Meeting Abstract
HPA axis activation and glucocorticoid (GC) secretion in response to a predator is well studied, but common methods expose subjects to live or model predators for 15 – 60 min, whereas most predatory attacks are considerable shorter (e.g., < 5 sec). Given the moderate success rates of most predators (< 50%) and many species learn antipredator behavior by observing attacks upon other individuals, escaping or witnessing a predatory encounter occur commonly. Yet, the nature of the assumed stress response from these exposures is largely unknown, including whether these short-lived exposures actually induce a pronounced (or even measurable) GC response. To better understand the nature of the HPA axis response to predation, we measured levels of GCs in wild-caught European starlings (Sturnus vulgaris) in response to witnessing a live raptor attack (ca. 2 sec duration) upon a conspecific, witnessing a human ‘attack’ (i.e., a researcher handling a conspecific), capture and restraint, and an undisturbed control. GC levels were highest after witnessing a raptor attack (mean ± SD; 34.1 ± 12.4 ng/ml), which paralleled levels in response to capture and handling (34.7 ± 11.0 ng/ml). GC levels were substantially different after witnessing a human ‘attack’ (21.3 ± 7.7 ng/ml), and after undisturbed controls (7.2 ± 3.9 ng/ml), which mirrored baseline values (7.1 ± 3.6 ng/ml), Our results indicate that 1) a stimulus lasting only seconds can activate the HPA axis to a similar extent as the widely used capture and restraint protocol, and 2) witnessing a predator attack can be a physiological stressful event in free-living birds, which may affect how birds learn to recognize and appropriately react to predators.
