the result of migration on the part of some of the ancestral stock,
with subsequent loss of regular migration because the need to return
south was lost. Early in development, and before the migrational
tendency was entirely lost, an isolated population, which later became
sedentary, as it was an island population, diverged to give rise to
the Dulinae. The Dulinae are a homogeneous group since on the islands
now inhabited by the birds, they have not been isolated sufficiently
long to produce even well-marked subspecies.
[Illustration: Fig. 49. Hypothetical family tree of the
Bombycillidae.]
The present day _Phainoptila_ is most nearly like the ancestral group,
and the remainder of the Ptilogonatinae have diverged to fit
conditions similar to those to which the Tyrannid flycatchers, which
parallel them, are also fitted.
In comparatively recent geological time, two basic lines developed
from the Bombycilline stock, the future _B. garrula_ and _B.
cedrorum_. Possibly _garrula_ originally was isolated in Europe and
Asia, and later came into contact with _B. cedrorum_, following the
time at which the two species were genetically well differentiated. It
appears certain that _B. japonica_ was an offshoot of the Bombycilline
stock at an early time, since it has characteristics that seem
relatively unspecialized. It possibly was isolated in the Orient.
Structural affinities of _Dulus_ and _Bombycilla_ are more pronounced
than are those of _Dulus_ and _Ptilogonys_, for example. Many of the
structural features of _Dulus_ parallel those of _Phainoptila_, and it
seems likely that the Dulinae were separated early in the history of
the family, perhaps as an isolated offshoot of the early migratory
Bombycillinae.
CONCLUSIONS
Nomenclature, as used by a taxonomist, should of course indicate
affinities as well as apply a name, and the rank of the family should
be applied to a structural unit based on common anatomical characters
that are more fundamental than, in my opinion, are those used by
Ridgway (1904) in proposing family status for the silky flycatchers
and the palm-chats. The characters in the diagnosis (page 478) of the
family Bombycillidae are common features regarded as warranting a
single family unit for the waxwings, silky flycatchers, and
palm-chats. The differences in morphology used by previous workers to
characterize each of these groups: (1) the silky flycatchers; (2)
waxwings and; (3) palm-chats are regarded as more properly characters
of only subfamily rank.
The existing coloration of the species of the Bombycillidae appears to
have been acquired relatively late, geologically speaking. The three
subfamilies responded to ecological stimuli in three different ways,
and the resulting color patterns are unlike in the three groups.
Dulinae to this day have a color pattern that is most like the
ancestral color pattern, and this is recapitulated in the juvenal
plumage of the Bombycillinae before they attain their adult plumage.
Consideration of the geographic distribution of the species of the
family indicates that the center of origin of the family Bombycillidae
was south of the present range of the waxwings (subfamily
Bombycillinae). Waxwings probably are the descendants of a migratory
population that diverged from the primitive population at an early
time in the history of the family. Owing to their adaptations to
survive in the north, waxwings no longer return south in the autumn.
Palm-chats (subfamily Dulinae) are descendants of an isolated
population of the family stock that developed communal living habits
as one specialization. Silky Flycatchers (subfamily Ptilogonatinae)
became modified to catch insects, and have specializations that
roughly parallel those of the Tyrannid flycatchers.
Osteologically, the various species of the Bombycillidae are
remarkably similar. Small variations do exist, but these are primarily
differences in relative size. The modifications of the beak enable
palm-chats to feed on parts of plants, and the beak of _Phainoptila_
shows some similarity in this respect. Rounded wings, which cause a
bird to fly by means of short, relatively weak strokes, are correlated
with a comparatively long humerus, whereas long and pointed wings,
which enable a bird to fly with more powerful strokes of the wing, are
correlated with a relatively short humerus. There is a positive
correlation between a short humerus and a long external condyle, and
between a long humerus and the absence or smallness of the external
condyle.
In the Bombycillidae short bones of the leg are adaptive, and long
bones of the leg are the generalized condition. Although all passerine
birds were differentiated relatively late in geologic time, long hind
limbs still could have been present in the immediate ancestors of
passerine birds. As adaptive radiation took place in the class Aves,
some birds, the Bombycillidae included, became more and more adapted
for an arboreal, and eventually an aerial habitat, with consequent
loss of saltatorial and running ability.
Birds, like mammals, have a short femur, the most proximal element in
the leg, if the species is adapted to run fast. If the species is not
adapted to run fast, birds, unlike mammals, have the tibiotarsus
longer than any of the other elements; in mammals that are not adapted
to run fast, the femur and tibia are approximately the same length. In
non-running birds as compared with running birds, the leg element
distal to the tibiotarsus, and the one proximal to it, are
considerably shortened. In waxwings, all three elements of the hind
limb are shortened, indicating that the reduction in length has been,
evolutionarily speaking, a rapid process, in order to reduce the limbs
to a convenient size as soon as possible.
The shape of the pygostyle varies in the Bombycillidae, but the simple
shieldlike bone of _Phainoptila_ is judged to resemble closely the
ancestral type. In _Ptilogonys_ there is a tall dorsal spine, coupled
with a wide and heavy centrum and flattened lateral areas, for support
of the long rectrices. In _Bombycilla_ the bone is small with knobs on
the centrum that have been developed for muscle attachment.
The muscles were carefully dissected in each genus and in most of the
species. The same homologous muscles are present in all species.
Significant differences were found only in the relative size of
certain muscles. No satisfactorily accurate method of measuring these
differences was found. Consequently, less use was made of the results
of the dissections than was originally planned.
The set of pectoral muscles varies but slightly in relative mass, and
the variation is not considered significant. The deltoid muscle was
selected for measurement since its point of insertion is unusually
variable, while the mass of the muscle varies little. We can conclude
that the extent of the area of insertion of the tendon of a muscle can
determine that muscle's relative efficiency, while the muscle itself
remains the same in bulk.
The muscles of the hind limb are notably larger in species that have
long legs, and a good index of the hopping ability may be gained by
study of certain of these muscles. In the Bombycillidae, and in those
Ptilogonatinae that do not use the hind limbs for hopping, the bones
are shortened, and the associated muscles are correspondingly smaller.
The gross anatomy of the digestive tract is practically identical in
the members of the family. The variability noted is mainly in the
degree of compactness of the visceral mass in _Bombycilla_ and in
_Phainopepla_. Also there is a tendency for the Bombycillinae and the
Dulinae to have the mass situated more posteriorly than it is in the
Ptilogonatinae. Moreover, _Bombycilla_ has a shorter intestine than do
the other genera. All of this indicates that the waxwings
(Bombycillinae) have the center of gravity situated more
advantageously for flight than do the birds of the two other
subfamilies.
SUMMARY
1. The silky flycatchers, waxwings, and palm-chats are included in the
family Bombycillidae; the Ptilogonatidae and Dulidae are reduced to
subfamily rank.
2. The coloration of the birds of each subfamily is different because
the ecological needs are different.
3. Waxwings were at one time regularly migratory, but are now nomadic,
since they are adapted to live in northern latitudes for the entire
year.
4. The corresponding bones in different members of the family closely
resemble one another, and the differences which do exist are the results
of responses within relatively recent times to changes in habits.
5. In the Bombycillidae a rounded wing is judged to be the primitive
condition. As the wing becomes more pointed, the humerus becomes shorter
and its external condyle longer.
6. The hind limbs are short in birds that depend most on flight power,
but are longer and the distal elements are disproportionately longer in
birds that depend on saltation or on running.
7. The pygostyle varies in shape and size between genera and even
between some species.
8. The pectoral muscles differ in size only slightly in the different
members of the family, but the insertions are more extensive for these
muscles in birds that fly a great deal.
9. The muscles of the hind limb vary in mass, but not in kind, in the
members of the family Bombycillidae.
10. In the Bombycillidae that depend on flight power, rather than on
saltation or on running power, there is a tendency for the digestive
tract to become shorter and for the whole visceral mass to become more
compact.
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_Transmitted July 29, 1949._
Mention should be made here of an important paper by Jean Delacour and
Dean Amadon (1949). The Relationships of _Hypocolius_ (Ibis,
91:427-429, plates 19 and 20) which appeared after the present paper
by Arvey was written. Delacour and Amadon stated that _Hypocolius_, a
monotypic Persian genus, should be assigned to the Bombycillidae.
Their conclusions (_op. cit._:429) were as follows: "It might be
advisable to set up three subfamilies in the Bombycillidae, one for
_Bombycilla_, one for _Hypocolius_, and a third for the silky
flycatchers, _Ptilogonys_, _Phainopepla_ and _Phainoptila_. Further
study may show that _Dulus_ can be added as a fourth subfamily.
"Previously the Bombycillidae appeared to be an American group of
which one genus (_Bombycilla_) had reached the Old World. Inclusion of
_Hypocolius_ in the family makes this theory uncertain. Without
obvious affinities to other families, and consisting of a small number
of scattered and rather divergent genera, the Bombycillidae would seem
to be a declining group whose origin cannot safely be deduced from the
distribution of the few existing species."
--Eds.
23-1019
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This series contains contributions from the Museum of Natural History.
Cited as Univ. Kans. Publ., Mus. Nat. Hist.
Vol. 1. 1. The pocket gophers (genus Thomomys) of Utah. By Stephen D.
Durrant. Pp. 1-82, 1 figure in text. August 15, 1946.
2. The systematic status of Eumeces pluvialis Cope, and
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August 15, 1946.
3. The tadpoles of Bufo cognatus Say. By Hobart M. Smith.
Pp. 93-96, 1 figure in text. August 15, 1946.
4. Hybridization between two species of garter snakes.
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5. Selected records of reptiles and amphibians from Kansas.
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6. Kyphosis and other variations in soft-shelled turtles.
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October 6, 1947.
9. Additions to the list of the birds of Louisiana.
By George H. Lowery, Jr. Pp. 177-192. November 7, 1947.
10. A check-list of the birds of Idaho. By M. Dale Arvey.
Pp. 193-216. November 29, 1947.
11. Subspeciation in pocket gophers of Kansas. By Bernardo
Villa-R. and E. Raymond Hall. Pp. 217-236, 2 figures in
text. November 29, 1947.
12. A new bat (genus Myotis) from Mexico. By Walter W. Dalquest
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December 10, 1947.
13. Tadarida femorosacca (Merriam) in Tamaulipas, Mexico.
By Walter W. Dalquest and E. Raymond Hall. Pp. 245-248,
1 figure in text. December 10, 1947.
14. A new pocket gopher (Thomomys) and a new spiny pocket
mouse (Liomys) from Michoacan, Mexico. By E. Raymond Hall
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July 26, 1948.
15. A new hylid frog from eastern Mexico. By Edward H. Taylor.
Pp. 257-264, 1 figure in text. August 16, 1948.
16. A new extinct emydid turtle from the Lower Pliocene of
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August 16, 1948.
17. Pliocene and Pleistocene records of fossil turtles from
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Pp. 281-284, 1 figure in text. August 16, 1948.
18. A new species of heteromyid rodent from the Middle
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August 16, 1948.
19. Speciation in the Brazilian spiny rats (genus Proechimys,
Family Echimyidae). By Joao Moojen. Pp. 301-406,
140 figures in text. December 10, 1948.
20. Three new beavers from Utah. By Stephen D. Durrant and
Harold S. Crane. Pp. 407-417, 7 figures in text.
December 24, 1948.
21. Two new meadow mice from Michoacan, Mexico. By E. Raymond
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