Bill deformities in songbirds

This compilation of bill deformities is property of the Rouge River Bird Observatory. Do not use or cite without written permission. Copyright for photos is held by photographers. Please do not use without permission from individual listed.

Flycatchers to Horned Lark (pg 1)
Swallows through bluebirds (pg 2)
Thrushes through European Starling (pg 3)
Warblers through towhees (pg 4)
Sparrows through orioles (pg 5)
Purple Finch through House Sparrow + Literature Cited (below)
Bill Tumors, Most Due to Avian Pox

Crossbills through House Sparrow + Literature Cited




Purple Finch (Haemorhous purpureus)24 Oct 2016; U-F; Thompson Falls, MT; maxilla slightly elongatedJim Greaves (lbviman AT blackfoot DOT net)
White-winged Crossbill (Loxia leucoptera)AHY-U; 11 Feb 1973; Fairbanks, Alaska; maxilla 15.2mm beyond lowerWest 1974
Common Redpoll (Carduelis flammea)6 Apr 2012; Thompson Falls, MT; maxilla slightly miniaturizedJim Greaves (lbviman AT blackfoot DOT net)
Pine Siskin (Spinus pinus)19 Oct 12; U-U; Santa Fe, NM; no maxilla; mandible elongated and frayed lookingMaria Higuara (maria AT higuerapope DOT com)
American Goldfinch (Carduelis tristis)HY-M; 28 Dec 2003; Dearborn, MI, mandible elongated, maxilla crossedRouge River Bird Observatory, Julie Craves (jac.rrbo AT
American GoldfinchAHY-F; 9 Apr 2007; Walden, Orange Co., NY; very elongated mandibleMark Eis (markeis AT mac DOT com)
American Goldfinch17 Aug 2007; Lolo, MT; maxilla appears to have been put through a shredderJeanne Elliott (jeanne.elliott AT bresnet DOT net)
American Goldfinch20 April 2008; AHY-F; near St. Ignitius, Montana; very slightly shortened maxilla; bird also has patches of white feathersEugene Beckes via Judy Hoy (bjhoy AT
American GoldfinchApril 2008; AHY/ASY-M; near St. Ignitius, Montana; shortened maxillaEugene Beckes via Judy Hoy (bjhoy AT
American Goldfinch20 Oct 2011; U-F; Richland, MI; extremely elongated and downturned maxillaReported on MLive news web site
Evening Grosbeak (Coccothraustes verspertinus)Boise, ID; mandible curved to leftAl Larson (allarson AT
Evening Grosbeakphoto dated 26 Oct 2012; U-M; VT; maxilla thickened and decurved, crossed at tipFlickr
House Sparrow (Passer domesticus)Cuyahoga, Co., OH; July 2004; male with hugely elongated maxilla, curved downMaureen McEneryu 
House Sparrow23 Sep to at least 14 Oct 2006; Potomac, MD; entire bill greatly enlargedvia Birder's World forum
House Sparrowapprox fall 2001; maxilla curved downFlickr
House SparrowOhio; 17 Sep 2004; maxilla elongated and scoop shapedBecky Stanton
House SparrowPhoto labeled 25 Apr 10; southern NV; tips crossedFlickr
House Sparrow20 Aug 2010; U-U; Dallas, TX; maxilla nearly absent, mandible grossly enlarged and scoop-shapedFlickr
House Sparrow21 July 2015; HY-U; Illinois; maxilla spoon-shapedFlickr
House Sparrow16 Oct 2015; U-F; Kennebunk, ME; slightly crossed at tipFlickr

Maxilla = Top, Mandible = Bottom.

Literature Cited

Anon. 1999. Vermont Institute of Natural Science, Atlantic Flyway review: northeast coastal region 1 — Fall 1998. N. Amer. Bird Bander 24:54-55.

Craves, J. A. 1994.  Passerines with deformed bills.  North American Bird Bander 19(1): 14-18.

Fiala, K.L. 1981. Survival of a demaxillate Red-winged Blackbird. Wilson Bulletin 93:563-565.

Green, D. S. 1969. Bill deformity in Clark’s Nutcracker. Blue Jay 27:36.

Eltzroth. E. 1996. Cross-beaked Western Bluebirds. Sialia 18:3-4.

Ferreira de Vasconcelos, M. and M. Rodrigues. 2006. Bill deformity in a White-winged Becard (Aves: Subsocines: Tityridae) from Minas Gerais, Brazil. Revista Brasileira de Ornitologia 14:165-166.

Kinch, B. 1998. Deformed chickadee. Ontario Birds 16:45-46.

Small, M. F., & C. L. Pruett. 1998. Rhamphothecal hyperkeratosis in a Bronzed Cowbird. Bull. Texas Ornithol. Soc. 31: 27–29.

Sogge, M. K. and E. H. Paxton. 2000. A summary of observed physical deformities in the Willow Flycatcher: 1996-2000. U.S.G.S. Forest and Rangeland Ecosystem Science Center, Colorado Plateau Field Station, Flagstaff, AZ.

Sperry, D, D. Cimprich, and J. Marquess. 2007. Beak deformity in the endangered Black-capped Vireo. N. Amer. Bird Bander 32: 1-3.

Speirs, J.M. and M. Wilson. 1994. Blue Jay with “crossed” bill. N. Amer. Bird Bander 19:100.

Van Hemert, C. R. 2007. Alaskan Birds at Risk: Widespread Beak Deformities in Resident Species (pdf). Birding 39 (5):48-55.

West, G.C. 1959. Effects of high air temperature on the bill and claw keratin structures of the tree sparrow. Auk 76:534-537.

—–. 1974. Abnormal bill of a White-winged Crossbill. Auk 91:624-626.

Woodruff, F. M. 1907. Malformed bill of Rose-breasted Grosbeak. Auk 24:220-221.

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