1998 Volume 30 Issue 2 Pages 59-82
Stable isotope analysis has been recognized as a useful tool in ecological science. The reason is that stable isotope ratio change with given enrichment factor through food chain: stable carbon isotope ratio in an animal become close to that of diet. Stable nitrogen isotope ratio in it reveal stepwise enrichment with generally recognized enrichment factor of 3.4±1.0‰. Conventional methods for diet analysis, such as content analysis of digestive organs, provide "snap-shot information" on diet of birds. And there is possibility to overor underestimate diet composition due to different digestive rate on different diet components. In contrast, stable isotope analysis overcame these problem, since isotope ratio in animals reflects the ratio of assimilated diet. As additional information, turnover rate of carbon stable isotope in bird tissues and enrichment factor of carbon and nitrogen isotopes between diets and various kinds of bird tissues have been confirmed. These knowledge supported to evaluate diet of birds in different period from a week to over a year. Based on these understanding, stable isotope analysis have been applied to bird ecology: to reconstruct diet composition, to evaluate relative contribution of various kinds of diets, to trace movements in wintering sites and migration pattern, to estimate carbon and nitrogen cycles in rookeries, and to assess physiological condition of birds. These researches suggested that stable isotope analysis is powerful tool in avian ecology. In future research more laboratory experiments should be required to assess ecological, physiological and biochemical dynamics of isotopes through metabolic process in body of birds and assimilation process of diet components. In addition, multiple use of stable isotopes not only carbon and nitrogen, but also hydrogen, oxygen, sulfur and strontium will also be expected to get insight of bird life such as migration movement of birds.
