Stable isotopes in ornithology:: A brief introduction

Over the last ten years, stable isotopes have become a widely used fool in ornithology and animal ecology. Here we review the nomenclature and methods used to analyze the isotopic composition of bird tissues and describe the uses of this technology in the study of birds. We argue that stable isotope analyses allow researching the niche dimensions characterized by George Evelyn Hutchinson as scenopoetic and bionomic. The use of stable isotopes to populate the scenopetic axes of the niche depends on the existence of "isoscapes" generated by the hydrogen and oxygen isotopic composition of environmental water, as well as by the strontium composition of soils. These isoscapes allow pinpointing the geographic site of origin of birds, the climatic environment that they inhabit, and to tack their local and migratory movements. The metabolic processes of primary producers, such as photosynthesis and nitrogen fixation, create a large number of isotopic signals that permit exploring the bionomic axes of the ecological niche. The isotopic composition of carbon and nitrogen can be used to find out the type of resources used by birds and/or their position in food webs. Stable isotopes are a especially useful tool to, investigate the trophic diversity of individuals, populations, and communities.