A breeder in the high mountains of the West, Cassin’s Finches move to lower elevations in winter, and will sometimes come to bird feeders. Cassin’s Finches are talented vocal mimics, and can imitate songs of other species surprisingly well.
Cassin’s Finches breed in loose groups, although individual nests are usually about 25 yards apart. They are often seen together with Evening Grosbeaks, crossbills, and Pine Siskins, and in the winter they can occur in very large flocks.
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Description of the Cassin’s Finch
The Cassin’s Finch is related to Purple and House Finches and has a thick, pointed bill and brownish upperparts.
Males have a rosy red head, throat, breast, and rump. Length: 6 in. Wingspan: 11 in.
Females are white below, heavily streaked with brown, and lack the red found in males.
Seasonal change in appearance
Similar to adult females.
Cassin’s Finches occur in high elevation coniferous forests.
Primarily seeds, buds, and berries.
Forages in trees, but also on the ground when not covered with snow.
Cassin’s Finches occur in large parts of the western U.S., as well as southwestern Canada and in Mexico. The population has declined in recent decades.
Bent Life History
Visit the Bent Life History for extensive additional information on the Cassin’s Finch.
The shape of a bird’s wing is often an indication of its habits and behavior. Fast flying birds have long, pointed wings. Soaring birds have long, broad wings. Different songbirds will have a slightly different wing shape. Some species look so much alike (Empidonax flycatchers) that scientists sometimes use the length of specific feathers to confirm a species’ identification.
Wing images from the University of Puget Sound, Slater Museum of Natural History
Cassin’s Finches are nomadic, commoner in a given area in some years than others, probably due to changing food supplies.
Cassin’s Finches are sometimes found far to the east of their normal range during the winter months.
The song is a musical warble. Calls include a high, warbled “krdlee”.
The top bill of the House Finch finch is curved, not straight as on the Cassin’s Finch. Sides heavily streaked on the male House Finch. Note gray cheek on the male House Finch.
Female Finch has a very plain face and stronger streaks on the side than female Cassin’s.
The Purple Finch male is more extensively red on the head and upperparts. House Finch males have grayer auriculars and heavily streaked flanks, along with a curved culmen. Female Purple Finches have a bold white eyeline, while female House Finches have blurry rather than crisp streaking on the underparts.
The nest is an open cup of twigs, weeds, and bark strips, usually placed 30-40 feet high in a coniferous tree.
Number: Usually lay 3-6 eggs.
Color: Bluish-green and marked with brown or black.
Incubation and fledging:
The young hatch at about 12-14 days and leave the nest in another 14 days, though continuing to associate with the adults for some time.
Bent Life History of the Cassin’s Finch
Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.
Bent Life History for the Cassin’s Finch – the common name and sub-species reflect the nomenclature in use at the time the description was written.
CARPODACUS CASSINII Baird
Cassin’s finch is a bird of the high, cool, semiarid, coniferous forests of western North America. Locally, its range may overlap that of either the other two species of Carpodxicus found in this general area, the house finch and the California purple finch. However, the house finch generally prefers situations that are lower altitudinally and warmer, while the California purple finch is largely confined to moist, shaded forests at low and middle elevations.
In Tuolumne County, Calif., on June 10, 1950, I made a point of examining an area where both Cassin’s finches and California purple finches occur. During the course of a morning walk just west of Strawberry Lake the purple finch was found to outnumber Cassin’s by about four to one. The elevation was approximately 5,600 feet, and the forest was composed of yellow pine, sugar pine, lodgepole pine, white fir, and incense cedar. On the afternoon of the same day along Herring Creek, 43~ miles to the northeast, at an elevation of about 7,300 feet, California purple finches were absent while Cassin’s finches were numerous. Here the forest consisted largely of lodgepole pine with scatterings of aspen.
Grinnell, Dixon, and Linsdale (1930) make the following comments regarding Cassin’s finch in the Lassen region of California:
This finch was found in loose companies or singly, on the ground or in tree tops, usually in rather open forest growths. Activity of one sort or another was definitely noted in types of trees exemplified by the following: white alders along streamlet, aspen, lodgepole pine, yellow pine, hemlock, small red fir. These trees were used for singing and resting perches and sometimes as foraging places, while a greater share of the foraging for food took place on the ground in clearings or at the edges of forest bordering large meadows *
A review of all the field notes gathered by us leaves the impression that the center of the summer metropolis of this purple finch lies within the red fir belt, in other words, within the Canadian life-zone.
Grinnell (1908) records this species as very common in most of tho higher parts of the San Bernardino Mountains of southern California, between elevations of 5,000 and 10,000 feet.
With regard to Cassin’s finch in Oregon, Gabrielson and Jewett (1940) say: “It is particularly abundant in the Cascades, the Blue Mountains, and the Warner Mountains, where it is a conspicuous element in the avifauna from the yellow pine up to timber line.”
In northwestern Montana, Burleigh (1921) says: “This was a plentiful bird not only toward the tops of the mountains but in the slashings and open woods in the valley.”
Spring: At this season as in fall and winter, these finches tend to stay in flocks, although single individuals are occasionally seen. In certain regions where there has been a downward population movement in the fall, the reverse trend may be noted in March and April. In 1927 James Moffitt (MS.) noted the first Cassin’s finch on the western side of Lake Tahoe, Calif., on March 17. On April 3 another individual was seen and three more on April 7. On the 20th of that month these finches suddenly appeared in numbers and could be considered common a few days later.
Willett (1933) in summing up various published and unpublished records for this species in southern California mentioned Cassin’s finches seen on March 23 in San Diego, up to April 26 in Los Angeles, and May 1 on San Nicholas Island. Such observations, of course, were made in years when these finches underwent unusual population movements during winter and spring in the areas concerned.
Scott (1887) records Apr. 27, 1885, as the latest seasonal date on which this species was observed in the Santa Catalina Mountains of Arizona.
Nesting: The nesting season for this species begins in May, which is rather early for an inhabitant of high montane regions, and extends through July. It is only during these 3 months that Cassin’s finches are not found in flocks. The nests are almost invariably situated in large conifers and usually near the terminal ends of limbs at a considerable height above the ground. Nests are constructed of fine twigs, weed stems, rootlets, and are frequently embellished with lichens. The lining is generally of rootlets and hair, and occasionally shredded bark.
Milton S. Ray (1918) observed a pair of Cassin’s finches building a nest in a tall Jeffrey pine near Bijou at the south end of Lake Tahoe, Calif., on May 14, 1911. He comments that snow was still present on the ground in patches, and winter conditions in general still prevailed. The same author (1912a) referring to this species at Star Lake in the Tahoe region, on June 5, 1910, says: “The most important find on the meadow was a nest of the Cassin Purple Finch (Carpodacua cassini) with three eggs in a state of advanced incubation. The nest was placed on almost the top branch of a pine, about thirty feet up, on the edge of the meadow.”
Grinnell and Storer (1924) write as follows regarding the nesting of this species in the Yosemite region: At Mono Mills on May 17, 1916, an individual was seen finishing a nest 40 feet above ground in the outermost crotch of a pine branch. Near Peregoy Meadow on May 20, 1919, a female was seen to disappear into a dense fir bough 60 feet above the ground. At Ellery Lake, 9,500 feet altitude, on July 6, 1916, a female Cassin Purple Finch was observed feeding fully grown young, while at the same time the members of another pair were engaged in building a nest. A male bird taken in LyclI Cafion on July 23, 1915, had passed the height of the breeding season. It would seem, therefore, that the Cassin Purple Finch here as elsewhere has a long nesting season, beginning in late May and lasting at least until the end of July.
Rowley (1939) makes the following statement: “On July 7, 1930′ near Virginia Lakes [Mono County, Calif.J, Sheffler found a nest about fifty feet up in a lodgepole pine. The nest contained five heavily-incubated eggs (fig. 51), and I found one the next day with two fresh eggs about eight feet up in an aspen. In July 1939, several nests in lodgepole pines near camp at Virginia Lakes contained young about half-grown, except for one that was being built; no eggs were found.” Regarding the nesting of this species in the San Bernardino Mountains, Grinnell (1908) says:
Three nests were found near Dry Lake, 9,000 to 9,200 feet altitude, June 23 and 26, 1906, each containing four eggs. One of the sets was fresh, and the other two were incubated to an advanced stage. As full-grown young were seen in the same locality June 18, 1907, the breeding season must cover at least two and a half months, which is a long period for the Boreal zone. All three nests were in tamarack pines, near the bushy ends of out-stretching branches. They were fortyfive, fifty, and fifteen feet above the ground, respectively. The three nests are so much alike that a description of one will apply to all. Externally it consists of a foundation-work of coarse, dry, crooked weed stems and gooseberry twigs, in this respect something like a tanager’s. But the internal cup is much better formed and deeper. It consists of fine yellow and brownish rootlets and grass stems, with an intermixture of finely slivered plant fibers, probably bark from small stems. The inside diameter of the cup is 2.30 inches, the depth 1.10.
Willett (1933) mentions four slightly incubated eggs collected by W. M. Pierce at Bear Valley, San Bernardino Mountains, on July 10, 1920. In the Lassen Peak region of California, Grinnell, Dixon, and Linsdale (1930) state: “Near Bogard R. S., on June 21, 1929, a female was watched building a nest fifteen meters up in the end of a branch of a large yellow pine at the edge of the meadow. The bird foraged on the ground for nest material.”
Gabrielson and Jewett (1940), referring to this species in Oregon say: “Although the streaked newly fledged young are a familiar sight, the only definite breeding records for the State that have come to our attention are a set of eggs taken May 24, 1924, by Patterson (MS.) and a set of three eggs taken May 25, 1931, near Bly, Klamath County, by Braly.” In northern Humboldt County, Nev., Taylor (1912) states that:
A nest was found June 26 in a Pinu.~ flezilis near the head of Big Creek. The tree itself was surrounded by a grove of quaking aspens. The nest was located five feet from the trunk of the pine on the slender twigs of a branch thirty feet above the ground. Sticks and greenish yellow lichens had been used in its construction. The lining consisted of shreds of bark and sheep’s wool. The structure was rather frail and loosely built. The depth of the cavity was 30 mm. (l~s inches), its diameter 79 mm. (3~j inches). When it was first noted one parent was seen on the nest, but when a close examination of the site was made neither bird was seen. There were five young in the nest.
Johnstone (1949) comments as follows on the nesting of this species in the East Kootenay region of British Columbia: “June 20, 1937, a pair feeding young at Peckham’s lake, nesting high up in a fir tree; July 17, 1946, male feeding young out of nest in Cranbrook; May 7, 1947, a pair carrying nest material into the top of a high fir tree in Cranbrook.”
Eggs: The number of eggs laid by this species ranges from three to six, with four or five comprising the usual set. They are ovate, sometimes tending to either elongated-ovate or short-ovate, and are slightly glossy. The ground color is “pale Niagara green” or “bluish glaucous,” and they are speckled and spotted with “olivaceous black,” “Natal brown,” “bone brown,” “dark olive,” and less frequently with “Carob brown.” On many eggs the very minute spots are so dark that they appear to be black, while others may have larger spots of the shades of brown with undermarkings of “ecru drab.” In general, the spots are more numerous toward the top of the egg, and often form a loose wreath around the large end.
The measurements of 50 eggs average 20.3 by 14.7 millimeters; the eggs showing the four extremes measure ~3.9 by 16.3, 18.5 by 14.8, and 19.2 by 13.4 millimeters.
Young: Mrs. Wheelock (1912) says that 12 days are required for incubation. It seems likely, however, that in some instances this period may extend a day or so longer. So far as known incubation is solely the responsibility of the female, although both parents participate in feeding the young. No information is available as to the length of time the young remain in the nest.
IRay (1912a) records finding a nest containing four fully fledged young on June 5, 1910, at Star Lake in the Tahoe region of California. Grinnell (1908) reports that full grown young were found about Bear Lake on July 31, 1905, in the San Bernardino Mountains and that they were common on Sugarloaf in August. Taylor (1912) ~referring to this species in northern Humboldt County, Nev., says: “Young birds out of the nest were noted as early as the middle of July. Upon their appearance purple finches were very much in evidence on the highest ridges in the mountains (altitudes of 9,000 feet and above). The juvenals kept up a continuous vociferous clatter. A bird would fly from one tree to another and then the other members of the family would follow. Feeding of the young was by regurgitation.”
On Mount Rainier Taylor and Shaw (1927) comment that: “On August 8 a company of adults and young was observed at Glacier Basin, on the northeast side of the park. At this date the immature birds were still being fed by their parents. Young birds were also seen at Sunset Park a month later.”
Judging from the egg dates it appears probable that, in some instances at least, two broods may be reared in a single season. By the end of the nesting season in the middle of summer family groups tend to move temporarily to higher elevations in the mountains.
Plumages: No information is at hand regarding the natal plumage of the Cassin’s finch. Regarding the juvenal plumage Ridgway (1901) says: “Similar to adult female, but streaks on lower parts narrower and less distinct, and wing-edgings more or less ochraceous or buffy.” Two juvenals in the collection of the California Academy of Sciences have the feathers of the back and top of the head with decidedly buffy margins in contrast to the olive-gray tones so characteristic of the adult females. Furthermore, the central streaks on these feathers are black rather than dusky as in the adult female.
The first winter plumage is indistinguishable from that of the adult female plumage. It is acquired by the end of the first summer and retained for a year.
Arvey (1938) has presented some interesting information relating to color changes, seemingly induced by diet in a captive Cassin’s finch. The bird was in the adult red plumage when captured in December. During the succeeding months it was fed on a seed diet until the start of the annual molt, at which time it was noted that the new flight feathers were nearly white. The bird was then given a soft-bill type of food containing animal matter in addition to the seeds, but the additional new flight feathers came in white and the red contour feathers were gradually being replaced by new yellow-colored feathers. Before the molt had been completed, red pyracantha berries were added to the diet with the result that all the flight feathers that came in after this time were normally pigmented, and the remaining old red contour feathers were replaced by new ones that were red, not yellow. A. J. van Rossem (1921) had previously reported an adult male Cassin’s finch that had the red replaced by lemon yellow, taken in Sierra County, Calif.
Food: Throughout most of the year members of this species are vegetarians, living largely on buds, berries, and seeds, particularly those of conifers. No doubt a certain amount of animal food is taken during the nesting season. The birds forage to a large extent on the ground according to Salt (1952).
Grinnell and Storer (1924) offer the following comments on the food of these finches in the Yosemite region: “The feeding habits of the Cassin Purple Finch are like those of the California. It forages either in the tops of the trees or on the ground, rarely feeding in bushes and then only on the outer foliage. Near Tamarack Flat, on May 24, 1919, a male of this species was seen feeding on the urn-like buds of the green manzanita. Young buds of one sort or another, especially needle buds of the coniferous trees, seem to be the preferred food. These and similar tender growths are likely the staple food of the Cassin Purple Finch during the long winter season when the ground is covered with snow.~~ In the Lassen region of California, Grinnell, Dixon, and Linsdale (1930) found the gullet of a bird shot from high in a hemlock to be “filled with the shelled kernels of two kinds of seeds, but no animal matter was detected.” Swarth (1901) records these finches feeding in pepper and willow trees in Los Angeles in April. Arnold (1937) observed a male Cassin’s finch feeding on cotoneaster berries on January 18, 1934, in the Coalinga area of California, and Gander (1929a) records seeing these finches in mixed flocks with California purple finches and house finches feeding on sunflower seeds on the grounds of the San Diego Zoo on Mar. 23, 1927.
Scott (1887) records members of this species feeding on the young buds of cottonwood in the Santa Catalina Mountains of Arizona in winter. Mrs. Bailey (1928) mentions the seeds of yellow pine found in the crop of one Cassin’s finch obtained in the Manzano Mountains of New Mexico. She also mentions that in the Yellowstone these finches had been found eating rock salt spread on the ground for deer. Taylor (1912) records two individuals observed in northern Humboldt County, Nev., feeding in the foliage of a quaking aspen at 7,500 feet. Munro (1950) comments on a juvenal observed feeding on mulberries on August 21 in the Creston region of British Columbia.
Behavior: Except during the nesting season, extending from May to July, members of this species are generally found in flocks. Cassin’s finch, as lloffmann (1927) states, “shares the restlessness of the family, starting for no apparent reason on long flights from one feeding place or perch to another.”
In the Yosemite region Grinnell and Storer (1924) noted “a number of Cassin Purple Finches foraging in company with several Sierra Crossbills and a few California Evening Grosbeaks.” They also add that, “In early summer when nesting duties were engaging their attention, single birds or pairs were seen as a rule; but later, after the broods had been reared, family parties were encountered.” In the San Bernardino Mountains Grinnell (1908) says: “Small companies composed solely of male birds were often met with, feeding in open places among the pines. These bachelor parties were in evidence all through June and July at the same time that other individuals were paired off and occupied with their nests and young.”
Taylor (1912) referring to this species in northern Humboldt County, Nev., observed that “Especially cold mornings seemed to drive the birds to slightly lower altitudes.” He also states that “It was very easy to approach the females and juvenals, but the brightly colored males were more cautious.” In commenting on this species in New Mexico Mrs. Bailey (1928) says: “During the month of October, 1904, when Mr. Gaut found the Cassins quite numerous in the Manzano Mountains, they stayed most of the time in the spruce timber, usually in company with Crossbills. During the middle of the day flocks could always be seen around the springs on the slopes of the mountains.”
Voice: Those familiar with the house finch and purple finch agree that the song of the Cassin’s finch seems to combine the qualities of the songs of both these species yet differs in a manner that is difficult to describe. Grinnell and Storer (1924) write: “The song of the Cassin Purple Finch is more varied than that of either the California Purple Finch or the linnet, yet it reminds one strongly of the linnet’s song. There are full rounded notes and also some ‘squeals’ like those in the song of the linnet. On the other hand Mrs. Wheelock (1912) describes the song of this species as “rich and melodious, of a softer quality than that of the California purple finch, but less varied. Its call-note is a clear ‘cheep.'” Referring to Cassin’s finch in Colorado, Minot (1880) says: “To the northward a common summer resident up to 10,000 feet, often singing from a high perch almost identically with the Eastern bird [probably the eastern purple finch]. May 31, a large flock appeared at Boulder in the fields, feeding on the ground, springing up with a che’-u-we’-u as they flew, and all alighting in one tree, where, in a subdued way, they warbled, or almost twittered, in a confused chorus.” Taylor (1912) records individuals of this species in full song in northem Nevada on June 24: “They continued singing until about the last of July when they became very quiet and correspondingly inconspicuous. Our observations with regard to the singing powers of the young males in the dull plumage of the first winter accord with those of Ridgway (1877), who asserts that they sing almost if not quite as vigorously and sweetly as those in the adult livery. On several occasions purple finches were heard singing while in flight.”
Field marks: The adult male Cassin’s finch can be distinguished readily from the house finch by its larger size, faint rose throat and breast, and by the absence of dusky streaks on the flanks and belly. From the adult male California purple finch it differs in having a much paler rose on the throat and breast and by the fact that the top of the head is crimson and sharply defined from the back of the neck and back which are brown with but a faint rosy tinge.
The female and immature male may be distinguished from the house finch in comparable plumages by larger size and more sharply defined ventral streaking. From the California purple finch in female or immature male plumage Cassin’s finch differs in having less of an olive tinge on the back and more sharply defined streaks on the ventral surface.
Enemies: No doubt the Cassin’s purple finch, like other small passerine birds that frequently forage on the ground, is subject to attack by a number of bird and mammal enemies. Clabaugh (1933) records collecting a pigmy owl with a freshly caught Cassin’s finch in its claws on Aug. 18, 1930, near Hat Creek, Shasta County, Calif. Dixon and Dixon (1938), after listing a number of species of birds, including a pair of Cassin’s finches, that were found nesting within 100 yards of a goshawk nest in Mono County, Calif., wondered “if these nesting birds did not gather there for the protection afforded from other predators which might be driven off by the hawks.”
Late spring and summer storms are undoubtedly a serious hazard to birds of the high mountains. De Greet (1935) records finding a Cassin’s finch frozen to death on her nest and three eggs one morning in the latter part of June, 1934, at Echo Lake in the Tahoe region. There had been a freak snowstorm the night before. Hanford (1913) comments as follows on the effect of heavy rain and hail in midsummer in the central Sierra Nevada at Lake of the Woods: “A mother Cassin Purple Finch continued to feed her young in a nest high up in a hemlock during a few hours of rain; at the first crashing downpour of the hail, the nestlings were silenced and the parent was seen no more.”
Fall: Throughout many parts of the range of this species, especially in the Great Basin region, there appears to be a downward migration after the flocks are formed in fall. Taylor and Shaw (1927) mention a flock of 25 to 50 seen August 21 flying over Mount Ruth (8, 700 feet) in Mount Rainier National Park, Wash. They believed that these birds were either migrating or preparing to do so. A downward movement of Cassin’s finches was noted by van Rossem (1936) in the Charleston Mountains of southern Nevada in the autumn.
Henshaw (1877) comments that this species was not common in September in the Lake Tahoe region of California and that after this month none was seen. It has been the experience of others, however, that during most years a few of these finches regularly remain in this region the year around.
Winter: Although some Cassin’s finches remain in the higher mountains throughout the winter, these birds are frequently encountered in foothill and valley regions at this season. Willett (1933) referring to this species in southwestern California says: “In winter occurs occasionally in foothill country and sometimes straggles down into valleys. Has been recorded by H. Michener (Condor, .~7, 1925: 222) at Pasadena from February 9 to April 7 (1925); by H. S. Swarth (Condor, 3, 1901 :66) at Los Angeles from February 25 to April 26 (1901), and by F. F. Gander (Condor, 31, 1929:131) at San Diego March 23, 1927, and February 25, 1929. Immature male (D. R. Dickey coll.) taken by H. H. Sheldon on San Nicolas Island May 1, 1929.” Barlow (1900) recorded a Cassin’s finch that was shot on Jan. 1, 1896, 5 miles south of San Jose, Calif., where it was found in company with a flock of juncos in a eucalyptus tree.
Johnson, Bryant, and Miller (1948) state: “These finches were present as winter visitants chiefly in the sagebrush: juniper area above 5,000 feet altitude in the Mid Tills section of the Providence Mountains [Californial. In the vicinity of Stott’s house, five miles northeast of Granite Well, they were especially abundant. Solitary individuals and small flocks foraged in pii’ions on rocky hillsides and in junipers on the adjacent fiats. The largest flock, seen on January 2, contained 39 birds. Sometimes these finches perched quietly for long periods in the centers of junipers.”
Taylor and Shaw (1927) state that “In winter the Cassin purple finch is a not infrequent visitor in the valley lands of eastern Washington.” Regarding this species in Oregon, however, Gabrielson and Jewett (1940) comment as follows: “Our field notes and those of other members of the Biological Survey show it to be a regular permanent resident of all of the principal ranges of Oregon, except the Coast Ranges.” In Nevada Linsdale (1936) says that Cassin’s finch is “probably of regular occurrence in the valleys in winter.”
A. J. van Rossem (1936) found this species principally in the pifion belt between 6,000 and 8,000 feet in the Charleston Mountains of southern Nevada in winter. Scott (1887) records a large flock of these finches at Tucson, Ariz., on Feb. 19, 1886.
Range: British Columbia and Alberta to Zacatecas and San Luis Potos!.
Breeding range: The Cassin’s finch breeds from southern interior British Columbia (Stuie, Arrow Lake), southwestern Alberta (Waterton Lakes Park), northwestern, central, and southeastern Montana (Fort Howe in Powder River County), and northern Wyoming (Yelstone Park, Black Hills) south through eastern Washington and Oregon (west to Cascade Mountains) to interior northwestern California (Horse Mountain, South ‘Yolla Bolly Mountain), interior southern California (San Jacinto Mountains), northern Baja California (Sierra San Pedro M~rtir), southern Nevada (Charleston Mountains), northern Arizona (Grand Canyon), and central northern New Mexico (mountains near Taos).
Winter range: Winters from southern British Columbia (Okanagan Landing), northwestern Montana (Missoula), and northwestern and central eastern Wyoming (Teton County, Converse County) south to coastal and southern California (Berkeley, San Nicolas Island, San Diego), and southeastern Arizona (Tucson), and through the highlands of Mexico to Zacatecas (Jerez) and San Luis Potosi (Charcas).
Casual records: Casual east to southeastern Colorado (Fort Lyon), Nebraska (Crawford, Monroe Canyon), and Kansas (Hays), south to Tres Marias Islands, Valley of Mexico, and Veracruz (Orizaba, Mirador in June).
Migration: Early dates of spring arrival are: Idaho: Moscow, March 11 (median of 11 years, April 8). Montana: Libby, February 16 (median of 6 years, April 5). Wyoming: Laramie, February 25 (average of 5 years, April 21); Casper, March 10.
Late dates of spring departure are: New Mexico: Los Alamos, May 15 (median of 7 years, April 25). Colorado: Boulder, May 21. Wyoming: Casper, May 11.
Early dates of fall arrival are: Colorado: Denver, September 8. Arizona: Tucson, October 21. New Mexico: Los Alamos and Silver City, October 5 (median of 5 years at Los Alamos, November 11).
Late dates of fall departure are: Montana: Missoula, October 18; Libby, October 6 (median of 6 years, August 27). Wyoming: Laramie, November 1 (average of 5 years, October 12). Arizona: Nogales, November 12.
Egg dates: British Columbia: 5 records, April 18 to July 15.
California: 70 records, May 29 to July 13; 52 records, June 15 to June 29.
Colorado: 10 records, June 11 to July 10; 5 records, June 20 to June 30.