Seabirds: Canaries in the mine or elephants with wings?

by Kate Waterhouse

In this article, Kate Waterhouse summarises some recent seabird research findings reported at the Hauraki Gulf Marine Park Seminar: Taking Flight, held on 6 September 2017 at the Auckland Museum.

The Hauraki Gulf, Te Moana Nui a Toi, Tikapa Moana, is a global seabird hotspot.  And here, seabirds, forest birds, lizards and even some marine ecosystems are recovering where rats and other predators have been removed from islands and sanctuaries.

The Hauraki Gulf is a magnet for seabird researchers and those learning how to protect breeding colonies.

All over the world, seabirds have been marginalised to the most remote areas and islands. They have no defences, having evolved without mammalian predators – so stopping predation in breeding colonies is a global issue. 

All eyes on New Zealand

The Hauraki Gulf is a magnet for seabird researchers and those learning how to protect breeding colonies. Dr Andre Raine of the Kaua’i Endangered Seabird Recovery Project in Hawaii told the 400 strong audience at the Auckland Museum that New Zealand is at the forefront of new methods - including traps, island eradications, fenced sanctuaries, translocation, and social attraction projects, such as Tawharanui, where seabirds are breeding again. He described Predator Free New Zealand as a globally significant goal. 

Why is the Hauraki Gulf a global seabird hotspot?

The numbers tell the story – of the 10,400 species of birds globally, only 359 are seabirds, around 20% of the world’s seabirds have been recorded here (over 70 species), and 26 species of seabird breed in the gulf ,with four endemic to the region (including the black petrel (Procellaria parkinsoni), fairy tern (Sternula nereis) (our nation’s rarest bird) and the recently rediscovered New Zealand storm petrel (Fregetta maoriana)1. 

About 70% of New Zealand’s territory is ocean and it’s easy to see from submarine topography and oceanic currents, that upwellings and convergence zones near New Zealand make our waters extremely productive. So said illustrator Chris Gaskin, one of the founders of the Northern New Zealand Seabird Trust (NNZST). Chris pointed out that in the Hauraki Gulf, trevally, kahawai and other school fish feed on krill – so it’s not surprising seabirds have become concentrated here also.

Shapeshifters: Why seabirds are so amazing - across distance and the air/water divide

Chris Gaskin explained that being able to locate food scattered over vast areas of ocean is key to survival for all seabirds. Multiple senses come into play when they do this – especially sight and smell.

They have extraordinary physiology – for example for gannets, terns and gulls, sight and body shape define them. They can see very well below water as well as above it, and can keep flying through air and into the much denser water with ease. Some shearwaters can dive down to 90 m. The titi/sooty shearwater (Puffinus griseusan) dive into water, a medium 800 times denser than air, up to 92 m under water, and for 90 seconds. 

Matt Rayner, who with Gaskin, rediscovered the New Zealand storm petrel, explained that the titi is able to achieve such feats by storing oxygen in its muscles, not its lungs. 

Seabird islands are transformed at night, the air is alive with thousands and sometime millions of birds returning to burrows.

But seabirds must come to land to breed, whether it’s gannets on a rock stack off the Broken Islands, or petrels in the forests of Hauturu/Little Barrier, Aotea, or the Poor Knights. In the daytime you can see gannets, shags and terns because they are active by day, when most petrels and shearwaters are at sea, only returning to land at night. Seabird islands are transformed at night, the air is alive with thousands and sometime millions of birds returning to burrows.

On Hauturu the noise can be deafening – the equivalent of Auckland’s population in Cook’s petrels (Pterodroma cookie) alone arrive nightly. Before mammalian predators arrived and seabirds were lost, this is what many of our forests would have been like.

The imperative to breed is what brings seabirds to land, but getting back to sea can be tricky with many species, such as Buller’s shearwaters, climbing trees to gain a platform to take off. A seabird’s most difficult time in life is their first year – it is a miracle time for many.  Gaskin described a 35 g New Zealand storm petrel – hatched in deep forest high on Hauturu, fed by parents for two months before emerging and stretching over several nights.  “It might be raining, or windy, but eventually it must fly out through the forest, down a valley and out to sea – a whole new world opens before it... It has to find food - the right type of food, but its body is fit for purpose, strong and waterproof enough to survive.  With each passing year its survival chances increase”.

Elephants with wings: Burrowing seabirds are ecosystem engineers

Dave Towns of the Auckland University of Technology (AUT) believes burrowing seabirds are like “elephants with wings”. Seabirds in the Hauraki Gulf are burrowing species which makes them ecosystem engineers, just like elephants in the African savannah. On a seabird island you will see what looks like elephant damage on the ground and in the trees. They raise the nutrient content through excreting guano and lower the pH level of the soil. Why is this important?

As Dr James Ross from Tawharanui Open Sanctuary points out, this nutrient cycling process helps to restore ecosystems, on land and in the ocean. 

But just how big is the impact of seabirds? Ross went to Hauturu to determine just how much guano is produced by one million Cook’s petrels. Estimates were based on how long the birds are resident, the altitude and guano production rates. The answer turned out to be about 55 tonnes per year, the equivalent of about 50 kilograms per hectare per year of fertiliser. Literature suggests that this estimate is at the low end. Wedge-tailed shearwaters (Puffinus pacificus) in the Pacific are thought to add 230 kilograms per hectare – a very significant nutrient input to the ecosystem2!

The amazing effects on islands when seabirds do come back

So where do the nutrients go?

The answer is into both the forests and the sea. The benefits seabirds bring flow to plants, trees, small reptiles and invertebrates and nearby marine ecosystems. Comparing islands with and without seabirds shows that the food webs of invertebrates are much more complex on seabird islands than non-seabird islands.  In fact, according to Towns, they approach the most complex food webs found anywhere.

Seabird islands have healthier marine environments too. AUT researchers Rachel Buxton and Steph Borrell found unexpected results in the intertidal and subtidal seaweed communities around seabird islands studied. Species diversity is higher and three species showed evidence of enrichment. Such a finding has implications for the way we design our marine reserves. If seaweeds are healthier at the base of the food chain, then other biodiversity will benefit too.

How seabirds recolonise a place: the halo effect and social attraction

When James Ross heard Chris Gaskin talk in 2010 about a grey-faced petrel (Pterodroma macroptera) that he had found flying around the Tawharanui Open Sanctuary, he decided to take action to bring seabirds back to the peninsula. This goal proved to be a challenge, as researcher Rachel Buxton outlined, but it shows what is possible on Rakitu and other islands off Aotea’s coast in a very short time, should rats and cats be removed.

Recolonisation is helped considerably by being near to a source population of birds – because social cues are very important too. Sound systems played seabird calls all night every night from prominent headlands all over Tawharanui. Within months, they had attracted diving petrels (Pelecanoides urinatrix), fluttering shearwaters (Puffinus gavial) and non- target species. After decades of farming, the soil at Tawharanui was very compacted, so the team provided nest boxes as an alternative to burrows. Breeding has been successful. About 350 birds have been banded and these diving petrels and fluttering shearwaters may be the first mainland breeding records in the gulf for many decades.

How long will it take for the elephants with wings to perform the role of ecosystem engineers?

Elsewhere in the gulf, recolonisation is happening very rapidly, with Pycroft’s petrel (Pterodroma pycrofti) now back on Great Mercury three years after the removal of mammalian pests - the first time in 800 years. Buxton and Borrell have also turned their attention to how far seabirds will go to recolonise islands. The answer may be up to 25 km from their natural home. The pair have mapped ‘recruitment halos’ showing how rat-free island groups like the Mokohinaus and Hen and Chickens can provide new colonisers for neighbouring islands.

Aotea and Hauturu are on the outer limit of these halos and the recruitment halo of the Mercury Islands is south of Aotea. Seabird experts are confident that using the social attraction techniques tested at Tawharanui (and elsewhere) will be successful. The Mokohinau Islands sustain seven seabird species and Rakitu and the north coast of Aotea sit squarely on the seabird highway.3 

Can seabirds recover? What do they need from us?

AUT’s Steph Borrell has looked at the multiple challenges seabirds face at sea and how seabirds recover following predator eradications. On a rat island, seabird population growth never reaches its maximum rate, although as soon as rats are gone, the pressure reduces and seabird populations start to recover. Steph’s work included 14 species of petrels and shearwaters (Procellariae) and created a model for population growth in the absence of other types of pressure i.e., optimal conditions. Seabirds generally have long lifespans and low breeding rates which makes breeding success very important to long term survival of a species.

...fisheries bycatch alone, sends most seabird species into decline and pushes population growth below zero.

She added other threats to the model – plastic pollution, fisheries impacts, and climate change. The results show that fisheries bycatch alone, sends most seabird species into decline and pushes population growth below zero. Climate change impacts are also variable, although even a fractional adjustment for change in some climate parameters means some populations will decline.

Tracking seabirds and ocean productivity

 Seabirds are following productivity in the oceans, say Dr Matt Rayner of Auckland Museum and Dr Brendon Dumphy of University of Auckland. So they have been looking at where seabirds go. From the gulf, it’s all over the Pacific, connecting us culturally, spiritually and genetically to other places – a spatial imprint they have been able to obtain via geo-locators attached to seabirds.  Rayner says it’s clear that climate change is warming the gulf, but the east coast, where many seabirds are breeding and feeding, has less temperature ‘headroom’ than the west coast. The team studied the diving petrel, a species that migrates to the polar front in winter in 13-15 days to follow ocean productivity. In the summer months, tracking showed that Tiritiri Matangi-based birds and Mokohinau Island birds feed on different things – plankton offshore (Mokes birds) and fish inshore (Tiri birds). But the Mokohinau birds are more stressed - their blood stressors are higher and they are lighter over time. The team believes this is being driven by stronger and more frequent El Niño seasons.

Last words

Seabird scientists know that the more we learn, the more we know how much we don’t know. This raises the question of how close are we to missing indications that some species might be about to go, and how close were we to losing the New Zealand storm petrel?

Town concluded that the ecosystem engineering of seabirds is well known - we can reinstate species by removing predators, and advance our knowledge on natural re-colonisation. But how big we can get when it comes to eradications depends on working on inhabited islands with people. “If people engage in this process they may themselves get to see elephants with wings.” 

...how big we can get when it comes to eradications depends on working on inhabited islands with people.

Dame Anne Salmond went further, saying we cannot continue to separate human activities from ecosystems. We’re all linked, and the science of complex systems backs this up. If we think these things are there to serve us, or are resources for our purposes, the outcomes won’t be good for anyone.

As scientists at the seminar demonstrated, seabird islands support significantly more life than those where seabirds have been eaten out by predators. So without more focus on how to protect and expand seabird breeding sites, we run the risk not only of losing birds to extinction, but changing the fertility and biomass of islands forever.

Notes:

1 Gaskin, C. P. and Rayner, M. J., 2013. Seabirds of the Hauraki Gulf: Natural History, Research and Conservation. Hauraki Gulf Forum.

2 Holtmeier, F., 2015. Animals’ Influence on the

Landscape and Ecological Importance: Natives,

Newcomers, Homecomers. Springer.

3Graphic from Rayner, M.J., Gaskin, C.P. (2013). Hunting the New Zealand Storm Petrel in a world centre for seabird diversity. Presentation at the Australasian Ornithological Conference, 4-7 December 2013, Auckland, New Zealand. Photos: Shelley Heiss-Dunlop, Dylan van Winkel, Neil Fitzgerald, Kim Westerskov, Karen Baird, Chris Gaskin.

4Cronin, E., 2017. Seabird Super Highway - a return to the Hauraki Gulf. Environment News, Issue 37. Autumn 2017. Great Barrier Island Environment Trust.

Environmental News Issue 38 Spring/Summer 2017