An isotopic technique to mark mid‐sized vertebrates non‐invasively

Although dispersal is an important attribute of animal population ecology, knowledge of dispersal rates or distances for many wide‐ranging species is lacking. Current methods require capturing and restraining animals, which can be cost‐prohibitive, fail to collect sufficient samples or change animal ranging behaviors. Herein, we describe a novel, cost‐effective and non‐invasive method, using bait enriched with stable isotopes to mark the hair of American martens Martes americana . Captive martens that consumed isotopically labeled glycine exhibited significant and progressive enrichment in the isotopic signature of 13 C, 15 N and 2 H in both whole blood and hair. A distinct mark in hair, >2 standard deviations above natural abundance, occurred within 14 days of the second dose. The rate of isotopic labeling of hair was higher in spring, possibly because labeled amino acids became diluted among the many hairs growing during the autumn. Because hair and feathers can be collected non‐invasively from large geographic areas without capturing animals, this labeling method can be used to mark and study the movement and dispersal rates of animals across landscapes efficiently.