bentsen and Santa Ana, the wall threatens to destroy critical remaining habitat and strand the parks in “no-man’s land”, preventing public access. Dozens of articles have been written regarding the impacts to everything from butterflies to ocelots.

Sabal Palm is unique, in that the natural area is south of the wall. Visitors pass thru the wall in order to visit the park. However, there is no guarantee this arrangement will be made at other sites. Should public access be denied at Bentsen, the park could revert back to the Bentsen family per a historical agreement. The national wildlife refuges are especially at risk. As they are already federal properties, the Administration doesn’t have to deal with acquiring private property. Thus, they are the easiest places to build.



The decline of Mountain Plovers in two graphs

I live in Yolo County, California, near Sacramento, where Mountain Plovers used to be an annual winter specialty. Searching for “dirt clods with legs”, we used to be able to find dozens of these unique shorebirds, sometimes over a hundred.

Those days are over. They are now “irregular”, meaning we don’t find them every year. We’ve struck out five of the last eleven years. Before that, we averaged a high count of 72 individuals. The first graph, built from records in the Yolo Audubon Society newsletter, emails to the Central Valley Birds listserv, and eBird, shows the high count each winter in Yolo County.



This second graph backs out a bit in space and time, looking at all Mountain Plovers worldwide, starting in 1980. They are a bird of the steppe, breeding mostly on the Great Plains between the Rockies and the flat lands, between the Canadian and Mexican borders. They winter in open country in a vast arc west and south of there, mostly in California, Arizona, New Mexico, and Texas.

MOPL cbc

All the Christmas Bird Counts nationwide, plus Mexico, averaged 728 birds per count thru 1994, but have never hit that mark since. Fewer than 200 individuals have been enumerated six of the last ten years. Adjusted for party hours, the graph basically looks the same.

Why are so many Eurasian Collared-Doves leucistic?

0V2A6850In 2006, I wrote a paper about the spread of the non-native Eurasian Collared-Dove into the Central Valley of California. At that time, there were about 43 records. Now, of course, the species is widespread and common. Quoting from that paper, here’s the backstory of their spread throughout North America:

The Eurasian Collared-Dove was first observed in Florida in the late 1970s. These birds likely originated from an accidental release in the Bahamas in 1974. Since then, their spread has been well documented by Christmas Bird Count and by state bird record committees. By the mid 1990s, the species had been recorded throughout the southeast United States. By 2000, Arizona, Idaho, Oregon, Utah, and Washington had documented records. On the 106th CBC (December 2005 – January 2006), over 30,000 individual birds were reported nationwide, compared to just 560 fifteen years earlier. Their rate of increase has averaged 34% per year.

Today, it seems that in any large aggregation of Eurasian Collared-Doves, there are one or two that are unusually pale, blotched with white and cream. They seem to be about 1% of the population or more, though it’s yet to be studied. These birds bare a strong resemblance to African Collared-Doves, which is generally this pale.  However, based on the dark outer web of the outermost tail feather (see below), as well as size and vocalizations, these birds are clearly leucistic Eurasian Collared-Doves.


EUCD diagram

All of the photos on this page involve the same two darker doves and one pale dove. Above, the tail patterns of the dark dove (left) and pale dove (right) both suggest Eurasian Collared-Dove.  Woodland, California, October 2018.

0V2A6835Many birders suspect this is due to the Founder Effect, a phenomenon that occurs when a small population colonizes a large area. Eventually, all of the birds (or other animal species) are descended from few individuals. In this context, certain recessive traits that were once rare may become more common.

See the Wikipedia account of the Founder Effect for examples of this in human populations.


Here, one of the darker doves is mating with the pale dove.


How to stop birds from flying into your windows

Window strikes kill hundreds of millions of birds each year. It’s a terrible feeling when you’ve set up a feeder just so you can watch the birds and it becomes a death trap, luring birds into food, only to be followed by a sharp “thunk” against your window, resulting in a stunned and sometimes dead bird.


My falcon decals look great from the inside, but they are nearly impossible to see from the outside. Since they don’t move, they don’t attract attention. They did little to stop window strikes.

Here I present one solution from my backyard. The key is something in front of the window that allows the birds to see it and realize what it is. Moving objects, like ribbons that move in the wind, work best. Still objects, like falcon decals and plastic owls, work poorly. Additionally, the maximum range of effect of a window marker is only about 18 inches. I’ve had birds hit my window within 18 inches of the falcon decoy.

Here is my solution, which is quite effective. Tack a shiny ribbon to the top middle of each window, hanging down most of the length of the window.  I had a name brand mylar ribbon designed for the purpose (probably a Father’s Day gift), but any shiny ribbon will probably work. There are other similar brands on Amazon. The key is that it moves in the slightest breeze, reflecting off and revealing the window behind it.


This 8-second video illustrates how the slightest wind moves the ribbons, making the windows apparent. Note the falcon decals are still there, just hard to see.

Finally, here’s a view from inside the house with the ribbons in place. From the inside, they are much less noticeable than the decals. From the outside, it’s a different story.


Another thing to experiment with is the placement of your feeders. I once hung a thistle feeder very near the windows. This resulted in several goldfinch deaths, as they tend to flush from the feeder in a fast direct flight. I moved the feeder back ten feet, which made a huge difference, apparently giving them time to see their options while flushing.