The Gulf of Seabirds  by Jo Ritchie

Environmental News Issue 12

The Hauraki Gulf is a seabird mecca. I don’t know how many times I have been out sailing and come across a ‘boil up’. It’s like kids at a lolly scramble. The water is seething with fish frantically trying to weave themselves into a tighter and tighter ball against a massive aerial assault and occasionally large mouths from below in the form of Brydes whales and common and bottlenose dolphins.

The aerial assault is a combination of a ballet and a rugby scrum. The sleek bullet shaped bodies of gannets with their wings tightly folded against their bodies’ streak in from great heights, a flash of yellow as the sun hits their heads and a splash as they hit the water and then pop up with a shining silver victim. The gulls are probably the scrum contenders as they are constantly scrapping and nicking in to steal fish. Petrels and terns are more delicate in their meal gathering tactics.

Seabirds are birds that have adapted to life in the marine environment. In general, seabirds live longer, breed later and have fewer young than other birds do, but they invest a great deal of time in their young. Most species nest in colonies, which can vary in size from a few dozen birds to millions. Many species are famous for undertaking long annual migrations, crossing the equator or circumnavigating the Earth in some cases. They feed both at the ocean’s surface and below it, and even feed on each other. Seabirds can be highly pelagic (living on the open ocean), coastal, or in some cases spend a part of the year away from the sea entirely.

Shorebirds are often interchanged with seabirds. Shorebirds however prefer to do their thing close to land. It’s the difference between having webbed landing and paddling pads as opposed to longer, slimmer waders. Shorebirds occupy wetlands and inshore coastal environments such as beaches, rock pools and estuaries. The majority of species eat small invertebrates picked out of mud or exposed soil. Different lengths of bills enable different species to feed in the same habitat, particularly on the coast, without direct competition for food. Many waders have sensitive nerve endings at the end of their bills which enable them to detect prey items hidden in mud or soft soil. Some larger species, particularly those adapted to drier habitats will take larger prey including insects and small reptiles. Some of our better known shorebirds are the NZ dotterel and the variable oystercatcher but they also include that wonderful sentinel, the grey heron which you often see standing statue like with its lemon yellow legs in the water and then all of a sudden it impales a struggling silver victim on the end of its elegant beak.

Some species like shags (alias cormorants), are in between the two. Although they are classified as seabirds, they spend a lot of time inshore in large, noisy colonies often in cliff edge pohutukawa on which they snow down droppings. Their nests are nothing to be proud of – resembling little more than a ramshackle collection of twigs, flotsam and jetsam precariously piled together on a branch.

The Hauraki Gulf has some very special seabirds. Petrels comprise the largest number of species feeding in the waters of the gulf and breeding on the islands. They range from the delicate storm petrels or Mother Carey’s chickens, to the great albatrosses and the more common shearwaters, prions and mollymawks. At least a dozen of these species breed on the islands. Breeding colonies are often large. This not only makes for a very noisy neighbourhood but a very crowded one. On islands where the ground is soft the birds make tunnel like burrows turning the surface of many small islands into giant spongy honeycombs. If you have ever wondered why there are not many trees on islands like the Grey group out from Port Fitzroy, this is partly because of the poor soil but also because of the way seabirds and their burrows have undermined the ground and made it unstable for many large trees to anchor their roots.

The islands of the Hauraki Gulf are petrel strongholds. Cooks and Black petrels only breed on Little Barrier and Great Barrier. Two and a half million Buller’s shearwaters nest at the Poor Knights, the grey faced petrel breeds on most islands (you may know these birds if you have stayed a night on Tiritiri Island) and the sooty shearwater has small colonies on the Aldermen, Hen and Chicken, Poor Knights and Mercury Islands.

A number of petrel species spend time in the Kaipara Harbour as well as the Hauraki Gulf. Some enjoy endless summers, migrating overseas during our winter months. Flesh footed, Buller’s and sooty shearwaters fly regularly to the North Pacific and have been recorded off the Californian coast with the Buller’s traveling as far as South America – wouldn’t it be nice to have free air miles and a zero carbon footprint!

Many of you will have heard the distinctive calls of petrels. Groaning or yelling sounds with some cat like (yup cat like!) mews are made by the larger species of petrel and the shearwaters. Rapidly repeated ti-ti-ti or kek-kek-kek notes are given by Cooks and Pycroft’s petrels. Hence the Maori name Titi. The diving petrel makes wailing and cooing calls but perhaps the most distinctive caller is the fluttering shearwater which has a rapid, repetitive cry best described as a wild laugh.

The best time to hear the birds is in summer during the breeding season. Returning birds begin to assemble offshore at dusk and as darkness falls they move to land and descend to greet their waiting mates in the burrows. The noise is usually greatest on dark or misty nights when the birds need to call to make contact with their mates. I have this theory (thoroughly untested of course!) that they also use their calls to echo locate as they fly up valleys on their way to places like Hirakamata – Mt Hobson. Their landing tactics are not pretty as they often crash down through the foliage. One of the most remarkable facts is that some petrels are occasional breeders and have extended overseas tours at least a few years and then they return to nest within a few metres of where they were born.

There is still much to learn about seabirds even in the Hauraki Gulf where it seems sometimes that every man and his dog are out fishing. The NZ storm petrel was presumed extinct for 150 years until 2003 when a sighting was made by a group of ornithologists off the Whitianga coast.

Seabirds are affected by human use of the oceans. Marine debris is attractive to many species as nesting material. I have seen gannet nests off the coast of Muriwai Beach on Auckland’s west coast that were comprised entirely of plastic and strapping from bait boxes. I have also removed many 6 pack can holders from around bird’s necks and at Tawharanui seen the terrible sight of a dead shag suspended in a tree with fishing line around its neck – a terrible way to die. Picking up rubbish particularly plastic and fishing line around our coast is such a simple thing to do and it does make a difference. Disposing of rubbish responsibly when boating or fishing is a simple way to help.

However the biggest threats to seabirds that nest in the Hauraki Gulf are introduced pests namely cats and rats. Kiore predation of Cook’s petrel chicks resulted in a 90% failure rate of Cook’s petrel on Little Barrier Island between 1996-2003. Following their eradication from Codfish Island Cook’s petrel achieved 80% breeding success in a 4 year period – the same trend is being repeated at Little Barrier now that kiore have been eradicated.

The Department of Conservation has pioneered techniques to eradicate rodents from islands with 100% success rates in most cases. It is important to the survival of seabird ecosystems that D.o.C is supported in these endeavours. Seabird colonies and the rich guano in turn support many unique species of native plants found nowhere else. Our only dinosaur the tuatara often shares lodgings with nesting petrels as do many species of lizards and large invertebrates.
We can all help protect the seabird islands of the Gulf by treading gently. Enjoy small islands from a distance. Resist the urge to go ashore, some are nature reserves and many are privately owned. Don’t take the dog ashore for a walk, check your boat for rats regularly and think carefully before you run a shore line from your boat to a tree – rats run these very easily. And above all take time to enjoy the many seabirds that call the Hauraki Gulf home.