The _Turdidæ_, with the _Saxicolidæ_ and _Cinclidæ_, form a group
closely related, by common characters, and appreciably different from
the other _Oscines_ with slender bills and specially insectivorous
habits, having, like them, ten primaries (the first much shorter than
the second, but nearly always appreciable), and the nostrils
uncovered. The great family of _Sylvicolidæ_, with similar characters
of the bill, never present more than nine primaries. The most striking
of these common characters is seen in the deeply cleft toes, of which
the outer is united by the basal joint alone to the middle toe, while
the inner is separated almost to the very base of its first joint.[21]
The frontal feathers extend, with rare exceptions, to the very
nostrils. The bill is elongated and subulate, moderately slender, and
usually notched at tip; the culmen moderately curved from the base,
and the mouth well provided with bristles, except in a few cases.
Usually the scutellæ covering the front and sides of the tarsus are
fused into one continuous plate, or else scarcely appreciable, except
on the inner edge only; in the Mocking Thrushes they are, however,
distinctly marked. The lateral toes are nearly equal, the outer rather
the longer. With these as some of the principal characteristics, they
may be distinguished from each other as follows:—
NOTE.—In the present work the length of the tail is measured from the
coccyx, inside of the skin, and not, as usually the case, from the
base of the quills at their insertion. The wings are measured from the
carpal joint, with dividers.
A. Nostrils oval. Loral and frontal feathers with bristly points, or
interspersed with bristles; rictus with longer or shorter bristles.
Saxicolidæ. Wings very long and much pointed, reaching beyond the
middle of the short square or emarginated tail, and one and a half
times or more the length of the latter. The spurious primary very
short, the second quill longer than the fourth. In the closed wing
the outer secondary reaches only about two thirds the length of
longest primary.
Turdidæ. Wings moderate, more rounded, not reaching beyond middle of
the often rounded tail, and not more than one and a third the
latter, usually more nearly equal. Spurious primary sometimes half
the length of second quill; the second quill shorter than the
fourth. In the closed wing the outer secondary reaches three fourths
or more the length of longest primary.
B. Nostrils linear, in lower edge of nasal membrane. Loral and frontal
feathers soft and downy, and no bristles or bristly points whatever
about the mouth.
Cinclidæ. Body very short and broad. Wings short, rounded, and
concave.
The American _Sylviidæ_ are in some respects very closely related to
the _Saxicolidæ_, but may be distinguished by their much smaller size,
more slender and depressed bill, more strongly bristled rictus, etc.;
on which account they are more strictly “fly-catchers,” taking their
prey in great part on the wing.
Of the three families, the _Turdidæ_ contain a great variety of forms,
and exhibit widely different characters, rendering it exceedingly
difficult to arrange them in any systematic or regular sequence, or to
accurately define their boundaries. In the _Birds of North America_,
the Mocking Thrushes were placed among the Wrens, on account of the
distinct tarsal scutellæ, and other characters. We are now, however,
inclined to believe, with Dr. Sclater, that their place is with the
recognized _Turdidæ_; and, among other reasons, on the ground of their
more deeply cleft toes, and greater extension forward of frontal
feathers. The following synopsis of the North American forms will
serve the purpose of determining the genera, even if these are not
arranged or combined in a strictly natural manner.
A. Turdinæ.—Tarsus covered anteriorly with a continuous plate
without scales.
Wings decidedly longer than the tail, which is nearly even.
Bill considerably shorter than the head.
First quill usually not one fourth the second. Wings pointed.
Tarsus hardly the length of head, but yet longer than middle
toe; outstretched toes falling short of tip of tail … _Turdus_.
B. Miminæ.—Tarsi scutellate anteriorly; scales seven.
Wings decidedly longer than the tail, which is nearly even.
Tarsus as long as the head.
Bill decidedly shorter than the head, scarcely notched; wings
pointed; first quill less than half the second, third and
fourth longest. Claws not peculiar. Bristles prominent.
Tarsus considerably longer than middle toe and claw …
_Oreoscoptes_.
Wings decidedly shorter than the tail, which is considerably
graduated; first quill half or more than half the second.
Bill notched at tip, shorter than head; straight.
Scutellæ very distinct; gonys straight, or even declining
at tip.… _Mimus._
Scutellæ more or less obsolete; gonys convex, ascending at
tip.… _Galeoscoptes._
Bill not notched at tip, lengthened; sometimes much decurved.…
_Harporhynchus._
NOTE.—In the Review of American Birds, I., May, 1866, 409, I have
advanced the suggestion that the N. American genus _Myiadestes_,
usually placed under the _Ampelidæ_, really belongs under _Turdidæ_ in
a group _Myiadestinæ_. The relationships are certainly very close, as
is shown by the characters given below.
COMMON CHARACTERS.—Tarsi without regular transverse scutellæ, except
at lower end. Wings acute, pointed, as long as or longer than tail,
which is but slightly graduated. First primary rarely half second,
which exceeds the secondaries. Base of quills buffy yellow, as are
inner edges. Tail spotted or varied at the end. Young birds with many
light spots. Very melodious singers.
Myiadestinæ. Bill short, much depressed; mouth deeply cleft; width at
base about equal to the distance from nostril to tip, or greater;
commissure more than twice distance from nostrils to tip of bill, and
nearly two and a half times length of gonys. Legs weak; tarsi rather
longer than middle toe and claw. Tail feathers tapering slightly from
base to near tip, giving a slightly cuneate appearance to the tail.
Turdinæ. Bill stouter, more lengthened; narrow at base and more
compressed; width at base less than distance from nostril to tip;
commissure not more than twice distance from nostrils to tip of bill,
and about twice length of gonys. Tarsi stouter, longer than middle toe
and claw. Tail feathers widening slightly from base to near tip,
giving a parallel-sided or slightly fan-shaped appearance to the tail.
The _Miminæ_ differ, as already mentioned, in the scutellate tarsi:
more rounded wings, etc.—S. F. B.