World largest gadfly petrel is endangered by cats and rats | Polarjournal
White-headed petrels(Pterodroma lessonii) nest on islands in the Southern Ocean close to Antarctica, where they form colonies near areas rich in squid and lanternfish. (Image : Michaël Parisot )

On Mayes Island, in the Morbihan Gulf of the Kerguelen archipelago, white-headed petrels fall into two categories: those that breed every year and those that only return every other year. This recent discovery raises questions about their resistance to introduced predators.

Mayes Island, a mecca for polar ornithologists, is home to a soon-to-be 40-year-old observatory, where several species of petrels nest in the peaty slopes below the rocky walls that dominate the shores of the small island. Entrances to the tunnels are lost between clumps of acaenas, Kerguelen cabbage and introduced plants such as various types of grass.

During the day, the birds lie in wait, safe from their natural predators such as giant petrels, jaegers (skuas) and kelp gulls. “At night, thousands of birds fly overhead, leaving or returning from the sea,” explains Christophe Barbraud, researcher at the Centre d’Étude Biologique de Chizé, part of the French Polar Institute, and lead author of a recent study on white-headed petrels. Scientists have discovered that the latter doesn’t reproduce every year like its fellow members of the genus Pterodroma, literally winged runners.

It is the world’s largest pterodroma with an average wingspan of 1.05 meters and a body weight of 700 grams. According to the latest results published in the Journal of Ornithology last June, two-thirds of the individuals that successfully raise their chicks to fledgling, skip a breeding season before returning to Mayes Island.

The other third return to nest the following year. ” We observe that the reproductive success of these birds is lower,” explains the researcher. These petrels take less time to regain their strength and undergo moulting between the two seasons. This interlude only lasts a total of 4 months in the middle of winter.

These petrels arrive earlier to nest and leave later than other seabirds on the island. “They arrive in September and leave in March, whereas the peak of food production in the Southern Ocean lies between January-February”, reminds the researcher. This strategy enables them to avoid competition with other species by extending their reproduction time.

The white-headed petrel reproduces slightly faster than the great albatross, which nests every other year, but slower than annual species such as the black or soft-plumaged petrels. However, this also exposes them to a longer period of dangers such as terrestrial predators introduced to the archipelago like feral cats and brown rat.

Feral cat attacks on wandering albatross chicks were documented in 2017 on the west coast of the Courbet Peninsula. Image: Camille Lin

An estimated ten thousand breeding pairs of white-headed petrels live on Kerguelen. A population that is difficult to estimate in a territory as vast as Corsica. According to researchers, their survival rate is lower where cats are present. But those on Mayes Island still lead a more protected life while in colonies such as the Sourcil Noir canyon on the Jeanne d’Arc peninsula, remains of wings litter the ground.

Camille Lin, PolarJournal

Link to study : Barbraud, C., Joubert, D., Delord, K., 2023. The demography of the White-headed Petrel at Mayes Island, Kerguelen. J Ornithol. https://doi.org/10.1007/s10336-023-02079-3.

Learn more about this topic:

Cherel, Y., Delord, K., Barbraud, C., Weimerskirch, H., 2022. Diet, isotopic niche, and spatial distribution of the white-headed petrel (Pterodroma lessonii) at Kerguelen Islands. Polar Biol 45, 1607-1621. https://doi.org/10.1007/s00300-022-03092-7.

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