Bill deformities in songbirds

Deformed bills in songbirds (passerines) are uncommon, perhaps because they are further down the food chain and have less opportunity to accumulate toxins, perhaps because bill deformities pose a more serious threat to survival for small birds, or for a host of other reasons. There are many factors that may contribute to deformed bills in birds.

After banding a Gray Catbird with a grossly crossed bill in 1993, the Rouge River Bird Observatory’s Julie Craves looked into the incidences of passerines with deformed bills. Her article, Passerines with deformed bills (pdf), was published in the journal North American Bird Bander. It provides a primer on the anatomy of bird bills, discusses possible causes for bill deformities, and several tables summarize reports of passerines with deformed bills from the literature. As you’ll see in her paper, Icterids (the blackbird family) and Mimids (catbirds, mockingbirds, and thrashers) appear to have a higher rate of bill deformities than other families.

The Tables below list reports provided to RRBO by the public.

As of fall 2017, I am no longer taking reports of bill deformities.

I encourage people to submit their reports to the Alaska Science Center, which has taken the lead in trying to determine the causes of many of these deformities. Their reporting form is on this page, and more information on their bill deformity work on this page.

Also, if you post your photos on the online photo sharing site Flickr, there is a photo pool called Birds with Deformed Bills. You can add your photos of any species of bird with a deformed bill by joining the pool.

Finally, the British Trust for Ornithology sponsors a project called Garden BirdWatch. After an increase in sightings of birds with deformed bills, they started the Big Garden Beak Watch project to compile information. British birders are encouraged to participate.

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 (below)
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 (p6)
Bill Tumors, Most Due to Avian Pox

Flycatchers to Horned Lark




(Contopus sordidulus)
Fall 2003; Great Falls, MT; severely crossedJudy Hoy (bwrehab AT
Western Wood-Pewee18 Sep 2011; U-U; Boone's Draw, Roosevelt Co., NM; severely crossedFlickr
Willow Flycatcher (Empidonax
1996-2000; 13 birds with bill deformities in various western statesSogge and Paxton (2000)
"Traill's" Flycatcher (Empidonax traillii/alnorium)21 Aug 1975; HY-U; Rector, PA; crossedPowdermill Nature Reserve, Robert S. Mulvihill (mulvipnr
AT westol DOT com)
Gray Flycatcher (Empidonax wrightii)25 May 2008; AHY-U; Bohart Ranch Field Station, Ellicott, El Paso Co., CO; mandible overgrownBill Schmoker (bill.schmoker AT
Great Crested Flycatcher ((Myiarchus crinitus)19 Aug 2011; U-U; near Ellicott City, MD; bill crossedFlickr
Great Crested Flycatcher14 Aug 2015; U-U; Circle B Bar Reserve, Polk Co., FL; maxilla thickened, elongatedFlickr
Northern Shrike Lanius excubitor7 Feb 2012; AHY-U; Rigaud, QC, Canada; mandible curving up and crossing maxilla at tipMark Dennis (mtlbirdguide AT gmail DOT com)
White-eyed Vireo (Vireo griseus)10 Oct 2009; HY-U; Fort Morgan, AL; mandible severely downcurvedJenn Mizen (jennmizen AT gmail DOT com
(Least) Bell's Vireo (Vireo belli)May 1980; AHY; Santa Barbara, CAJim Greaves (LBVIMAN AT BLACKFOOT.NET)
Warbling Vireo (Vireo gilvus)31 Aug 2008; HY-U; Redwood Creek, CA south of Point Reyes near Muir Woods National Park); maxilla eroded, down-turned, and crossed strongly.PRBO/Mark Dettling (mdettlin AT hotmail DOT com)
Warbling Vireo17 Aug 2009; HY-U; Dearborn, Wayne Co., MI; maxilla 2 mm shorter than mandible, curved to left.Rouge River Bird Observatory, Julie Craves (jac.rrbo AT gmail DOT com)
Red-eyed Vireo (Vireo olivaceus)Ft. Morgan, ALBob Sargent (RubyThroat 
Red-eyed Vireo11 Sep 1987; HY-U; Rector, PA; crossedPowdermill Nature Reserve, Robert S. Mulvihill (mulvipnr
Red-eyed Vireo30 Jul 2004; HY-U; Oxford, OH; crossedDavid Russell (russeld AT
Black-capped Vireo (Vireo atricapilla)8 May 2006; AHY-M; Fort Hood, TX; mandible crossed right, maxilla tip downward (condition not as pronounced when first captured on 5 Jun 2005)Sperry et al. 2007
Green Jay (Cyanocorax yncas)2011?; U-U; Santa Clara Ranch, TX; slightly crossed at tipFlickr
Steller's Jay (Cyanocitta stelleri25 Jan to 10 Jun 2005; Berkely, CA;
maxilla and mandible strongly decurved downward
Terry Coddington (tlcodd AT
Steller's Jay22 May 2007 and 25 July 2008 (same bird?); Stanford University campus, Palo Alto CA: maxilla broken off, mandible elongated and scoop-shapedTom Grey (tgrey AT law DOT standford DOT edu)
Steller's JayPhoto dated April 2006; maxilla
slightly elongated and curved to one side; Vancouver, BC, Canada
Florida Scrub Jay (Aphelocoma coerulescensPhoto dated 4 Mar 2014; U-U; Florida; slightly crossed at tipFlickr
Blue Jay (Cyanositta cristata)Alberta, Canada(gmbooth AT
Blue JayPickering, Ontario, Canada; crossedSpiers and Wilson 1994
Blue Jay1 May 1973; SY-U; Rector, PA; crossed Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr
AT westol DOT com)
Blue Jay25 Oct 2010; AHY?-U; near Ellsworth, Hancock Co., ME; maxilla strongly curved to one side, mandible possibly scoop-shaped and somewhat elongatedFlickr
Blue Jay28 April 2007; AHY (ASY?)-U; near Bethlehem, PA; maxilla and mandible
decurved downward
Jim Figlar (figlar AT pdt DOT net)
Blue Jay4 Apr 2010; U-U; Hamilton, Ontario, Canada; both appear thickened, mandible elongated and slightly scoop-shapedFlickr
Blue JayMarch 2013; AHY-U; Flint Hills, KS: mandible elongated and flattened, thrusting up above maxillaFlickr
Blue Jay30 Aug 2013; U-U; Thunder Bay, ON, Canada; mandible greatly elongatedSherri Hare (slhare AT shaw DOT ca)
Blue Jay9 Apr 2016; AHY-U; Raymond, MS; crossed at tipDebbie Keen <(ebkeen AT bellsouth DOT net)
(Aphelocoma coerulescens)
15 May 2003; Lake Wales Ridge State Forest, Polk Co., FL; maxilla crossed leftBill Pranty (billpranty
Western Scrub-Jay (Aphelocoma
27 Apr 2004; Oakland, CA; hooked maxillaDebbie Viess (amanitarita
Western Scrub-JayJuly (unable to close bill) to mid-August
(now crossed) 2008; Santa Rosa, CA
Karen Wagner (karwag
Western Scrub-Jay28 Sep 2011; U-U; Ridgefield NWR, WA; maxilla looks short, mandible very elongated, thinFlickr
Clark's Nutcracker (Nucifraga
24 Feb 2007; Island Park, ID;
maxilla sideways, hugely overgrown, and curled upwards
Cliff Weisse (ClifffAndLisa AT octobersetters DOT com)
Black-billed Magpie (Pica hudsonia)Photo labeled 20 Jun 2010; Mt. Olivet, CO; maxilla shortened, mandible elongated, scoop-shaped.Flickr
Clark's NutcrackerJasper Nat'l Park, Saskatchewan,
Canada, crossed
Green 1969
Corvus sp.
(C. brachyrhynchos or C. caurinus)
14 Jan 2008; Coupeville, Island Co.,
WA; maxilla slightly elongated and hooked down
Craig Johnson (highseasmarine AT
Crow sp. (C. brachyrhynchos/caurinus)10 Sep 10; DuPont, WA.Flickr, also here.
Corvus sp. (C. brachyrhynchos or C. caurinus)5 Mar 2003; maxilla very elongated and curved down; Mukilteo, WA
Judy Rowe Taylor
(judyrowetaylor AT
Corvus sp. (C. brachyrhynchos or C. caurinus)9 Aug 2013; U-U; Tacoma, WA; maxilla elongated and downcurvedFlickr
American Crow (Corvus brachyrhynchos)Chillicothe, OH; badly crossedJoe McMahon (jmcmahon AT
American Crow17 Apr 2004; Bellvue and 
Mukilteo, WA (presumably same bird)
Megan Lyden (meganlyden
American CrowJuly 2008; maxilla short, mandible
elongated, scoop shaped; Hockinson, WA
American Crow30 Mar 2010; Magnuson Park, Seattle, WA; maxilla shortened, mandible elongated.Flickr
American Crow18 April 2009; Thompson Falls, MT;
slightly crossed at tip
Common Raven (Corvus corax)5 Nov 2006; Samish Flats, Skagit
Co., WA; maxilla curved and slightly hooked down at end, longer than mandible, gap when bill was closed
Dennis Paulson (dennispaulson AT
comcast DOT net)
Common Raven26 Sep 2006; Dunraven Pass;
Yellowstone National Park (WY); maxilla overgrown
Ralph Kerr
(ralphk48 at
Common Raven18 Mar 2008; Littlerock, Los Angeles Co., CA (Mojave Desert approximate coordinates: 34.52112 N, -117.98367 W); maxilla and mandible very elongated and strongly downcurved. John (bewickwren AT earthlink DOT net)
Common RavenPhoto dated 20 Sep 2010; U-U; near Old Faithful, Yellowstone National Park, WY; mandible elongated, curving upFlickr
Horned Lark, (Eremophila alpestris)22 Feb 2012; AHY-U; north of Pierre, SD; crossed at tipFlickr

Maxilla = Top, Mandible = Bottom.

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