Bill Deformity in a Pearly-Eyed Thrasher from Montserrat, West Indies
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Ridgway, R. 1901. The birds of North and Middle Whittle, C.L. 1927. Some additional bird weights. Bull. America. Bull. U.S. Nat. Mus., No. 50:343-346. Northeastern Bird-Banding Association 3:70-71. Stewart, P.A. 1937. A Preliminary List of Bird Weights. Whittle, C.L. 1930. Additional live bird weights. Bird- Auk 54:324-332. Banding I:192-193. Stewart, P.A. and R.W. Skinner. 1967. Weights of Birds Wolfson, A. 1954. Weight and fat depositionin relation from Alabama and North Carolina. Wilson Bull. to springmigration transient White-throated Sparrows. 79:37-42. Auk 71:413-434. Wetherbee,K.B. 1934. Measurementand weights of live birds. Bird-Banding 5:55-64. {Inland} Wetmore, A. 1936. The number of contour feathers in Passeriform and related birds. Auk 53:159-169. Bill Deformity in a Pearly-Eyed Thrasher from Montserrat, West Indies Wayne J. Arendt Angela L Arendt U.S. Department of Agriculture, Forest Service P.O. Box U Institute of Tropical Forestry Palmer, Puerto Rico 00721 Southern Forest Experiment Station P.O. Box 21390 Rio Piedras, Puerto Rico 00928 hecauses of bill deformities in birds have been sum- On the morningof 20 May 1984,we capturedand band- marized in an excellent review by Pomeroy {Brit. ed {1433-78863} a Pearly-eyedThrasher with an abnormal- Birds 55:49-72, 1962}. Causesinclude genetic mutations, ly long {length42.84 mm}, decurvedbill {Fig. 1}. Upon disease,accident, poor nutrition, and, in cagedbirds, an examination of the deformed bill, we found that about half absenceof bill-filing substrates{e.g., stones, coarse bark}. of the distal portion of the mandible had been severed, In wild birds, however, bill deformities are most often leavinga jaggededge to the remainingmandibular base. associatedwith injury to the bill. Easterlaand Todd {Auk The maxilla extendedabout 20 mm beyondthe truncated 88: 677•678,1971} reported such an apparentinjury in mandible.The tomia {cuttingedges} of the bill appeared a free-livingYellow-headed Blackbird {Xanthocephalusxan- normal from the baseof the feathersdistally to the frac- thocephalus}from Clay County,Missouri. The blackbird tured portion of the mandible, forming a smooth com- apparentlyhad suffereda fracturedmandible {dentary}, missure{line alongwhich the mandiblesmeet}. Beyond resultingin a longitudinalfissure and jaggedbroken edge. the broken mandible, however, the tomia of the maxilla The injury allowed unchecked growth and abnormal were lessdistinguishable. The sidesof the maxilla were developmentof the rhamphotheca{horny sheathcover- growinginward, giving the maxilla an almost tubular ing the bony mandibles}. appearance. In the passerinefamily Mimidae {mockingbirds,thrashers, Figure 1. Pearly-eyedThrasher with deformed bill. and allies} at least two eastern North American species with deformed bills have been reported. Allard {Auk 47: 93, 1930}reported a Catbird {Durnetellacarolinensis} with an upturned maxilla, while more recently Post{Chat 49: 20}21, 1985} reporteda Brown Thrasher {Toxostorna rufurn}with a long decurvedbill, the mandible apparent- Iy having suffered a previousfracture. A similar bill in- jury in a West Indian mimid, a Pearly-eyedThrasher {Margaropsfuscatus} from Montserrat, is reported herein. The Pearly-eyedThrasher was capturedduring studieson Montserrat from 15 May to 2 August, 1984. During 19-21 May 1984, we sampledthe bird communityin the Centre Hills at a siteknown locallyas Jubilee Heights in a secon- dary hygrophyticforest at an elevationof about 450 m. Apr.-Jun. 1986 North AmericanBird Bander Page51 Measurements of the deformed thrasher are compared in weighedless and was smallerin all of the principalap- Table 1 with mensuraldata for 9 morphometriccharacters pendicularmeasures Ichord, primary 9, tarsus,tail I than from 82 Pearly-eyedThrashers without deformitiescap- the averagethrasher ITable 11. Sexual dimorphism is slight tured at the JubileeHeights banding site. Althoughthe in the Pearly-eyedThrasher, although females often weigh deformed individual was not a juvenile Ino dark irisl, 7 more than males and have longer culmens, while males of 9 morphometriccriteria lexcludingmaxillar and man- exhibit longerwing chord and longertails IArendt, un- dibular lengthslsuggest that it was a second-yearbird. It publ. datal. Table 1. A comparisonof 9 morphonmetric characters{g and mm) between a single Pearly-eyedThrasher with a physicallydeformed bill and 82 Pearly-eyedThrashers with no apparent physicaldeformities. Culmen Measurements Wing Body Lengthfrom Lengthfrom Lengthof Lengthof Lengthof Chord Weight Feathers Nares Depth Width Primary9 Tarsus CenterRectrix •' 136.1 102.7 27.35 18.55 8.24 6.51 87.3 37.82 109.9 S.D. 4.45 8.67 1.11 0.84 0.32 0.34 3.03 1.06 4.93 Range 123-145 86-131 23.84-30.15 16.86-21.30 7.17-8.96 5.78-7.35 80.8-89.3 34.27-40.85 96.6-128 * 130.0 96.0 42.84 33.77 7.68 6.73 83.2 36.68 103.8 *Individual Pearly-eyed Thrasher with deformed bill. Exceptingthe abnormally long, decurved bill, all other We thank Bill Johnson (former U.S. Peace Corps morphologicalfeatures of the deformedthrasher appeared Volunteer), Mr. and Mrs. Dennis Gibbs, and other normal. Although it was almost 7 g lighter than the members of the Montserrat National Trust for their average thrasher, the handicappedthrasher was 10 g assistance.C. Delannoy,W. Elder, J. Faaborg,and an heavier than the three lightestindividuals, all of which anonymousreviewer offered helpful suggestionson the appearedto be healthybut alsoyoung. The averageweight manuscript. Funding for our researchcame from the (102.7 g) of the 82 thrashers captured at Jubilee Heights Montserrat National Trust, U.S. Agencyfor International was affected by the inclusion of gravid females. The Development,and the U.S. Department of Agriculture heaviest female thrasher recorded (131 g) exhibited the Forest Service, which included wildlife assessmentsas beginningsof a brood patch. Fifteen of 82 thrasherscap- part of the United Nations Environment Programrods tured (18.3%) weighed lessthan the deformed thrasher, Caribbean Action Plan. further suggestingthat the bird was not starving and would not necessarilydie from the injury. (Eastern) Like many other passerinespecies, Pearly-eyed Thrashers frequently wipe their bills on the nearest substrateupon WBBA Research Grant completionof a meal. In additionto cleaningexcess food particles from the exterior surfacesof the bill, this wip- ing action servesto file the tips of the mandibles,assur- The WesternBird Banding Association annually ing that they remain close-fitting.Broken mandibles ap- awardsa grant for researchincorporating banding parently lower the effectivenessof bill wiping in general by a student or non-professionalornithologist. Ap- and bill filing in particular.Besides the uncheckedgrowth plicationsare invited for the 1986 award of up to of the rhamphothecaof the maxilla in the deformed $250.Applicants should submit the followingitems: thrasher,food and dirt particleswere foundon bothinner (1) a descriptionof the project (3 pagesor less), (2) and outer surfacesof the maxilla extendingbeyond the a projectbudget, (3) a curriculumvitae, and (4) a let- broken tip of the mandible and on the outer surfacesof ter of recommendation(from the majorprofessor or the mandible. Moreover, the bird's plumage appeared otherperson familiar with the applicant'swork). Ap- "ragged"and it hostedan abnormally heavy infestation plication materialsshould be sent to Dr. Martin H. of bird lice (Mallophaga).Therefore, while a bird that has Balph,Chairman of the WBBAResearch Grant Com- suffereda brokenmandible may not die directlyas a result mittee,Department of Fisheriesand Wildlife, UMC of its deformity,chances of a prematuredeath are increas- 52, Utah State University, Logan, UT 84322. ed by threat of diseaseand heavyinfestation of parasites, resulting from an inability to preen and clean itself It is hopedthat recipientsof this award will consider properly. submitting an article on their findings to North American Bird Bander. Page 52 North American Bird Bander Vol. 11, No. 2 .