Our Blue Backyard: NZ is a seabird Mecca

Auckland University seabird researcher Dr Brendon Dunphy. Photo / Supplied by Jamie Morton

Did you know one species of seabird must feed a chick that reaches 120 per cent of its body weight? That's akin to a 60kg woman breastfeeding a 72kg baby. In the second of a five-part series looking at Auckland University's research in the region's blue backyard, science reporter Jamie Morton talks to seabird expert Dr Brendon Dunphy.

Why is New Zealand such an important hotspot for seabirds?

It's essentially because of our geographic position and a lack of mammalian predators.
New Zealand is an extensive archipelago surrounded by productive oceans.

Habitats found in New Zealand range from offshore islands through to high altitude mountain ranges close to the sea, all of which provide ideal habitat for seabird species.

We struggle to imagine this today, but much of New Zealand was once blanketed by seabirds, and the lack of significant predators allowed them to flourish.

Tell us a little about the work you and your team lead.

My lab is interested in understanding how resilient seabird populations are to environmental change.

To do this requires strong collaborations with Auckland Museum, the Department of Conservation, Auckland Council, the Northern New Zealand Seabird Trust, and Tiritiri Matangi supporters.

A key question is, as human induced pressures mount, what does this mean in terms of stress levels and colony persistence in an uncertain future?

The sooty shearwater is also known by its Maori name ti-ti and as "muttonbird". Photo / Mike Baird

This has involved unpicking stress profiles and metabolism of seabirds.

For example, we have shown that haemoglobin levels in the blood are closely linked to stages of breeding cycle with greater oxygen delivery during the high intensity incubating and chick-rearing phases.

Also, over the past three years warm water conditions in the North Pacific resulted in sooty shearwaters returning to New Zealand in increasing states of anaemia and mortality from year to year, suggesting that the sub-optimal conditions in the North Pacific had flow-on physiological effects.

Lastly, those species that dive to greater depths, such as sooty shearwaters, rely more on muscle oxygen stores underwater to fuel dive activity, as opposed to their lungs.

This makes sense as reducing buoyancy is key in order to reduce energetic costs.

So what are some of the key pressures and threats they face in our environment?

The key threats are introduced predators, particularly for burrow nesting petrel species where the chick spends all its time trapped within a burrow; there have been reports of a single stoat having consumed 70 diving petrels at Bethells beach.

A storm petrel chick on Burgess Island in the Hauraki Gulf. Photo / File

Other threats are destruction of habitat - especially removal of native forest and coastal development - and for some species, interactions with fisheries and ingestion of pollution are big threats as well.

Unless we do something fast, these threats will worsen.

Steps are being taken to remedy some of these issues, and predator free sanctuaries, such as Tawharanui Marine Reserve near Auckland, are a necessary effort in their recovery.

Unfortunately, seabirds will nest on land and feed at sea so unless food supplies at sea are also protected their future is vulnerable.

Scientists describe seabirds as nature's "superbeasts". Why?

Some species of Hauraki Gulf seabird, such as diving petrels, are the ultimate in "stressed executive", in that they never get a break.

Once they have laid an egg they must then feed a chick which gets up to 120 per cent of their body weight - that's akin to a 60kg woman breastfeeding a 72kg baby.

Auckland University seabird researcher Dr Brendon Dunphy. Photo / Supplied

Feeding this huge chick is made by daily flights diving for krill and other zooplankton within the Hauraki Gulf.

Once they've provisioned their chick with enough body reserves to survive, they then fly 5000 km from the gulf to the southeast of New Zealand, reaching the polar front within 13 days.

Here, they almost continually feed, moult their feathers and then return in early autumn to repeat the process all over again.

Possibly more impressive are sooty shearwaters which migrate to the North Pacific - places like Alaska and Japan - to feed and then migrate back to New Zealand within 11 days where they breed and feed, diving up to 90m to prey on squid and fish.

What's more, they can hold their breath for over a minute and half when diving.

So not only does this bird make an impressive 60,000km round trip using aerobic metabolism, but we suspect it can sustain huge anaerobic loads when foraging underwater.

A white-faced storm petrel's yellow webbed feet in the Hauraki Gulf. Photo / File

What can they tell us about our own environment and how it's changing?

Given that different seabird species feed at different locations, from the gulf through to subantarctic waters, seabirds are able to tell us the state of oceans food webs both locally and beyond the horizon.

Many species appear poised on a metabolic knife-edge thus any shift in prey quality or quantity can have significant effects on their ability to rear a chick and maintain their own condition.

If fish and squid prey are reduced due to El Nino-Southern Oscillation conditions, we see shifts in foraging efforts, such as more trips to subantarctic waters to feed on lower quality prey, and the chicks consequently struggle to fledge.

Obviously, future climate change is a big concern.

How impressive is seabird biodiversity in Auckland's backyard?

Despite New Zealand's largest city being located here, the seabird biodiversity of the Auckland region is equal to isolated locales such as the Kermadec and Chatham Islands.

Of the 27 taxa that breed in Auckland, 16 are endemic and our country is rightly known as a hotspot of seabird diversity.

For the wider Hauraki Gulf, the hydrodynamic environment is complex creating blooms of plankton which support productive food webs.

Moreover, the many islands offer prime breeding locations close to feeding grounds and increasingly free of predators.

The fact that the "extinct" New Zealand storm petrel can quietly live its life unnoticed for 150 years within the Hauraki Gulf show's what a special place it is.