American Crow (Corvus Brachyrhynchos) Thanatology

Résumé du livre

Given the complexity with which some animals respond to dead conspecifics, how and why non-human animals respond to dead conspecifics is of increasing scientific interest. Among vertebrates, few experimental studies have been conducted to better understand the motivations and manifestations of behavioral responses towards dead conspecifics. Some members of the Corvidae family, including American crows (Corvus brachyrhynchos), are among the animals that respond strongly to their dead. Like some mammals, their responses can vary from alarm calling and group formation, to physical contact with corpses. In the following three chapters I use experimental approaches to explore aspects of American crow thanatology (the study of death) that improve our understanding of how crows respond to their dead, what motivates their responses, and how such behaviors are neurologically mediated. In the first chapter I investigate the prevalence and nature of tactile interactions between wild crows and taxidermy prepared crows positioned in "dead" or "life-like" postures, and taxidermy prepared "dead" heterospecifics. I find that tactile interactions with dead crows can take a variety of forms including exploratory, aggressive and sexual, but occur infrequently, do not appear to be food motivated, and are partly correlated with the onset of the breeding season. In addition, I find that life-like crows evoke responses more consistent with intruder eviction than do crows postured in death-like position. That tactile interactions with corpses are somewhat seasonally constrained suggests that breeding-season induced changes likely downregulate the ability of some birds to appropriately respond to complex stimuli. In the second chapter I explore if responses to dead crows are influenced by the season in which they are encountered or the age of the dead bird. I find that robust responses to dead crows wane during the breeding season, particularly in response to dead juveniles, which are a less salient cue of danger. How higher breeding season recruitment to adult corpses is facilitated remains unclear, but may be tied to differences in call rate or variability. In the last chapter, I find that observations of dead crows stimulate brain regions associated with executive function, and higher order decision-making (NCL; nidopallium caudolaterale), rather than emotional processing or a simple stimulus-fear mechanism. In addition, I find that crows rapidly learn from previous negative experiences, and show higher brain activity in the amygdala and to some extent the striatum during subsequent responses to nonthreatening stimuli. Together these finding suggest that, among crows, attention to dead conspecifics is driven by danger avoidance, and how they ultimately respond is the product of context-dependent decision-making and seasonal influences