Recently, a story about species introduction and bad outcomes made the news. I had to write about this, but for a different reason than you might expect.
This story seems to have appeared in hundreds of news outlets over the past few days:
- “Tasmanian devils devastate penguin population on Australian island“: “A project to preserve endangered Tasmanian devils on a small island has backfired after the predators killed seabirds in large numbers, a conservation group says.”
- “Tasmanian Devils Devastate Penguin Population on Australian Island“: “Every time humans have deliberately or accidentally introduced mammals to oceanic islands, there’s always been the same outcome … a catastrophic impact on one or more bird species.”
- “Tasmanian devils were given a safe, island home. Then the devils slaughtered 3K penguins.” “Although the loss of penguins is sad, it doesn’t come as a surprise to some.”
In 2012 a government initiative relocated 26 Tasmanian devils to Maria Island, a small island off the Tasmanian coast. The Tasmanian devil population has been in decline for years, due to a facial tumor cancer that spreads when they bite each other.
Unfortunately, Maria Island was also home to 3,000 little penguins — small, slow-walking birds that nest on land. (This species is actually called the “little penguin” as well as the “little blue penguin” and the “fairy penguin.”) With a new predator introduced, the penguins were all eaten.
However, this is just a slice of the story. A research study about the Tasmanian devil introduction (“Conservation trade-offs: Island introduction of a threatened predator suppresses invasive mesopredators but eliminates a seabird colony“) shows a fuller picture.
First, Tasmanian devils also wiped out another local seabird species on Maria Island, after just four years. That bird was the short-tailed shearwater. Why didn’t we hear about the shearwater as well? One explanation is that penguins (especially little penguins) are cute. Shearwaters are not. Penguins fit the Bambi effect model (people feel a greater objection toward killing cute animals).
On a cuteness continuum, we have little penguins near the top, shearwaters somewhere in the middle of the list, and Tasmanian devils with negative cuteness.
But there are an estimated 500,000 breeding pairs of little penguins. They are not endangered. For the short-tailed shearwater, the population is estimated at 23 million.
Meanwhile, Tasmanian devils are endangered. Their population has declined to an estimated 20,000, with an 80% decline in the past two decades, following the growth of facial tumor cancer among their population.
To really think about long-term effects we also need to consider the potential speed of reproduction. Neglecting how fast something can spread was an error many made early in COVID pandemic, for example. Tasmanian devils can reproduce by the time they are two years of age. Their gestation period is just 21 days, but they only have one litter a year. Females give birth to 20 to 30 young, of which most do not survive. Female offspring also outnumber males about two to one, so the potential for rapid growth is there in good conditions. (After all, in four years the introduced population grew to 4x its original size.) But there again, a small island like Maria Island will soon limit the number of Tasmanian devils capable of living there. The little penguins and shearwaters find much of their food off island and so are not as limited by the island’s small land area.
Was the risk of the Tasmanian devil introduction worth it? At just 26 animals introduced and with a local island carrying capacity of 100, Maria Island would at most be a small win, but possibly one worth trying if we value the more endangered animals.
I was also worried that the news articles misread the impact of the introduction, possibly making future introductions more difficult.
Until then, watch out for the Bambi effect.