San Diego Natural History Museum--Your Nature Connection[San Diego County Bird Atlas Project]

Focus On...

Purple and Cassin's Finches
fronts of finches, sketch by Nicole Perretta 2001

Underparts of females: Left, Cassin's Finch; right, Purple Finch.
sketch by Nicole Perretta

Backs of finches, sketch by Nicole Perretta 2001

Upperparts of females: Left, Cassin's Finch; right, Purple Finch.
sketch by Nicole Perretta

Heads of finches, sketch by Nicole Perretta

Heads of males: Left, Cassin's Finch; right, Purple Finch.
sketch by Nicole Perretta

The invasion of Cassin's Finches that descended on San Diego County's mountains this winter was, if not the biggest in history, certainly, because of the atlas, the best documented. Purple Finches also invaded, in numbers smaller than those of Cassin's but still larger than in the three previous winters. Sometimes the birds formed mixed flocks and could even be seen in the same binocular field. Thus these easily confused species suggested themselves as subjects for this issue of Wrenderings.

The genus Carpodacus numbers at least 20 species, the males richly colored in shades of red, the females subtly patterned in brown. Unfortunately for us in San Diego, this diversity is centered in the high mountains of Sichuan and Qinghai provinces in western China. Only three of the 20, the Purple, Cassin's, and House Finches, reside in North America. Despite their general similarities, each is quite distinct in shape and voice as much as in plumage; it would not surprise me if a detailed study of relationships in the genus would reveal that each American species is independently derived from an Old World ancestor.

The males of the Purple and Cassin's Finches are readily distinguished from the House Finch by lacking distinct streaking on the flanks and belly, the females by their distinctly streaked heads and pale eye stripes. Distinguishing between the Purple and Cassin's, however, requires attention to finer details. Familiarity with both species helps. This past winter's invasion helped familiarize me with Cassin's enormously, and I hope many of you had the same opportunity

The adult males are perhaps easier to distinguish than the females and first-year males, which resemble the females closely and help explain why "females" outnumber males so lopsidedly. The deep burgundy color of the adult male Purple Finch is rather uniform over its whole head—dark on the crown and ear coverts, somewhat paler in the eye stripe and throat. The cheeks and ear coverts form the most contrasting item on a male Purple Finch's head. The dark red of the crown blends gradually into the streaked back, also heavily tinged red. In Cassin's Finch there is strong contrast between the bright red crown, the pale pastel pink throat and breast, and back streaked in shades of brown only. The ear coverts of the Cassin's contrast less than those of the Purple—the crown is the most contrasting element on a male Cassin's Finch's head. Some guides discuss the variation in the undertail coverts, usually plain in the Purple, streaked in Cassin's. Many Purple Finches, though, do have heavily streaked undertail coverts, while in some Cassin's Finches the streaking may be so fine as to be invisible in the field.

In the females and young males of both species the underparts are heavily streaked. In the Purple Finch, though, this streaking is diffuse, softened by a buffish "halo" around the streaks. In the Cassin's the streaks are crisp. Likewise, on the upperparts, the streaks of the Purple contrast only softly against the comparatively dark background color. In Cassin's, the streaks contrast boldly against a lighter brown background. Here in California we have the advantage that our local subspecies of the Purple Finch, californicus, differs more from Cassin's than the eastern subspecies of the Purple does. Female California Purple Finches have an olive tinge to their upperparts, extending to the edges of their rectrices, lacking in either the eastern Purple or Cassin's, so any olive on one of these finches readily identifies it as a Purple.

In the female Purple Finch, the cheeks are almost uniform dark brown, giving greater contrast to the paler eye stripe. In the female Cassin's Finch, the cheeks are paler but fine dark streaks can be seen within them. The pale eye stripe contrasts less that in the Purple, in part because Cassin's eye stripe contains fine dark streaking. The edges on the wing feathers, too, are whiter and more contrasting in Cassin's, darker brown and so less contrasting in the Purple. Again, a bird lacking streaks on the undertail coverts is a Purple but one having them could be either.

The two species differ noticeably in shape, too. The Purple is a plump bird with comparatively short bill, wings, and tail, recalling many other members of the finch family like the Red Crossbill and Evening Grosbeak. Its bill is more curved and bulbous when viewed from both the side and below. Cassin's Finch has a longer straight-edged bill. Its wings are longer (about 15%) in proportion. The bill of the Purple grades more smoothly into the rounded crown; the bill of Cassin's breaks the outline of the bushier crown abruptly. All these features combine to give the Cassin's a rather slender shape more like that of the sparrows and buntings of the family Emberizidae than of the finches of the family Fringillidae. One female Cassin's Finch I saw this winter gave this impression so strongly I checked the unpatterned notched tail to assure myself the bird wasn't a female Lark Bunting.

The calls of the two species are easily distinguished. The Purple calls a single-noted kip or pip. The call of Cassin's is variably two or three syllabled. Various books express it as kee-up, tee-dee-yip, chidiup, or chidilip. I suggest squeejit or sa-queejit since this conveys intuitively that the emphasis is on the first or middle syllable. At a distance, the calls of Cassin's Finch suggest the twittering calls of the American Goldfinch or Pine Siskin. Along Kitchen Creek at old Highway 80 this winter I heard the call, scanned the treetops expecting to see American Goldfinches, and was surprised by some pink breasts!

Apparently these finches sing only in their breeding ranges, so we do not hear Cassin's song in San Diego County. The Purple's usual song is an even rollicking warble, recognizably related to the song of the House Finch but with almost no variation in pitch or rhythm. Occasionally, though, the Purple Finch switches to a completely dissimilar song—a phrased song maddeningly close to that of Cassin's Vireo.

Map showing winter distribution of Cassin's Finch

Cassin's Finch: Winter records
Black=Maximum daily count 10 or greater
Gray=Maximum daily count fewer than 10

Cassin's Finch nests widely in the western United States at high elevations in arid coniferous forests. It is resident just to the north of us in the San Jacinto and Santa Rosa mountains of Riverside County and just to the south of us in the Sierra San Pedro Mártir of Baja California. The mountains of San Diego County do not rise quite high enough to support Cassin's Finch habitat. Nonetheless, after an invasion year, might some remain to nest near the summits of Hot Springs Mountain or Cuyamaca Peak? An intriguing possibility for another first county nesting record for the atlas' final breeding season!

The invasion of 1975-1976, when up to 103 were counted in a day in the Laguna Mountains, may have been greater than this past winter's invasion. But because of the atlas this year's was far better documented. Cassin's Finch has been recorded on rare occasions near the coast, out to Point Loma, but our results show this winter's invasion clearly focused in the mountains and upper foothills, above about 2600 feet elevation. Though Cassin's Finch is characteristically a bird of pine forest, visitors this winter were found just as readily in oaks and willows. Water rather than vegetation seemed to be the habitat element attracting them.

The distribution of the Purple Finch in San Diego County is more complex. Our breeding population is apparently sedentary, but it is augmented by a variable number of winter visitors, which can spread anywhere from the mountains to the coast. Since the past four winters have seen only modest incursions of Purple Finches (very few in 1997-1998, 1998-1999, 1999-2000), the map of our winter atlas results for this species shows only modest spread outside the breeding range.

The map of our atlas results for the breeding season for the Purple Finch, though, reveals one of the most remarkable discoveries of the whole project. Although before the atlas evidence for nesting of Purple Finches anywhere in San Diego County was essentially nil, this species had long been known as a resident in pine/oak woodland at high elevations on Palomar, Hot Springs, Volcan, Cuyamaca, and Laguna mountains. There had even been a suggestion of their residing at a little lower elevation in the band of black oak and big-cone fir woodland more or less joining Palomar with Volcan, now clearly demonstrated by our results. What is completely new knowledge is the Purple Finch's breeding distribution at low elevations in northwestern San Diego County. In the past four breeding seasons, the species has been recorded at low elevations 69 times in 15 squares from Palomar Mountain west to De Luz and the eastern parts of Camp Pendleton. Numbers in these lowland habitats range up to 10 in a day, as counted by Ken Weaver around De Luz (B6) on 20 June 2000. The Purple Finch has now been confirmed nesting in this region, too—Jim Determan found an occupied nest at Ray Lodge's ranch at the mouth of Castro Canyon in the southwestern corner of square C12 on 30 April 2000. Why should a mountain bird be spreading into lowlands now? Does the extensive planting of avocado orchards in the region make the habitat look more wooded and therefore more attractive on a broad scale, even though the birds are using native oak and riparian woodland? Yet another intriguing question in biology to which our atlas results lead us!

Purple Finch: map of winter records Purple Finch: map of breeding distribution
Purple Finch: Winter records
Black=Maximum daily count 10 or greater
Gray=Maximum daily count fewer than 10
Purple Finch: Breeding distribution
Black=breeding confirmed
Dark gray=breeding probable
Light gray=breeding possible

--Philip Unitt

Focus On ... | Spring 2001 Wrenderings | Bird Atlas Introduction