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Home , Melospiza, Sierra Madre sparrow, Song sparrow

ON THE , XENOSPIZA BAILEYI, OF

ROBERTW. DICKERMAN,ALLAN R. PHILLIPS, AND DWAIN W. WARNER

THE SierraMadre or Bailey'sSparrow, Xenospiza baileyi, was described as a new and speciesfrom the high mountainsof and Jaliscoless than 35 yearsago (O. Bangs,Proc. •VewEngland Zool. Cl., 12: 85-88, 1931). It has sincebeen consideredrare, and even 19 years ago, when F. A. Pitelka (Condor, 49: 199-203, 1947) describeda new ,only 11 specimenswere known, of whichhe had at handonly 1 from La Cima, Distrito Federal, and 3 from westernMexico. Today the populationfrom the sacatonbunch grass areas of La Cima, in the pass betweenthe Valleyof Mexicoand Cuernavaca,is well representedby series in the collectionsof Phillips and the University of Minnesota Museum of Natural History. These seriesinclude specimens in all the plumage stagesfrom stubby-tailedjuveniles to worn adults and those having recently completedthe prebasicmolt. Other specimensare scattered through several museumsin the United States. The populationof Du- rangois now representedby additionalspecimens in the collectionof the Robert T. Moore Laboratoryof Zoology,Occidental College. With the accumulationof this material,and notesfrom severalseasons' field work by the authors,it is a propitioustime to gather togetherthe information on this restricted endemic Mexican sparrow.

ACI•N'OWLEDGEM. Ei•TS We wish to expressour appreciation to the curators of the following collections for permitting us to examine materials in their care: American Museum of Natural History, ; Denver Museum of Natural History; Museum of Comparative Zoology, Harvard College, Cambridge, Massachusetts; Robert T. Moore Collection, Occidental College, Los Angeles, ; and Museum of Vertebrate Zoology, University of California, Berkeley, California. Eugene Eisenmann critically read the manuscript, and the diagram of generic relationships was largely developed during Dickerman's conversations with him.

TAXONOMIC AND MORPHOLOGICAL CONSIr)ERATIONS North American ornithologistshave long used the convenient terms "sharp-tailedsparrows" and "grassland-nestingsparrows" to denotespecies currently in the genera Passerculus,Ammodramus, Passerherbulus, and Ammospiza.I If thesefour generawere to be combinedthey would take the name Ammodramus. In comparisonwith these, for the sake of con-

XA review of the close relationshipswithin this complex is being presentedelse- where as will also be a description of a Passerculus sandwichensisX Am- modramus savannarum.

49 The Auk, 84: 49-60. January, 1967 50 DICKER3/rAIgET.dL., Xenospiza baileyi [ Vol.Auk 84 1967Jan. ] DICKERlWANETAL., Xenospiza baileyi 51 veniencein this discussion,we use the term "brushland-nestingsparrows" for the closelyrelated speciesnow in the generaPasserella, , Zonotrichia,and .runco.L. L. Shortand S. W. Simon(Condor 67: 438- 442, 1965) haverecently presented the evidenceof the relationshipswithin this group with the tentative suggestionthat the generabe all combined and the bear name .runco. In namingXenospiza baileft sierrae,Pitelka (op. cit.) comparedhis April specimenwith three comparablyplumaged specimens of the north- western population Xenospiza b. baileft, from and Durango. He characterizedthe sierrae as: a number having blacker, broader spots on the breast,with a medialcluster as in Melospizamelodia; the malar streak blacker and more prominent; the streakingson the sides of the belly blacker; the sidesof the head grayer; the crown blacker with narrower brown feather margins; and the bill blacker dorsally. He thought that sierraewas composedof larger than was the northern population. In the presentstudy we have comparedin detail 17 specimensof sierrae, includingthe type, with 7 specimensof baileft, includingthe type. In worn specimens,we found completeoverlap in all characterscited by Pitelka. The breast spotsof somesierrae are less well developedthan in baileft (taking wear into consideration). The specimensof the latter form ex- aminedin detail have more or lesswell developedconcentrations of breast spots,whereas three of the sierraehave no central concentrationof black. The malar stripeson at least three sierraeare lesswell developedthan in baileft. Dorsally,sierrae averages slightly darker russetbrown, less richly colored,with slightly moreextensive central black areasof the back feathers; there is, however,much overlap. The russetbrown of the interscapular area of the type of sierraeis actually slightly paler than it is in the type of baileft. The crownsand sidesof the headsare not appreciablydifferent in the worn series. There are no differences in the color of the bills in dried specimens,nor are there significantsize differences (Table 1). Specimensof Xenospiza are grossly reminiscentof some forms of Melospiza,and Pitelka (op. cit.) wrote that a surveyof somegeneric char- actersamong the sparrowswhich had been linked with Xenospiza in the literature causedhim to doubt that Xenospizashould be segregatedas a distinct genus. He thought that is was closelyrelated to Melospiza and that it waspossibly a memberof that genus.However, Pitelka usedchar- actersof adult externalmorphology, such as wing and bill size and pro- portionsand extent of ventral streaking,which are notoriouslyvariable even intraspecificallyamong certain North Americansparrows. We think that the followingdata on the nest,eggs, juvenal and freshbasic (autumn) plumages,song, and behaviorprovide a more reliable basisfor evaluating the systematicrelationships of this elusivesparrow. 52 DICKERI•,IANET,4L., Xenospiza baileyi [ Vol.Auk 84

Figure 1. N•ting of Xenos•za b•Iey•, n•r La Cima, Mexico, D. F., 25 July 1•57. 196•Jan. ] DICKERMANEr -•L., Xenospiza baileyi 53

Figure 2. Nest and young of Xenospiza baileyi, near La Cima, Mexico, D. F., 25 July 1957. 54 DICKEIC3,iAI•ETAL., Xenospiza baileyi [ Vol.Auk 84

I-IABITAT,NEST, AND EGGS The habitat (Figure 1) of Xenospigais a primaryassociation of medium and tall bunchgrasses, Epicampes macrura, Festuca amplisima, Stipa icku, and Muklenbergiaa]finis, interspersedwith park-like standsof Pinus montegu•naeon the ridgesand knolls. Bushesare absentin the grassland areas. In the periodsince 1954, when Phillips and Warner first collected in the La Cima area, a largeportion of the tillable area of this habitat has beenplowed and destroyedas nestingcover. Approximately25 to 35 per cent of the habitat visitedby the authorshas been destroyedin this time span. The fields are usedas feedingareas by the birds to a varying degree during the year. The gizzardof one adult taken 20 Novembercontained a fine gravel, small Coleopteraof the family Tenebrionidae,and the re- mainsof a smallspider. Our knowledgeof the nestof Xenospizabailyei dates from 12 July 1954, whenWarner discovered an adult at a thick-walled,unlined cup nest, near, but not on, the groundbetween elumps of bunchgrasses. On 25 July 1957, Warner and Dickermanobserved adults feedingyoung severaldays old in a nest in a similar location(Figure 2). This nest was later collected. On 15 September1961, Phillipsand Dickermanfound an abandonednest

Figure 3. Two nestsof Xenospizabaileyi, collected at La Cima, Mexico, D. F., 31 July 1962. The nest on the right was abandoned. 1967Jan. ] Dxc•c•a•^•ET AL., Xenospiza baileyi 55

containingone punctured egg, in the middle of a clump of bunch grass about a foot above the ground level, and on 31 July 1962 they collected an adult femalewith her nest and three slightly incubatedeggs. This nest was located in a clump of low grassesclose to the ground betweenlarger bunch grasses.In the edge of a clump of bunch grasswithin six feet of this active nest,Phillips found anothernest, abandoned,of the . The outer shells of the four nests which were collected are constructed of moderatelycoarse grass with a few forbs (Figure 3). The nestsare lined with fine grassand grassrootlets, and small amountsof horsehair. When fresh, these nests measured: cup diameter, 55 to 70 mm; cup depth,42 to 48; outsidediameter, 100 to 115; outsidedepth, 85 to 95. The foureggs measured 19.3 X 14.2, 20.0 X 14.5,20.1 • 14.6,and 20.6 X 14.5 mm, the first three being in the same nest. The three slightlyincubated eggs are pale greenishblue in color,be- tween,but palerthan Pale Nile Blueand Etain Blueof R. Ridgway(Color standardsand colornomenclature, Washington, D.C., 1912); the fourth eggfrom the abandonednest is muchfaded. The eggshave fine spotsand flecks,burnt umberto blackishin color,in a wreatharound the larger end with occasionalspots scattered over the entire sh'ell. The eggsof Xenospizaresemble those of all the North Americansharp-tailed, grass- land nestingsparrows in havingdark, nearly black, spotting,in contrast to the reddishspotting of the eggsof all speciesof the brushlandnesting sparrowsin whichthe eggsare spotted.However, the eggsof noneof the other grasslandsparrows have a blue-greenground color, whereas this is occasionallyfound in the brushland-nestinggroup.

JUVENALPLUMAGE Juvenilesof the specieswere first collectedby Warner and Phillips in June, 1954. We now have 10 specimensin juvenal plumage. Stubby-tailed youngwere taken 13 Juneand 4 August. Young taken 3 Septemberranged from birds with fresh, little-worn juvenal plumage to others well into the first prebasicmolt with their interscapularareas largely in the first basic plumage. The juvenal plumage, like the basic plumage, is, upon grossexamination, similar to the correspondingplumages of Melospiza. However, detailed examinationreveals this to be, in our opinion, a mis- leadingimpression. On analysisthis plumage,wh'en not worn or faded, presentscloser similarities to the grasslandnesting sparrows. Ventrally, juvenal Xenospizaare weakly and variably streakedin a band acrossthe breastand along the sidesof the throat and breast, much as are many young Emberizinae (Figure 4). The streakstend to concentrateinto a submalarstreak in someindividuals. The underpartshave a warm, pale buffy cast throughout, similar to that of juvenal Henslow's Sparrows 56 DICKERMANET AL., Xenospizabaileyi [ Auk [ Vol. 84

(Passerherbulushenslowii) and (Nelson's)Sharp-tailed Sparrows (Am- mospizacaudacuta nelsoni). This fades and wears rapidly, but evenyoung whichare worn retain a creamycast below rather than becoming whitish, as do youngof the Juncocomplex which are worn. The flanksand undertail covertsare a deeperbuff thanthe breastand belly regions. Dorsally,a stubby-tailedjuvenal (ARPoriginal no. 3486) is super- ficiallysimilar in generalappearance to a stubby-tailedjuvenal Lincoln's Sparrow,Melospiza lincolnii, from Apache County, , but is darker. In contrast,a full-grown,unworn, juvenal-plumaged Xenospiza is approxi- matelyintermediate in dorsalpattern between juvenal Passerculus sand- wichensisbrunnescens (Savannah Sparrows) and Passerherbulus henslowii, thoughslightly darker than either; it is quite distinctfrom a comparably agedM. lincolnii. JuvenalXenospiza have broad, central,black, shaft streaksabove; thoseare edgedwith' olive brown to olive buff, richer on the scapularsand interscapulars,and grayeron the nape,but exhibiting considerableindividual variation. The edgesof the tertialsand remigesare ochraceousbrown. Crownstripes are not well differentiated.The super- ciliary line is rich buffy, becomingyellow in front of the eye. The most strikingcharacter is the presenceof more or lesswell developed"scallop- ing" on the tips of dorsalcontour feathers, much as in the youngof the grasslandsparrows and immediatelyseparating the youngof Xenospiza fromth'ose of the Juncoassemblage (Figure 4).

BASIC PLUMAGE The freshlymolted basic plumage of Xenospizais nowrepresented by an adultin prebasicmolt taken 15 Septemberand by fourspecimens taken 20 November.The worncondition of thisplumage differs so greatly from theunworn condition as to haveapparently misled Pitelka into considering Xenospizato be most similar to Melospiza. If he had had these fresh specimenshe almostcertainly would have hesitated to contestBang's (op. cit.) inclinationto alignXenospiza with the grasslandsparrows. The inter- scapularregion of Xenospiza,like that of Le Conte's (Passerherbulus caudacutus),Henslow's, Baird's (Ammodramus bairdii), and Grasshopper (A. savannarum)sparrows, is heavilyscalloped dorsally, contrasting markedlywith any speciesof the Juncoassemblage. The interscapulars of the freshbasic plumage are indeedlonger in Xenospizathan in the brushlandsparrows by actualmeasurement. As statedby Bangsin the originaldescription of Xenospiza,long interscapularsare apparentlya characteristicof the grasslandsparrows. In two charactersPitelka's com- parisonwith Lincoln'sSparrow is apt. First, the freshplumage of the cheekis quitesimilar in thetwo species, with a buffysubauricular region. However,this color is presentin the Junco(brushland) complex only in 1967Jan. ] DICKERMANtrZ•tœ., Xenospiza baileyi 57

Figure 4. Ventral and dorsal views of sparrows in juvenal plumage. Left to right: Melospiza rnelodia, M. lincolnii, Xenospiza baileyi, Passerculussandwichensls, and Passerherbulus henslow•i. 58 DICKERMANET AL., Xenospizabaileyi [ Vol.Auk 84

Figure 5. Sparrows in fresh basic (autumn) plumage, showing the similarity of Xenospiga to the sharp-tailed sparrows. Left to right: Passerculussandwichends, Xenospiga baileyi, Ammodramus savannarum, A. bairdii, Passerherbuluscaudacuta, P. hemlowii, Melosp•ga!incolnii, and M. melodia. lincolnii,whereas the samecharacter is presentin all of the grasslandspar- rows. Secondly,the crownstripes are not dissimilarto thoseof the ,M. georgiana.Ventral streakingof Xenospizais reminiscentof the Melospiza condition,although hardly more so than that of the more blackly streaked races of SavannaIfSparrow. The bend of the wing is yellow, as in most of the grasslandsparrows, in contrast to the usually white bend of the wing in the brushlandcomplex (although it is yellow in someforms of Zonotrichia). The tail shapein adult (secondbasic or later) plumageis far less strongly double-roundedand the rectricesare more acutely tipped than illustrated by Pitelka, whosetype is apparently in first basic plumage with a worn tail showinga more double-rounded condition.

MOLT AND SOFT PARTS The first prebasic(postjuvenal) molt is incomplete,involving only the body and wing coverts,excepting the outer greaterprimary covertswhich, at least, were retainedby our one fall immaturespecimen. This molt apparentlybegins in someindividuals in middleJuly and extendsthrough Septemberor beyondin others. We have no specimenstaken between3 Septemberand 20 November;however, as noted before,young taken 3 Septemberwore plumage varying from a fresh,little-worn juvenal plumage to the mixedplumage of individualswell into the prebasicmolt. Judging from a male taken 21 May, there is, at least in someindividuals, a partial prealternatemolt involving the chin and malar area as there is in so Jan.1967 ] DICKER•^>rEr AL., Xenospiza baileyi 59 many sparrows.Pitelka did not mentionevidence of a prealternatemolt on the April birdshe examined,nor did Dickermanfind it on two April specimenshe collected. Softpart colors,of fourjuvenal-plumaged birds, as recorded in the field by Phillips,were as follows:iris, grayish' brown to darkbrown; maxilla, drabto dark drab; mandible,drab with basepaler and with tomiapaler, buffy to ochre-tinged,especially basally; gonys, ochre-tinged; mouth, pale fleshto reddish;maxillary palate, yellow; tarsi and toes, flesh-colored to darker,more drab, especially toes in olderyoung. Soft part colorsof two adultmales taken in Junewere; iris, grayish brown; bill, duskybluish gray below,buffy at andbefore Bonydeal angle; tarsi, buffy fleshto palebuffy drab,paler inside; toes, darker, especially joints, varying to drab.

SONG AND BEHAVIOR Thesong of Xenospizain highlyvariable. From notes taken in thefield overseveral seasons since 1954, the song may be summarized asoften begin- ningwith two to three(or evenmore) "signal" notes as in th'eSong or Savannahsparrows, but theseare never clear and ringing as in the former. Theremainder of thesong varies greatly but generallycontains a buzzing seriesof notesbest expressed by "tzee"or "zhip"or a scratchy"jeep." Thesemay be higherand lower alternately or on an ascendingscale. Re- semblancemay be claimedto portionsof thesongs of a numberof species but,except for the signalnotes, not to thoseof the SongSparrow. It is unfortunatethat, in spiteof theease of accessto theXenospiza .habitat, goodrecordings have not beenmade for spectrographicanalysis. We have neveryet hearda songresembling that attributedto thisspecies by H. O. Wagner (in Pitelka, op. cit.; quotedby E. R. Blake, Birds of Mexico, Chicago,Univ. ChicagoPress, 1953; p. 589). It is interestingto note that Alfred M. Bailey,who made the first field noteson thisspecies, compared its behaviorwith that of the Seaside(Am- mospizamaritima) and Savannahsparrows (pers. comm. and Nat. Hist., 35: 255, 1935). We find its behaviormost like that of the Grasshopper, or, possibly,the Sharp-tailed,Sparrow. In the springand summer, males are conspicuous,singing from tall grassor eventelephone wires. At this time an occasionalalarmed may evenperch in a tree. At other sea- sonsof the year, however,they are highly secretive.They are difficult to flush and, upon droppingback into the grass,often run, much in the mannerof Sharp-tailedSparrows, and reflush(if at all) at somedistance from the placewhere they alighted.

GENERIC RELATIONS The informationpresented above leads us to think that Xenospiza shouldoccupy a systematicposition close to the other grassland-nesting 60 D•CXERM^•ETAL., Xenospiza baileyi [ Vol.Auk 84

sparrows,as recommendedby Bangs (op. cit.) and followed by C. E. Hellmayr(Field Mus. Nat. Hist., Zool.Series, vol. 13,pt. 11, 1938;see pp. 503-504),and not closeto Melospiza,of the brushlandsparrows, as recom- mendedby Pitelka (op. cit.) and A. H. Miller et al. (Paci]ic CoastAvif., no. 33, 1957; pp. 396-397). The exact positionwithin this group is less obvious. Bangs (op. cit.) tkought it to be closer to Passerherbulus caudacutus;Warner, in a paperread at the 1956 meetingof the American Ornithologists'Union, discussedit in relationto Passerculussandwichensis; and Mayr (pers. comm.) consideredit closerto Passerherbulushenslowii. Xenospiza may have arisen from the same basic stock as the grassland sparrows,yet early enoughto be, in some respects,intermediate towards the Juncoor brushlandcomplex. Whether it is to be combinednomenclatur- ally with the grasslandsparrows in an enlargedgenus Ammodramus; or be retainedas a monotypicgenus may neverbe settledby a decisionbetter than arbitrary. We think at present it is best retained as a monotypic genusplaced betweenthe genera Ammodramus(enlarged to include most of tke grasslandsparrows) and Junco (enlargedto includemost or all of the brushlandsparrows).

SUMMARY Xenospiza baileyi sierrae from the region of is not a recognizablesubspecies. Characters of the unworn basic and juvenal plumages,the eggs,and songssuggest that Xenospizais more closelyre- lated to the sharp-tailed,grassland-nesting sparrows of the Ammo&amus complexrather than to the brushland-nestingsparrows of the Juncocom- plex. Departmentof Microbiolo,ey,Cornell UniversityMedical College,New York, New York; Institutode Biologia,Universidad Nacional Autonoma de Mexico,Mexico, D. F.; and Universityoj MinnesotaMuseum of Natural History, Minneapolis, Minnesota.