A SECOND HYBRID WILLIAMSON’S X RED-NAPED SAPSUCKER AND AN EVOLUTIONARY HISTORY OF SAPSUCKERS

LESTER L. SHORT

AND JOHN J. MORONY, JR.l

American Museum of Natural History New York, New York 10024

The discovery of a second hybrid between the presence of a red crown patch, and its more Williamsons’ Sapsucker (Sphyrapicus thyroi- extensive red throat. Its crown patch is less deus) and the Red-naped Sapsucker (S. nu- extensive posteriorly than is that of the Red- chulis) is noteworthy because the first re- naped Sapsucker, and it is mixed with (about ported hybrid of these woodpeckers (Ober- one-third) black. The throat patch is unusual holser 1930) was only casually mentioned and in that the red extends farther posteriorly incompletely described. Hybridization be- than in nuchalis, nearly bisecting the black tween these sapsuckers also is interesting in breast band and closely approaching the yel- view of the hybridization among the three low of the lower breast and abdomen. This species (S. varius, S. Tuber, S. nuchalis) com- red area is narrow; if broader and accompa- prising the superspecies Sphyrapicus varius nied by red on the face, it would suggest the (Howell 1952; Short 1969). The hybrid re- influence of S. ruber. The red of the crown ported by Oberholser, a female (Carnegie and throat is orangish (even yellowish), like Museum collection, bearing Cleveland Mu- the throat of variant Williamsons’ Sapsuckers seum no. 10042), was obtained 25 October and not the darker red of nuchalis. Although 1929 at an elevation of 6000 ft in the Hua- approaching thyroideus in most of its color chuca Mountains of Arizona by W. W. Brown. patterns, the hybrid exceeds variation in males We found in the collection of the American of that species, and tends toward nuchalis in Museum of Natural History a male hybrid the following features. A white superciliary (no. 56494) taken by F. Robinette on 1 Janu- line is present and the subocular stripe is ary 1891 at Rancheria de 10sApaches, northern broader. The central rectrices are asymmetri- Chihuahua, M6xico. Both hybrids are adults, cally barred, with threemoderately broadwhite and both resemble the Williamsons’ Sapsucker bars on the inner vane of the left feather, but more closely than they do the Red-naped Sap- only one broad bar on the right feather. The sucker. In contrast to the almost completely bases of these feathers are broadly white. allopatric distribution of the three sapsuckers Males of thyroideus usually have no barring, comprising the S. varius complex, the William- and, if barred, have up to three very narrow sons’ Sapsucker is widely sympatric with the white bars. The black of the breast of the Red-naped Sapsucker and, to a lesser extent, hybrid is less extensive, especially laterally, with the Red-breasted Sapsucker (S. ruber); where it is broken by pale tips of the black it is not sympatric with the Yellow-bellied Sap- feathers. Feathers at the sides of its breast sucker (S. varius). Both hybrids reported have white bars, as in nuchalis, whereas the herein were collected south of the breeding black feathers of this area in thyroidem have ranges of all of the sapsuckers. Both William- gray bars. The hybrid differs especially from sons’ Sapsucker and the Red-naped Sapsucker nuchalis and strongly tends toward thyroid-em regularly winter in southern Arizona and Chi- in its lack of a red nuchal patch, its black back huahua, where the hybrids were found. The (feathers with white bases, as in many thy- Red-breasted Sapsucker is unknown in Mexico, roideus), its broader white wing bar, and its except for Baja California, and it occurs rarely much brighter yellow abdomen. to casually in Arizona ( A.O.U. 1957). In various mensural features (table 1) the male hybrid resembles nuchalis in wing length DESCRIPTION OF THE HYBRIDS and tail length, while its tarsal length and the The male hybrid is similar in appearance to length of its hallux fall within the range of thyroideus. In other features (including some an adult male Williamsons’ Sapsucker. It dif- not listed in table 1) the two species overlap fers most conspicuously in its smaller size, the broadly, and the hybrid falls within the range 1Present address: P.O. Box 898, Alamo, Texas 78516 of overlap. The search for mensural characters The Condor, 72:310-315, 1970 [3101 A HYBRID SAPSUCKER AND SAPSUCKER HISTORY 311

TABLE 1. Comparison of measurements(in mm) of Sphyrupicus nuchalis, S. thyroideus, and their hybrids. ’

s. nuchalis S. thyroideta Character n Range MeaIl Hybrid n Range Mean Males Wing length 25 121-131 126.3 126 133.5 129-140 18 Tail length 24 69.7-78.9 74.5 78.6 83.5 80.4-88.5 17 Gonys length 14 16.0-20.6 17.7 16.7 17.2 16.4-19.1 10 Tarsal length 14 18.8-20.2 19.4 21.7 21.0 19.0-21.0 10 Bill width 13 5.9-6.9 7:: 6.0 5.7 5.4-6.3 8 Hallux length 9 6.8-7.5 6.5 6.4 6.1-6.7 9 Females Wing length 11 123-132 126.9 130 133.4 130-138 12 Tail length 11 74.0-82.5 76.7 78.0 83.5 74.p87.1 9 Gonys length 12 15.2-18.3 17.6 18.5 17.5 15.9-19.5 11 Tarsal length 12 18.0-19.9 19.1 18.8 20.5 19.2-21.5 11 Bill width 9 5.8-6.7 6.1 5.6 5.5 5.2-5.9 9 Bill tip depth 9 0.95-1.10 1.01 0.90 0.87 0.80-0.95 Hallux length 12 6.1-8.3 6.9 5.2 6.1 5.6-6.8 1:

8 Adult males taken December-February, adult females, September-November. All specimens of S. thyroidem repnesentthe racenataliae. Win length is the chord, bill width was taken at the center of the nostrils, bill tip depth is the depth at the tip of the mandible, and %allux length is without the claw. in which the two species did not overlap the wing bar is much more pronounced on clearly indicated to us the great structural one wing than on the other. The hybrids similarity of these distinctively patterned wings are blacker and less heavily barred than woodpeckers. in thyroideus ( Oberholser, op. cit. ) . The inner The female hybrid resembles rather closely secondaries and tertial feathers are barred, but the adult female Williamsons’ Sapsucker, from the barring is not the same on inner and outer which it differs most notably in having a pale vanes as in thyroidem. Rather, the inner vanes red crown patch (paler red than in nuchalis, have broader white bars tending toward the but as extensive, and with some yellowish bar-patches of nuchalis. posteriorly). Otherwise it appears superfi- Underparts. The hybrids throat is tan as in cially to be a small female of thyroideus. How- thyroidem, its breast has a black patch (pres- ever, details of its color pattern show many ent in nuchalis, present or absent in females of tendencies toward nuchalk. These are sum- thyroideus), its sides are barred, and its abdo- marized below. men is pale yellow (as n&&s; paler than Head. As noted by Oberholser ( 1930), the that of any female thyroidem we have seen). head pattern of the hybrid tends toward nu- Subtle tendencies toward nuchalis are evident, chalk in its well-developed red crown patch, other than the color of the abdomen. Lateral and in the faint indication of a superciliary to the black breast patch the barring (a trait stripe and a dark postocular line. The subocu- of thyroideus; nuchalis lacks barring there) is lar region is paler brown than in thyroidms, irregular, and the light interspaces are paler. tending toward the white stripe of nuchalis. Likewise, the flanks and sides are barred, but The hybrid also has its hind-crown posterior the bars tend toward a chevron shape that is to the red patch partially colored black. A characteristic of nuchalk few females of thyroideus have a black area Oberholser (1930) did not compare mea- here, and many are barred in this region (see surements of the hybrid female with the paren- discussion below). As in the male hybrid, a tal species. The female hybrid mensurally red nuchal patch is lacking. (table 1) tends to be intermediate or more Upperparts. The hybrid is barred above, like thyroideus (gonys, bill width, depth of like thyroidms, but the bars tend to be irregu- bill at tip, hallux length) in most measure- lar in shape. The pale interspaces are whiter, ments. The greater overlap in measurements tending toward nuchalis (Oberholser, op. cit.). of females, compared with males, appears due Also the dark bars tend to be narrower in the to female Red-naped Sapsuckers exceeding center of the back and broader to the sides, males in tail length and possibly wing length tending toward the unbarred condition of (see Short, in press, concerning such sex re- feathers in the central back region of nuchulis. versal) . Wing. A moderately broad wing bar is Thus, in color pattern both hybrids tend present, half the size of that found in nuchalis; more toward thyroidem, while in measure- thyroideus females lack a wing bar. However, ments they are intermediate or show a mixture 312 LESTER L. SHORT AND JOHN J. MORONY, JR.

of resemblances to nuchalk and to thyroidem black breast patch which may be quite exten- The male hybrid is clearly in adult plumage. sive. This may represent a vanishing element The female was thought to be an immature of an earlier, blacker, male-like plumage. It bird by Oberholser (op. cit.), but it too is an is certain of these black-breasted females that adult. Immature females of Williamsons’ Sap- exhibit some red in their throats, and show suckers attain full adult plumage well before other male-like attributes. The characteristics late October, when the hybrid was taken. On of four of these specimens are summarized the contrary, immature Red-naped Sapsuckers below. (Two others were seen by Short in do not completely attain their adult plumage the Carnegie Museum and Field Museum of until late fall or winter. Molting immature Natural History collections. ) Red-napecl Sapsuckers can be distinguished 1. Female A.M.N.H. no. 755216, taken 15 from adults by a mixture of barred juvenal April 1921 at Colonia Pacheco, Chihuahua, breast feathers around incoming (adult) black MBxico. This specimen has a nearly complete, feathers in the breast patch area. Adult fe- male-like red throat patch, the red being males retain a black breast patch through the orangish with some yellow traces. Its belly is molt, although incoming feathers are buffy bright yellow as in males and unlike the pale tipped, giving a scaliopeaeffect and tending yellow typical of most females. The breast to obscure the breast patch; they lack barred patch is fully developed and black; the sides (juvenal) feathers on the breast, however. of the throat and malar areas are black with It should be noted that females of the Red- paler edges, and the hind-crown is almost naped Sapsucker are colored like males, al- entirely black, thus tending toward the adult though many show some white at the anterior male plumage. end of the red throat region, which is entirely 2. Female A.M.N.H. no. 363044, taken 5 red in males. Female Williamsons’ Sapsuckers July 1918 at Taos Peak, Colfax County, New are completely different from males, having a Mexico. Three or. four red feathers mark the barred pattern like that of the juvenal female anterior throat of this specimen. This worn- and very like the juvenal plumage of sap- plumaged specimen has a fully black hind- suckers of the S. varius superspecies. crown which connects with black lines extend- The two hybrids are considered to represent ing over the eye suggesting the males’ black a cross between Williamsons’ Sapsucker and orown patch. Its malar region is almost all the Red-naped, rather than the Yellow-bellied black and connects with the black sides of the Sapsucker because the latter is not sympatric throat. The larger black breast patch extends with thyroideus, and, in view of that fact, anteriorly to the white posterior edge of the the occurrence of two separate instances of throat patch, around it to the malar area, and hybridization between Yellow-bellied and Wil- onto the sides, very much as in the adult male. liamsons’ sapsuckers is improbable. The Yel- However, its yellow belly is not unusually low-bellied Sapsucker infrequently reaches bright for a female. Arizona (Phillips et al. 1964:72), and has not 3. Female A.M.N.H. no. 363050, collected been reported from Chihuahua (Miller et al. at Taos Peak, New Mexico, on 13 July 1918. 1957:37). The Red-breasted Sapsucker was This female has red, orange-red, and yellow eliminated from consideration as a possible feathers scattered throughout its throat region. parent by virtue of the hybrids ’ lack of red on It is intermediate between the above two fe- the face, and their tendency toward the chev- males in the extent of black on its breast, sides ron-barred sides of nuchulis rather than the of the throat, malar region, and hind-crown. streaked sides of ruber. Its belly is yellow as in typical females. 4. Female A.M.N.H. no. 755200, taken in VARIANT FEMALE the Chiricahua Mountains, Arizona, on 7 Oc- WILLIAMSONS’ SAPSUCKERS tober 1918. This female has some red traces In addition to the hybrid specimens discussed in its throat, and is the least melanic of all such above, we found several peculiarly plumaged specimens that we have seen. Its breast has only a small black mark, and its crown has female Williamsons’ Sapsuckers. These fe- some black bars (like many other females). males are peculiar in their tendency toward It is otherwise colored like normal females of male plumage in several features. The adult this species. female plumage of the Williamsons’ Sapsucker is especially variable. It is largely like the DISCUSSION juvenal female plumage, and thus resembles The occurrence of these two hybrids, and the the juvenal plumage of other sapsuckers as variation in female Williamsons’ Sapsuckers well. Some females, as noted above, have a described above, are significant with regard A HYBRID SAPSUCKER AND SAPSUCKER HISTORY 313 to the evolution and relationships of the sap- more fully barred sides, abdomen, and under suckers. The genus Sphyrapicus clearly be- tail coverts; and more strongly barred central longs to the melanerpine assemblage of wood- rectrices. Many juveniles have spots on the peckers (Bock and Short, MS) by virtue of its crown and traces of breast barring, and they internal and external morphology and habits, average more barring in the wings and streak- and is a specialized (“sapsucking” habits) ing on the back than do adults. All of these derivative of Melanerpes. Its closest relatives tendencies away from the condition found in probably include the Acorn Woodpecker adult males are toward the condition of these ( Melanerpes formicivorus) and Red-headed features in the juvenal female plumage. The Woodpecker (M. eythrocephalus) group of juvenal female plumage of thyroideus differs the genus Melanerpes. The ancestor of Sphy- little from the juvenal plumage of species of rapicus probably was characterized by: (-1) the varies complex; these juvenal plumages an adult plumage of unknown pattern, but also resemble the juvenal plumage of the Red- resembling somewhat that of the Acorn Wood- headed Woodpecker. pecker; (2) no (or little) sexual dimorphism The distinctive plumages of S. thyroideus in plumage; and (3) a distinct juvenal plum- and the occurrence of two hybrids between age like that of M. erythrocephalus (and thyroideus and nuchalis suggest that thyroid- modern species of the S. varies superspecies). eus is very closely related to the species of Following this view, the divergence of Sphy- the varius complex and that interactions be- rapicus from Melanerpes involved, in addition tween them have affected the evolution of to the evolution of distinctly different habits their distinctive plumages. The Red-naped, ( and related structural modifications), the Red-breasted and Yellow-bellied Sapsuckers evolution of a distinctive head pattern (inci- diverged recently, and are barely specifically dentally, convergent upon the head pattern distinct (Short 1969). Their direct ancestor of various species of Dendrocopos). Species probably evolved in eastern North America as of the S. Darius complex particularly show the an isolate of a once continuous ancestral sap- black (or red) and white head markings, while sucker population; the western isolate evolved adult males of S. thyroideus exhibit them to into S. thyroideus. Both isolates were prob- a somewhat lesser extent. Another develop- ably sexually monomorphic in plumage, but a ment in Sphyrapicus was the evolution of tendency toward sexual dimorphism occurred sexually very distinctive plumages in the an- in both. This tendency may have been em- cestor of S. thyroideus. phasized in thyroideus and suppressed in the We suggest that, among the plumages of western populations of the varius complex, modern species of the genus, the adult male Tuber and nuchalis, as a result of interaction plumage of S. thyroideus, although distinctive, between Tuber and thyroideus and between is closest to that of the melanerpine ancestor nuchalis and thyroideus following their sec- of Sphyrapicus. The location of black in the ondary contact. adult male plumage of thyroideus resembles Simple reversion to a juvenal pattern in that of M. formicivorus, M. cruentatus, and female thyroideus sufficed to bring about a other species of Melanerpes. The restricted distinctive sexual difference in that species. throat patch of males of thyroideus resembles Thus, in thyroideus, visual cues, whatever that found in Xiphidiopicus percussus and their nature, are sufficient for sexual recogni- Melanerpes (Trichopicus) cactorum, two me- tion. The western species of the varius com- lanerpine species. (Such a narrow, brightly plex, S. ruber and S. nuchalis, are sexually colored throat patch is rare in woodpeckers.) monomorphic (the slight sexual difference in The white rump and wing patches, yellow amount of red on the throat in nuchalis does belly, and tendency toward barred central not appear to involve all individuals ), and rectrices in males of thyroideus are other mela- sexual recognition must be based on other nerpine features shared to a greater or lesser (behavioral) differences. The eastern (and extent with species of the S. varius complex. northern) S. varius, allopatric with thyroideus, Juvenal males are colored strikingly like the shows moderate sexual dimorphism (in throat adult male, as emphasized by Swarth (1917: color only). We view the variant thyroideus 64). They differ from adults in having a white females described above as indicative of a instead of a red throat patch. This is not by former male-like plumage in females of the any means the only difference between juve- ancestor of modern S. thyroideus. The slight nal and adult males of thyroideus, for, com- sexual dimorphism or monomorphism in adult pared with adult males, juveniles exhibit plumages of other sapsuckers and of related browner coloration; paler yellow belly color; species of Melanerpes also indicates that the 314 LESTER L. SHORT AND JOHN J. MORONY, JR.

strong dimorphism in thyroideus is a derived nuchalis ever to overlap broadly because each condition. Swarths’ (1917:64) view that the is broadly sympatric with thyroideus, with female plumage of thyroideus is “primitive” is, which interactions, even including hybridiza- in a sense, correct; that is, ancestral sapsuckers tion, are still occurring. It is questionable had a similar plumage, but it was a @venal whether as many as three species of sapsuckers plumage. Reversion to this type of plumage in can coexist, but at any rate this is unlikely to the adult female is a derived condition, unique occur as long as hybridization, however rare, in melanerpine woodpeckers and perhaps in remains possible. the Picidae. It is tempting to suggest that the genes re- The occurrence of strong color (and pre- sponsible for the distinctive male and female sumably behavioral) differences between S. plumages of the Williamsons’ Sapsucker are thyroideus and species of the S. varius com- largely dominant to those of the Red-naped plex, and the occurrence of the two hybrids Sapsucker. Hybrids, even of the F1 type, may discussed above are not the only evidence vary tremendously. Also, there is the remote suggesting that they are still affected by selec- possibility that the two known hybrids repre- tion against their hybridization and interac- sent backcross, rather than F1 hybrids. Rather tion. Although broad sympatry exists between than speculate on the possible dominance of S. thyroideus and S. nuchalis (Rocky’ Moun- thyroideus genes over those of nuchalis, we tain region), and between S. thyroideus and prefer simply to note that thyroideus features S. Tuber ( California to British Columbia), thy- do predominate in the two known hybrids roideus is largely ecologically separated from representing this cross. the other two species. In Nevada, Ridgway SUMMARY (in Bent 1939: 142) found nuchalis “as strictly confined to the aspens as S. thyroideus was to An adult male hybrid Williamsons’ x Red- the pines.” Likewise, Bent ( 1939:156) stated naped Sapsucker from Chihuahua is described, that “all observers seem to agree” that thy- and an adult hybrid female, reported earlier roideus “is confined to the higher elevations by Oberholser ( 1930) as an apparent juvenile, among the pines, in sharp contrast to the is more fully described. Also described are haunts of the red-breasted sapsucker at lower several variant female Williamsons’ Sapsuckers levels among the deciduous trees.” Such eco- which tend toward males in their plumage. logical separation may act as a reproductive The two hybrids and the variant females form isolating mechanism, as well as reducing com- the basis for an hypothesized evolution of the petition between these species, since encoun- genus Sphyrapicus. The major features of the ters between individuals of these species are proposed evolutionary history are: (1) the reduced when they occur in different habitats. evolution of distinctive “sapsucking” habits in Detailed studies of the ecological and behav- a line of melanerpine woodpeckers, the ances- ioral isolating mechanisms operating largely, tor of Sphyrapicus; (2) the evolution of east- if not completely, to prevent the interbreeding ern (ancestor of varius group) and western of thyroideus with nuchalis and ruber would (pre-thyroideus) sapsuckers, both with a pat- be welcome, and they might provide data use- terned face, melanerpine juvenal plumage, and ful for analyses of isolating mechanisms op both sexes colored alike or nearly alike; (3) erating among the species of the varius com- secondary contact of thyroideus and western plex as well. populations of the varius complex resulting in The presence of a closely related but dis- reinforcement of isolating mechanisms, initial tinct species of sapsucker (thyroideus) in sym- hybridization lessening with time, and com- patry with S. ruber and S. nuchalis may be petitive interactions; (4) enhancement of sex- affecting the evolution of reproductive isolat- ual dimorphism in thyroideus (through rever- ing mechanisms and factors promoting re- sion to a juvenal plumage by females), its duced competition among the more recently suppression in ruber and nuchalis, and in- creased ecological separation of the two evolved and interacting species of the S. varius groups; and (5) the evolution of partial iso- complex. For example, S. varius and S. ruber lating mechanisms and secondary contacts ultimately may be able to evolve effective among varius, ruber and nuchalis. The con- isolating mechanisms and come to coexist tinued interaction of thyroideus with ruber broadly north of, but not within, the range and nuchalis may be affecting the course of of S. thyroideus. Or, S. nuchalis and S. varius evolution in relation to feature (5). The hy- ultimately may be able to coexist outside brid sapsuckers discussed in this report tend (north and east) the range of thyroideus. toward the Williamsons’ Sapsucker in appear- Likewise it may be impossible for ruber and ance. A HYBRID SAPSUCKER AND SAPSUCKER HISTORY 315

ACKNOWLEDGMENTS entiation in the Yellow-bellied Sapsucker. Con- dor 54:237-282. This report was the result of research conducted with MILLER, A. H., H. FRIEDMANN, L. GRISCOM, AND R. T. support of the National Science Foundation (grant MOORE. 1957. Distributional check-list of the GB-5891 to Short), to the authorities of which we birds of Mexico. Part II. Pacific Coast Avifauna are grateful. We thank K. C. Parkes for calling to our no. 33. attention the presence of one of the hybrids in the OBERHOLSER, H. C. 1930. Notes on a collection of Carnegie Museum, and Dr. Parkes and E. R. Blake birds from Arizona and New Mexico. Sci. Publ. for facilitating studies by the senior author in the Cleveland Mus. Nat. Hist. 1:83-124. collections under their charge. W. Bock kindly com- FILLIPS, A., J. MARSHALL, AND G. MONSON. 1964. mented on the manuscript, offering helpful sugges- The birds of Arizona. Univ. Arizona Press, tions. Tucson. SHORT, L. L. 1969. Taxonomic aspects of avian LITERATURE CITED hybridization. Auk 86:84-105. SHORT, L. L. In press. Reversed sexual dimorphism AMERICAN ORNITHOLOGISTS ’ UNION. 1957. Check- in tail length and foraging differences in wood- list of North American birds. Fifth ed., A.O.U., peckers. Bird-Banding. Baltimore. SWATH, H. S. 1917. Geographical variation in BENT, A. C. 1939. Life histories of North American Sphyrapicus thyroideus. Condor 19:62-65. woodpeckers. U.S. Natl. Mus., Bull. 174. HOWELL, T. R. 1952. Natural history and differ- Accepted for publication 31 December 1969.