Abstract
The semipalmated sandpiper Calidris pusilla and the spotted sandpiper Actitis macularia are long- and short-distance migrants, respectively. C. pusilla breeds in the sub-arctic and mid-arctic tundra of Canada and Alaska and winters on the north and east coasts of South America. A. macularia breeds in a broad distribution across most of North America from the treeline to the southern United States. It winters in the southern United States, and Central and South America. The autumn migration route of C. pusilla includes a non-stop flight over the Atlantic Ocean, whereas autumn route of A. macularia is largely over land. Because of this difference in their migratory paths and the visuo-spatial recognition tasks involved, we hypothesized that hippocampal volume and neuronal and glial numbers would differ between these two species. A. macularia did not differ from C. pusilla in the total number of hippocampal neurons, but the species had a larger hippocampal formation and more hippocampal microglia. It remains to be investigated whether these differences indicate interspecies differences or neural specializations associated with different strategies of orientation and navigation.
Highlights
There is growing evidence that cognitive abilities are influenced by specific ecological conditions to which animals are exposed, and migratory birds are a good example of this [1]
Investigations focused on the neurobiological basis of hippocampal plasticity in birds have largely been directed at volumetric changes and numerical estimates of hippocampal neurogenesis, with only a few reports dedicated to examining the relationship between glial cells and hippocampal function [8,9]
The parahippocampal area in C. pusilla and A. macularia is the larger component of the hippocampal formation through most of the rostro-caudal axis
Summary
There is growing evidence that cognitive abilities are influenced by specific ecological conditions to which animals are exposed, and migratory birds are a good example of this [1]. One such study examined variations in glial cells numbers in birds that store and retrieve food and measured the effect of environmental influences on the number of hippocampal glia in Poecile atricapillus [8]. These authors found that animals living freely under the influence of natural environmental pressures tend to have significantly more glial cells than those living in captivity, suggesting that the environment influences the number of glial cells. They showed that hippocampal volume increases with the number of glial cells, but not with increasing neurogenesis [8]
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