An unexpected number of reports of Scott's Oriole brought this
striking species to our attention this last winter. Twenty years
ago there were very few winter records of the species in San Diego
County. Since then, the Borrego Springs and Escondido Christmas
bird counts have revealed it to winter regularly at least locally,
and now our atlas effort is finally giving us a view of the surprising
breadth of Scott's Oriole's distribution. The diversity of places
where the Scott's Orioles have been found wintering, especially
this past winter, has led me to a hypothesis: Scott's Oriole is
not a migrant governed by the calendar in the same way as the Bullock's
and Hooded Orioles, which arrive and depart almost like clockwork
each year. Instead, I propose that the Scott's is a facultative
or opportunistic migrant, more migrating in cold, wet winters,
more staying in mild, dry winters like the last. Possibly, large-scale
climate change is playing a role, warmer weather allowing the birds
to winter farther north than previously. The historic winter range
of Scott's Oriole is not far to the south of usboth A. W.
Anthony and Laurence M. Huey found it in January and February near
San Quintìn, just 150 miles south of Tijuana.
In the winter, Scott's Orioles seem to gather into flocks and
wander in search of food. Several atlas participantsSue and
Jim Berg in Rancho Cuca (F14), Gail and Roger Wynn in Sherilton
Valley (N19)have noticed the orioles raiding the fruits of
prickly pear cacti, then moving on once the supply of fruit is
exhausted. Prickly pear thickets are the habitat for the Scott's
Orioles found annually on the Escondido Christmas bird count on
the grounds of the San Diego Wild Animal Park (J12, J13). They
have been found since the count was inaugurated, as Ken Weaver
points out, suggesting the species has long been a regular if rare
and localized winter visitor. A predilection for prickly pears
explains the late Eleanor Beemer's repeated observations of Scott's
Oriole in Pauma Valley (E12), among the few pre-1980 winter reports
from the coastal slopethickets of prickly pear are prominent
on the steep south-facing slopes at the base of Palomar Mountain.
Another food source for wintering Scott's Orioles is the nectar
of flowering eucalyptus trees, as I noted in north Jamul (R15)
on 1 January 2000. In the Borrego Valley date palms are the prime
habitat, with ornamental trees also frequented. During our desert
blockbuster on 8 and 9 January 2000 we found the birds using native
palm oasesJim Wilson and Phil Nelson had one at Mountain
Palm Springs (O26), Brennan Mulrooney had three at Bow Willow Palms,
and Ann and Tom Keenan had one at Mortero Palms (S29).
Yet the orioles occur in winter in places where it seems there
is little if any food for them at that season, nowhere more so
than on the tops of the Santa Rosa
Mountains, where during our January trip I found three
males in C27 and Lori Hargrove found one in D28 at elevations over
5000 feet. Perhaps the males find it worth it to endure slim pickings
for a few months for the sake of being first in line for reoccupying
prime breeding habitat in the spring.
The atlas effort has improved our knowledge of the breeding distribution
and ecology of Scott's Oriole enormously as well. Rather than inhabiting
a general vegetation community or landscape type, the oriole focuses
on a few species of plants that supply it with specific needs:
yuccas and the Desert Agave. The Mojave Yucca or Spanish Dagger
(Yucca schidigera) is the most important species, being
the primary provider of the fibers with which the oriole builds
its nest. I don't know if the orioles strip the curly fibers fringing
the Mojave Yucca's leaves, in the same way that the Hooded Oriole
strips fibers from a fan palm, but the old leaves of the yucca
decompose into long tough but flexible fibers ideal for weaving.
The Mojave Yucca also offers Scott's Oriole an ideal nesting sitePaul
Jorgensen clued me into the bird's habit of attaching its nest
beneath the crown of the tallest yucca in its territory. Nevertheless,
Scott's Oriole may place its nest in a wide variety of other desert
plantsjuniper, smoketree, jojoba, catclaw acaciaplaced
as high in the shrub as possible while still taking advantage of
the shrub's (often meager) ability to conceal it. The nests last
for months, long after they have been used, so it is quite possible
to confirm Scott's Oriole nesting on the basis of used nests even
in the winter.
The flowers of the Desert Agave (Agave deserti) offer the
Scott's Oriole its best feeding, presumably on both nectar and
insects. Thus desert scrub in which both the yucca and agave are
common constitutes ideal Scott's Oriole breeding habitat. I once
thought of Scott's Oriole as restricted to the high-desert scrub
along the steep east-facing slopes overlooking the Anza-Borrego
Desert. Our atlas effort has shown the species to be much more
widespread, nesting sparsely even on the desert floor where the
plants favoring it are concentrated. Likewise, Scott's Oriole nests
farther west, onto the coastal slope in arid chaparral, where the
Mojave Yucca also grows. If Yucca schidigera is sparse or absent,
a few birds on the edge of their range take advantage of the more
montane Yucca whipplei.
The adult male Scott's Oriole in its stunning yellow and black
dress is nearly unmistakable. Fortunately, the adult males are
so conspicuous that when entering a Scott's Oriole territory you
normally seeor hearthe male first. The song is remarkably
similar to a Western Meadowlark's, with the flutelike notes more
delicately phrased. Perhaps aware of their conspicuousness, the
birds are shy, so scan the shrub tops at a distance before heading
toward the source of the song.
The females and immature males, however, are comparatively drab,
plus highly variable, creating opportunities for confusion. As
in the corresponding plumages of the Hooded, the belly and undertail
coverts are yellow, albeit a darker muted yellow. The back is more
streaked with dusky than in the other orioles, sometimes strongly
so. The greatest variation is in the extent of black on the head.
In both immature males and adult females the black can range from
practically none to covering the whole face and throat. Only the
immature female lacks black on the face or throat consistently.
In adult females, even if the head is entirely greenish, it is
a dusky grayish green, often forming a shadow hood in the pattern
of the male's.
The Hooded and Bullock's Orioles are far more familiar to most
of us, but it may be worth reviewing the females' identifying features.
The female Hooded Oriole is a more uniform paler, yellower greenish,
lacking noticeable streaking on the back. Again, the belly and
undertail coverts are entirely yellowish. Females lack a black
bib, whereas immature males have one in the same pattern as the
adult males. The Hooded's bill is the most notably curved of all
our regular species of oriole.
Female Bullock's Orioles are distinguished by always having whitish
bellies, becoming grayish on the flanks. Their undertail coverts
may be slightly tinged yellow, but there is always wide separation
between the yellow of the breast and that of the undertail coverts.
The females vary greatly in possessing or lacking a small black
bib, smaller than the Hooded's. Their white wingbars are broader
than in the other species, echoing the large white wing patch of
the adult males. The Bullock's Oriole's bill is absolutely straight,
being shaped much like a Brewer's Blackbird's, and deeper at the
base than a Hooded's or a Scott's, giving the head a noticeably
The San Diego County Bird Atlas has revealed interesting details
of the distribution of the Hooded and Bullock's Orioles, too. The
Hooded was an early adapter to urbanization, and the widespread
planting of Washingtonia fan palms has favored them greatly. In
the foothills, the uphill limit of the Hooded Oriole on the coastal
slope appears to coincide with the planting of fan palms, the birds
occurring above 1500 feet elevation only around homes where these
have been used in landscaping. Closer to the coast, however, the
Hooded uses other trees for nest placement, if not for nest materialunder
banana, fig, and dense clumps of eucalyptus leaves. In places it
still uses its original nest site of sycamore trees in natural
habitats, as in San Onofre Canyon in square D4 and along the Sweetwater
River in R15.
Bullock's Oriole exemplifies an interesting pattern of distribution
evident more strongly in several other species such as the Lark
Sparrow and Lazuli Bunting. I might term it "anticoastal"a
distribution extensive over the coastal slope avoiding the coast
itself. We think of the Hooded as the urban oriole par excellence
but a surprising number of Bullock's nest within the city, especially
where sycamores have been used in landscaping, as in Hilltop Park,
Chula Vista (U11). Less frequent is the birds' nesting in urban
eucalyptus trees, as on the grounds of the Educational Cultural
Complex in southeast San Diego (S10).
While Scott's Oriole is now revealed as a regular winter visitor
in the inland regions of San Diego County, it seems to avoid the
coastthough this may be an artifact of the elimination of
cactus thickets with urbanization. Bullock's Oriole, on the other
hand, is a regular though rare winter visitor to urban parks and
lowland riparian woodland.
Perhaps the biggest surprise of our Campo/Boulevard blockbuster
weekend on 22 January 2000 was the Bullock's Oriole at the Crestwood
Ranch in R24 by Ann & Tom Keenan and Jane Larson. There had
been only winter record for San Diego County at so high an elevation,
Mary Beth Stowe's on 16 January 1999 at Banner (K21). Yet it found
another parallel this year, with Clark Mahrdt and Ed Hall discovering
another Bullock's Oriole not far away near Campo in U22. Were these
records symptoms of the mildness and dryness of the last two winters?
The Hooded Oriole, though the most familiar in the summer, is
by far the least likely species to be seen in the winterless
likely, in fact, than the vagrant Orchard and Baltimore Orioles.
It's a pleasure that our three regular orioles, so delightful
to see, can also teach us so much about adaptation to both natural
and man-made environments.
For more about the Santa Rosa Mountains habitat,
please see Exploring the Santa Rosa