Burrowing into the Past 

ANDRÉ BELLVÉ (University of Auckland)

For many people, the word ‘seabird’ probably conjures the image of a gull cawing for your chips, a shag snatching the under-sized snapper you just threw back, a little blue penguin bobbing in the distance, or maybe a picture/documentary you once saw that featured an albatross. Or at least, that was largely my experience before I began studying seabirds, a realisation I found profoundly dissonant when I learned that Aotearoa is often called the “seabird capital of the world”. 

Here, I refer to seabirds as “those species that spend some part of their lifecycle at sea, feeding in inshore or offshore water”(1). There are roughly 370 species of seabird globally, split across four taxonomic Orders; Charadriiformes (e.g., gulls, terns, auks), Suliformes (e.g., gannets, shags, frigatebirds), Sphenisciformes (i.e., penguins), and Procellariiformes (e.g., storm petrels, petrels, shearwaters and albatross). Of these 370 species, 88 breed in Aotearoa (nearly 25% of the total!), and 37 (10%) are endemic breeders (Forest & Bird 2015, Whitehead et al. 2019). In particular, Tikapa Moana o Hauraki (the Hauraki Gulf) is home to at least 28 of Aotearoa’s seabirds, at least five of which have been found nowhere else (including Aotea’s black petrel - Procellaria parkinsoni), and has led to the Tikapa Moana being recognised as an international “Important Bird Area”(2)(3). 

So how is it that we have such incredible diversity, but they often exist on the fringes of Aotearoa? Many of these species live most of their life out at sea, only returning to land to breed(4). While there are obvious exceptions (e.g., Australasian gannets and numerous shag species around Aotearoa), many of these birds are ephemeral residents with cryptic habits. For instance, all of the smaller (< 1.6 kg) procellariiforms (nearly half of Aotearoa’s seabird species) typically nest in underground burrows among tree roots and boulders or rock crevices (hereafter ‘burrowing procellariiforms’), often favour steeply sloped sites, and typically return after dusk, only to leave in the early hours of the morning(5)(6). Furthermore, many such seabird only reside on our off-shore islands and predator-free sanctuaries, which are carefully managed by mana whenua, DoC and conservation groups(2). In fact, the best chance to see many of these birds is out on the waters of Tikapa Moana, where they drift as large ‘rafts’ floating on the surface or the chaotic swirling storm clouds they form to feed on ‘boil-up’; a phenomenon where plankton are pushed to the surface by fish and cetaceans feeding from below. 

Seabirds’ cross-ecosystem lifestyle is the basis of a key ecological function in Aotearoa’s terrestrial and near-shore ecosystems. Many of Aotearoa’s forests are impoverished of bioavailable phosphorus(8), but the diet of seabirds is rich in this element and many other essential nutrients, which is why seabird guano (fossilised faeces) has long been used as an organic fertiliser(9). By feeding at sea and then returning to land to breed and raise their chicks, seabirds flux nutrients from the ocean to the land, and hence can fundamentally alter the composition and productivity of their environment. For instance, Bosman and Hockey (1988)(10) showed that seabirds fertilise the intertidal zone, which promotes foliose algae growth, in turn providing habitat for a range of marine invertebrates, which are subsequently prey for many shorebird species. Similarly, McCauley et al. (2012)(11) found that the presence of seabirds on islands not only fertilised the forests they roosted in but that discarded nitrogen-rich foliage from the forest gets blown into coastal waters and together with nutrient run-off from the forest, promotes phytoplankton growth. In turn, the increase in phytoplankton leads to a greater abundance of zooplankton, which attracts manta rays. These rays are typically absent from the relatively nutrient depauperate waters of islands that have lost their seabirds. Numerous studies have explored the effects of seabirds on Aotearoa’s forests and demonstrated their multi-faceted influence on ecological communities(12)(13). Given that Aotearoa is home to an incredible diversity and abundance (estimated to be in the hundreds of millions of birds currently!), seabirds play a critical role in our terrestrial and near-shore ecosystems. 

Seabirds are the most threatened group of birds on earth(14), and up to 90% of northern Aotearoa’s seabirds are threatened with extinction(1). The loss of seabird species will be accompanied by the loss of the critical ecological functions they supply. The threats in the marine environment primarily stem from pollution, by-catch, and climate change(15). In Aotearoa, the most significant terrestrial threats arise from predation by introduced mammals (e.g., dogs, cats, rats, mice, stoats, pigs, etc..) and habitat destruction(16), although these are not new. Early accounts by European naturalists describe breeding colonies of burrowing procellariiforms as far inland as the slopes of Mount Ruapehu near the centre of the North Island and throughout the Southern Alps of the South Island. Unfortunately, nearly all of these inland colonies were lost by the start of the 21st century. The writings of some early European naturalists describe the devastating effects of introduced mammals. Reischek (1885)(17) noted: 

A decline which the author ironically contributed to when he was ‘examining’ black petrel burrows:

Clearly, mammals had a rapid and devastating effect on many of our seabirds. However, at present we lack an adequate baseline (what was the former distribution of seabirds? How much material did they move from the ocean to the land?) From which to assess the ecological consequences of these changes. 

As species decline or disappear, we will lose their ecological functions. Predicting how these ‘functional extinctions’ (or losses) will affect ecosystems is challenging. However, information from the past may allow us to understand the impacts of previous environmental change (whether by humans or not), which can inform our understanding of what continued losses may mean, and guide restoration interventions. The primary motivation for my doctoral research was to create a methodological framework with which to reconstruct these lost ecological functions, using the ocean-land nutrient fluxes supplied by the burrowing procellariiforms of Aotearoa as a case study. In this article, I will focus on how we determined where burrowing procellariiforms were before the arrival of European mammals. 

To determine the former range of our burrowing procellariiforms, I gathered three key lines of evidence on the location of their breeding grounds: fossil data, historical records, and contemporary observations. 

First, I compiled fossil data from the Holocene (c. the last 10,000 years), giving us insights into where these species bred in the past, possibly before human arrival. However, fossil records hold intrinsic biases due to the conditions required for a fossil to preserve, meaning fossils cannot inform us about some environments. Moreover, there is also some temporal uncertainty with these records as they have only been dated to the last 10,000 years, so we do not know precisely when these individuals lived. 

To complement the fossil records, I scoured historic documents and records to identify other sites these birds occupied. The historic records were a combination of old newspapers, using Papers Plus (a national repository of digitised news articles), historical accounts by early naturalists(17)(18)(19), and early scientific publications that provided breeding colony locations(20)( 21). These historic records covered known breeding locations before 1990, which we used as a cut-off for the “historic” period due to the advent of modern mammalian predator control methods around this time. Historic records can tell us about colony locations that do not occur in sites that favour fossilisation, but they carry their own biases, as authors tend to focus on ‘remarkable’ locations (e.g., the slopes of Mount Ruapehu) and may already be impacted by anthropogenic influences. Together, historic and fossil records can broaden our understanding of a species’ ecological niche and provide insights into where they likely occurred in the past. 

Finally, to determine the contemporary (1990 – present) breeding ground distributions, we worked off more recent publications(2)(22)(23), for sites which have already suffered marked contractions due to human actions. These records of breeding colonies were broken up into three size-classes based on the mass of adult birds. We then linked known occurrences with environmental conditions to predict where each size-class may have occurred in the past and the present. 

Aotearoa’s seabirds once had breeding colonies much further inland than they do today. In particular, the records of breeding colonies in the Southern Alps and on the ranges around the volcanic plateau of the North Island are highlighted by my model. Furthermore the model predictions suggest that there were many other inland locations with similar conditions that would have been favourable to burrowing procellariiforms. 

So while Aotearoa is currently the “seabird capital of the world”, it is likely a fraction of its former glory, as it has been hollowed out. Islands in the Tikapa Moana o Hauraki, such as Aotea, would likely have been home to hundreds of thousands, if not millions, of burrowing procellariiformes before the large-scale clearance of forests with fire and the introduction of predators like cats, rats, and pigs. However, there is still hope. Aotea and Te Hauturu-o-Toi are the last refuges for black petrels, through careful control of introduced predators, the populations appear to have stabilised. However, we cannot be complacent, the climate is changing, and we have seen an increased frequency and intensity of extreme weather events. The last few years have seen two extraordinary marine heat-waves, which can have catastrophic effects on the availability of seabirds’ prey and their ability to feed their chicks. Only by being kaitiaki of the oceans and the land will we be able to hand these treasures down to the next generation, and hopefully, they will no longer be cryptic denizens existing on the fringes of Aotearoa’s consciousness. 

Acknowledgements:

I would like to thank my supervisors and collaborators George Perry (Uni Auckland), Chris Gaskins (NZ Seabird Trust), Janet Wilmhurst (Manaaki Whenua), Jamie Wood (Uni Adelaide), Edin Whitehead (Uni Auckland), Paul Schofield (Cant Museum) and Trevor Worthy (Flinders Uni). I acknowledge the mana whenua of Aotearoa who have kaitiaki of the whenua and all its taonga, without whom this work would not have been possible. Also the Northern New Zealand Seabird Trust who provided a large portion of the data on post-1990 distributions and invaluable support and experience. Thanks also to Alan Tennyson and Colin Miskelly of Te Papa Museum who shared both data and knowledge on the seabird distributions.

References:

1. Whitehead, E., N. Adams, K. A. Baird, E. Bell, S. Borelle, B. J. Dunphy, C. Gaskin, T. J. Landers, M. J. Rayner, and J. C. Russell. 2019. Threats to sea birds of northern Aotearoa New Zealand. Auckland Council 1:1–76. 

2. Forest & Bird. 2015. New Zealand Sea birds: Sites on Land, Coastal Sites and Islands. The Royal Forest & Bird Protection Society of New Zealand. 

3. Gaskin, C., and M. Rayner. 2017. Sea birds of the Hauraki gulf. Auckland Council. 

4. Schreiber, E., and J. Burger. 2001. Sea birds in the marine environment. Pages 19–34 Biology of marine birds. CRC Press. 

5. Warham, J. 1990. The petrels: their ecology and breeding systems. A&C Black. 

6. Brooke, M. 2004. Albatrosses and petrels across the world. Oxford University Press. 

7. Friesen, M. R., C. E. Simpkins, J. Ross, S. H. Anderson, S. M. Ismar-Rebitz, A. J. Tennyson, G. A. Taylor, K. A. Baird, and C. P. Gaskin. 2021. New population estimate for an abundant marine indicator species, Rako or Buller’s Shearwater (Ardenna bulleri). Emu-Austral Ornithology 121:231–238. 

8. Parfitt, R., W. Baisden, and A. Elliott. 2008. Phosphorus inputs and outputs for New Zealand in 2001 at national and regional scales. Journal of the Royal Society of New Zealand 38:37–50. 

9. Wainright, S. C., J. C. Haney, C. Kerr, A. N. Golovkin, and M. V. Flint. 1998. Utilization of nitrogen derived from sea bird guano by terrestrial and marine plants at St. Paul, Pribilof Islands, Bering Sea, Alaska. Marine Biology 131:63–71. 

10. Bosman, A. L., and P. A. R. Hockey. 1988. The influence of sea bird guano on the biological structure of rocky intertidal communities on islands off the west coast of southern Africa. South African Journal of Marine Science 7:61–68. 

11. McCauley, D. J., P. A. DeSalles, H. S. Young, R. B. Dunbar, R. Dirzo, M. M. Mills, and F. Micheli. 2012. From wing to wing: the persistence of long ecological interaction chains in less-disturbed ecosystems. Scientific Reports 2:409. 

12. Mulder, C. P. H., and S. N. Keall. 2001. Burrowing sea birds and reptiles: impacts on seeds, seedlings and soils in an island forest in New Zealand. Oecologia 127:350–360. 

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14. Dias, M. P., R. Martin, E. J. Pearmain, I. J. Burfield, C. Small, R. A. Phillips, O. Yates, B. Lascelles, P. G. Borboroglu, and J. P. Croxall. 2019. Threats to sea birds: A global assessment. Biological Conservation 237:525–537. 

15. Fletcher, D., Newman, J., McKechnie, S., Bragg, C., Dillingham, P, Clucas, R., Scott, D., Uhlmann, S., Lyver, P.O., Gormley, A.M., Bull, S., Davis, K., Davis, R., Davis, R., Davis, T., Edwards, L., Kitson, J., Nixon, T., Skerrett, M., and Moller, H. 2021. Projected impacts of climate change, by-catch, harvesting, and predation on the Aotearoa New Zealand tītī Ardenna grisea population. Marine Ecology Progress Series 670:223–238. 

16. Bellingham, P. J., D. R. Towns, E. K. Cameron, J. J. Davis, D. A. Wardle, J. M. Wilmshurst, and C. P. Mulder. 2010. New Zealand island restoration: sea birds, predators, and the importance of history. New Zealand Journal of Ecology 34:115. 

17. Reischek, A. 1885. Notes on the habits of some New Zealand birds. Pages 106–107. 

18. Dieffenbach, E. 1841. An account of the Chatham Islands. The Journal of the Royal Geographical Society of London 11:195–215. 

19. Oliver, W. 1955. Birds of New Zealand. Second edition. A. H. & A. W. Reed, Wellington, NZ. 

20. Falla. 1934. The distribution and breeding habits of petrels in northern New Zealand. Auckland War Memorial Museum 1:245–260. 

21. Imber, M. J. 1976. Comparison of prey of the black Procellaria petrels of New Zealand. New Zealand journal of marine and freshwater research 10:119–130. 

22. Miskelly, C. M., C. R. Bishop, G. A. Taylor, and A. J. D. Tennyson. 2019. Breeding petrels of Chalky and Preservation Inlets, southern Fiordland–a test of the ‘refugia from resident stoats’ hypothesis. Notornis 66:74–90. 

23. Miskelly, C. M., A. J. Tennyson, J.-C. Stahl, A. F. Smart, H. K. Edmonds, and P. G. McMurtrie. 2017. Breeding petrels of Dusky Sound, Fiordland–survivors from a century of stoat invasions. Notornis 64:136–153.