A new intergeneric wood warbler hybrid (Parula americana×Dendroica coronata) (Aves: Fringillidae)

8 Pages·1993·3.5 MB·

by  G R Graves

1
PROC. BIOL. SOC. WASH.
106(2), 1993, pp. 402-409
A NEW INTERGENERIC WOOD WARBLER HYBRID
{PARULA AMERICANA X DENDROICA CORONATA)
(AVES: FRINGILLIDAE)
Gary R. Graves
Abstract.—A new intergeneric wood warbler hybrid {Parula americana x
Dendroica coronatd) is described from a male in first basic plumage taken
during fall migration on the Gulf coast ofFlorida. The hybrid is nearly inter-
mediate between the parental species in plumage pattern and color, but is more
similar to its smaller parent, P. americana, in size and shape.
When Gray's compendium of avian hy- the National Museum of Natural History,
brids was published in 1958, eight hybrid Smithsonian Institution. Measurements of
combinations (according to the latest tax- wingchord, wingtip length (longestprimary
onomy, (American Ornithologists' Union minus longest secondary), tail length (from
1983) had been reported among wood war- point ofinsertion ofcentral rectrices to tip
blers (Fringillidae: Parulinae). Since then the of longest rectrix), tarsus length, and bill
number ofhybrids has more than doubled: length (from anterior edge ofnostril), were
no fewerthan 20 hybrid combinations, nine made with digital calipers to the nearest 0.
ofthem intergeneric, are now known (Bled- mm. Color comparisons were made under
soe 1988, Graves, unpubl.). The purpose of Examolites (Macbeth Corp.).
this paper is to describe a previously unre- Diagnostic assumptions and methods of
ported intergeneric hybrid wood warbler. hybrid diagnosis based on plumage color
The late Henry M. Stevenson collected andpattern andexternalmorphology follow
an unusual hybrid wood warbler on St. Graves (1990). Although the specimen was
George's Island, Franklin County, Rorida, collected in coastal Florida, I considered all
on 24 October 1970. Stevenson's penciled migratory species of wood warblers as po-
notation on the specimen label (Tall Tim- tential parents of the hybrid. The analysis
bers Research Station No. 2881) identified followed a two-step procedure. First, the
it as a hybrid, Parula americana x Den- presumedparental species ofthehybridwere
droica coronata. Here I confirm Stevenson's determined by the comparative analysis of
identification and present a diagnosis ofthe plumage pattern and color. This hypothesis
hybrid specimen. wasthenexaminedwithmorphometricdata.
Concordance of results are interpreted as
Materials and Methods
strong support for the presumed parentage
&
The specimen, sexed as a male, has nar- of the hybrid (see Graves 1990, Graves
rowly pointed rectrices and dull, weakly Zusi 1990).
patterned plumage, indicative of first basic I used principal components analysis
plumage in the Parulinae (Pyle et al. 1987). (PCA) on untransformed variables to re-
I compared itwith series ofimmature males duce dimensionality ofdata andto facilitate
in firstbasic plumage ofall North American the analysis of morphology in two dimen-
species of wood warblers that breed in the sions. Unrotated principal components were
United States and a specimen ofthe hybrid, extracted from correlation matrices (SYS-
Parula americana x Setophaga ruticilla, in TAT).
VOLUME 106, NUMBER 2 403
Fig. 1. Dorsal view ofParula americana (left), a presumed P. americana x D. coronata hybrid (Tall Timbers
Research Station No. 2881), and Dendroica coronata (right).
Results (contrasting tips of the greater and middle
wing coverts); (4) spots on two outermost
Plumage characters.—VromirvQrvXpdiXXQm pairs of rectrices (rectrix 5 and 6); and (5)
elements possessed by the hybrid include: dark streaks on the flanks and sides of the
(1) a semiconcealed coronal patch; (2) short breast. Distinctive color characters of the
superciliaryand subocularspot; (3)wingbars hybrid include: (1) gray dorsal plumage with
404 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig. 2. Lateral view ofParula americana (left), hybridP. americana x D. coronata, andDendroicacoronata
(right) (see Fig. 1).
a triangular olive-brown patch on the man- skin); and (6) brownish-black legs (in dried
tle; (2) pale ventral plumage with a yellow- skin) (Figs. 1-3).
ish wash on the breast; (3) buffy or pale The pool ofpotential parental species can
chestnut spots on breast and sides oflower be quickly reduced by concentrating on
breast; (4) buffy flanks with blackish shaft characters that the hybrid shares with just
streaks; (5) pale lower mandible (in dried a few species. Of the many possible color
VOLUME 106, NUMBER 2 405
Fig. 3. Ventral view ofParulaamericana (left), hybridP. americana x D. coronata. andDendroica coronata
(right) (see Fig. 1).
and plumage characters present in the hy- americana and the largely sedentary P. pi-
brid, only one appears to be synapomorphic tiayumi of southern Texas. Phenotypic ex-
(shared derived)—the olive mantle which pression of this pattern element has also
contrasts with the neutral gray dorsal plum- occurred in other hybrids of P. americana
age. Among the potential parental species {P. americana x Setophaga ruticilla, see
this character is shared only with Parula Burleigh 1944; P. americana x Dendroica
406 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Table 1.—Ranges and means (±one standard de- Table 2.—Factor loadings for the first two principal
viation) ofmeasurements offalljuvenile male Parula componentsfrom analysis ofmalesin firstbasicplum-
americana, Dendroicac. coronata, andthehybrid(Tall age ofParula americana, Dendroica c. coronata, and
Timbers Research Station No. 2881). the hybrid (see Fig. 4).
p. americana D. coronata Principalcomponentaxes
{n = 10) («= 10) Hybrid
Variable I II
Wing chord 55.4-62 .0 66.2-74 .4 64.7
Wing chord 0.96 -0.02
60.1 ± 2.1 70.9 ± 2.5
Wing tip 0.87 0.08
Wing tip 12.1-16.9 15.6-19.8 14.2 Tail 0.94 0.02
14.6 ± 1.9 17.1 ± 1.2 Tarsus 0.78 0.51
Tail 39.9-46 .5 51.0-58.6 44.7 Bill -0.71 0.66
43.4 1 2.0 55.4 ± 2.3 Percent variance
:
Tarsus 16.3-17.9 17.3--19.4 16.3 explained 73.5 13.9
16.9 ± 0.5 18.2 ± 0.7
:
Bill 7.2-•8.2 6.5--7.8 8.0
7.7 ±:0.3 7.1 ± 0.4
^f *: 1 — -• 1 — •*!_ a1
exception of D. coronata, has dark buffy
flanks with blackish shaft streaks. The pre-
dominica, see Haller 1940). Other charac- dominately white throat and restricted dis-
ters of the hybrid that are shared with P. tribution of white tail spots in the hybrid
americana include whitish superciliary and suggest the eastern subspecies, D. c. coro-
subocular spot, yellowish wash across the nata.
breast, small buffy or chestnut spots on the In sum, plumage characters ofthe hybrid
breast and sides of the lower breast, pale can be accounted for by the two most prob-
unmarkedbellyandundertailcoverts, white able parental species, Parula americana and
tail spots (rectrix 5 and 6), well-developed Dendroica coronata (see Appendix). Other
wing bars, and pale lower mandible. pairs of species lack the range of pattern
By a process ofelimination, the remain- elements and plumage colors exhibited by
ing diagnostic characters ofthe hybrid, in- the hybrid and, barring atavism or some
cluding its streaked buffy flanks, concealed unrecognized genetic phenomenon, could
pale coronal spot, and dark legs, must have not have produced the hybrid.
been contributed by the other parental spe- External morphology.—Tht hypothesis
cies. Among wood warblers in first basic of parentage derived from plumage char-
plumage, a well-developed white or yellow acters was tested with an analysis of mor-
coronal spot, similar to that possessed by phological size and shape. Because size and
the hybrid, is present in Dendroica coronata shape characters are presumably controlled
and to a lesser extent in D. fusca and D. by many genes, the mensural dimensions of
cerulea. Dendroicafusca can discarded as a the hybrid are expected to fall within the
parental choice because the hybrid lacks cumulative ranges of parental characters.
traces of the dark yellow or yellowish-or- Four ofthe five measurements ofthe hybrid
ange superciliary and throat found in that fall within the range of those for Parula
species. Several other wood warblers have americana, but all five are outside the rang-
yellow crowns or concealed coronal spots es for Dendroica coronata (Table 1). Thus,
{Vermivora pinus, V. chrysoptera, Dendroi- the hybrid is much more nearly the size and
ca virens, and D. occidentalis) or a central shape of P. americana, the smaller of the
crown stripe {Mniotilta varia) that could po- two presumed parental species. The bill of
tentially produce a hybrid with a semicon- the hybrid is intermediate in structure be-
cealed whitish coronal spot. None of the tween the long, rather slender bill of P.
VOLUME 106, NUMBER 2 407
coronata
D.
2 - americana
P.
<
o
CL
-1
b-o
-2
-2 -1
PCA
Fig. 4. Bivariate plot of factor scores from a principal components analysis of measurements of Parula
americana, Dendroica coronata, and their presumed hybrid (filled circle).
americana and the shorter, wider bill ofD. c. coronata. The breeding ranges of these
coronata. two species overlap extensively from west-
The morphological similarity of the hy- em Minnesota and Ontario east through the
brid to P. americana is further demonstrat- Great Lakes to the northern Appalachians
ed by a principal components analysis (Fig. and the maritime provinces ofCanada.
4, Table 2). Factor scores ofthe hybrid fall
within the envelope of those for P. ameri- Acknowledgments
cana. Under the assumptions used here
(Graves 1990), had the hybrid's factor scores I thank Storrs Olson for bringing the hy-
occurred outside the region ofmultivariate bridto my attention, Todd Engstrom ofTall
space circumscribedbythecombined scores Timbers for loaning it, and Richard Banks,
of the presumed parental species, the P. Ralph Browning, George Hall, and Town
americana x D. coronata hypothesis could Peterson for comments on the manuscript.
have been rejected—provided that the PCA
axes described a large percentage ofthe total Literature Cited
variance and samples ofthe parental species
were large. Although this interpretation American Ornithologists' Union. 1983. Check-list of
North American birds, 6th ed. A.O.U.. Wash-
seems to be confirmed by a few case studies
ington. D.C., 877 pp.
ofavian hybridization (Graves 1988, 1990, Bledsoe, A. H. 1988. A hybrid Oporornis Philadel-
1992), this method has not been tested with phia X Geothlypis trichas, with comments on
large samples ofhybrids ofknown parentage the taxonomic interpretation and evolutionar>
(e.g., Vermivora pinus x V. chrysoptera). significance of intergeneric hybridization.—
Wilson Bulletin 100:1-8.
In conclusion, the parentage ofthe hybrid
Burleigh, T. D. 1944. Description of a new hybrid
can be attributed, with a high degree ofcer- warbler.-Auk 61:291-293.
tainty, to Parula americana and Dendroica Graves,G.R. 1988. EvaluationofKiprm/vora x (9/?o-
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
408
rornis hybrid wood-warblers.—Wilson Bulletin In coronata, the lower back is brownish gray with
100:285-289. darker shaft streaks, the rump is pale yellow, and the
1990. Systematics of the "green-throated upper tail coverts are blackwith broad darkgray mar-
.
sunangels"(Aves:Trochilidae):validtaxaorhy- gins. The lower back, rump and upper tail coverts in
brids?—Proceedingsofthe Biological Societyof americana are gray, faintly tipped with olive yellow.
Washington 103:6-25. The hybrid is intermediate in appearance; the lower
1992. Diagnosis of a hybrid antbird (P/z/^- back is gray with dark shaft streaks; feathers of the
.
gopsis nigromaculata x Phlegopsis erythrop- rump exhibit olive yellow tipping; the upper tail co-
terd) andthe rarityofhybridizationamongsub- verts are black with broad gray margins tinted with
oscines.—Proceedings ofthe Biological Society olive yellow.
ofWashington 105:834-840. The superciliary region ofcoronata is slightly paler
& R. L. Zusi. 1990. An intergeneric hybrid thanthedarkbrowncrown; thebrokeneyeringisbuffy
,
hummingbird{Heliodoxaleadbeateri x Helian- white;theloresandauricularsaredarkbrown;theneck
gelus amethysticollis) from northern Colom- is slightlypaler. In americana, the short superciliary is
bia.-Condor 92:754-760. yellowish white anteriorly, turning white overthe eye;
Gray, A. P. 1958. Bird hybrids. Commonwealth Ag- the subocular spot is white (this and the superciliary
ricultural Bureaux, Bucks, England, 390 pp. form a broken eyering); the lores, auriculars, and neck
Haller, K. W. 1940. A newwood warbler from West are gray. The hybrid is intermediate; the superciliary
Virginia.—Cardinal 5:49-53. and subocular spot are dull white; the lores, auriculars
Pyle,P.,S.N.G. Howell,R.P.Yunick,&D.F. DeSante. and neck are gray (superciliary somewhat obscured in
1987. Identification guide to North American Fig. 2).
passerines. Slate Creek Press, Bolinas, Califor- In coronata, the chin and throat are buffy white; the
nia, 278 pp. breast, sides, and flanks are buffy white to buff" with
dark brown orblack shaft streaks; margins offeathers
at the side ofthe breast are pale yellow; the belly, vent
Department of Vertebrate Zoology, Na- and undertail coverts are white. The chin and throat
ofamericana are yellow; feathers ofthe lower throat
tional Museum ofNatural History, Smith- and pectoral area are dark brown to chestnut brown
sonianInstitution, Washington, D.C. 20560, withyellowmargins; thepectoralareaisborderedpos-
U.S.A. teriorly by an unmarked yellow band; the sides and
ffanks are pale gray suffused with pinkish buff"feathers
that are occasionally tipped faintly with olive yellow;
Appendix
a fewbuff"orchestnut spots occurbelowtheunmarked
Comparative descriptions of the hybrid, Parula yellow breast band; the belly, vent, and undertail co-
americana x Dendroica c. coronata, and its parental verts are white, tinted with olive yellownearthe vent.
species in first basic plumage (males) (see Figs. 1-3). Theventerofthe hybridis somewhatintermediatebut
Thecrown, hindneck, mantle, andscapularso^coro- marked less than either of the parental species. The
nata are dark brown; central crown feathers are sub- chin and throat are white tinted with pale yellow; the
terminally yellow, forming a semiconcealed coronal breast is very pale yellow, some feathers have buffy or
patch; feathersofthemantleand scapularshaveblack- pale chestnut subterminal spots; feathers at the sides
ish shaft streaks. Inamericana, therespectivepartsare ofthebreast(nearthebendofthewinginthespecimen)
gray; feathers of the crown, hindneck, and scapulars have black shaft streaks; the sides and ffanks are buffy
are lightly tippedwith olive yellow; the mantle is dark with dark shaft streaks; the lower breast, abdomen,
olive yellow forming a triangular patch that contrasts vent, andundertailcovertsarewhite; afewbuffy spots
with the adjacent grayish plumage. Crown feathers of occur on the sides ofthe lower breast.
americana lack subterminal spots although the basal Theremigesandwingcovertsaredarkgrayishbrown
portion of the feathers near the rachi are pale. The incoronata;greaterandmiddlewingcovertsarebroad-
respective parts ofthe hybrid are intermediate in ap- lytippedwithbuffywhiteorbuff; outerwebsofremiges
pearance; feathers ofthe crown, hindneck, and scap- are margined with buff" or grayish-brown. In ameri-
ularsaregray, faintlytippedwithbrownish-olive;crown cana, the remiges and wing coverts are gray; greater
featherspossesswhite subterminalspotswith scattered andmiddlewingcovertsarebroadlytippedwithwhite;
yellow barbs; the mantle, which contrasts noticeably remiges have olive-tinted gray margins. The remiges
with the adjacent grayishplumage, exhibits a contrast- andwingcoverts ofthe hybrid are nearlyintermediate
ingpatchofpaleolivebrownplumagewithfaintdarker in color and pattern.
shaft streaks (contrast between the gray hindneck and Rectrices ofcoronata are dark brown with progres-
olive mantle ofP. americana and the hybrid appears sively larger white spots on the inner webs ofrectrix
indistinct in Fig. 1). four, five, and six. In americana, the white area on
VOLUME NUMBER
106, 2 409
rectrix fouris limited to a thin stripe along the margin skins). In americana, thebillisyellowish-brown, darker
ofthe inner web. The tail pattern ofthe hybrid is in- near the nostrils and along the culmen. Bill color of
termediate: rectrix fouris similarto that oiamericana, thehybridis intermediate. Legcoloris blackish-brown
while the two outer pairs ofrectrices (5 & 6) are nearly in coronata and the hybrid and medium brown in
identical to those ofcoronata. americana.
The bill o{coronata is dark brownish black (in dried