The relationship between environment, corticosterone, food caching, spatial memory, and the hippocampus in chickadees

Abstract

Many species in the family Paridae are well known for their food-caching behavior (Haftorn 1956; Pravosudov 1985; Brodin and Lundborg 2003; Lucas et al. 2004). All North American Parids have been reported to cache food whereas in Eurasia there are a few species that do not cache (Brodin and Lundborg 2003a; Lucas et al. 2004). Natural food caching in free-ranging Parids has been studied most intensively in Eurasian species—willow, coal, crested, marsh, and Siberian tits (Haftorn 1956; Pravosudov 1985; Brodin 1994)—whereas data on natural food caching in North American Parids are extremely scant (Odum 1942; Brodin 2005). Some well-studied Eurasian Parids (willow and Siberian tits) have been reported to make more than a 100 000 individual food caches each autumn (Haftorn 1956; Pravosudov 1985; Brodin 1994) to be used throughout the winter. Food caching thus appears to be an important adaptation, promoting the birds’ survival during the winter (e.g. Pravosudov and Lucas 2001), and it is important to understand how these birds retrieve their caches. It is known that food-caching birds rely, at least in part, on spatial memory to find their caches (review in Shettleworth 1995; Chapter 2) and research on spatial memory and the hippocampus, a part of the brain involved in spatial memory processing (Sherry and Vaccarino 1989; Hampton and Shettleworth 1996a, b), has focused on both Eurasian and North American Parids (Shettleworth 1995; Chapter 2). Glucocorticoid hormones are also known to affect spatial memory (Sapolsky 1996; McEwen and Sapolsky 1995; McEwen 2000) and thus the local environment might influence spatial memory via changes in glucocorticoid hormones levels (Pravosudov 2003). Here, I review studies dealing with the relationship between environment, food caching, spatial memory, corticosterone, and the hippocampus in North American chickadees while providing comparisons with similar studies done using Eurasian Parids.