, Volume 583, Issue 1, pp 213–222 | Cite as

From mass of body elements to fish biomass: a direct method to quantify food intake of fish eating birds

  • Alessandra Gagliardi
  • Adriano Martinoli
  • Damiano Preatoni
  • Luc A. Wauters
  • Guido Tosi
Primary Research Paper


The winter diet of great crested grebe (Podiceps cristatus) was studied in the major lakes of Insubria region, N Italy, in 2000–2003 by analysing stomach and oesophagus contents of birds found dead. Winter diet of cormorant (Phalacrocorax carbo) was studied using pellet analysis. Diet was expressed in terms of numerical abundance, frequency and biomass of prey. A detailed methodology is described of how to prepare a reference collection of otoliths, pharyngeal bones and chewing pads (key-elements), essential for species-specific identification of fish remains in stomachs and pellets, and to estimate ingested fish biomass. Correlations between mass (mg) of key-elements and mass of corresponding fish were significant, and exponential regression models were used to calculate biomass of each single prey item directly from the mass of its key-elements. Advantages of this method are compared with the more traditional two step approach in which size of elements is used to estimate fish length, followed by calculating fresh mass from fish length. Cyprinids formed the largest part of the diet for both predators. Great crested grebes selected small prey, feeding mainly on bleak (Alburnus alburnus alborella), while diet composition of cormorants varied significantly in relation to prey availability.


Podiceps cristatus Phalacrocorax carbo Fish biomass Otolith Chewing pad Pharingeal bone 



We are grateful to Bianchi A. and Luoni F. who collaborated with the laboratory work, and to fishery and environmental technicians of Como, Lecco and Varese Provinces and their staff. Authors are also indebted to Negri A., Puzzi C. and Trasforini S. who assisted with the collection of fish specimen. Three of us and three other researchers volunteered measuring and weighing key-elements to test measurement errors.


  1. Bianchi, E., 1962. Note ed osservazioni sull’avifauna acquatica del lago di Varese. Rivista Italiana di Ornitologia 32: 295–312.Google Scholar
  2. Boldreghini, P., R. Santolini & M. Pandolfi, 1997a. Abundance and frequency of occurrence of prey-fish in the diet of cormorants (Phalacrocorax carbo) in the Po River Delta (Northern Italy) during the wintering period. Ekologia Polska 45: 191–196.Google Scholar
  3. Boldreghini, P., R. Santolini, S. Volponi, L. Casini, F. L. Montanari & R. Tinarelli, 1997b. Variations in the use of foraging areas by a cormorant Phalacrocorax carbo wintering population: a case study in the Po Delta (Northern Italy). Ekologia Polska 45: 197–200.Google Scholar
  4. Buttiker, E., 1985. Die Nahrung der Haubentaucher Podiceps cristatus am Untersee (Bodensee) im Jahresverlauf. Der Ornithologische Beobacter 82: 73–83.Google Scholar
  5. Carss, D. N. & M. Marquiss, 1997. The diet of cormorants Phalacrocorax carbo in scottish freshwaters in relation to feeding habits and fisheries. Ekologia Polska 45: 207–222.Google Scholar
  6. Carss, D.N., The Diet Assessment And Food Intake Working Group, 1997. Techniques for assessing cormorant diet and food intake: towards a consensus view. Supplemento Ricerca Biologia della Selvaggina XXVI: 197–230.Google Scholar
  7. Chaine, J. & J. Duvergier, 1935. Recherches sur les otholithes des poisson. Étude descriptive et comparative de la sagitta des téléostéens. Actes Soc Limm Bordeaux 86: 5–254.Google Scholar
  8. Cherubini, G., N. Baccetti & M. Bon, 1997. Cormorants Phalacrocorax carbo wintering in the lagoon of Venice, Italy. Ekologia Polska 45: 31–37.Google Scholar
  9. Cramp, S. & K. E. L. Simmons, 1977. Handbook of the Birds of Europe, the Middle East and North Africa. Vol. 1. Oxford University Press, Oxford.Google Scholar
  10. Dirksen, S., T. J. Boudewijn, R. Noordhuis & E. C. L. Marteijn, 1995. Cormorants Phalacrocorax carbo sinensis in shallow eutrophic freshwater lakes: prey choice and fish consumption in the non-breeding period and effects of large-scale fish removal. Ardea 83: 167–184.Google Scholar
  11. Doornbos, G., 1984. Piscivorous birds on the saline lake Grevelingen, The Netherlands: abundance, prey selection and annual food consumption. Netherlands Journal of Sea Research 18: 457–479.CrossRefGoogle Scholar
  12. Duffy, D. C. & S. Jackson, 1986. Diet studies of seabirds: a review of methods. Colonial Waterbirds 9: 1–17.CrossRefGoogle Scholar
  13. Duffy, D. C. & L. J. B. Laurenson, 1983. Pellets of the Cape Cormorant as indicator of diet. Condor 85: 305–307.CrossRefGoogle Scholar
  14. Feltham, M. J. & J. M. Davies, 1997. Daily food intake of cormorants: a summary. Supplemento Ricerca Biologia della Selvaggina XXVI: 259–268.Google Scholar
  15. Forneris, G., M. Pascale & G. C. Perosino, 1996. L’ittiofauna. In Idrobiologia. EDA, Torino.Google Scholar
  16. Gagliardi, A., 2003. Prey–predator interactions in aquatic ecosystems: Great Crested Grebe (Podiceps cristatus) and Cormorant (Phalacrocorax carbo) as key species. Analysis of population dynamics, biomass consumption and management of some waterbirds in Insubria region (central-northern Italy). Unpublished PhD thesis, Insubria University, Varese.Google Scholar
  17. Gagliardi, A., A. Martinoli, L. A. Wauters & G. Tosi, 2003. A floating platform: a solution to collecting pellets when cormorants roost over water. Waterbirds 26: 54–55.CrossRefGoogle Scholar
  18. Hanzak, J, 1952. The Great Crested Grebe, Podiceps c. cristatus (L.), its ecology and economic significance. Sbornik Narod. Muz. Y Praze. Acta Musei Nationalis Pragae 8B: 3–37.Google Scholar
  19. Harkonen, T. J., 1986. Guide to the Otholits of the Bony Fishes of the Northeast Atlantic. Danbiu Aps, Hellerup.Google Scholar
  20. Johnson, J. H., R. M. Ross & D. R. Smith, 1997. Evidence of secondary consumption of invertebrate prey by double-crested cormorants. Colonial Waterbirds 20(3): 547–551.CrossRefGoogle Scholar
  21. Johnstone, I. G., M. P. Harris, S. Wanless & J. A. Graves, 1990. The usefulsess of pellets for assessing the diet of adult Shag Phalacrocorax aristotelis. Bird Study 37: 5–11.Google Scholar
  22. Le Louarn, H., 2003. Qualitative and quantitative estimation of the great cormorant Phalacrocorax carbo diet. Cormorant Research Group Bulletin N. 5: 26–30.Google Scholar
  23. Madsen, F. J., 1957. On the food habits of some fish-eating birds in Denmark. Danish Review of Game Biology 3: 19–83.Google Scholar
  24. Marteijn, E. C. L. & S. Dirksen, 1991. Cormorants Phalacrocorax carbo sinensis feeding in shallow eutrophic lakes in The Netherlands in the non-breeding period: prey choice and fish consumption. In Van Eerden, M. R. & M. Zijlstra (eds), Proceedings of the 1989 Workshop on Cormorants Phalacrocorax carbo, 135–155.Google Scholar
  25. Martinoli, A., A. Gagliardi, D. G. Preatoni, S. Di Martino, L. A. Wauters & G. Tosi, 2003. The extent of Great Crested Grebe predation on Bleak in Lake Como, Italy. Waterbirds 26: 201–208.CrossRefGoogle Scholar
  26. Martucci, O., 1997. Winter food habits of cormorants Phalacrocorax carbo in central Italy: some remarks. Ekologia Polska 45: 239–243.Google Scholar
  27. Martucci, O., L. Pietrelli & C. Consiglio, 1993. Fish otoliths as indicators of the Cormorant, P. carbo, diet. Bollettino di Zoologia 60: 393–396.Google Scholar
  28. Martyniak, S., M. Mellin, P. Stachowiack & A. Wittke, 1997. Food composition of cormorants Phalacrocorax carbo shot at two fish farms in north-eastern Poland. In Gromadzki, M. & J. Gromadzka (eds), Proceedings of the Third International Conference on Cormorants in Europe, Gdansk, Poland 13–17 April 1993, Ekologia Polska 45: 245.Google Scholar
  29. Mckay, H. V., K. A. Robinson, D. N. Carss & D. Parrott, 2003. The limitations of pellet analysis in the study of cormorant (Phalacrocorax spp.) diet. Vogelwelt 124(Suppl.): 227–236.Google Scholar
  30. Mellin, M., A. Ibron-Mirowska & S. Martyniack, 1997. Food composition of cormorants Phalacrocorax carbo shot at two fish farms in north-eastern Poland. In Gromadzki, M. & J. Gromadzka (eds), Proceedings of the Third International Conference on Cormorants in Europe, Gdansk, Poland 13–17 April 1993, Ekologia Polska 45: 247.Google Scholar
  31. Negri, A., 1995. La biologia dell’alborella (Alburnus alburnus alborella) del Lago di Como. Amministrazione provinciale di Como. Assessorato Caccia e Pesca.Google Scholar
  32. Nienhuis, J., 2000. The use of chewing pads and otoliths of Cyprinids for estimating food intake of cormorants Phalacrocorax carbo. Cormorant Research Group Bulletin 4: 40–42.Google Scholar
  33. Piersma, T., 1988. Body size, nutrient reserves and diet of Red-necked and Slavonian Grebes, Podiceps grisegena and P. auritus on Lake Ijsselmeer, The Netherlands. Bird Study 35: 13–24.CrossRefGoogle Scholar
  34. Platteeuw, M., 1988. Aalscholvers: activiteiten van de oudersen de groei van hun jongen in 1982, Ootstvaardersplassen en Naardermeer vergeleken. RIJP-rapport 32cbw, Rijksdient voor de Ijsselmeerpolders, Lelystad.Google Scholar
  35. Radke, R. J., T. Petzoldt & C. Wolter, 2000. Suitability of pharyngeal bone measures commonly used for reconstruction of prey fish length. Journal of Fish Biology 57: 961–967.CrossRefGoogle Scholar
  36. Suter, W., 1997. Roach rules: shoaling fish are a constant factor in the diet of cormorants Phalacrocorax carbo in Switzerland. Ardea 85: 135–138.Google Scholar
  37. Trauttmansdorff, J. & G. Wassermann, 1995. Number of pellets produced by immature Cormorants Phalacrocorax carbo sinensis. Ardea 83: 133–134.Google Scholar
  38. Van Dobben, W. H., 1952. The food of the cormorant in the Netherlands. Ardea 40: 1–63.Google Scholar
  39. Veldkamp, R., 1995a. Diet of cormorants, Phalacrocorax carbo sinensis, at Wanneperveen, The Netherlands, with special reference to bream, Abramis brama. Ardea 83: 143–155.Google Scholar
  40. Veldkamp, R., 1995b. The use of chewing pads for estimating the consumption of Cyprinids by cormorants Phalacrocorax carbo. Ardea 83: 135–138.Google Scholar
  41. Volponi, S., 2000. Cormorant research in the Po Delta (NE Italy). Cormorant Study Group Bulletin 4: 22–25.Google Scholar
  42. Volponi, S. & P. Callegarini, 1997. Osservazioni sul regime alimentare del cormorano (Palacrocorax carbo sinensis) nel Delta del Fiume Po nella stagione 1993/94. Laguna 97: 32–39.Google Scholar
  43. Zijlstra, M. & M. R. Van Eerden, 1995. Pellet production and the use of otoliths in determining the diet of cormorants Phalacrocorax carbo sinensis: trials with captive birds. Ardea 83: 123–131.Google Scholar

Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Alessandra Gagliardi
    • 1
  • Adriano Martinoli
    • 1
  • Damiano Preatoni
    • 1
  • Luc A. Wauters
    • 1
  • Guido Tosi
    • 1
  1. 1.Dipartimento Ambiente-Salute-SicurezzaUniversità degli Studi dell’InsubriaVareseItaly

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