Stress physiology of Grey-faced petrels

Grey-faced petrels (ōi) are one of Northern New Zealand’s most common burrowing seabirds. They’re found between Taranaki, East Cape and Cape Reinga, mainly on islands but also in small relict colonies on the mainland. At predator-free sites such as Tawharanui and Shakespeare, they are recolonising mainland peninsulas where they once bred.

In the Auckland region there are populations on both east and west coasts, but past research has shown that some colonies on the east coast are consistently performing poorly compared to the west coast – their chicks are slow growing, and often they don’t reach their full adult weight before fledging, if they fledge at all. This is apparent at small colonies on nearshore islands, which is where the population is re-establishing. My research was aimed at investigating whether or not there were physiological differences between the adults in these populations by looking at stress hormones and blood parameters that measure energy expenditure.

Over the course of the breeding season, I took blood samples from adult birds at west and east coast colonies. This was to see how their blood physiology changed during different stages of breeding, and to see if both the populations followed similar patterns. Once the chicks were about to fledge, I took feather samples from them to see how much of the stress hormone corticosterone (like cortisol in humans) they had been exposed to during their development. High measures of corticosterone would indicate that these chicks had been suffering from nutritional stress – not being fed enough – as they are sheltered from other environmental stressors in their burrows.

Grey-faced petrels are long-lived birds that can breed until they’re around 30. The other component of my work was determining if there were any differences with age in these physiological measures – if there were, it would confound results in populations where we don’t know the age of the birds (most of them!). Luckily, one of the colonies on the west coast has been monitored for 30+ years, so most of the breeding birds there are of known age. I didn’t find any differences in stress hormone expression or the blood parameters between birds of different age, ranging between 5-29 years old, which is good news!

Adult birds on the east coast have higher concentrations of stress hormones during their breeding stages, and they’re much more responsive to acute stressors (like handling) during incubation than west coast birds. By the time they reach chick-rearing, their blood parameters suggest that they’ve been expending a lot more energy than west coast birds, which makes it harder for them to provision both themselves and their chick.

This high cost of breeding for east coast birds is passed on to their chicks – east coast chicks have higher measures of developmental stress and are much lighter, on average, than west coast chicks near fledging. What does this mean? It means east coast chicks are less likely to survive after fledging, due to their poor body condition. This is problematic, as many of the new establishing colonies are on the east coast, in what we think may be a sub-optimal environment for the species.

We need to see if this pattern holds over years with different environmental conditions to see if it will be a problem for these establishing colonies. Using stress hormones extracted from chick feathers is an easy and less invasive measure to determine population stress than blood sampling, so it seems like a good method to use for monitoring in the future.

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Any questions? Email me at ewhi650@aucklanduni.ac.nz.