Seabirds – Flying goats in the gulf

Here in Rodney, the natural world provides signals that tell us that summer is on its way – for example, cabbage trees in full flower abuzz with bees, pohutukawa in bud (in some places already breaking out in flower), garden and bush birds actively into their breeding season, and shining cuckoos getting quieter after their spring flush of calls. But these are common through much of New Zealand. But in Rodney there’s one summer signal that’s unique to our region. This is heard as a rapid-fire ‘kek kek kek kek kek’ coming from the night sky. Megan Young, a student studying storm petrels on an island in the Hauraki Gulf, likened them to ‘flying goats’. They also modulate their staccato calls with strange duck-like calls, and sometimes you hear an intimate purring call.

These calls are made by Cook’s petrels. Ninety-five per cent of the world’s population of these petrels breed on Te Hauturu-o-Toi (Little Barrier Island), almost 2 million birds. Their population is steadily increasing since cats and rats were eradicated in the 1970s and 2004 respectively.

Cook’s petrels are a small petrel, smaller than a red-billed gull, and weigh about 180grams. They arrive back in New Zealand waters in September, following their migration to the North Pacific over a period of four to five months. They lay their eggs in November. After that we start to get this nightly audio show, which continues right through summer. It’s heard across Rodney; from Titirangi to the Kaipara in the west, and from East Coast Bays to Mangawhai in the east. What’s going on? Cook’s petrels find food well offshore during breeding, initially for themselves, then to raise their chicks once they’ve hatched. Each pair raises one chick. They can cover hundreds of kilometres on foraging trips over several days. They depart Hauturu and either fly past East Cape and down towards the Chathams, or they fly up around North Cape and the Three Kings, and out into the Tasman Sea. They feed mostly on squid, which they catch at night.

Like most petrels (and related shearwaters, prions, diving petrels and storm petrels) they are nocturnal over land. After the foraging trips to the Tasman Sea they take a ‘short cut’ back to the Hauraki Gulf and Hauturu. They hit Auckland’s West Coast at dusk and start making their way across the narrow stretch of mainland, an area seabird folk have dubbed the ‘North Auckland Flyway’. They appear to navigate by landmarks, ridges and valleys. It is possible they now recognise towns and strings of street lights. On misty nights, we see them flying along our road (Leigh Road), just above the lights or further up, ghosting through the mist and calling to each other. On some clear nights, they fly through silently – well almost. No calling, but it’s possible to hear the thrum of their wing beats as the pass over. It’s then that you realise their flight over land is very different from at sea. Over land their wings flutter rapidly; however, at sea they are extremely dynamic, using the wind to fly in easy fluent arcs with very little perceptible wing movement.

There are two million birds on Hauturu, and up to one third of these are non-breeding birds (that is, birds too young to breed or failed breeders). Without the need to raise a chick they have time on their hands (wings). If you are out in the outer Gulf through the summer months you can see many of them during the day, sometimes in rafts, often in flight. But as night approaches, they appear restless – some indulging in display flights, chasing each other in pairs or groups, their calls echoing across the water. At nightfall, they start making their way to Hauturu. If you have the privilege of working on this very special island at night, or just anchored close by, it’s an extraordinary event to witness. The sound of their calling can be deafening. Breeding birds, those with a purpose at the end of their long foraging flights, will make their way unerringly to their burrows deep within the forest on this spectacularly rugged island. Young birds will also make their way to land, some prospecting for a suitable place for a burrow. For a while, this remarkable small seabird becomes a forest bird – sharing the Hauturu night with kakapo, kiwi, kaka and morepork.

Chris Gaskin, Northern NZ Seabird Charitable Trust
chris@nzseabirds.com