Journal of Ornithology

, Volume 161, Issue 1, pp 17–24 | Cite as

A re-evaluation of the chemical composition of avian urinary excreta

  • Nicholas M. A. CrouchEmail author
  • Vincent M. Lynch
  • Julia A. Clarke
Original Article


Osmoregulation in birds is complicated, with different organs acting concurrently to regulate this physiological process. Of particular interest is how the urinary excretions of birds can remove excess nitrogen while minimizing the need for dietary water and balancing the physiological demands of oviparity. It has long been concluded from chemical analyses, and more recently from genetic studies, that uric acid is the principal constituent of urine in Aves. However, research has also demonstrated that waste material may be modified in the ceca immediately prior to it being expelled. Here, we quantify the chemical composition of the urine component of excreta of six avian species using X-ray diffraction techniques to test the hypothesis that it is principally composed of uric acid, as commonly reported. None of the analyzed samples were found to contain uric acid. Instead, a variety of compounds including ammonium urate, struvite (magnesium ammonium phosphate), and two unknown compounds, were found. Our results show that the uric acid pathway is indeed the system by which nitrogen is removed in these birds, but that additional modification occurs in the urine prior to excretion. These results raise questions for future research on the urinary excretions of birds, including identification of the unknown compounds found in the present study.


Birds Urine Uric acid Ammonium urate Struvite 


Eine Neubewertung der chemischen Zusammensetzung des Urins bei Vögeln

Osmoregulation bei Vögeln ist ein komplizierter Prozess, bei dem verschiedene Organe gleichzeitig zur Regulierung ihrer Physiologie aktiv sind. Von besonderem Interesse ist dabei, wie bei Vögeln mit dem Urin überschüssiger Stickstoff ausgeschieden und gleichzeitig der Bedarf an Flüssigkeit aus der Nahrung minimiert sowie die physiologischen Anforderungen der Oviparie ausgeglichen werden können. Chemische Analysen in Kombination mit neuesten genetischen Studien haben schon länger dargelegt, dass Harnsäure den Hauptbestandteil des Urins bei Vögeln bildet. Jedoch haben zusätzliche Untersuchungen ergeben, dass Abfallstoffe in den Blinddärmen unmittelbar vor der Ausscheidung umgewandelt werden. In dieser Studie quantifizieren wir die chemische Zusammensetzung der Urin-Bestandteile der Vogelexkremente von sechs Arten mittels Röntgenstrukturanalysen, um die Hypothese zu testen, dass dieser hauptsächlich aus Harnsäure besteht, wie stets berichtet wird. In unseren Ergebnissen konnte kein Beleg für Harnsäure in den analysierten Proben gefunden werden. Stattdessen konnten wir eine Vielzahl an verschiedenen Bestandteilen identifizieren, unter anderem Ammoniumurat, Struvit (Magnesium-Ammonium-Phosphat) und zwei unbekannte Verbindungen. Obwohl der Abbau zu Harnsäure weiterhin den Stoffwechselweg darstellt, über den Stickstoff ausgeschieden wird, zeigen unsere Ergebnisse, dass zusätzliche Umwandlungen vor der Ausscheidung stattfinden. Diese Ergebnisse werfen Fragen für zukünftige Untersuchungen auf, einschließlich der genaueren Bestimmung der hier entdeckten unbekannten Verbindungen.



We wish to honor the late Dr. Robert (Bob) Folk for discussion that inspired this work; his kindness, creativity and broad interests will be remembered. John, Marcy and the staff at Austin Zoo provided the urine samples. Chris Torres provided helpful discussion and comments on the manuscript.


This work received no project-specific funding.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.

Archiving of data

All raw data files will be deposited in Dryad upon acceptance of this manuscript.

Supplementary material

10336_2019_1692_MOESM1_ESM.pdf (132 kb)
Supplementary material 1 (PDF 131 kb)


  1. Anderson GL, Braun EJ (1985) Postrenal modification of urine in birds. Am J Physiol 248:R93–R98PubMedGoogle Scholar
  2. Blaine J, Chonchol M, Levi M (2015) Renal control of calcium, phosphate, and magnesium homeostasis. Clin J Am Soc Nephrol 10:1257–1272PubMedGoogle Scholar
  3. Bojakowska I (2016) Phosphorus in lake sediments of Poland–results of monitoring research. Limnol Rev 16:15–25Google Scholar
  4. Braun EJ (1999) Integration of organ systems in avian osmoregulation. J Exp Zool 283:702–707Google Scholar
  5. Braun EJ, Campbell CE (1989) Uric acid decomposition in the lower gastrointestinal tract. J Exp Zool Suppl 3:70–74Google Scholar
  6. Braun EJ, Pacelli MM (1991) The packaging of uric acid in avian urine. FASEB J 5:A1408Google Scholar
  7. Campbell JW (1995) Excretory nitrogen metabolism in reptiles and birds. In: Walsh PJ, Wright P (eds) Nitrogen metabolism and excretion. CRC, Boca Raton, pp 147–179Google Scholar
  8. Casotti G, Braun EJ (1997) Ionic composition of urate-containing spheres in the urine of domestic fowl. Comp Biochem Physiol 118A:585–588Google Scholar
  9. Casotti G, Braun EJ (2004) Protein location and elemental composition of urine spheres in different avian species. J Exp Zool 301A:579–587Google Scholar
  10. Chaplin SB (1989) Effect of cecectomy on water and nutrient absorption of birds. J Exp Zool 3:81–86Google Scholar
  11. Chong DP (2014) Theoretical study of uric acid and its ions in aqueous solution. J Theor Comput Sci 1:2. CrossRefGoogle Scholar
  12. Chruszcz M, Borek D, Domagalski M, Otwinowski Z, Minor W (2009) X-ray diffraction experiment: the last experiment in the structure elucidation process. Adv Prot Chem Str 77:23–40Google Scholar
  13. Clark NB, Wideman RF (1977) Renal excretion of phosphate and calcium in parathyroidectomized starlings. Am J Physiol 233:F138–F144PubMedGoogle Scholar
  14. Clench MH, Mathias JR (1995) The avian cecum: a review. Wilson Bull 107:93–121Google Scholar
  15. Cullen DJ (1988) Mineralogy of nitrogenous guano on the Bounty Islands, SW Pacific Ocean. Sedimentology 93:421–428Google Scholar
  16. Curtman LJ, Hart D (1921) The preparation and properties of some salts of uric acid. J Biol Chem 49:599–613Google Scholar
  17. Danztler WH, Roberts JT (1989) Glomerular filtration rate in conscious and unrestrained starlings under dehydration. Am J Physiol 256:R836–R839Google Scholar
  18. Dauter Z (2017) Collection of X-ray diffraction data from macromolecular crystals. Methods Mol Biol 1607:165–184PubMedPubMedCentralGoogle Scholar
  19. Davis WA, Sadtler SS (1913) Allen’s commerical organic analysis, vol 7. Blakiston’s, PhiladelphiaGoogle Scholar
  20. del Hoyo J, Elliott A, Sargatal J, Christie DA, Kirwan G (eds) (2018) Handbook of the birds of the world. Lynx, BarcelonaGoogle Scholar
  21. Donovan JJ, Grim EC (2007) Episodic struvite deposits in a northern Great Plains flyway lake: indicators of mid-Holocene drought? Holocene 17:1155–1169Google Scholar
  22. Echols MS (2005) Evaluating and treating the kidneys. In: Harrison G, Lightfoot T (eds) Clinical avian medicine, vol Chap 16. Spix, Palm BeachGoogle Scholar
  23. Elliott K, FitzSimons DW (2009) Purine and pyrimidine metabolism. Wiley, New YorkGoogle Scholar
  24. Engelking L (2002) Review of veterinary physiology. Teton New Media, JacksonGoogle Scholar
  25. Fisher JR, Eakin RE (1957) Nitrogen excretion in developing chick embryos. J Embryol Exp Morph 5:215–224Google Scholar
  26. Folk RL (1969) Spherical urine in birds: petrography. Science 166:1516–1518PubMedGoogle Scholar
  27. Friedrich W, Knipping P, Laue M (1913) Interferenzerscheinungen bei Röntgenstrahlen. Ann Phys 346:971–988Google Scholar
  28. Gill FB (2007) Ornithology, 3rd edn. Freeman, New YorkGoogle Scholar
  29. Griminger P (1976) Protein metabolism. In: Sturkie PD (ed) Avian physiology, chap 13. Springer, New York, pp 233–252Google Scholar
  30. Herd RM, Dawson TJ (1984) Fiber digestion in the Emu, Dromaius novaehollandiae, a large bird with a simple gut and high rates of passage. Physiol Zool 57:70–84Google Scholar
  31. Huether SE, McCance KL (2013) Understanding pathophysiology. Elsevier, LondonGoogle Scholar
  32. Hunger S, Sims JT, Sparks DL (2008) Evidence for struvite in poultry litter: effect of storage and drying. J Environ Qual 37:1617–1625PubMedGoogle Scholar
  33. Jahnen-Dechent W, Ketteler M (2012) Magnesium basics. Clin Kidney J 5:i3–i14PubMedPubMedCentralGoogle Scholar
  34. Karasawa Y (1989) Ammonia production from uric acid, urea, and amino acids and its absorption from the ceca of the cockerel. J Exp Zool Suppl 3:75–80Google Scholar
  35. Karasawa SJH, Nahm KH (2000) Effect of caecectomy on growth, moisture in excreta, gastrointestinal passage time and uric acid excretion in growing chicks. Br Poult Sci 41:72–74PubMedGoogle Scholar
  36. Keebaugh AC, Thomas JW (2010) The evolutionary fate of the genes encoding the purine catabolic enzymes in hominoids, birds, and reptiles. Mol Biol Evol 27:1359–1369PubMedPubMedCentralGoogle Scholar
  37. Laue M (1913) Eine quantitative Prüfung der Theorie für die Interferenzerscheinungen bei Röntgenstrahlen. Ann Phys 346:989–1002Google Scholar
  38. Laverty G, Skadhauge E (2008) Adaptive strategies for post-renal handling of urine in birds. Comp Biochem Phys A 149:246–254Google Scholar
  39. Lee IR, Yang L, Sebetso G et al (2013) Characterization of the complete uric acid degradation pathway in the fungal pathogen Cryptococcus neoformans. PLOS ONE 8:1–13Google Scholar
  40. Lonsdale K, Sutor DJ (1971) Uric acid dihydrate in bird urine. Science 172:958–959PubMedGoogle Scholar
  41. Lumeij JT, Remple JD (1991) Plasma urea, creatinine and uric acid concentrations in relation to feeding in Peregrine Falcons (Falco peregrinus). Avian Pathol 20:79–83PubMedGoogle Scholar
  42. Maiuolo J, Oppedisano F, Gratteri S, Muscoli C, Mollace V (2016) Regulation of uric acid metabolism and excretion. Int J Cardiol 213:8–14PubMedGoogle Scholar
  43. McNabb RA, McNabb A (1975) Urate excretion by the avian kidney. Comp Biochem Phys A 51:253–258Google Scholar
  44. Milroy TH (1903) The formation of uric acid in birds. J Physiol 30:47–60PubMedPubMedCentralGoogle Scholar
  45. Minkowski O (1886) Ueber den Einfluss der Leberexstirpation auf den Stoffwechsel. Arch Exp Pathol Pharmakol 21:41–87Google Scholar
  46. Mobley HLT, Hausinger RP (1989) Microbial ureases: significance, regulation, and molecular characterization. Microbiol Rev 53:85–108PubMedPubMedCentralGoogle Scholar
  47. Monk RD, Bushinsky DA (2010) Nephrolithiasis and nephrocalcinosis. In: Floege J, Johnson RJ, Freehally J (eds) Comprehensive clinical nephrology. Elsevier Saunders, St Louis, pp 687–701Google Scholar
  48. Nahm KH (2003) Evaluation of the nitrogen content in poultry manure. World Poult Sci J 59:77–88Google Scholar
  49. Parmar MS (2004) Kidney stones. BMJ 328:1420–1424PubMedPubMedCentralGoogle Scholar
  50. Reyes L, Braun EJ (2005) The functional morphology of the English Sparrow cecum. Comp Biochem Phys A 141:292–297Google Scholar
  51. Robinson MR, Norris RD, Sur RL, Preminger GM (2008) Urolithiasis: not just a 2-legged animal disease. J Urol 179:46–52PubMedGoogle Scholar
  52. Romer AS (1957) Origin of the amniote egg. Sci Mon 85:57–63Google Scholar
  53. Schmidt-Nielsen K (1997) Animal physiology: adaptation and environment. Cambridge University Press, LondonGoogle Scholar
  54. Sherwood L, Klandorf H, Yancey P (2012) Animal physiology: from genes to organisms. Cengage Learning, Thomson/Brooks/ColeGoogle Scholar
  55. Skadhauge E (1968) The cloacal storage of urine in the rooster. Comp Biochem Physiol 24:7–18PubMedGoogle Scholar
  56. Skadhauge E (2012) Osmoregulation in birds. Springer, BerlinGoogle Scholar
  57. Sommerfeld A (1912) Über die Beugung der Röntgenstrahlen. Ann Phys 343:473–506Google Scholar
  58. Stanley D, Geier MS, Chen H, Hughes RJ, Moore RJ (2015) Comparison of fecal and cecal microbiotas reveals qualitative similarities but quantitative differences. BMC Microbiol 15:51PubMedPubMedCentralGoogle Scholar
  59. Steel T (1922) Chemical notes–general. In: The Proceedings of the Linnean Society of New South Wales vol. 47. Sydney and Melbourne Publishing, pp 441–446 Google Scholar
  60. Stenkat J, Krautwald-Junghanns ME, Schmitz Ornés A, Eilers A, Schmidt V (2014) Aerobic cloacal and pharyngeal bacterial flora in six species of free-living birds. J Appl Microbiol 117:1564–1571PubMedGoogle Scholar
  61. Suryanarayana C, Grant Norton M (1998) X-ray diffraction: a practical approach. Springer, USAGoogle Scholar
  62. Tatur A (1989) Ornithogenic soils of the maritime Antarctic. Pol Polar Res 10:481–532Google Scholar
  63. van der Hoeven-Hangoor E, van de Linde IB, Paton ND, Verstegen MW, Hendriks WH (2013) Effect of different magnesium sources on digesta and excreta moisture content and production performance in broiler Chickens. Poult Sci 92:382–391PubMedGoogle Scholar
  64. Wagner CA, Mohebbi N (2010) Urinary pH and stone formation. J Neophrol 23:S165–S169Google Scholar
  65. Waite DW, Taylor MW (2015) Exploring the avian gut microbiota: current trends and future directions. Front Microbiol 6:1–12Google Scholar
  66. Wang Z, Königsberger L, Königsberger E (2017) Solubility equilibria in the uric acid-ammonium urate-water system. Monatsch Chem. CrossRefGoogle Scholar
  67. Wilcox WR, Khalaf A, Weinberger A, Kippen I, Klinenberg JR (1972) Solubility of uric acid and monosodium urate. Med Biol Eng 10:522–531PubMedGoogle Scholar
  68. Wollaston WH (1810) On cycstic oxide: a new species of urinary calculus. Philos Trans R Soc Lond 100:223–230Google Scholar
  69. Wu G (2013) Amino acids: biochemistry and nutrition. CRC, Boca RatonGoogle Scholar

Copyright information

© Deutsche Ornithologen-Gesellschaft e.V. 2019

Authors and Affiliations

  1. 1.Department of Geological Sciences, Jackson School of GeosciencesThe University of TexasAustinUSA
  2. 2.Department of Chemistry, College of Natural ScienceThe University of TexasAustinUSA

Personalised recommendations