Neuron production, neuron number, and structure size are seasonally stable in the hippocampus of the food-storing black-capped chickadee (Poecile atricapillus)

Neuronal recruitment in the black-capped chickadee (Poecile atricapillus) hippocampus occurs at a higher rate in the fall than at other times of the year. As a means of determining whether this increase in recruitment results from greater neuron production, chickadees were caught in the wild between October and March and injected with the cell-birth marker 5-bromo-2'-deoxyuridine. Two weeks later, birds were killed by overdose, and hippocampal neuron production, apoptosis, neuron number, and hippocampal volume were determined. Chickadees collected in October, November, January, February, and March did not differ in neuron production, apoptosis, hippocampal volume, or neuron number. These findings indicate that increases in neuronal recruitment in the chickadee hippocampus in the fall do not result from increased neuron production, but instead, enhanced survival of new neurons.