Research showing increased stress in seabirds as they struggle to find food is also an indicator of oceanic changes across hemispheres
Opinion: To understand seabirds allows us to better understand the oceans, and, I’d argue, ourselves. For generations they have guided us, inspired us, and provided cautionary tales for the consequences of our actions. For Polynesian voyagers they were but one of a suite of tohu (signs) used to ‘pull islands out of the sea’ as they expertly navigated vast distances. Their role as teachers continues today but what they must teach us has changed.
As top predators, seabirds (particularly the chicks) represent a summation of all the interlinked processes occurring out at sea. The sun’s energy captured by phytoplankton flows up food webs to zooplankton, to fish, squid and other sea creatures and ultimately to the bird itself. But seabirds live on an energetic knife edge. If there is a perturbation at sea, we can detect something is amiss from seabird chick health.
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We may think of the ocean as vast and endlessly productive, but from a bird’s eye view it consists of small green oases in a vast blue desert. Aotearoa New Zealand is one such oasis, and with its mountains, forests, ocean fronts, upwellings and rivers, the seabird capital of the world. We have the highest diversity of species either permanently living here or visiting to breed. We are home to the tītī (also known as muttonbird or sooty shearwater), the most abundant seabird on the planet.
Tikapa Moana/Te Moananui a Toi (Hauraki Gulf) is an internationally recognised hotspot for seabirds, and visitors travel from across the globe to see them here. I have lived my whole life here on its shores, and the first mountain I have memory of is Hauturu/Little Barrier Island with its cloud-covered peak.
Growing up I only knew of seabirds as the pesky seagulls squawking with their grating song as they argued among themselves for my leftover fish and chips. It was my mother who showed me what lessons seabirds can teach us, when she pointed out all the seagulls resting on my school rugby field before an easterly storm. I was struck by that, their weather forecasting abilities, and started to wonder what other lessons could be gleaned from them as well.
Years later a friend told me about the tītī, how it undertakes one of the largest migrations on the planet – an impressive 60,000km round trip up to the Bering Sea and back, each year. I then learned this bird, the size of a seagull, holds it breath for up to 90 seconds as it routinely descends to 50m underwater to hunt fish, squid, and krill. (The known record so far being 90 metres!) Colleagues have tracked another species, the rako/Bullers shearwaters flying from the Poor Knights Islands to halfway to Chile on a 16-day hunch there might be something tasty out beyond the Louisville Ridge.
But most of us don’t know much about these magnificent creatures – myself included. They forage far beyond the horizon, only returning to our shores under cover of darkness, on offshore islands free from predators. And this is a problem, as 90 percent of our seabirds face some form of threat, with some at critically low numbers. The threats they face include habitat modification and mammalian predators on land, along with fishing mortality – the intensity with which a stock is exploited – through accidental capture, plastics, and climate change.
Seabirds are often described as oceanic indicators, and over the past 10 years we’ve been researching what the biology of the birds might tell us about the ocean, particularly oceanic warming. It costs more than $50,000 a day to take a research vessel over the horizon, but these birds do it every day – so perhaps we could learn something from them?
We have discovered quite a lot from them. The birds are telling us of an increase in the cost of raising their young, that they’re frequently stressed out and struggling. We can see this by using many tools, such as measuring haemoglobin, the protein that makes our blood red. Haemoglobin carries oxygen around the body and is vital to meeting increased energy demand. Birds can increase their levels if times get tough.
My team and I stumbled across this in 2015 after a large number of dead adult tītī returning from migration washed up on our shores around Auckland. By analysing the blood of those that had survived the trip we could identify that they were unusually stressed from their high levels of haemoglobin.
We then realised they were responding to the longest marine heatwave recorded in the North Pacific, later nicknamed “the blob”, a disruption from warming oceans that resulted with starved seabirds washing up on beaches from California to Canada, leaving over a million guillemots (a seabird of the auk family) dead, along with other large-scale changes in the ocean ecosystems. It became apparent that a simple protein such as haemoglobin of seabirds can record oceanic changes across hemispheres.
Closer to home, last year we saw one of the longest marine heatwaves. Across multiple species (eight and counting) this caused increased stress, and elevated haemoglobin showing birds were struggling to find food to feed themselves and their chicks. Research by my colleague Edin Whitehead, for instance, has shown that fluttering shearwaters at the Mokohinau Islands respond to heatwaves by working harder and for longer to find food for their chicks in a warmer Hauraki Gulf. This starves their chicks, leading to higher stress levels, and slower growth. Heatwaves are forecast to increase in frequency, duration, and intensity.
What will this mean for seabirds? We anticipate more stress until breaking points are reached. We are working fast to provide information on the extent of this stress, to be fed into management and action plans. Climate change will be a multi-stressor ‘death by a thousand cuts’ situation. If we can continue to optimise our conservation approaches and reduce the number of threats the birds face, we will increase their chances. We have no choice but to remain hopeful.
Dr Brendon Dunphy will be giving a free talk, Stressed shearwaters and anxious albatrosses – life lessons from seabirds, at Raising the Bar in Auckland, August 29, 6.30pm
