Immunoreactive cortisone in droppings reflect stress levels, diet and growth rate of gull-billed tern chicks.
Blood levels of corticosterone have been traditionally analyzed to assess stress levels in birds; however, measuring steroid hormone metabolites in feces and droppings has gained much interest as a noninvasive technique successfully used for such purposed in vertebrates. Diet may affect these fecal metabolite levels (e.g., due to nutritional stress), however, this variable has not been taken into account in studies with chicks despite the great dietary flexibility of many avian species. In this study, we addressed for the first time this key issue and validated the technique in wild gull-billed tern chicks (Gelochelidon nilotica). Several enzyme immunoassays were used to determine the most appropriate test to measure the stress response. Subsequently, we performed an experiment in captivity to assess adrenocortical activity in gull-billed tern chicks fed with two diets: piscivorous vs. insectivorous. Finally, the relation between the chicks' growth rate and excreted immunoreactive glucocorticoid metabolites (EGMs) was also evaluated. We found the immunoreactive cortisone metabolites to be a good index of stress (as being an index of adrenocortical reactivity) in chicks of this species. Fish-fed chicks had higher levels of cortisone metabolites when comparing both concentration and total daily excreted metabolites. Within each treatment diet, cortisone metabolite levels and growth rates were negatively correlated. These findings suggest that the diet should be considered when using this technique for comparative purposes and highlight the trade-off between stress levels and chicks growth rates.
Conservation Biology Research Group, Zoology, University of Extremadura, Avenida de Elvas s/n, 06071 Badajoz, Spain.
Noelia
N
Albano
Conservation Biology Research Group, Zoology, University of Extremadura, Avenida de Elvas s/n, 06071 Badajoz, Spain. Electronic address: fquesada@unex.es.
Francisco
F
Santiago-Quesada
Conservation Biology Research Group, Zoology, University of Extremadura, Avenida de Elvas s/n, 06071 Badajoz, Spain.
José A
JA
Masero
Conservation Biology Research Group, Zoology, University of Extremadura, Avenida de Elvas s/n, 06071 Badajoz, Spain.
Juan M
JM
Sánchez-Guzmán
Department of Biomedical Sciences-Medical Biochemistry, University of Veterinary Medicine, Veterinärplatz 1, A-1210 Vienna, Austria.
Erich
E
Möstl
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000276:immunology / Q000378:metabolism; D046091:Charadriiformes / Q000502:physiology*; D003348:Cortisone / Q000276:immunology* / Q000378:metabolism*; D004032:Diet; D005243:Feces / Q000737:chemistry*; D007124:Immunoenzyme Techniques; D013312:Stress, Physiological
D000893:Anti-Inflammatory Agents; D003348:Cortisone
Chicks; Diet; Excreted glucocorticoid metabolites; Growth rate; Stress