Background/Question/Methods Ecologists are often interested in relationships between animal stress levels and variations in their environments or life stages, since elevations in stress can demonstrate when animals perceive unfavorable conditions. Stress levels of animals are commonly assessed via assessment of glucocorticoid hormones in plasma, though because of the rapid response time of hormones, this approach dictates that sampling be conducted immediately after capture to obtain ‘baseline’ measures, which can be logistically difficult in the field. An alternative approach that is not as time-sensitive relies on the known effect of stress hormones on circulating white blood cell populations. Specifically, counts of certain white blood cells can be obtained from standard blood smears to indirectly estimate baseline levels of glucocorticoids at the time the blood was drawn. Moreover, these counts are not immediately influenced by capture and handling. This presentation will outline this approach, reporting results from a recent literature review of the subject that demonstrated overwhelming support for its use in ecological research, and recent experiments conducted with amphibians where this ‘hematological stress’ method was used. These experiments include effects of captivity on stress levels of wild individuals, effects of larval rearing density of stress of metamorphic amphibians, as well as recent unpublished experiments involving direct injection of corticosterone into captive amphibians.

Results/Conclusions Results of experiments support those from our review of the literature, in that hematological stress indices increase when wild individuals are brought into captivity and when amphibians are reared in high-density environments. Further, direct injection of corticosterone into captive amphibians also results in elevated hematological stress indices. Taken together these results emphasize the close link between levels of stress hormones and white blood cell populations in vertebrate animals and support the utility of specific white blood cell counts for assessing stress in ecological research.