Boobies and gannets | Sulidae

Genten | Alcatraces

These seabirds hunt by folding the wings half back and dropping into the sea from a great height like an arrow; just before impact the wings close flat against the body, and the bird may swim on after the fish for several metres more. Air sacs under the skin of the neck and breast absorb the blow, the nostrils are sealed shut — breathing goes through the corners of the gape — and forward-facing eyes give the depth perception needed to judge a shoal. There is no brood patch: the egg is kept warm beneath the blood-rich webs of the feet, which the bird stands on. Nests lie in dense colonies on cliff ledges or flat islands, a heap of seaweed and droppings that the pair reaffirms at every return with an elaborate greeting of fencing bills and pointing skyward. At sea they are silent; in the colony a harsh, grating croaking carries on day and night.