Occurrence and variability of tactile interactions between wild American crows and dead conspecifics

Abstract

Observations of some mammals and birds touching their dead provoke questions about the motivation and adaptive value of this potentially risky behaviour. Here, we use controlled experiments to determine if tactile interactions are characteristic of wild American crow responses to dead crows, and what the prevalence and nature of tactile interactions suggests about their motivations. In Experiment 1, we test if food or information acquisition motivates contact by presenting crows with taxidermy-prepared dead crows, and two species crows are known to scavenge: dead pigeons and dead squirrels. In Experiment 2, we test if territoriality motivates tactile interactions by presenting crows with taxidermy crows prepared to look either dead or upright and life-like. In Experiment 1, we find that crows are significantly less likely to make contact but more likely to alarm call and recruit other birds in response to dead crows than to dead pigeons and squirrels. In addition, we find that aggressive and sexual encounters with dead crows are seasonally biased. These findings are inconsistent with feeding or information acquisition-based motivation. In Experiment 2, we find that crows rarely dive-bomb and more often alarm call and recruit other crows to dead than to life-like crows, behaviours inconsistent with responses given to live intruders. Consistent with a danger response hypothesis, our results show that alarm calling and neighbour recruitment occur more frequently in response to dead crows than other stimuli, and that touching dead crows is atypical. Occasional contacts, which take a variety of aggressive and sexual forms, may result from an inability to mediate conflicting stimuli.This article is part of the theme issue 'Evolutionary thanatology: impacts of the dead on the living in humans and other animals'.

Dead cells release a ‘necrosignal’ that activates antibiotic survival pathways in bacterial swarms

“…A large motile population, that can continuously acquire new territory, and that has a strategy to overcome stressful environments and survive mass extinction events promoted by the event itself, will also increase its chances of propagating beneficial mutations such as antibiotic resistance. We note that a response to cell death that benefits the living is not confined to bacteria, but is widespread in nature, as seen in insects (necromones) 63,64 , fishes 65 , birds 66 , and mammals 67 , possibly even in eukaryotic tumors 68 .…”

Comparative thanatology, an integrative approach: exploring sensory/cognitive aspects of death recognition in vertebrates and invertebrates

“…In scrub-jays (Aphelocoma californica), corpses of conspecifics and similar-sized heterospecifics elicit aggregations and site avoidance [125]. A corpse in prone posture elicits cacophonous aggregations, whereas an upright one elicits mobbing behaviour [124] (see also Swift & Marzluff [126] this issue). Moreover, unlike dead conspecifics, corpses of pigeons (Columba livia) elicit little reaction in crows.…”

Necrosignaling: Cell death triggers antibiotic survival pathways in bacterial swarms

“…A large motile population, that can continuously acquire new territory, and has a strategy to overcome stressful environments and survive mass extinction events promoted by the event itself, will also increase its chances of propagating beneficial mutations such as antibiotic resistance. We note that a response to cell death that benefits the living is not confined to bacteria, but is widespread in nature, as seen in insects (necromones) 48,49 , fishes 50 , birds 51 , and mammals 52 , possibly even in eukaryotic tumors 53 .…”