It was warmer and wetter than present when Oregon first emerged from the ocean during the Eocene. Larger trees included palms, nut trees, and avocados, and large grazing herbivores (rhinoceros-like brontotheres and hippo-like amynodonts) ruled the swamplands, hunted by hyaenadons. Later still, during the Miocene, the climate dried in central Oregon as volcanoes formed a ridge of mountains to the west, blocking some of the damp Pacific weather. Various savanna animals ruled including saber-toothed tigers, pig-like oreodonts, camels, and ancient horses. Metasequoia, the dawn redwood, was abundant. As the Cascades rose, the climate in central Oregon cooled and dried. Among the oak, sycamore, maple, gingko, and elm lived horses, camels, rhinoceroses, bears, dogs, cats, and sloths. Much more recently, but not documented by the older John Day fossils, an ice age came and went, with mammoth fossils in western Oregon. Since then the John Day Fossil Beds area has become a high sage desert and grassland with scattered juniper. Deer, pronghorn, and coyotes are the primary large native animals.
The point is, climate change is not unique to our time. Changes in bird populations have been happening in Oregon ever since it first rose from the sea. When people ask me if I see evidence of climate change or global warming in bird populations here, how can I answer? Bird populations are constantly changing. Bird populations may be changing more quickly now, in the last 50 years, than in the previous 100 years, but data from the reports of naturalists before the 1880's is quite limited. Earlier than that we have a very few fossils that show that some birds remained the same while others have changed.
Even in my own limited lifetime I have seen many changes in bird populations. When I started birding in the 1970's I read the 1940 book Birds of Oregon by Gabrielson and Jewett. I was surprised at all the changes to bird populations that had occurred in the previous 35 years. It is far easier to notice range expansions into new areas than to note gradual decreases in numbers or range reductions.
Most of the changes in bird populations in Oregon are of two kinds: man-caused (both increases and decreases) and expansion of California birds into Oregon due to assumed long-term climate warming. Some of the causes of population changes are obvious (see Bald Eagle and European Starling) while others are complex (Western Bluebird) or unknown (Common Nighthawk). It's almost always more complex than we can know.
Man-caused bird population changes
The activities of man have directly caused extinctions and also increases in and rearrangement of bird populations. The following list includes some notable examples of birds found in the Pacific Northwest whose population change I have noted and is presumed to be primarily man-caused. This list does not include climate change causes, whether man-made or "natural." Such climate-caused bird population changes are noted in a section following this.
Bald Eagle, Peregrine Falcon, Osprey: The year I started birding, 1972, DDT was banned in the United States. It had been used as an insecticide since World War II. The harm to fish-eating birds was obvious. DDT got into the water supply, fish ate contaminated insects, and fish-eating birds ate then-contaminated fish. Top predators like the Peregrine ate other contaminated birds and became contaminated themselves. Egg shells were so thinned by DDT poisoning that they would break when the adults tried to incubate the eggs. The population of these species crashed. It was a red letter day when I would see a Bald Eagle, Peregrine Falcon, or Osprey. These are now common birds in the Pacific Northwest. There are are about 7 Bald Eagle nests within 15 miles of my home now. The populations of these three species are probably higher now than ever in recorded history. Why? In addition to the US DDT ban (DDT is still used to control malaria in some countries) the birds of prey were highly persecuted by man prior to World War II. Concerning the Osprey, Gabrielson and Jewett wrote in 1940: "formerly common,... must now be considered one of the rarer Oregon hawks.... They are killed at every opportunity, both by farmer boys and... sportsmen." Such species now are protected by law and public opinion.
House Finch: I was surprised to learn that House Finches used to be restricted to the drier valleys of SW Oregon and ranches of eastern Oregon and eastern Washington. Now, of course, they are abundant throughout all human-inhabited lowland areas of the Pacific NW, especially in the Willamette Valley and Puget Trough, and to the coast. In the 1953 book, Birds of Washington State (Jewett, Taylor, Shaw, Aldrich) the authors noted that the House Finch was extending its range northward, but still not west of the Cascades. By 1966 the map in the Golden Guide (Birds of North America by Robbins, Bruun, Zim, and Singer) showed House Finch all the way to the coast from southern Canada southward. Evidently, House Finches exploded in western Oregon and Washington in the late 1950's. No doubt they were able to spread so rapidly due to backyard bird feeding growing in popularity along with an increase in the human population of the area.
Anna's Hummingbird: These little California birds began to be a regular part of western Oregon's avifauna in the 1960's. They are now widespread throughout western Oregon and Washington, especially in and near towns. In the local area I noted that they were most common in nurseries near Portland in the late 1980's and spread to the more rural areas of Forest Grove in the 2000's. They are still increasing in population and being found in more and more areas, including away from the immediate residential backyards. They are now found year round along the coast and inland valleys to southern British Columbia, and even in towns immediately east of the Cascades. The first commercial hummingbird feeder in the US was sold in 1923. No doubt the popularity of hummingbird feeding is a significant cause of the increase of this species, along with plantings of winter blooming non-native bushes.
European Starling: Most birders are aware that European Starlings were introduced into New York in the late 1800's and they spread across the continent. However, most birders do not know that there were Starlings released in Portland during the same time period. The Portland releases died out by about 1902. Gabrielson and Jewett wrote in 1940: "Introduced in Portland but now, fortunately, extinct." Well, the birds from New York spread to Oregon in the 1960's. They did, indeed, cause the destruction to the small-fruit industry and other cavity-nesting birds that Gabrielson and Jewett worried about.
Eurasian Collared-Dove: Released or escaped from cages in the Bahamas in the 1970's, made their way to Florida in the 1980's, and spread across the North American continent (primarily west and northwest) to reach Alaska by 2000. One of the fastest spreading non-native birds in North America. It is still increasing and filling in areas it "jumped over" in its rapid spread. Interestingly, they also spread northwest across Europe from Turkey/India/China region in the same manner starting about 1900, reaching the British Isles in the 1950's.
Ring-necked Pheasant, Northern Bobwhite: The pheasants were brought from China in 1880. The Oregon Game Commission raised and released "many thousands" each year by 1940. That practice continued with the Oregon Department of Fish and Wildlife until the 1980's. Since then, fewer pheasants have been released in western Oregon as they didn't do well, and it wasn't cost effective. The damp spring weather, loss of farmland, predation by dogs and cats, all combined to decrease the number of birds successfully breeding in the wild. They were certainly more common in the 1970's than today. In 1967 almost 100,000 pheasants were harvested in western Oregon. Only 2500 pheasants were harvested (shot by hunters) in the Willamette Valley in 2005, out of 65,000 state wide. They still do quite well in the drier lands east of the Cascades, but the number released is far smaller than formerly. Northern Bobwhites were also first released in the 1880's. They did very well, too. In 1940 it could be said "In every county of the Willamette Valley from Multnomah to Lane, the diversified farming practiced there provides conditions suitable for these quail" (Gabrielson and Jewett). Well, after World War II, and especially from the 1960's to today, farming practices changed considerably, and residential areas spread. The last "wild" populations disappeared from eastern Oregon in the 1990's. They were gone in western Oregon by the time I started birding in the early 1970's, though sometimes birds are released to train hunting dogs on Sauvie Island, and escape for a while.
Sharp-tailed Grouse: Gabrielson and Jewett quoted others that this bird was formerly "exceedingly abundant" in the grasslands east of the Cascades in the mid 1800's. However, by the time of writing their book in 1940 they said it was "apparently headed for early extinction" due to hunting and livestock pressure. They were right. The birds were gone by the 1970's. In the 1990's a reintroduction effort began in NE Oregon and some birds are seen occasionally in that area.
Western Bluebird: "Vies with the robin for first rank as a dooryard bird." Wow. In the 1970's when I read those words from 35 years earlier, nothing could have been further from reality. No more is every house a little farmstead suitable for bluebirds. Insecticides since World War II and European Starlings since the 1960's perhaps added to the pressure. A severe winter in the late 1960's caused a population crash in the Willamette Valley when I began birding. Since then, though, bluebird nest box trails have brought back more available nesting cavities and bluebirds are again to be found in the Willamette Valley, though they are not a dooryard bird.
Western Meadowlark, Short-eared Owl, Vesper Sparrow: These grassland species have disappeared as breeders from large portions of the Willamette Valley as farming practices changed to eliminate weedy field edges. Western Meadowlarks were fairly common in the Valley when I started birding in the 1970's, but now have joined the other two in being quite unusual breeders. Even the starlings have forgotten the meadowlarks near Portland; I never hear meadowlarks being mimicked anymore--a previously popular stolen song of the starlings.
Canada Goose, Cackling Goose: In order to get white-cheeked geese to land on several wildlife refuges for hunting and preservation purposes, wildlife managers introduced the mostly non-migratory Western Canada Goose to many areas. Success. More success than they could have imagined. Yes, the populations of Aleutian Cackling Geese and Dusky Canada Geese recovered from the brink of extinction. But the Western Canada Goose is now something of a pest in many areas, behaving more like domestic geese. A significant portion (tens of thousands) of the Ridgway's Cackling Geese now winter in the Willamette Valley rather than flying all the way to the Sacramento Valley as they did 40 years ago.
Marbled Murrelet, Spotted Owl: The timber wars of the 1970's and 1980's pitted the timber industry and related jobs against the requirement of these species for rather large tracts of unbroken old growth forest. In all my 40 years of birding, I've only come across Spotted Owls 3 times without a forest service guide. I volunteered to survey breeding Murrelets one summer in the Oregon Coast Range. My feeling is that the Spotted Owl is a "dead man walking." The remaining old growth is too small and fragmented. My pessimistic guess is that this species will probably be extinct within 50 years (see next species). The murrelet may last a bit longer in the Pacific Northwest, but become quite rare. There are still places where it can be found in good numbers off sandy beaches just beyond the ocean breakers--but for how much longer?
Barred Owl: First recorded in Oregon in 1974. Now an uncommon and increasing permanent resident throughout forested areas of the entire state. Birds followed the fragmented forest openings from the Rocky Mountains of British Columbia southward along the Cascades and Coast Range into California. It displaces, and even kills, the endangered Spotted Owl. Expansion of this species is directly tied to logging of forests.
Brown-headed Cowbird: The Buffalo Bird; it expanded from the Great Plains into the East after forests cut down there. In the West it has expanded following timber cutting and cattle. By the end of the 1800's it reached Eastern Oregon, but was considered "not common" in Oregon by Gabrielson and Jewett in 1940. There were only a few records for western Oregon then. Now it is a very common summer visitor. It is a brood parasite, laying its eggs in the nests of smaller birds such as warblers and flycatchers and making the adoptive parents raise the larger young which starves out the hosts' chicks by eating everything the parents bring to the nest.
Common Nighthawk: This crepuscular insect eating bird has shown a major population crash throughout North America, mirrored by near-extirpation as a breeding bird west of the Cascades in Oregon. In the 1970's when I began birding it was not unusual to see these birds nesting on gravel roofs in towns throughout western Oregon or gravel bars on the Willamette River or on logging landings in the Oregon Coast Range. Now, a couple of migrants are noted each year, but actual breeding birds are noteworthy. The cause(s) of the significant decline is unknown and probably complex. It could be that insecticides have eliminated prey species. Flat gravel roofs are less common now than formerly (no longer use real gravel). American Crows are no longer persecuted (shot) and their population in town is quite high--they would find any nest on flat roofs and eat the eggs. Nighthawks are less common, but still regular around Cascade lakes and in the high desert of central and eastern Oregon. The cause for the population decline is simply not known.
Great Egret: A symbol of bird preservation for the nation. These birds were hunted for their 2 breeding plumes to adorn women's hats. Breeding birds in the Harney basin were slaughtered each year until the Malheur NWR was established. Prior to the plume hunters (1875) there were at least 300 nests. The low point was 2 birds in 1908. Attitudes and fashions changed. Some time in the 1980's birds began wintering west in the Willamette Valley rather than south. In 1940 there was only one record for the Valley, now it is not unusual to see 50-100 birds in marshes around Portland in winter. How long before they start breeding there?
Climate-caused population changes
Most of the species on this list have expanded from California into Oregon in recent years, or small populations in the California-like habitats in the Rogue Valley of SW Oregon have expanded northward through the Willamette Valley. This follows at least a hundred years of general climate warming. One species (Sooty Shearwater) is affected by climate change of the entire Pacific Ocean. More species of seabirds are probably being affected but they are so hard to census off the Oregon coast that determining changes in populations is difficult.
Western Scrub-Jay: Gabrielson and Jewett indicated in 1940 that these jays were represented in the Portland area by scattered pairs and they rarely ventured across the Columbia to Washington state. Now they are abundant in the Portland area. Since I started birding in the 1970's they have expanded to the northern Oregon coast and eastward into towns in central Oregon. They have also expanded northward in Washington state to Olympia and farther. I suppose that the increase in these birds could be connected to expansion of people, but the jay's increase lags human city population so long that more must be involved.
Red-shouldered Hawk: The first modern record of Red-shouldered Hawk was reported in southwestern Oregon in 1971, along the California border. Since then they have become rare, but regular, northward through western Oregon (including the coast) and in western Washington state. When they first appeared they were immature birds coming north in the fall and returning toward California in the spring. But now they breed northward to the central Willamette Valley. Birds are also regular in Klamath area and Harney County. There were reports of Red-shouldered Hawks in the 1880's and 1890's, but Gabrielson and Jewett thought these to be misidentifications. Perhaps these were correct, after all.
White-tailed Kite: Another hawk of California's Central Valley. Gabrielson and Jewett recorded 2 birds for Oregon by 1940. These hawks really increased into SW Oregon in the 1970's and quickly moved north along the coast and to the mid-Willamette Valley and into SW Washington state. The advance seems to have halted by the 1990's, and perhaps they have declined in recent years.
Black Phoebe: Gabrielson and Jewett listed this species as hypothetical in their 1940 book based on unverified reports in the late 1800's. However, there were apparently Black Phoebes in the Rogue Valley beginning in the 1930's. When I began birding in the 1970's birds were found only in three SW Oregon counties--in the Rogue and Umpqua valleys and along the adjacent coastal meadows. Birds began expanding their range much more rapidly in the 2000's, with birds found in coastal marshes and dairy farms the length of the Oregon coast and regularly in the southern Willamette Valley. In my local area west of Portland in the northern Willamette Valley, half of the 10 records for Black Phoebe in the local county have been since 2011.
Wrentit: Formerly (pre-1940's) restricted to the Rogue Valley and immediately along the coast from California to the mouth of the Columbia. Entered the Umpqua Valley and then Willamette Valley to Eugene and expanded north to Corvallis in the 1970's. In the 40 years since I began birding Wrentits in the Willamette Valley have expanded along the east slope of the Coast Range from Corvallis northward about 40 miles to Grand Ronde. Other Willamette Valley birds in recent years have pioneered apparently isolated outposts at Lebanon, Minto Brown Park in Salem, and Troutdale near Portland. The coastal population has apparently not expanded at all in over 100 years. They are found to the Columbia River to Brownsmead, but are not advancing up the river.
Acorn Woodpecker: In 1940 there was only one record for Lane County where Eugene is located. All other records were from the Umpqua and Rogue Valleys to the south. Expanded into the Willamette Valley in the 1960's where common in the southern half to Corvallis and Salem. Isolated colonies in the NW Willamette Valley to Forest Grove. Largely absent north of Salem on the east side of the Willamette Valley. A small isolated colony was present 1960-1990's at The Dalles and across the Columbia River in Washington State.
Elegant Tern: First detected in Oregon following the major El Nino event of 1983 when hundreds invaded coastal waters from the south. They have occurred in about 2/3 of the summers since then. The timing is very strict--primarily only August and September. When they do occur they are often in larger flocks, more common on the southern Oregon coast.
Sooty Shearwater: There are 20 million of these birds in the world. Many migrated past Oregon's shores in the past. In fact, this species graced the cover of a state checklist in the 1970's, likely as it was the most abundant bird in the state. The past 15 years or so have seen a significant reduction in number detected off Oregon and California. Where did they go? It seems changes in ocean currents and temperatures have made them change their migration route.
Franklin's Gull: This species nests in the Harney Basin of SE Oregon. It had never been found in the state up to 1940 when Gabrielson and Jewett wrote Birds of Oregon. Now it breeds commonly at Malheur NWR and a few other locales in the remote alkaline desert lakes of SE Oregon. A bird of the northern Great Plains, mostly nesting on Canadian prairie potholes, but south to the Great Salt Lake.