The Hippocampus of Food-Storing Birds

Abstract

when we examined sections from our control birds we saw something very striking. The hippocampus was clearly much larger in chickadees than shown in the atlas. Where the canary atlas showed a smooth curve as the dorsal surface of the brain travelled medially and descended between the hemispheres, the chickadees had a large bump. Previous work by many researchers on the songbird brain had prepared us for the idea that regions of the bird brain could vary between species. Song control nuclei vary in relative size between species and it seemed a likely hypothesis that food-storing birds, which can remember the spatial location of thousands of scattered food caches, might have a hippocampus that was bigger than the hippocampus of non-storing birds. With help from the Long Point Bird Observatory in Ontario, Anthony and I began collecting food-storing and nonstoring birds, sectioning the brains and measuring the relative size of the hippocampus. I contacted my former postdoctoral supervisor at Oxford, John Krebs, and John proposed that his team would collect European species in a parallel project. In Canada, Anthony and I, with help from George Wallace and the banders at Long Point, were able to collect individuals of 23 species from 3 food-storing families (chickadees, nuthatches and jays) and 10 non-food-storing families and subfamilies (wrens, kinglets, thrushes, mimids, starlings, warblers, cardinals, buntings, finchIn 1984–1985, Anthony Vaccarino and I performed a number of experiments on the effects of hippocampal lesions on the accuracy of cache recovery in food-storing black-capped chickadees [Sherry and Vaccarino, 1989]. Like most research, the genesis of this project involved many people. I presented a poster on memory for cache sites at the Neurobiology of Learning and Memory meeting in Irvine, Calif. in 1984 and Larry Squire pointed out to me that the obvious next experiment was to test for hippocampal involvement. I mentioned this idea to my friend Michael Leon at the same meeting, noting that I had no experience doing neurosurgery on 11-gram passerine birds and Michael, with his usual aplomb said that was no problem, there were colleagues at my own institution, the University of Toronto, like Alison Fleming, who could easily teach me the surgical skills. Alison introduced me to Anthony, who was working in Alison’s lab as an undergraduate, and we were on our way. We found that hippocampal lesions severely disrupted the ability of chickadees to find their caches. Fortunately for us, the birds continued to make caches and search for them, they just searched in the wrong places. This work formed part of Anthony’s undergraduate thesis and we published the paper in Behavioral Neuroscience in 1989 [Sherry and Vaccarino, 1989]. We had used the Stokes, Leonard and Nottebohm canary brain atlas [Stokes et al., 1974] as a guide to lesion placement but Published online: August 26, 2011