Prior restraint stress inhibits habituation to novel objects in the European starlings (Sturnus vulgaris)

Abstract

Animals often avoid novel objects, a behavior known as neophobia. We examined behavioral responses of captive European starlings to novel objects placed at their food dishes. Exposure occurred concurrently to food reintroduction following overnight fasting. Behavior was analyzed for 10 min via video recording. We expected an increase in avoidance behavior compared with trials in which food was reintroduced without a novel object. Seven of 10 novel objects increased latency to approach the dish. In contrast to our expectations, neither prior restraint nor exogenous corticosterone changed the neophobic response to novel objects. While exposure to a novel object increased approach latency, there was no additional effect of restraining animals in a cloth bag for 15 min before food reintroduction.Furthermore, the subcutaneous injection of corticosterone did not affect approach latency by itself, nor did it affect the response to a novel object. Finally, we expected repeated exposure to the same object to extinguishing the neophobic response, and that restraint stress would prevent habituation. Our results show that European starlings habituate rapidly to exposure to a novel object, as approach latency returned to baseline within three repeated exposures to the same object. When the repeated presentation of the object was combined with prior restraint, however, the latency to approach never returned to baseline. These results reveal that neophobia in starlings is object-specific and that, while neither acute stress nor corticosterone directly affects the behavioral response to a novel object, acute stress appears to have a permissive effect on neophobia by inhibiting habituation. K E Y W O R D Sacute stress, corticosterone, European starling, habituation, neophobia

Chronic stress reverses enhanced neophobia following an acute stressor in European starlings

“…Seven different novel objects were used throughout the study, which all have been shown to elicit neophobic responses in starlings (de Bruijn & Romero, 2020). Each object modified a normal white square plastic feeding dish (100 × 70 × 75 mm).…”

“…However in contrast, glucocorticoids do not appear to play a role in the plasticity of boldness of rainbow trout ( Oncorhynchus mykiss ) in the context of hunger and predation (Thomson et al, 2012). In European starlings ( Sturnus vulgaris ), a previous study found that a stress response immediately preceeding exposure to a novel object increases the frequency of neophobic responses in European starlings (de Bruijn & Romero, 2020). This suggests that stress exerts permissive actions on neophobia, in that it can alter how an individual responds to novelty (Sapolsky et al, 2000; Vera et al, 2017).…”

“…We predicted that chronic stress would result in increased neophobia, as measured by longer approach latencies toward novel objects. Additionally, while acute stress has been shown to have permissive effects on neophobia and prevent habituation (de Bruijn & Romero, 2020), we expected that this effect would be reduced in chronically stressed birds due to dysregulation of stress physiology.…”

“…However, the exact relationship between glucocorticoids and behavior is not clear, as some studies have found correlations between glucocorticoids and behavior (e.g., Kralj‐Fišer et al, 2009; Wingfield & Silverin, 1986), while others have not (Garamszegi et al, 2012; Lendvai et al, 2011). The activation of the stress response (induced via restraint), but not circulating corticosterone concentrations, has been shown to alter neophobia to a novel object near the food dish in European starlings (de Bruijn & Romero, 2020). This suggests that a component of the stress response other than glucocorticoids may regulate this behavior, such as the release of epinephrine and norepinephrine (Hagemann et al, 1998) or CRF (Ohgushi et al, 2001), all of which can exhibit effects on feeding behavior.…”

No, you go first: phenotype and social context affect house sparrow neophobia

“…Sparrows saw each object once. These objects were based on objects shown to elicit delayed approach and feeding in another songbird species [32], but altered slightly to share fewer common features (e.g. red colour) that might incidentally target ecologically relevant cognitive biases [33].…”