Does Environmental Enrichment Reduce Stress? An Integrated Measure of Corticosterone from Feathers Provides a Novel Perspective

Abstract

Enrichment is widely used as tool for managing fearfulness, undesirable behaviors, and stress in captive animals, and for studying exploration and personality. Inconsistencies in previous studies of physiological and behavioral responses to enrichment led us to hypothesize that enrichment and its removal are stressful environmental changes to which the hormone corticosterone and fearfulness, activity, and exploration behaviors ought to be sensitive. We conducted two experiments with a captive population of wild-caught Clark's nutcrackers (Nucifraga columbiana) to assess responses to short- (10-d) and long-term (3-mo) enrichment, their removal, and the influence of novelty, within the same animal. Variation in an integrated measure of corticosterone from feathers, combined with video recordings of behaviors, suggests that how individuals perceive enrichment and its removal depends on the duration of exposure. Short- and long-term enrichment elicited different physiological responses, with the former acting as a stressor and birds exhibiting acclimation to the latter. Non-novel enrichment evoked the strongest corticosterone responses of all the treatments, suggesting that the second exposure to the same objects acted as a physiological cue, and that acclimation was overridden by negative past experience. Birds showed weak behavioral responses that were not related to corticosterone. By demonstrating that an integrated measure of glucocorticoid physiology varies significantly with changes to enrichment in the absence of agonistic interactions, our study sheds light on potential mechanisms driving physiological and behavioral responses to environmental change.

Experimental relationships between levels of corticosterone in plasma and feathers in a free-living bird

“…By analyzing the plasma-feather relationship on an individual basis, we found that plasma CORT at day 9 correlated positively with whole-feather CORT f . Lattin and colleagues did not detect a relationship between plasma CORT and CORT f from feather sections at any point in their experiment (Lattin et al, 2011); these findings are in contrast to evidence that CORT f from feather sections reflects experimental manipulations occurring during the growth of those sections (Fairhurst et al, 2011). In Lattin and colleagues' study (Lattin et al, 2011), between-group differences in CORT f from sections of feather grown prior to hormone implants may have been influential.…”

“…Work with birds has shown that feathers contain corticosterone (CORT) (Bortolotti et al, 2008;Koren et al, 2012), the primary avian GC. CORT in feathers (CORT f ) has been correlated with variation in parental provisioning (Fairhurst et al, 2012b), nest box microclimate (Fairhurst et al, 2012a), environmental enrichment (Fairhurst et al, 2011), expression of carotenoid-based signals (Bortolotti et al, 2009b;Mougeot et al, 2010;Kennedy et al, 2013), egg mass (Kouwenberg et al, 2013), stable isotopes of carbon (Fairhurst et al, 2013) and components of fitness (Bortolotti et al, 2008;Koren et al, 2012). This biomarker relates to diverse ecological factors, suggesting that it integrates CORT secretion in general, rather than expresses a response to any specific source of environmental variation.…”

Effect of environmental enrichment exposure on neuronal morphology of streptozotocin-induced diabetic and stressed rat hippocampus

“…[13] Environmental enrichment (EE) exposure treatment is widely used for managing fearfulness, abnormal behaviors, and stress in laboratory animals. [14] Exposure to EE was known to enhance spatial memory abilities and synaptic strength in the hippocampus of the brain. [15] EE exposure is known to influence the CNS at the functional, anatomical, and molecular levels, both during the critical period and during adulthood.…”

Feather corticosterone reveals developmental stress in seabirds

“…The potential ecological applications of this technique are broad and already the few published studies that employ it address questions ranging from the impact of the pre-breeding body condition on egg production (Kouwenberg et al, 2013) to the effect environmental enrichment has on the physiological state of captive passerines (Fairhurst et al, 2011). There is evidence, however, that during development variations in resource allocation may produce feather CORT results opposite to those expected from plasma CORT studies (Patterson et al, 2014).…”