Fear of predators suppresses neurogenesis in the brains of wild songbirds

Fear of predation can lead to behavioural changes indicative of an enduring memory of fear, as acknowledged by both ecologists, and biomedical scientists studying post-traumatic stress disorder (PTSD). Enduring memories are often linked to suppressed neurogenesis in laboratory rodents as a potential mechanism to prevent the replacement of existing memories. We used predator vocalizations to assess the enduring effects of fear on neurogenesis in a wild songbird, black-capped chickadees (Poecile atricapillus), quantifying cell proliferation (PCNA immunoreactivity) and immature neurons (doublecortin immunoreactivity) in both sexes. Seven days after predator cue exposure we found suppression of hippocampal cell proliferation in males, with no effect in females, and suppression of immature neurons in the avian amygdala (medial ventral arcopallium) in both sexes. Our results are consistent with the hypothesis that animals retained an enduring memory of fear, with potential sex differences in the behavioural and ecological consequences of these enduring neuronal changes. Finding effects indicative of an enduring memory of fear in wild caught animals supports the notion that there may be evolutionarily adaptive value to retaining an enduring, PTSD-like memory.