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Comparative Study
. 2012 Aug 23;8(4):657-9.
doi: 10.1098/rsbl.2011.1180. Epub 2012 Feb 22.

Hummingbirds Have a Greatly Enlarged Hippocampal Formation

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Comparative Study

Hummingbirds Have a Greatly Enlarged Hippocampal Formation

Brian J Ward et al. Biol Lett. .
Free PMC article

Abstract

Both field and laboratory studies demonstrate that hummingbirds (Apodiformes, Trochilidae) have exceptional spatial memory. The complexity of spatial-temporal information that hummingbirds must retain and use daily is probably subserved by the hippocampal formation (HF), and therefore, hummingbirds should have a greatly expanded HF. Here, we compare the relative size of the HF in several hummingbird species with that of other birds. Our analyses reveal that the HF in hummingbirds is significantly larger, relative to telencephalic volume, than any bird examined to date. When expressed as a percentage of telencephalic volume, the hummingbird HF is two to five times larger than that of caching and non-caching songbirds, seabirds and woodpeckers. This HF expansion in hummingbirds probably underlies their ability to remember the location, distribution and nectar content of flowers, but more detailed analyses are required to determine the extent to which this arises from an expansion of HF or a decrease in size of other brain regions.

Figures

Figure 1.
Figure 1.
(a) Scatterplots of relative hippocampal formation (HF) size, as expressed as the log-transformed percentage of telencephalon volume, of food-caching and non-food-caching songbirds, woodpeckers, seabirds, swifts and hummingbirds. The lines depict the means of each group. (b) Scatterplots of log10-transformed HF volume plotted against log10-transformed telencephalon (minus HF) volume of hummingbirds and all other birds. The lines indicate the 95% CI: solid lines denote conventional statistics; dashed lines denote incorporating phylogeny.

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