Abnormally Long Bill in a Young Curve-Billed Thrasher

JOURNAL OF FIELD ORNITHOLOGY Publishedby Associationof Field Ornithologists

Vo•.. 62, No. 2 Svva•c 1991 P^cv.s157-292

J. Field Ornithol., 62(2):157-161

ABNORMALLY LONG BILL IN A YOUNG CURVE-BILLED THRASHER

CHRISTOPHER W. THOMPSON AND BARBARA A. TERKANIAN Departmentof Zoology Arizona State University Tempe,Arizona 85287-1501 USA Abstract.--We report an approximately40-d-old male Curve-billed Thrasher, Toxostoma curvirostre,with a bill more than three times normal adult length. Its excessivebill length was causedby growth of the rhamphothecaand not the bonesunderneath it. This is the largestproportional increase in bill growth rate due to a pathologicalcondition yet documented.

PIGO ANORMALMENTE LARGO EN INDIVIDUO DE TOXOSTOMA CURVIROSTRE Sinopsis.--Informamosen un individuo de Toxostomacurvirostre de aproximadamente40 diasde edad, un picotres veces mils largo que el deun aveadulta. Este tamafio anormal del pico fue causadopor el crecim•entode la ramfotecay no del huesobajo •sta. Este es el aumento proporcionalmils grande que se ha documentadoen el crecimientode un pico, causadopor una condici6npato16gica. On 27 September1989, a juvenile male Curve-billedThrasher, Tox- ostomacurvirostre, with a severelydeformed bill was foundfreshly dead in a suburbanyard in Tempe, Arizona,U.S.A. The maxilla and mandible wcrc stronglyticcurved to the right and left respectively,and wcrc com- pletely nonoverlappingfor most of their lengths(Fig. la). The maxilla measured107.0 mm along the curvature of the culmcn from the baseof the foreheadto the tip of the maxilla. The mandiblemeasured 62.5 mm along its curvaturefrom the gonysto the tip of the mandible.Using the methodsdescribed above, wc measuredthe maxilla and mandiblelengths of 15 normal adult male T. curvirostrespecimens from central Arizona in the ornithologycollection at the University of Arizona. Maxilla and mandiblelengths (mcan _+ SD) wcrc 32.97 _+ 1.49 mm and 20.75 _+ L45 mm, respectively.Wc could not detectany other abnormalitiesin external or internal morphology. However, the specimenwas heavily infestedwith featherlice. Heavy cctoparasitcloads have bccn frequently reportedin birds with deformedbills, presumablybecause of difficulty preening(e.g., Barlow 1967, Kennedy 1969, Pomeroy 1962).

157 158] c. w. Thompsonand B. A. Terkanian J.Field Ornithol. Spring 1991

FIGUgE1. (A) Dorsolateralview of skullof juvenile male Curve-billed Thrasher, Toxostoma curvirostre,with abnormally long decurvedand crossedmaxilla and mandible. (B) Lateral view of high resolution(unscreened) mammography x-ray of sameskull. The skull was depositedin the ornithologycollection of Arizona StateUniversity.

The specimenwas a juvenile basedon severalcriteria: 1) its skull had not yet begun to ossify,2) all remigesand rectriceswere sheathedand incompletelygrown, 3) its iris color was gray, 4) the tips of its outer rectriceswere buff colored,and 5) down featherswere presenton its head (Pyle et al. 1987, Walters and Lamm 1986). The specimenwas a male with testes less than 1 mm in diameter. We estimatethat this specimenwas 35-45 d old basedon severallines of evidence.In a study of the ontogenyof T. curvirostre,Rand (1941) statesthat on the thirty-fifth day after hatching"the tail is almostthree- quartersgrown" and by the forty-fifth day "the tail is full length." The specimen'smiddle pair of rectriceswere 112 mm long or about 93% full grown (Walters and Lamm 1986). Assuminga linear rate of rectrix Vol.62, No. 2 Curve-billedThrasher Bill Deformity [159 growth, this suggeststhat the specimenwas about42 d old. Rand (1941) alsostates that by the forty-fifth dayjuveniles "appear similar to the adult except for the pale grayish-white eye." The iris of our specimenwas smoke-gray(color 45, Smithe 1975). This color precedesthe grayish- white color mentionedby Rand (1941)(Walters and Lamm 1986). This also suggeststhat the specimen was less than 45 d old. Nestling T. curvirostrefledge 14-18 d after hatching and continueto be fed by their parents until 30-40 d after hatching (Rand 1941). If the specimenwere unable to feed itself as we believe (see below), then it could not have survivedmuch beyond30-40 d of age. Many birds with lessdeformed bills, including one report of a Brown Thrasher, T. rufum (Brown 1976), manageto surviveand reproduceby behaviorallyadapting to their handicap(e.g., Fox 1952, King and Rolls 1968, Pomeroy 1962, Thorpe 1956). However, this specimenclearly starvedto death probably shortly after becomingindependent from its parents.Adult maleT. curvirostreweigh 80.9 _+5.0 g (mean_+ SD)(Walters and Lamm 1986), but the specimenweighed only 55.7 g, had extremely emaciatedpectoral muscles, no subcutaneousfat, and no discerniblefood in its alimentary canal. Lateral x-rays of the skull using high resolution(i.e., unscreened) mammographyfilm clearly illustratedthat the abnormal bill elongation was causedby excessivegrowth of the rhamphothecaand underlying dermotheca.The bonesunderlying the rhamphothecaappeared normal in length and structure (Fig. lb), which agreeswith previousreports of birds with abnormally long bills. In all suchcases reported in which the underlyingbones were examinedby dissectionor x-ray, they appeared normal and the abnormal bill elongationwas due to excessivegrowth of the rhamphothecaand dermotheca(Barlow 1967, Carothersand Balda 1970, Easterla 1972, Easterla and Todd 1971, Fox 1952, Harris 1962, Taylor and Anderson1972). The causesand occurrencesof bill abnormalitieswere reviewed by Pomeroy (1962), and hundredsof additional casesof bill abnormalities havebeen publishedsubsequently. This is the first recordof an abnormal bill in T. curvirostre,but similar casesof abnormally long bills have been reportedin Brown Thrashers (Brown 1976, Goertz and Mowbray 1969, Mason 1962, Post 1985, Prescott 1968, Steffee 1968, Stitt 1968, Taylor 1973) and California Thrashers, T. redivivum (Fox 1952), as well as many other mimids (e.g., Allard 1930, Arendt and Arendt 1986). Abnormal elongationof the bill may be genetic(e.g., mutationscaused by environmentalteratogens [Gochfeld 1975]) or developmentalin origin. Developmentalelongation may result from disease,injury, malocclusion of the maxilla and mandible, or environmentalinduction (Pomeroy 1962, West 1959). The specimendid not exhibit any sign of diseaseor injury to the bill. In addition,disease or injury was unlikely to causeproportional increasesin growth of both the maxilla and mandibleas exhibitedby this specimenand, therefore,probably did not causethe excessivebill growth in this specimen. 160] C. W. Thompsonand B. A. Terkanian j. Field Ornithol. Spring 1991 Bill lengthin juvenilesreaches that of adultsseveral weeks after fledging when bill growth is completed(Walters and Lamm 1986). The growth of this specimen'smaxilla and mandibleto greaterthan three timesnormal adult length within 3-4 wk after fledgingrepresents at least a threefold increasein growth rate over normal and is the greatestproportional increasein bill growthrate dueto a pathologicalcondition yet documented.

ACKNOWLEDGMENTS

We thank Larry Nienaber for preparingthe skull, Dr. Elizabeth M. King, D.V.M. for doing x-rays of the skull, and Tom HueIs for accessto the ornithologycollection at the Universityof Arizona. We thank Michael Gochfeld,Michael C. Moore, David L. Pearson, and Glenn E. Walsberg for valuable commentson earlier versionsof this manuscript.

LITERATURE CITED

At,LARD, H.A. 1930. Bill deformity in a Catbird. Auk 47:93. ARENDT,W. J., ANDA. I. ARENDT. 1986. Bill deformityin a Pearly-eyedThrasher from Montserrat, West Indies. N. Am. Bird Bander 11:51-52. BARLOW,J. C. 1967. A bill deformity in a European Tree Sparrow, Passermontanus (Linnaeus). Can. J. Zool. 45:889-891. BROWN, L. N. 1976. Prevalence of bill abnormalities in Florida Brown Thrashers. Fl. Field Nat. 4:11-13. CAROTHERS,S. W., AND R. P. BALDA. 1970. Abnormal bill of a Western Meadowlark, Sturnellan. neglecta.Auk 87:173-174. EASTERLA,D.A. 1972. Bronzed Cowbird in west Texas and two bill abnormalities. Southwest. Nat. 17:293-294. --, ANDJ. M. TODD. 1971. Bill deformity of a Yellow-headedBlackbird. Auk 88: 677-678. Fox, W. 1952. Behavioraland evolutionarysignificance of the abnormalgrowth of beaks of birds. Condor 54:160-162. GOCHFELD,M. 1975. Developmentaldefects in CommonTerns of westernLong Island, NY. Auk 92:58-65. GO•.RTZ,J. W., AND E. E. MOWBK.•Y. 1969. Brown Thrasher with a bill deformity. Southwest. Nat. 14:254-255. H^RmS,M.P. 1962. Herring Gull with abnormalbill. Br. Birds 55:236-237. KENNEDY,R.J. 1969. Guillemots with crossedor broken mandibles.Br. Birds 62:156- 157. KINo, B., AND J. C. Ro•4,s. 1968. Feeding methodsof Rook with malformed beak. Br. Birds 61:417-418. M•,soN, E.A. 1962. Brown Thrasher life history data. Bird-Banding 33:99-101. POMEROY,D. E. 1962. Birds with abnormal bills. Br. Birds 55:49-72. POST, W. 1985. A Brown Thrasher with an aberrant culmen. Chat 49:20-21. PR•.S½OTT,K.W. 1968. Bill deformity in a Brown Thrasher. Bird-Banding 39:134. PYLE, P., S. N. G. HOWELL, R. P. YUNICK. AND D. F. DESANTE. 1987. Identification guideto North Americanpasserines. Slate Creek Press, Bolinas, California. 283 pp. RAND,A.L. 1941. Resultsof the ArchboldExpeditions. No. 34. Developmentand enemy recognitionof the Curve-billed Thrasher, Toxostomacurvirostre. Bull. Am. Mus. Nat. Hist. 78:213-242. SMITHE,F. 1975. A naturalists'color guide. Am. Mus. Nat. Hist., New York, New York. STEFFEE,N.D. 1968. Number of deformedBrown Thrashers(Toxostoma rufum), reported from scattered locations. Fl. Nat. 41:126-127. STITr, W.T. 1968. More on deformed thrashers. Fla. Nat. 41:171. TAYLOR, W. K. 1973. Bill deformities in two Florida birds. Fl. Field Nat. 1:21-23. --, AND B. H. ANDERSON. 1972. Brown Thrasher (Toxostomarufum) with a bill abnormalityin SeminoleCounty. Fl. Nat. 45:129. Vol.62, No. 2 Curve-billedThrasher Bill Deformity [ 161

THORPE,W.H. 1956. Recordsof the developmentof original and unusualfeeding methods by wild passerinebirds. Br. Birds 44:389-395. WALTERS,P.M., ANDD. W. LAMM. 1986. Noteson the ageingand sexingof the Curve- billed Thrasher (Toxostomacurvirostre). N. Am. Bird Bander 11:2-3. WEST,G. C. 1959. Effectsof high air temperatureon the bill and claw keratin structures of the Tree Sparrow. Auk 76:534-537. Received23 Apr. 1990; accepted2 Aug. 1990.

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