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molivares's picture

Central Pattern Generators in the Common Cuckoo

Hearing about the experiment with the birds in straightjackets and its affect on its ability to fly made me think of another behavior in a particular kind of bird that I now recognize as a central pattern generator. The Cuckoo is an interesting species in that it is a brood parasite species, meaning that the offspring of the Common Cuckoo require parental care from unrelated host parents (usually a Reed Warbler) while the host parents gain no reproductive rewards from the cuckoo nest-invader. A female Cuckoo simply drops its egg into the nest of a Reed Warbler and leaves it there to be raised by host parents. The parasitized nest is detrimental to the host species because the Common Cuckoo not only requires food and care from its host parents, but it also ejects the eggs of the host parents out of the nest within hours of first hatching.

Upon hatching in the Reed Warbler’s nest, the baby Cuckoo, blind and featherless, begins what is believed to be a natural instinct for baby Cuckoos. Unsteady and wobbling, the baby Cuckoo positions the unhatched host’s eggs onto the dip in its back and pushes them toward the edge of the nest and with a determined thrust, expels the egg out of the nest.  The Cuckoo repeats this action until all the remaining eggs are rid of the nest. (If you want to see this behavior for yourself, watch this http://www.youtube.com/watch?v=DbvDQjhO9nY&feature=player_embedded)

I found this behavior quite fascinating. At first was hard for me to understand how a newly hatched Cuckoo could carry out such a complex, nonlearned behavior.  I now see that it is a central pattern generator, or a circuit of neurons, that allows this behavior to play out so early in life. The egg-ejecting behavior is clearly a highly developed survival mechanism and I am interested to learn more about how evolution shapes the formation of central pattern generators.  

 

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