Beak (English Wikipedia)

Pomeroy, D.E. (February 1962). "Birds with abnormal bills" (PDF). British Birds. 55 (2): 49–72. Archived from the original (PDF) on 2018-02-19. Retrieved 2018-02-18.

cam.ac.uk

zoo.cam.ac.uk

Hauber, Mark & Rebecca M. Kilner (2007). "Coevolution, communication, and host-chick mimicry in parasitic finches: who mimics whom?" (PDF). Behav. Ecol. Sociobiol. 61 (4): 497–503. Bibcode:2007BEcoS..61..497H. doi:10.1007/s00265-006-0291-0. S2CID 44030487. Archived from the original (PDF) on 2012-03-20.

chicagotribune.com

Bierma, Nathan (12 August 2004). "Add this to life list: 'Birding' has inspired flock of words". Chicago Tribune. Retrieved 6 June 2011.

deakin.edu.au

dro.deakin.edu.au

Clayton, [deficient citation]; Lee, [deficient citation]; Tompkins, [deficient citation]; Brodie, [deficient citation] (September 1999). "Reciprocal Natural Selection on Host-Parasite Phenotypes" (PDF). The American Naturalist. 154 (3): 261–270. Bibcode:1999ANat..154..261C. doi:10.1086/303237. hdl:10536/DRO/DU:30056229. ISSN 1537-5323. PMID 10506542. S2CID 4369897. Archived from the original (PDF) on 2020-09-12. Retrieved 2019-09-05.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)^{[full citation needed]}

doi.org

Seki, Yasuaki; Bodde, Sara G.; Meyers, Marc A. (2009). "Toucan and hornbill beaks: A comparative study" (PDF). Acta Biomaterialia. 6 (2): 331–343. doi:10.1016/j.actbio.2009.08.026. PMID 19699818. Archived from the original (PDF) on 2012-04-02.
Mayr, Gerald (2005). "A new eocene Chascacocolius-like mousebird (Aves: Coliiformes) with a remarkable gaping adaptation" (PDF). Organisms, Diversity & Evolution. 5 (3): 167–171. Bibcode:2005ODivE...5..167M. doi:10.1016/j.ode.2004.10.013.
Bonser, R.H. & Witter, M.S. (1993). "Indentation hardness of the bill keratin of the European starling" (PDF). The Condor. 95 (3): 736–738. doi:10.2307/1369622. JSTOR 1369622.
Pitocchelli, Jay; John F. Piatt; Harry R. Carter (2003). "Variation in plumage, molt, and morphology of the Whiskered Auklet (Aethia pygmaea) in Alaska". Journal of Field Ornithology. 74 (1): 90–98. Bibcode:2003JFOrn..74...90P. doi:10.1648/0273-8570-74.1.90. S2CID 85982302.
Knopf, F.L. (1974). "Schedule of presupplemental molt of white pelicans with notes on the bill horn" (PDF). Condor. 77 (3): 356–359. doi:10.2307/1366249. JSTOR 1366249.
Chernova, O.F.; Fadeeva, E.O. (2009). "The peculiar architectonics of contour feathers of the emu (Dromaius novaehollandiae, Struthioniformes)". Doklady Biological Sciences. 425: 175–179. doi:10.1134/S0012496609020264. S2CID 38791844.
Hieronymus, Tobin L.; Witmer, Lawrence M. (2010). "Homology and evolution of avian compound rhamphothecae". The Auk. 127 (3): 590–604. doi:10.1525/auk.2010.09122. S2CID 18430834.
Stettenheim, Peter R. (2000). "The Integumentary Morphology of Modern Birds—An Overview". Integrative and Comparative Biology. 40 (4): 461–477. doi:10.1093/icb/40.4.461.
Klasing, Kirk C. (1999). "Avian gastrointestinal anatomy and physiology". Seminars in Avian and Exotic Pet Medicine. 8 (2): 42–50. doi:10.1016/S1055-937X(99)80036-X.
Borras, A.; Pascual, J.; Senar, J. C. (Autumn 2000). "What Do Different Bill Measures Measure and What Is the Best Method to Use in Granivorous Birds?" (PDF). Journal of Field Ornithology. 71 (4): 606–611. doi:10.1648/0273-8570-71.4.606. JSTOR 4514529. S2CID 86597085.
Wheelwright, N.T. (1985). "Fruit size, gape width and the diets of fruit-eating birds" (PDF). Ecology. 66 (3): 808–818. Bibcode:1985Ecol...66..808W. doi:10.2307/1940542. JSTOR 1940542. Archived from the original (PDF) on 2016-04-08. Retrieved 2013-10-31.
Soler, J.J.; Avilés, J.M. (2010). Halsey, Lewis George (ed.). "Sibling competition and conspicuousness of nestling gapes in altricial birds: A comparative study". PLoS ONE. 5 (5): e10509. Bibcode:2010PLoSO...510509S. doi:10.1371/journal.pone.0010509. PMC 2865545. PMID 20463902.
Hauber, Mark & Rebecca M. Kilner (2007). "Coevolution, communication, and host-chick mimicry in parasitic finches: who mimics whom?" (PDF). Behav. Ecol. Sociobiol. 61 (4): 497–503. Bibcode:2007BEcoS..61..497H. doi:10.1007/s00265-006-0291-0. S2CID 44030487. Archived from the original (PDF) on 2012-03-20.
Hunt, Sarah; Kilner, Rebecca M.; Langmore, Naomi E.; Bennett, Andrew T.D. (2003). "Conspicuous, ultravioletrich mouth colours in begging chicks". Biology Letters. 270 (Suppl 1): S‑25–S‑28. doi:10.1098/rsbl.2003.0009. PMC 1698012. PMID 12952627.
Schuetz, Justin G. (October 2005). "Reduced growth but not survival of chicks with altered gape patterns". Animal Behaviour. 70 (4): 839–848. doi:10.1016/j.anbehav.2005.01.007. ISSN 0003-3472. S2CID 53170955.
Nicola, Saino; Roberto, Ambrosini; Roberta, Martinelli; Paola, Ninni; Anders Pape, Møller (2003). "Gape coloration reliably reflects immunocompetence of barn swallow (Hirundo rustica) nestlings" (PDF). Behavioral Ecology. 14 (1): 16–22. doi:10.1093/beheco/14.1.16. Archived from the original (PDF) on 11 July 2011. Retrieved 27 June 2010.
Noble, D.G.; Davies, N.B.; Hartley, I.R.; McRae, S.B. (July 1999). "The Red Gape of the Nestling Cuckoo (Cuculus canorus) is not a supernormal stimulus for three common hosts". Behaviour. 136 (9): 759–777. doi:10.1163/156853999501559. JSTOR 4535638.
Tanaka, Keita D.; Morimoto, Gen; Ueda, Keisuke (2005). "Yellow wing-patch of a nestling Horsfield's hawk cuckoo Cuculus fugax induces miscognition by hosts: Mimicking a gape?". Journal of Avian Biology. 36 (5): 461–64. doi:10.1111/j.2005.0908-8857.03439.x. Archived from the original on 2012-10-21.
Bock, Walter J. (1989). "Organisms as functional machines: A connectivity explanation". American Zoologist. 29 (3): 1119–1132. doi:10.1093/icb/29.3.1119. JSTOR 3883510.
Harris, Mike P. (2014). "Aging Atlantic puffins Fratercula arctica in summer and winter" (PDF). Seabird. 27. Centre for Ecology & Hydrology: 22–40. doi:10.61350/sbj.27.21. Archived from the original (PDF) on June 11, 2016.
Mougeo, François; Arroyo, Beatriz E. (22 June 2006). "Ultraviolet reflectance by the cere of raptors". Biology Letters. 2 (2): 173–176. doi:10.1098/rsbl.2005.0434. PMC 1618910. PMID 17148356.
Parejo, Deseada; Avilés, Jesús M.; Rodriguez, Juan (23 April 2010). "Visual cues and parental favouritism in a nocturnal bird". Biology Letters. 6 (2): 171–173. doi:10.1098/rsbl.2009.0769. PMC 2865047. PMID 19864276.
Conover, Michael R.; Miller, Don E. (November 1980). "Rictal Bristle Function in Willow Flycatcher" (PDF). The Condor. 82 (4): 469–471. doi:10.2307/1367580. JSTOR 1367580.
Cunningham, Susan J.; Alley, Maurice R.; Castro, Isabel (January 2011). "Facial Bristle Feather Histology and Morphology in New Zealand Birds: Implications for Function". Journal of Morphology (PDF). 272 (1): 118–128. doi:10.1002/jmor.10908. PMID 21069752. S2CID 20407444.
Ralph, Charles L. (May 1969). "The Control of Color in Birds". American Zoologist. 9 (2): 521–530. doi:10.1093/icb/9.2.521. JSTOR 3881820. PMID 5362278.
Jouventin, Pierre; Nolan, Paul M.; Örnborg, Jonas; Dobson, F. Stephen (February 2005). "Ultraviolet spots in king and emperor penguins". The Condor. 113 (3): 144–150. doi:10.1650/7512. S2CID 85776106.
Bhullar, Bhart-Anjan S.; Morris, Zachary S.; Sefton, Elizabeth M.; Tok, Atalay; Tokita, Masayoshi; Namkoong, Bumjin; Camacho, Jasmin; Burnham, David A.; Abzhanov, Arhat (July 2015). "A molecular mechanism for the origin of a key evolutionary innovation, the bird beak and palate, revealed by an integrative approach to major transitions in vertebrate history: DEVELOPMENTAL MECHANISM FOR ORIGIN OF BIRD BEAK". Evolution. 69 (7): 1665–1677. doi:10.1111/evo.12684. PMID 25964090. S2CID 205124061.
Abzhanov, Arhat; Protas, Meredith; Grant, B. Rosemary; Grant, Peter R.; Tabin, Clifford J. (2004-09-03). "Bmp4 and Morphological Variation of Beaks in Darwin's Finches". Science. 305 (5689): 1462–1465. Bibcode:2004Sci...305.1462A. doi:10.1126/science.1098095. ISSN 0036-8075. PMID 15353802. S2CID 17226774.
Abzhanov, Arhat; Kuo, Winston P.; Hartmann, Christine; Grant, B. Rosemary; Grant, Peter R.; Tabin, Clifford J. (August 2006). "The calmodulin pathway and evolution of elongated beak morphology in Darwin's finches". Nature. 442 (7102): 563–567. Bibcode:2006Natur.442..563A. doi:10.1038/nature04843. ISSN 0028-0836. PMID 16885984. S2CID 2416057.
Ito, Yoshihiro; Yeo, Jae Yong; Chytil, Anna; Han, Jun; Bringas, Pablo; Nakajima, Akira; Shuler, Charles F.; Moses, Harold L.; Chai, Yang (2003-11-01). "Conditional inactivation of Tgfbr2 in cranial neural crest causes cleft palate and calvaria defects". Development. 130 (21): 5269–5280. doi:10.1242/dev.00708. ISSN 1477-9129. PMID 12975342. S2CID 10925294.
Mallarino, R.; Grant, P. R.; Grant, B. R.; Herrel, A.; Kuo, W. P.; Abzhanov, A. (2011-03-08). "Two developmental modules establish 3D beak-shape variation in Darwin's finches". Proceedings of the National Academy of Sciences. 108 (10): 4057–4062. Bibcode:2011PNAS..108.4057M. doi:10.1073/pnas.1011480108. ISSN 0027-8424. PMC 3053969. PMID 21368127.
"Vibration-sensing beak organ found in ibises, kiwi birds, and sandpipers". 2021. doi:10.1036/1097-8542.BR0105211. {{cite magazine}}: Cite magazine requires |magazine= (help)
Clayton, [deficient citation]; Lee, [deficient citation]; Tompkins, [deficient citation]; Brodie, [deficient citation] (September 1999). "Reciprocal Natural Selection on Host-Parasite Phenotypes" (PDF). The American Naturalist. 154 (3): 261–270. Bibcode:1999ANat..154..261C. doi:10.1086/303237. hdl:10536/DRO/DU:30056229. ISSN 1537-5323. PMID 10506542. S2CID 4369897. Archived from the original (PDF) on 2020-09-12. Retrieved 2019-09-05.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)^{[full citation needed]}
Boyd, [deficient citation] (1951). "A survey of parasitism of the Staling Sturnus vulgaris L. in North America". Journal of Parasitology. 37 (1): 56–84. doi:10.2307/3273522. JSTOR 3273522. PMID 14825028.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)^{[full citation needed]}
Ash, [deficient citation] (1960). "A study of the mallophaga of birds with particular reference to their ecology". Ibis. 102: 93–110. doi:10.1111/j.1474-919X.1960.tb05095.x.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)^{[full citation needed]}
Clayton, Dale H.; Moyer, Brett R.; Bush, Sarah E.; Jones, Tony G.; Gardiner, David W.; Rhodes, Barry B.; Goller, Franz (2005-04-22). "Adaptive significance of avian beak morphology for ectoparasite control". Proceedings of the Royal Society of London B: Biological Sciences. 272 (1565): 811–817. doi:10.1098/rspb.2004.3036. ISSN 0962-8452. PMC 1599863. PMID 15888414.
Moyer, Brett R.; Peterson, A. Townsend; Clayton, Dale H. (2002). "Influence of bill shape on ectoparasite load in western scrub-jays" (PDF). The Condor. 104 (3): 675–678. doi:10.1650/0010-5422(2002)104[0675:iobsoe]2.0.co;2. hdl:1808/16618. ISSN 0010-5422. S2CID 32708877.
Clayton, D.H.; Walther, B.A. (2001-09-01). "Influence of host ecology and morphology on the diversity of Neotropical bird lice". Oikos. 94 (3): 455–467. Bibcode:2001Oikos..94..455C. doi:10.1034/j.1600-0706.2001.940308.x. ISSN 1600-0706.
Tattersall, Glenn J.; Andrade, Denis V.; Abe, Augusto S. (24 July 2009). "Heat Exchange from the Toucan Bill Reveals a Controllable Vascular Thermal Radiator". Science. 325 (5949): 468–470. Bibcode:2009Sci...325..468T. doi:10.1126/science.1175553. PMID 19628866. S2CID 42756257.
Greenbert, Russell; Danner, Raymond; Olsen, Brian; Luther, David (14 July 2011). "High summer temperature explains bill size variation in salt marsh sparrows". Ecography. online first (2): 146–152. doi:10.1111/j.1600-0587.2011.07002.x.
Phillips, Polly K.; Sanborn, Allen F. (December 1994). "An infrared, thermographic study of surface temperature in three ratites: Ostrich, emu and double-wattled cassowary". Journal of Thermal Biology. 19 (6): 423–430. Bibcode:1994JTBio..19..423P. doi:10.1016/0306-4565(94)90042-6.
Amerson, A. Binion (May 1967). "Incidence and Transfer of Rhinonyssidae (Acarina: Mesostigmata) in Sooty Terns (Sterna fuscata)". Journal of Medical Entomology. 4 (2): 197–9. doi:10.1093/jmedent/4.2.197. PMID 6052126.
Park, F. J. (March 2011). "Avian trichomoniasis: A study of lesions and relative prevalence in a variety of captive and free-living bird species as seen in an Australian avian practice". The Journal of the Australia Veterinary Association. 89 (3): 82–88. doi:10.1111/j.1751-0813.2010.00681.x. PMID 21323655.
Cunningham, Susan J.; Alley, M.R.; Castro, I.; Potter, M.A.; Cunningham, M.; Pyne, M.J. (2010). "Bill morphology or Ibises suggests a remote-tactile sensory system for prey detection". The Auk. 127 (2): 308–316. doi:10.1525/auk.2009.09117. S2CID 85254980.
Demery, Zoe P.; Chappell, J.; Martin, G.R. (2011). "Vision, touch and object manipulation in Senegal parrots Poicephalus senegalus". Proceedings of the Royal Society B. 278 (1725): 3687–3693. doi:10.1098/rspb.2011.0374. PMC 3203496. PMID 21525059.

georgealozano.com

Nicola, Saino; Roberto, Ambrosini; Roberta, Martinelli; Paola, Ninni; Anders Pape, Møller (2003). "Gape coloration reliably reflects immunocompetence of barn swallow (Hirundo rustica) nestlings" (PDF). Behavioral Ecology. 14 (1): 16–22. doi:10.1093/beheco/14.1.16. Archived from the original (PDF) on 11 July 2011. Retrieved 27 June 2010.

handle.net

hdl.handle.net

Clayton, [deficient citation]; Lee, [deficient citation]; Tompkins, [deficient citation]; Brodie, [deficient citation] (September 1999). "Reciprocal Natural Selection on Host-Parasite Phenotypes" (PDF). The American Naturalist. 154 (3): 261–270. Bibcode:1999ANat..154..261C. doi:10.1086/303237. hdl:10536/DRO/DU:30056229. ISSN 1537-5323. PMID 10506542. S2CID 4369897. Archived from the original (PDF) on 2020-09-12. Retrieved 2019-09-05.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)^{[full citation needed]}
Moyer, Brett R.; Peterson, A. Townsend; Clayton, Dale H. (2002). "Influence of bill shape on ectoparasite load in western scrub-jays" (PDF). The Condor. 104 (3): 675–678. doi:10.1650/0010-5422(2002)104[0675:iobsoe]2.0.co;2. hdl:1808/16618. ISSN 0010-5422. S2CID 32708877.

harvard.edu

ui.adsabs.harvard.edu

Mayr, Gerald (2005). "A new eocene Chascacocolius-like mousebird (Aves: Coliiformes) with a remarkable gaping adaptation" (PDF). Organisms, Diversity & Evolution. 5 (3): 167–171. Bibcode:2005ODivE...5..167M. doi:10.1016/j.ode.2004.10.013.
Pitocchelli, Jay; John F. Piatt; Harry R. Carter (2003). "Variation in plumage, molt, and morphology of the Whiskered Auklet (Aethia pygmaea) in Alaska". Journal of Field Ornithology. 74 (1): 90–98. Bibcode:2003JFOrn..74...90P. doi:10.1648/0273-8570-74.1.90. S2CID 85982302.
Wheelwright, N.T. (1985). "Fruit size, gape width and the diets of fruit-eating birds" (PDF). Ecology. 66 (3): 808–818. Bibcode:1985Ecol...66..808W. doi:10.2307/1940542. JSTOR 1940542. Archived from the original (PDF) on 2016-04-08. Retrieved 2013-10-31.
Soler, J.J.; Avilés, J.M. (2010). Halsey, Lewis George (ed.). "Sibling competition and conspicuousness of nestling gapes in altricial birds: A comparative study". PLoS ONE. 5 (5): e10509. Bibcode:2010PLoSO...510509S. doi:10.1371/journal.pone.0010509. PMC 2865545. PMID 20463902.
Hauber, Mark & Rebecca M. Kilner (2007). "Coevolution, communication, and host-chick mimicry in parasitic finches: who mimics whom?" (PDF). Behav. Ecol. Sociobiol. 61 (4): 497–503. Bibcode:2007BEcoS..61..497H. doi:10.1007/s00265-006-0291-0. S2CID 44030487. Archived from the original (PDF) on 2012-03-20.
Abzhanov, Arhat; Protas, Meredith; Grant, B. Rosemary; Grant, Peter R.; Tabin, Clifford J. (2004-09-03). "Bmp4 and Morphological Variation of Beaks in Darwin's Finches". Science. 305 (5689): 1462–1465. Bibcode:2004Sci...305.1462A. doi:10.1126/science.1098095. ISSN 0036-8075. PMID 15353802. S2CID 17226774.
Abzhanov, Arhat; Kuo, Winston P.; Hartmann, Christine; Grant, B. Rosemary; Grant, Peter R.; Tabin, Clifford J. (August 2006). "The calmodulin pathway and evolution of elongated beak morphology in Darwin's finches". Nature. 442 (7102): 563–567. Bibcode:2006Natur.442..563A. doi:10.1038/nature04843. ISSN 0028-0836. PMID 16885984. S2CID 2416057.
Mallarino, R.; Grant, P. R.; Grant, B. R.; Herrel, A.; Kuo, W. P.; Abzhanov, A. (2011-03-08). "Two developmental modules establish 3D beak-shape variation in Darwin's finches". Proceedings of the National Academy of Sciences. 108 (10): 4057–4062. Bibcode:2011PNAS..108.4057M. doi:10.1073/pnas.1011480108. ISSN 0027-8424. PMC 3053969. PMID 21368127.
Clayton, [deficient citation]; Lee, [deficient citation]; Tompkins, [deficient citation]; Brodie, [deficient citation] (September 1999). "Reciprocal Natural Selection on Host-Parasite Phenotypes" (PDF). The American Naturalist. 154 (3): 261–270. Bibcode:1999ANat..154..261C. doi:10.1086/303237. hdl:10536/DRO/DU:30056229. ISSN 1537-5323. PMID 10506542. S2CID 4369897. Archived from the original (PDF) on 2020-09-12. Retrieved 2019-09-05.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)^{[full citation needed]}
Clayton, D.H.; Walther, B.A. (2001-09-01). "Influence of host ecology and morphology on the diversity of Neotropical bird lice". Oikos. 94 (3): 455–467. Bibcode:2001Oikos..94..455C. doi:10.1034/j.1600-0706.2001.940308.x. ISSN 1600-0706.
Tattersall, Glenn J.; Andrade, Denis V.; Abe, Augusto S. (24 July 2009). "Heat Exchange from the Toucan Bill Reveals a Controllable Vascular Thermal Radiator". Science. 325 (5949): 468–470. Bibcode:2009Sci...325..468T. doi:10.1126/science.1175553. PMID 19628866. S2CID 42756257.
Phillips, Polly K.; Sanborn, Allen F. (December 1994). "An infrared, thermographic study of surface temperature in three ratites: Ostrich, emu and double-wattled cassowary". Journal of Thermal Biology. 19 (6): 423–430. Bibcode:1994JTBio..19..423P. doi:10.1016/0306-4565(94)90042-6.

jstor.org

Bonser, R.H. & Witter, M.S. (1993). "Indentation hardness of the bill keratin of the European starling" (PDF). The Condor. 95 (3): 736–738. doi:10.2307/1369622. JSTOR 1369622.
Knopf, F.L. (1974). "Schedule of presupplemental molt of white pelicans with notes on the bill horn" (PDF). Condor. 77 (3): 356–359. doi:10.2307/1366249. JSTOR 1366249.
Borras, A.; Pascual, J.; Senar, J. C. (Autumn 2000). "What Do Different Bill Measures Measure and What Is the Best Method to Use in Granivorous Birds?" (PDF). Journal of Field Ornithology. 71 (4): 606–611. doi:10.1648/0273-8570-71.4.606. JSTOR 4514529. S2CID 86597085.
Wheelwright, N.T. (1985). "Fruit size, gape width and the diets of fruit-eating birds" (PDF). Ecology. 66 (3): 808–818. Bibcode:1985Ecol...66..808W. doi:10.2307/1940542. JSTOR 1940542. Archived from the original (PDF) on 2016-04-08. Retrieved 2013-10-31.
Noble, D.G.; Davies, N.B.; Hartley, I.R.; McRae, S.B. (July 1999). "The Red Gape of the Nestling Cuckoo (Cuculus canorus) is not a supernormal stimulus for three common hosts". Behaviour. 136 (9): 759–777. doi:10.1163/156853999501559. JSTOR 4535638.
Bock, Walter J. (1989). "Organisms as functional machines: A connectivity explanation". American Zoologist. 29 (3): 1119–1132. doi:10.1093/icb/29.3.1119. JSTOR 3883510.
Conover, Michael R.; Miller, Don E. (November 1980). "Rictal Bristle Function in Willow Flycatcher" (PDF). The Condor. 82 (4): 469–471. doi:10.2307/1367580. JSTOR 1367580.
Ralph, Charles L. (May 1969). "The Control of Color in Birds". American Zoologist. 9 (2): 521–530. doi:10.1093/icb/9.2.521. JSTOR 3881820. PMID 5362278.
Boyd, [deficient citation] (1951). "A survey of parasitism of the Staling Sturnus vulgaris L. in North America". Journal of Parasitology. 37 (1): 56–84. doi:10.2307/3273522. JSTOR 3273522. PMID 14825028.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)^{[full citation needed]}

ku.edu

kuscholarworks.ku.edu

Moyer, Brett R.; Peterson, A. Townsend; Clayton, Dale H. (2002). "Influence of bill shape on ectoparasite load in western scrub-jays" (PDF). The Condor. 104 (3): 675–678. doi:10.1650/0010-5422(2002)104[0675:iobsoe]2.0.co;2. hdl:1808/16618. ISSN 0010-5422. S2CID 32708877.

livescience.com

"Platypus". LiveScience. 4 August 2014. 27572.

loc.gov

lccn.loc.gov

Whitney, William Dwight; Smith, Benjamin Eli (1911). The Century Dictionary and Cyclopedia. Vol. 6. New York: The Century Company. p. 4123. LCCN 11031934.
Elliot, Daniel Giraud (1898). The Wild Fowl of the United States and British Possessions. New York, NY: F. P. Harper. p. xviii. LCCN 98001121.

merriam-webster.com

"Beak". Merriam-Webster. Retrieved 1 July 2016.
Webster's Unabridged Dictionary of the English Language

nature.com

Abzhanov, Arhat; Kuo, Winston P.; Hartmann, Christine; Grant, B. Rosemary; Grant, Peter R.; Tabin, Clifford J. (August 2006). "The calmodulin pathway and evolution of elongated beak morphology in Darwin's finches". Nature. 442 (7102): 563–567. Bibcode:2006Natur.442..563A. doi:10.1038/nature04843. ISSN 0028-0836. PMID 16885984. S2CID 2416057.

nih.gov

pubmed.ncbi.nlm.nih.gov

Seki, Yasuaki; Bodde, Sara G.; Meyers, Marc A. (2009). "Toucan and hornbill beaks: A comparative study" (PDF). Acta Biomaterialia. 6 (2): 331–343. doi:10.1016/j.actbio.2009.08.026. PMID 19699818. Archived from the original (PDF) on 2012-04-02.
Soler, J.J.; Avilés, J.M. (2010). Halsey, Lewis George (ed.). "Sibling competition and conspicuousness of nestling gapes in altricial birds: A comparative study". PLoS ONE. 5 (5): e10509. Bibcode:2010PLoSO...510509S. doi:10.1371/journal.pone.0010509. PMC 2865545. PMID 20463902.
Hunt, Sarah; Kilner, Rebecca M.; Langmore, Naomi E.; Bennett, Andrew T.D. (2003). "Conspicuous, ultravioletrich mouth colours in begging chicks". Biology Letters. 270 (Suppl 1): S‑25–S‑28. doi:10.1098/rsbl.2003.0009. PMC 1698012. PMID 12952627.
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Parejo, Deseada; Avilés, Jesús M.; Rodriguez, Juan (23 April 2010). "Visual cues and parental favouritism in a nocturnal bird". Biology Letters. 6 (2): 171–173. doi:10.1098/rsbl.2009.0769. PMC 2865047. PMID 19864276.
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