Seabird stress as a conservation tool

Maira Fessardi

Fish (blue mackerel) work-up with shearwaters and prions. Photo: Edin Whitehead.

Seabirds and climate change

We often hear about climate change and how its consequences might affect our lives. Ocean temperatures are rapidly rising, causing a range of problems to the incredible biodiversity that inhabits that ecosystem. Seabirds are one group of animals that rely on a healthy ocean to thrive, and they represent the most threatened group of birds in the world [1, 2]. With approximately half of seabird species experiencing population declines, it becomes important to understand what is driving this trend and how it relates to the drastic changes in the marine environment [1].

New Zealand, and particularly the Hauraki Gulf, has been identified as a hotspot of international interest for seabird diversity [1]. New Zealand has the highest number of unique seabird species in the world, with over 70 species visiting the gulf. However, 78% of those are either threatened or at risk of extinction [3].

That is particularly problematic because seabirds play a very important role in the ecology of our terrestrial ecosystems. They are classified as “Ecosystem Engineers”, meaning their behaviour and ecology play a crucial role in the health of the terrestrial environment they inhabit [4]. Even though these birds spend most of their lives feeding in the ocean, they come to land (or “breeding sites”) to find their pairs and breed. Their nesting habits include digging through soil, building a safe burrow for courtship, incubation, and chick-rearing. This physical disturbance brings in crucial nutrients from the ocean to our forests, carried in their faeces, dead tissues, and eggs [4]. The disappearance of seabird populations is often associated with a loss of biodiversity, causing a cascade effect of ecological loss in terrestrial communities [2, 4]. Additionally, they occupy the top of the marine food chain, being carnivores that feed on fish and invertebrates. That means their population success is highly dependent on variations in ocean conditions and biodiversity [6]. Higher ocean temperatures, for instance, may cause a decline in seabirds’ food availability and quality, which impacts their ability to survive and fulfil their biological duties [6, 7]. Thus, observing their lives and breeding outcomes can provide incredible amounts of information on the health of their environment, becoming powerful environmental indicators [5].

A better understanding of how climate shifts affect ocean conditions allows decision-makers to put more well-informed plans in place. Monitoring ocean health, however, can be expensive and logistically challenging. The good news is, we may be able to investigate those changes by watching and quantifying their effects on seabird’s population processes (i.e. breeding and physiology). Their habit of coming to land to breed provides an opportunity to observe their condition, constituting an accessible indicator of environmental health. Seabird population monitoring may give us powerful insights into the ocean dynamics in remote marine environments that the birds use as feeding grounds [7, 8].

Black Petrel nesting in burrow - Aotea/Great Barrier Island. Photo: Maira Fessardi

Out of all seabird species breeding in the Hauraki Gulf, one stands out: The Grey-faced petrel (Pterodroma macroptera). This species can only be found breeding in New Zealand and, unlike its seabird relatives, remains widespread to this day, with many successful colonies around the Gulf [9]. They are long-lived, with high fidelity to their breeding sites and partners, feeding close to the coast [10, 11]. That combination of factors facilitates access to birds and allows for long-term monitoring efforts, earning them the status of key indicator species [12]. Monitoring Grey-faced petrels may reveal important information about what is happening where they feed in the ocean, which could help us predict future population declines [10]. Although seabirds as environmental indicators may sound like an ideal solution for some of our climate conundrums, there is still a long way to go in using their population processes as a reliable and precise monitoring tool.

Black Petrel chick in what can be a successful breeding event. The eggshells will decompose and integrate nutrients into the soil. Photo: Maira Fessardi

How Does it Work?

It is understood that the relationship between environmental conditions and stress physiology is stronger than ecological processes, such as breeding [13, 14]. Chicks raised in poor environments may still survive stressful periods as youngsters and go on to become adults. That would be classified as a successful breeding event for monitoring [7, 13]. However, an entire generation of seabirds facing stress may suffer life long impacts, affecting their ability to become good parents and fulfil their duty to sustain their population legacy [7, 13]. In this case, information on the ecological process of breeding is misleading as evidence of success and population numbers, which might eventually start declining.

Like humans, seabirds undergoing stressful events will ultimately exhibit a physiological response to these stressors [8, 10]. Stressful events may be, for example, situations where food supply is limited by poor ocean conditions, either inducing nutritional stress or requiring longer travel distances and a waste of energy to find a good meal [7, 8]. Animals that are more stressed will produce higher levels of stress hormones that can indicate something is not right in their environment. Very stressed parents can also transmit some of their stress hormones to their eggs, and be forced to reduce feeding trips to chicks. That means chicks growing in stressful scenarios often produce higher levels of stress hormones than adults, imposed both by stress in their environment (such as predation) and their stressed parents [15]. Long-term stress and high amounts of stress hormones circulating in their body may cause health issues, lower immunity, and result in lower fitness [7, 13]. Thus, stress hormones in seabird populations may have the power to connect events in their life throughout space and time, and record that information [7, 8]. Looking at a population of bird’s stress response can represent an exciting and integrative new monitoring tool.

In birds, the predominant stress hormone is called corticosterone (or CORT, for short) and their physiological responses to environmental stressors often result in high levels of CORT circulating in their bodies [16].

Black Petrel chick in what can be a successful breeding event. The eggshells will decompose and integrate nutrients into the soil. Photo: Maira Fessardi

What are the Research Gaps?

Even though stress hormones in seabirds sound like an excellent new tool for conservation, some gaps still need to be filled. Traditionally, research in environmental stress relies heavily on blood or faecal samples, which can be challenging to collect and are invasive for the bird [17, 18]. They also reflect only short-term stress undergone by seabirds (one day for blood hormones, one week for faecal hormones). If we are facing the fast-changing consequences of climate change, we will be better equipped using long-term, integrative information on how variations in ocean conditions are affecting seabird populations [17, 18]. The good news is there is a potential new tool that ticks all the boxes: stress hormones found in feathers. CORT produced by seabirds during stress events is continuously deposited in growing feathers [7]. More stressed birds are expected to have higher levels of CORT in their developing feathers, which can be extracted in a quick and non-invasive procedure, with no risk of degradation across time [16, 17].

Using feather stress to monitor ocean conditions and population health has great potential and deserves more attention. The patterns of variation in feather CORT and how stress hormones affect population quality, however, varies among species and their environment. To use feather CORT as a reliable conservation tool, it is necessary to advance our knowledge of the specific physiological stress response that different species have to changing conditions in their respective oceanic feeding grounds. [6, 7, 16].

Changes in the environment affect seabird chick fitness, and this has consequences for seabird populations in both the short term and long term. Addressing both the future of seabird populations and oceanic ecosystem health can be aided by monitoring of bird feather CORT

Next Steps

My novel research looks at the Grey-faced petrel stress hormone deposited in feathers to help with one piece of a complex puzzle and validate feather CORT as a conservation tool. Specifically, it is important to understand the pattern of deposition of feather CORT in Grey-faced petrel chicks, and how that compares to variables of changes in ocean conditions. I selected variables that influence food quality, such as temperature, to statistically compare with stress hormone levels. My research also aims to unravel whether feather CORT can predict breeding success and, therefore, population success over time. That more detailed knowledge will help to improve this method as a monitoring tool and test its ability for application conservation and environmental management.

Where is the Information Coming From?

This validation study focuses on a population of Grey-faced petrels that inhabits Te Henga (Bethells Beach), with a substantial colony nesting off the intertidal island Ihumoana. This population is ideal, as it has been subject to previous monitoring projects, and it is stable and thoroughly understood [19].

Feathers and oceanic data have been collected over four years, with adult birds being captured when arriving or leaving the colony to feed, while chicks are extracted from burrows and held inside a bag for measurements of mass and length. Morphological information provides an understanding of the bird’s condition and health. Feathers are processed in the laboratory to extract CORT for analysis. The analysis focuses on differences in stress hormone levels between different years where there has been a variation of ocean conditions, and the relationship between feather CORT and breeding success in those years.

Plots showing the predicted pattern expected for the study results. They only show the expected relationship between feather CORT and environmental variables, with no real data involved. Designed by Maira Fessardi

Expected Results

Ideally, results would show evidence of a significant relationship between feather CORT and ocean temperature/breeding success. That means a population would show higher detectable levels of feather CORT in chicks for years under increased environmental stress, with poorer oceanic foraging conditions (higher temperatures). It is also predicted that higher CORT levels in adult feathers will result in lower quality offspring and relate to lower population breeding success.

More detailed knowledge will help us improve the potential sensitivity of this method as a conservation tool, allowing for more accurate conclusions and predictions [20]. Validating this technique across different species may allow for the development of future models to alert us to dangerous variations in the ocean and population oscillation. Novel technologies increase our chances to fight climate change and implement changes that will hopefully give seabirds, and all the biodiversity in their surrounding environment, a more realistic fighting chance.

References

[1] J. P. Croxall et al., “Seabird conservation status, threats and priority actions: A global assessment,” Bird Conservation International, vol. 22, no. 1, pp. 1–34, 2012, doi: 10.1017/S0959270912000020.

[2] Ç. H. Şekercioğlu, G. C. Daily, P. R. Ehrlich, G. C. Daily, and P. R. Ehrlich, “Ecosystem Consequences of Bird Declines,” vol. 101, no. 52, pp. 18042–18047, 2016.

[3] Hauraki Gulf Forum, State of our Gulf 2020 - full report. 2020. [Online]. Available: https://www.aucklandcouncil.govt.nz/about-auckland-council/how-auckland-council-works/harbour-forums/docsstateofgulf/state-gulf-full-report.pdf

[4] J. L. Smith, C. P. H. Mulder, and J. C. Ellis, “Seabirds as Ecosystem Engineers: Nutrient Inputs and Physical Disturbance,” Seabird Islands: Ecology, Invasion, and Restoration, 2011, doi: 10.1093/acprof:osobl/9780199735693.003.0002.

[5] D. K. Cairns, “Seabirds as Indicators of Marine Food Supplies,” no. November 1986, 2016.

[6] J. F. Piatt et al., “Seabirds as indicators of marine food supplies : Cairns revisited,” vol. 352, pp. 221–234, 2007, doi: 10.3354/meps07078.

[7] A. Will et al., “Feather corticosterone reveals stress associated with dietary changes in a breeding seabird,” Ecology and Evolution, vol. 5, no. 19, pp. 4221–4232, 2015, doi: 10.1002/ece3.1694.

[8] A. Harding et al., “Does location really matter? An inter-colony comparison of seabirds breeding at varying distances from productive oceanographic features in the Bering Sea,” Deep-Sea Research Part II: Topical Studies in Oceanography, vol. 94, pp. 178–191, 2013, doi: 10.1016/j.dsr2.2013.03.013.

[9] C. P. Gaskin and M. J. Rayner, “Seabirds of the Hauraki Gulf,” p. 143, 2013.

[10] J. R. Welch, “Variations in the breeding biology of the grey-faced petrel Pterodroma macroptera gouldi,” vol. 1994, 2014.

[11] M. J. Imber, “Breeding Biology of the Grey-faced petrel,” no. 1952, pp. 51–64, 1976.

[12] J. C. Russell et al., “Developing a national framework for monitoring the grey-faced petrel (Pterodroma gouldi) as an indicator species. DOC RESEARCH AND DEVELOPMENT SERIES 350,” p. 19, 2017.

[13] W. H. Satterthwaite, A. S. Kitaysky, and M. Mangel, “Linking climate variability, productivity and stress to demography in a long-lived seabird,” Marine Ecology Progress Series, vol. 454, pp. 221–235, 2012, doi: 10.3354/meps09539.

[14] A. S. Kitaysky et al., “Food availability and population processes: severity of nutritional stress during reproduction predicts survival of long-lived seabirds,” Functional Ecology, vol. 24, no. 3, pp. 625–637, 2010, doi: 10.1111/j.1365-2435.2009.01679.x.

[15] J. J. Fontaine, E. Arriero, H. Schwabl, and T. E. Martin, “Nest predation and circulating corticosterone levels within and among species,” Condor, vol. 113, no. 4, pp. 825–833, 2011, doi: 10.1525/cond.2011.110027.

[16] C. P. Fischer, R. Rao, and L. M. Romero, “Exogenous and endogenous corticosterone in feathers,” Journal of Avian Biology, vol. 48, no. 10, pp. 1301–1309, 2017, doi: 10.1111/jav.01274.

[17] G. R. Bortolotti, T. Marchant, J. Blas, and S. Cabezas, “Tracking stress: localisation , deposition and stability of corticosterone in feathers,” pp. 1477–1482, 2009, doi: 10.1242/jeb.022152.

[18] G. D. Fairhurst, T. A. Marchant, C. Soos, K. L. Machin, and R. G. Clark, “Experimental relationships between levels of corticosterone in plasma and feathers in a free-living bird,” Journal of Experimental Biology, vol. 216, no. 21, pp. 4071–4081, 2013, doi: 10.1242/jeb.091280.

[19] T. J. Landers, Muriwai Beach to Te Henga (Bethells) 2016 grey-faced petrel and little penguin survey, no. November. 2017.

[20] G. H. Sorenson, C. J. Dey, C. L. Madliger, and O. P. Love, “Effectiveness of baseline corticosterone as a monitoring tool for fitness: a meta-analysis in seabirds,” Oecologia, vol. 183, no. 2, pp. 353–365, 2017, doi: 10.1007/s00442-016-3774-3.