House sparrows (Passer domesticus) adjusted hypothalamic‐pituitary‐adrenal axis negative feedback and perch hopping activities in response to a single repeated stimulus

Abstract

Chronic stress has been extensively studied in both laboratory and field settings; however, a conclusive and consistent phenotype has not been reached. Several studies have reported attenuation of the hypothalamic–pituitary–adrenal axis during experiments intended to cause chronic stress. We sought to determine whether this attenuation could be indicative of habituation. Importantly, we were not investigating habituation to a specific stimulus—as many stress physiology studies do—but rather we assessed how the underlying physiology and behavior changed in response to repeated stressor presentation. We exposed house sparrows (Passer domesticus) to a single stimulus twice per day at random times for 8 consecutive days. We predicted that this period of time would be long enough for the birds to determine that these acute stressors were not, in fact, dangerous and they would, therefore, acclimate. A second control group remained undisturbed for the same period of time. We measured baseline, stress‐induced, negative feedback strength, and maximum production of corticosterone as well as neophobic behavior before, during, and after this 8‐day experiment. When birds experienced a stimulus for 4 days, their negative feedback strength was significantly diminished, but recovered after the second 4 days. Additionally, perch hopping decreased and recovered in this same time frame. These data suggest that distinct physiological and behavioral responses arise when house sparrows are exposed to the same stressor for several consecutive days as opposed to many stressors layered on top of one another. Furthermore, they indicate that habituation—as with chronic stress—can appear differently depending on the metric being examined.

Neophobia, but not perch hopping, is sensitive to long‐term chronic stress intensity

“…In the present study, no group approached food differently over time compared to the captivity‐only group during control trials (no object present; Figure 2, top panels), but over time, only the high‐stress group approached food slower than the captivity‐only group during object trials (Figure 2, bottom panels). This was the opposite result than we expected, as chronic stress (<3 weeks) tends to either have no effect on neophobia (de Bruijn & Romero, 2021; Gormally & Romero, 2018) or makes birds less neophobic (a faster approach; Beattie et al, 2022; Gormally et al, 2018). However, two details should be noted: the birds in the present study experienced chronic stress for about six times as long as the previous studies to monitor neophobia through chronic stress (Beattie et al, 2022; de Bruijn & Romero, 2021; Gormally & Romero, 2018; Gormally et al, 2018) and the relationship between stress and behavior seems to be complicated.…”

“…This was the opposite result than we expected, as chronic stress (<3 weeks) tends to either have no effect on neophobia (de Bruijn & Romero, 2021; Gormally & Romero, 2018) or makes birds less neophobic (a faster approach; Beattie et al, 2022; Gormally et al, 2018). However, two details should be noted: the birds in the present study experienced chronic stress for about six times as long as the previous studies to monitor neophobia through chronic stress (Beattie et al, 2022; de Bruijn & Romero, 2021; Gormally & Romero, 2018; Gormally et al, 2018) and the relationship between stress and behavior seems to be complicated. Even studies that isolate just the glucocorticoid arm of the stress response show conflicting data regarding its effects on behavior.…”

“…Animals in the wild must balance the potential benefit of a new resource with the risk of predation or other adverse consequence (reviewed in Greenberg & Mettke‐Hofmann, 2001). Neophobia can be affected by both chronic (e.g., Beattie et al, 2022; de Bruijn & Romero, 2021; Gormally & Romero, 2018; Gormally et al, 2018) and acute stress (e.g., de Bruijn & Romero 2019, 2021), as well as exogenous glucocorticoid manipulation (e.g., Kelly et al, 2022; Spencer & Verhulst, 2007), though the effects are not consistent. A decrease in neophobia (e.g., a faster approach to novel food) with chronic stress could indicate that an animal is more willing to take risks to obtain food (Crino et al, 2017; Martins et al, 2007), whereas an increase in neophobia (slower approach) could indicate a more anxious animal (Dickens et al, 2009).…”

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

“…This trade‐off is clearly dependent upon species, environmental context, place in the dominance hierarchy, and so forth (e.g., Mettke‐Hofmann et al, ). One such factor, however, is the current amount of stress experienced by the animal (e.g., Gormally & Romero, ).…”

Captive house sparrows (Passer domesticus) show little evidence of seasonality of neophobia responses

“…Note that although stress is known to alter neophobia (e.g. Gormally & Romero, 2018) and introduction to captivity is a powerful stressor (Fischer, Wright-Lichter, & Romero, 2018), all birds had the same two-week adjustment period to captivity. This should have mitigated any differential effects of chronic stress resulting from captivity.…”