An American Ecologist in New Zealand: Part III
I’d like to to introduce you to some international travelers unique to this area of the world.
Last week we visited a gannet colony on the west coast of the North Island of New Zealand, near Muriwai. Members of the booby family, Australasian Gannets (Morus serrator), known as “takapu” in Maori, have a wingspan of up to 180 cm. They lay an egg in the colony in spring here (September through November) and incubate it for 44 days. The chicks stay in the colony until late summer/early fall, and then migrate to Australia, where they remain for the next two to six years. Their destination is 2,000 km away, over the Tasman Sea. Gannets return to the same nesting site each year.
The birds are expert fishers of small squid and fish, and can dive from heights of up to 30 meters, entering the water at 145 kilometers/hour. They have special adaptations that allow them to dive so spectacularly, including a strong skull and inflatable air sacs that help cushion the shock. They don’t mate in earnest till after they are five years old. Then, they mate for life, and spend most of their adult lives around the colony site in coastal New Zealand.
The colony at Muriwai has been around since the early 20th century. The colony started on the small island of Oaia, but due to overcrowding, it moved to the mainland cliffs. The Auckland Regional Council established the Takapu Refuge in 1979 to protect the colony. Mysteriously, in the spring of 1995 the population dropped suddenly over six weeks. It has rebounded since to around 1,500 individuals.
A theory for the large increase in New Zealand’s population (it is home to 46,000 breeding pairs as of 1980) is that the increase in inshore commercial fishing has reduced numbers of predatory fish causing an increase in small fish – the food of the gannets. New Zealand is currently home to 87% of the total population of adult birds.