This video from Bermuda says about itself:
Why Do Bermuda Petrels Shake Their Heads? – Jan. 23, 2017
Some viewers have been wondering why the Bermuda Petrel (aka cahow) often shakes its head when sitting on the nest. According to Jeremy Medeiros, Bermuda Petrel expert and senior terrestrial conservation officer for the Bermuda Department of Environment and Natural Resources, this is a common behavior among gadfly petrels. These birds have salt-excreting glands in their nostrils, and shaking the head helps them remove the salt from these glands in the form of briny droplets. This is also why the cahow’s bill often looks wet!
The CahowCam is a collaboration between the Cornell Lab of Ornithology and the Nonsuch Expeditions. You can watch the cam live here; and learn more about Nonsuch Island‘s environs (including the cahow) here.