Journal
JOURNAL OF EXPERIMENTAL ZOOLOGY PART A-ECOLOGICAL AND INTEGRATIVE PHYSIOLOGY
Volume 331, Issue 10, Pages 521-529Publisher
WILEY
DOI: 10.1002/jez.2317
Keywords
adrenocortical; altricial; birds; corticosterone; glucocorticoid; hypothalamic-pituitary-adrenal axis; ontogeny; parrots; stress; Venezuela
Categories
Funding
- National Science Foundation (IOS) [1558145]
- National Geographic Society [EC0494-11, EC0558-11]
- Direct For Biological Sciences
- Division Of Integrative Organismal Systems [1558145] Funding Source: National Science Foundation
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Life history theory predicts that physiological and behavioral responsiveness to stress should be delayed in development until the benefits of heightened reactivity outweigh the costs of potentially chronic glucocorticoid levels. Birds often acquire stress-responsiveness at locomotor independence, however, both stress-responsiveness and locomotor ability are delayed in birds with altricial developmental strategies. Parrots (Psittacidae) are extremely altricial, but it is not known whether they also postpone physiological responsiveness to stress until locomotor independence. We quantified individual variation in baseline and stress-induced plasma corticosterone (CORT) concentrations, the main avian glucocorticoid, in wild green-rumped parrotlets (Forpus passerinus) of Venezuela at four stages of nestling development. Parrotlet neonates are very underdeveloped and compete for parental care among extreme sibling size hierarchies, a competitive scenario that might benefit from early hypothalamic-pituitary-adrenal (HPA) functionality. Nestlings that underwent a standardized restraint stress-treatment showed higher average CORT concentrations compared to baseline in all age groups sampled, and exhibited no evidence of age-related changes in the stress response. This is 2 weeks before locomotor independence and earlier than previously documented for altricial species. Results suggest that precocity of HPA function may be advantageous to growth and survivorship in extremely altricial birds.
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