Drone Survey Finds Erect-Crested Penguins Stable on One Island, Falling on Another

One of New Zealand's least understood penguin species is doing well in one place and badly in another, according to a University of Otago study published in PLOS ONE. Erect-crested penguins breed on only two remote island groups, and a drone survey found that one population has held steady for at least 25 years while the other has dropped by more than 40 percent over three decades.

The findings, reported by ScienceDaily, overturn a long-held assumption about which island group matters most to the species.

What the drone survey counted

The penguins breed only on the Bounty and Antipodes islands, which lie roughly 800 kilometers southeast of New Zealand's South Island. Between 2022 and 2024, researchers used drones to photograph and count every breeding colony on both island groups, producing the first comprehensive population survey of the entire species.

The results surprised the team. The Bounty Islands, only 50 hectares in size, hold about 27,800 breeding pairs. The Antipodes Islands, which are 40 times larger and were historically seen as the species' stronghold, hold about 29,800. Dr. Thomas Mattern, who led the study for the university's Tawaki Project, said the long-standing assumption did not hold up.

Why one population is shrinking

When the new counts were compared with historical records going back to the mid-1990s, the Bounty Islands population turned out to be essentially unchanged. The Antipodes population has fallen by more than 40 percent since 1995.

The researchers believe several pressures overlap. One is predation by skuas, native subantarctic birds that eat penguin eggs and chicks. Mattern said that as Antipodes colonies shrank, the protection they once gained from nesting in large groups weakened, so losses to predators rose and colonies broke up further.

Co-author Dr. Klemens Pütz of the Antarctic Research Trust suggested that another species may have made this worse. Eastern Rockhopper penguins suffered a severe collapse in the second half of the 20th century, likely driven by warming ocean waters, and fewer than 1,000 breeding pairs now remain on the Antipodes Islands. Pütz said skuas may have turned to Erect-crested eggs and chicks as Rockhoppers disappeared.

Storms are another factor. Increasingly powerful storms, consistent with wider climate trends across the Southern Ocean, have caused landslides that split up breeding colonies and leave birds more exposed.

Movement at sea may also play a part. According to Mattern, Antipodes birds travel long distances into the Antarctic Polar Frontal Zone once breeding ends, while Bounty Islands birds stay nearer their nesting grounds, where the water is more sheltered and may hold more food.

Why it matters: one species, two different outlooks

The researchers named the situation Schrödinger's Penguin, a twist on the physics thought experiment of a cat that is both alive and dead until a box is opened. Mattern said the penguins work the other way around: from a distance, everyone assumed a single answer for the whole species, but once scientists looked, they found two states, stable on the Bounty Islands and declining on the Antipodes Islands.

The practical lesson, the report says, is that looking at a species as a whole can hide what is happening within individual populations. For an endangered penguin that breeds in only two places, the survey shows that the overall picture can look reassuring while one of its two strongholds is steadily losing birds.

The study was carried out with the Antarctic Research Trust and the Global Penguin Society.

Around Prague, based on reporting by ScienceDaily

Cover photo: C00ch / Wikimedia Commons, CC BY-SA 4.0, cropped

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