Sometimes they can be seen pulling it out of a passing gannet’s beak while still on the wing, or pilfering it straight off a neighbour’s nest. “Sometimes you see four or five birds all pulling in different directions on one bit of brown algae,” says Steffi Ismar, from The University of Auckland, who has recently studied the significance of seaweed among gannets for her PhD.
It turns out that seaweed is an excellent insulation material, capable of keeping the nest—and the eggs it contains—considerably warmer than nests without. This is useful in areas such as the Cape Kidnappers gannetry, where temperatures can drop to 9ºC at night during the laying period.
Also it appears to be the males who bring home the seaweed, which suggests that it is a gender-specific trait, and a more successful seaweed-gatherer could be more attractive to the opposite sex.
“Now we’re planning to look at whether good padding on the nest leads to increased hatching probability,” says Ismar, “and whether seaweed gathering serves to strengthen the pair-bond.” Or, alternatively, whether poor seaweed gathering increases divorce rates.