420SHORTCOMMUNICATIONSROGERS, T. H., JR. 1972.
Northern Rocky Mountain-Intermountain
Regions. Am. Birds 26:783787.
SALT, G. W.
1952. The relation of metabolism
to climate and distribution in three finches of thegenus CaTpodacus. Ecol. Monogr. 22:121-152.
SAUNDERS, A. A.
1921. A distributional list of thebirds’ of Montana.
Pacific Coast Avifauna. No.
14.
SHEA, I). S. 1974. Barred Owl records in western
Montana. Condor 76~222.
SILLOWAY, P. M.
1901.
Summer birds of Flathead
Lake. Bull. Univ. Montana No. 3. Biol. Ser.
No. 1.
SILLOWAY, P. M.
1903. Additional notes to sum-COMMENTS
ON FEEDING
AND VULTURE-MIMICRY
THE

ZONE-TAILEDDALE

A. ZIMMERMAN

HABITSIN

HAWK

That the Zone-tailed Hawk (Buteo albonotatus) is anaggressive mimic of the Turkey Vulture(CathaTtesaura) has been convincingly
suggested by Willis(Condor 65:313-317,1963). Essential to this thesisis the conditioning of vertebrate prey to the benign
presence of the ubiquitous vulture, thus permitting
approach of the predatory hawk to within striking
distance.
Mueller(Condor74:221,1972) believed aerodynamic considerations, not mimicry,
to be responsible for the Zone-tail’s dihedral and manner offlight.
He noted that raptors which habitually fly
near the ground share this design, not only theTurkey Vulture and Zone-tailed Hawk, but also theharriers (Circus spp.). Unfortunately,
we lack information on the relative frequency and importanceof “high” vs. “low” hunting by Buteo albonotatus.
Willis (op. cit.; Condor 67: 104-105)
twice witnessed Colombian Zone-tails pursuing prey, but hefound little informationon the hunting of North
American birds. The few references he cited leave
much to be desired, one of them possibly not referring to Buteo albonotatus at all. Despite several attempts over the past six years I have not succeededin following a Zone-tail from its breeding site to afeeding area. The following account is of a chanceencounter with an individual
actively seeking preyon 3 July 1969.
Driving northwest of Silver City, New Mexico, myattention was drawn to a flying vulture-likebird.
As the time was 08:55 (MountainDaylight Time),
30 to 40 minutes before Turkev Vultures take wing
locally, I stopped and confirmed my suspicion thatthe bird was a Zone-tailed Hawk.
It flew slowly,
15 to 20 m above ground, near some low hills flanking a dry valley several km long and less than 1
km across. Occasionally the bird descended to about
10 m, tilting irregularly as it progressed along thehillsides precisely as do vultures in their regularefforts to detect carrion in this valley.
For 40 minutes the hawk cruised back and forthparallel to the elevated ridges, occasionally returning
to certain favored areas over which it flew re-mer birds of Flathead Lake, with reference toSwan Lake. Bull. Univ. Montana No. 18. Biol.
Ser. No. 6.
SKAAR, P. D.
1969. Birds of the Bozeman latilong.
P. D. Skaar, Bozeman, Montana.
WEYDEMEYER, W.
1927.
Some new birds fromwestern Montana. Condor 39: 159.
WEYDEMEYER, W.
1973.
The spring migration pattern at Fortine, Montana.
Condor 75:400413.
ZIMMERMAN,D. A.
1973.
Range expansion ofAnna’s Hummingbird.
Am. Birds 27:827-835.
Department of Zoology, University of Montana, Missoda, Montana 59801. Accepted for publication 15July 1975.

peatedly.
It concentrated on the bases of the hills,
but neglected neither their summits nor the yuccaand mesquite-studded
valley floor. Once, over thelatter, from a height of about 25 m, the hawk halffolded its wings and plunged
almost vertically(Spermophilus
towarda spotted ground squirrel
It dropped almost to the ground butspilosomus).
swooped upward as the rodent escaped under amesquite.
Following this attempt, the hawk slowly
passed over the valley, hunting continuously.
As it
approached the juniper and oak scrub on the opposite side, it was attacked by a male American
Kestrel (Falco sparverius) which swooped repeatedly,
not striking but coming very close and protesting
vocally. The Zone-tail promptly accelerated and leftthe vicinity, flying just above ground for a shortdistance, then ascending to its usual hunting altitude
of about 25 m. The falcon returned to its perch
after pursuing the hawk for a minute or SO. On themeceding dav I had seen two fledgling kestrels here
kith the; parents. Their presence possibly triggered
the falcon’s aggressive reaction.
During the entire hunting episode the Zone-tailcovered a linear distance of at least 1 km. At 09:40
several Turkey Vultures appeared along the hills.
By then the hawk had climbed to an elevation ofperhaps 200 m over the valley floor, still maintaining
its vulturine
appearance, gliding and occasionallyflapping.
At no time did it flatten its wings. Suddenly, it plummeted
earthward
toward something
invisible to me. Missing again, it came out of its
impressive dive barely above ground-thistime pursued vigorously and vociferously by two Western
Kingbirds ( Tyrannus verticalis) which launched fromsome tall yuccas, one of which held their nest. Afterthe flycatchers returned to their territory, the hawk
remained in view for another ten minutes before
disappearing over the ridge.
It did not join thevultures which were taking advantage of rising warm
air currents near the hills.
Birds and mammals
witnessing
other species’
aggressive reactions toward a Zone-tailed Hawk probably would be alerted and ready for escape. Certainly the attention-attracting
responses of the kingbirds and kestrel cited above should have aroused
most potential avian and mammalian prey in thevicinity.
Such reactions to Zone-tails could be construed as an argument against the efficacy of any
alleged mimicry. On the other hand, these observations do not necessarily indicate recognition of theZone-tailed Hawk as a predator.
Kingbirds com-

SHORTCOMMUNICATIONS

421

monly chase from their territories most kinds of large
predators such as
birds, not only acknowledged
ravens (porous spp.) and raptors, but also inoffensive
herons. Both Western and Cassin’s kingbirds(T.
oociferuns) pursue Turkey Vultures at times. The
kestrel’s reaction may be more significant,for I
often have seen Turkey Vultures flying near kestrels in their nest-trees without eliciting any noticeable reaction. In the same parts of southwestern
New Mexico I have observed these falcons dive repeatedly upon circling Red-tailed and Gray hawks(Buteo jamaicensis and B. nit&s).
I have also
watched a kestrel fiercely attack a flying Black
Hawk (Buteogallus anthracinus),
striking and actually alighting on the latter’s back, apparently biting
forcefully while being transported a considerable distance by the hawk whose aerial agility neverthelessfailed to dislodge the falcon.
One morning I twice saw a low-flying
TurkeyVulture startle a mixed flock of migrant birds resting beside a desert rain-pool near Lordsburg, NewMexico.
The vulture’s
initial appearance promptly
scattered the assemblage; ducks scrambled into thewater, Avocets (Recuroirostruamericana)flew tothe opposite shore, dowitchers ( Limnodromus sp. )became airborne as a unit and circled several times
before realighting.
Ten minutes later a vulture
appeared as before, producing a similar but weakerreaction:
the avocets not taking wing and theducks and dowitchers moving much less than formerly though remaining alert.
Nor do small mammals altogether ignore Turkey

Vultures. Near Tucson, Arizona, where Spermophihs
harrisi and S. tereticaudus were frequent visitors infront of my photographic
blinds, vultures
often
passed overhead. As I would notice their shadowsthe squirrels invariably became alterted. They would
either assume an upright “picket-pin”
position orremain crouched and motionless. Momentary “freezing” also was their usual response to the occasional
Red-tailed Hawk or Common Raven (Corvus corer)that aoneared
overhead. But would such attentive_*ness-merely
being alerted to a vulture’s presencedetract from the mimicry value of a Zone-tailed
Hawk that might appear at rare intervals? In hunting,this uncommon predator often (and I suspect typically) ranges far from its nest. Zone-tails forage
over vast areas and a given populationof preyanimals probably would not encounter them freauentlv. The ground sauirrels I observed invariably
r*emained still \ntil
an; large overhead bird passed
by; but I did not time them, and a split-second’s
difference in a rodent’s reaction time following recognition of a vulture or vulture-mimic
as opposed toan obvious hawk, might be significant.
To beeffective mimicry need not work all of the time.
Although I am inclined to accept Mueller’s premise,
vulture mimicking
by the Zone-tailed
Hawk
remains an intriguing
concept and is deserving of
consideration by field observers.

REMAINSIn April 1970, we, assisted by Robert L. Wisnerand Ronald R. McConnaughey, of Scripps Institution,
discovered four fragments of avian fossils in a small
area of the formation about 30 m from the southeastern tip of what we call “Red Cinder Cone
Point,” where the eastern coastline turns abruptly
southwestward for a very short distance, at 29”OO’50”N., 117”13’1O”W.
(as measured on H. 0. Chart
1688, Survey of 1951; new number N. 0. 21661),
8.0 miles northerly from the southeastern tip of theisland. The bones were taken from well-cemented
material filling some crevices in the rock on a slightbench a little above present high-tide line. Althoughnumerous other exposures of the formation have been
worked, here and elsewhere on the island, no additional fossil bird bones have been found. The specimens being reported are the only fossil vertebrates
known from Isla Guadalupe, which, being an oceanicisland rising from the sea floor, was almost surely
never prehistorically reached by amphibians, or byterrestrial reptiles or mammals.
Considering the conditions of deposition it seems
remarkable that even these fragmentary bird bones
have survived, along with invertebrate fossils typicalof the formation. Only two of the four avian fossils
can be identified. They represent:
Puffinus cf. puffinus opisthomelus.-Distal
22 mmof a right humerus (San Diego Nat. Hist. Mus.
Paleo. ~011s. no. 04294).
The fragment is worn on
the articular surface and is split longitudinally.
The
shaft is flattened and enough remains to indicatethat it represents a small procellariiformbird thesize of Puffinus puffinus opisthomelas.
Endomychuru
cf. E. hypoZeuca.-SDNHM
no.

BIRDS

OF PLEISTOCENEFROMGUADALUPE,CARLISLADEMEXICO

L. HUBBSANDJOSEPH

R. JEHL,JR.

In the course of extensive field work on Isla deGuadalupe,
Hubbs has discovered, and has extensively sampled, a fossil-rich formation that extends intermittently
along “two thirds of the eastern
shoreline (for about 12 miles) and up the west coast
for about 2 miles” . . . . . and “occurs consistently
from one to five meters above present sea level”(Hubbs, in Proc. Symp. Calif. Islands, Santa Barbara
Botanic Garden, 1967). The formation is interpreted
as of Sangamon Interglacial age because two samples
have been isotope dated at about 110,000 and
130,000 yr. BP, and because of the large representation of tropical marine invertebrates:
a tropicalcoral of the genus Pocillopora comprises the bulkof the fossils and there are several tropical gastropods
that are likewise now confined to the warm watersfrom near the mouth of the Gulf of California tonorthern Peru. These tropical elements are intimately
admixed with San Diegan (warm-temperate)fauna1elements. These fossils occur in a calcareous matrix
that has more or less firmly cemented the fine tovery coarse debris that had fallen down the precipitous cliffs, in large part after the material had beenreworked by the moderate wave action of this coastline ( fi%g.1).

Depadmentof Biological Science, WesternNew
Mexico University, Silver City, New Mexico 88061.
Accepted for publication 2 September 1975.