Black-capped Chickadees survive the winter months in southern Canada and northern parts of the USA by caching surplus food within the individual bird's territory. This provides a vital reserve of food, ensuring the bird a steady supply of energy.
Hiding food in scattered nooks and crannies means other animals are unlikely to steal it, but a chickadee must remember each location for all the effort to pay off.
Black-capped Chickadees rely on remembering scattered caches of food to avoid pilfering by other animals (Jon Mercer).
Research published in Behavioural Neuroscience demonstrated that the total size of the chickadee hippocampus increases in autumn and winter, as does the rate at which neurones are formed in the brain.
Factors controlling these changes in birds are not fully understood, but it is possible that the hippocampus grows as the birds increase the rate at which they store and remember the locations of food items, in a similar way to the growth of this region of the brain in taxi drivers as they learn 'The Knowledge'.
The researchers said: "Available evidence suggests that changes in hippocampal size and neurogenesis may be a consequence of the behavioural and cognitive involvement of the hippocampus in storing and retrieving food."
The hippocampus is relatively much larger in food-storing birds than non-storing species, demonstrating the importance of memory function in species such as chickadees and tits.
Although a spring peak is sometimes observed, most food-storing species largely abandon the behaviour at the end of the winter.
Colin Saldanha, assistant professor of biological sciences at Lehigh University, said: "To see this happen under natural conditions is truly awe-inspiring. Our hypothesis is that this exaggerated growth occurs when the birds need it the most."
Sherry, D F, & Vaccarino, A L. 1989. Hippocampus and memory for food caches in black-capped chickadees. Behavioral Neuroscience 103.2: 308. DOI: https://doi.org/10.1037/0735-7044.103.2.308