Big Word of the Month: suprachiasmatic nucleus

September 13, 2009 | Larry Boles


I saw my first “V” formation of Canada geese of this fall and it got me thinking about migratory triggers. Here in North America the days are starting to get notably shorter, sunset is now about an hour earlier than it was in June. Most animals have circadian rhythms that are tuned to environmental cues like day length. In many species, the shorter day length along with cooler temperatures is the sign of coming winter and triggers migratory behavior.

Inside the brain of mammals like ourselves lies a tiny organ called the suprachiasmatic nucleus (SCN for short). Despite being the size of a rice grain, the SCN plays a large role in the body’s biological clock. It exerts control over other regions of the brain through nerve signals and biochemical activity and research shows that individuals with damaged SCNs have difficulty with daily sleep/wake cycles. The SCN gets input from light receptors and thus able to adjust the body’s clock to match external light patterns. The adjustment of the internal clock is gradual though (why do think that is?) and it can take a few days to adapt to a rapid change in day length. We humans call this condition “jet lag”; do you think geese feel jet lag? Birds do have a SCN but the system doesn’t work exactly that of mammals and their brain anatomy is different.

I’ve posted two questions this month, you can write your answers in the comment section if you want some feedback from me.

Geese migration photo from Wikicommons

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