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Thursday, January 3, 2019

In findings published yesterday in Ecological Applications, scientists from the University of Washington and Center for Ecosystem Sentinels report the reason for the plummeting numbers of female Magellanic penguins (Spheniscus magellanicus) that have been reported at the birds’ breeding sites in South America for over twenty years.

“Two decades ago, there were about 1.5 adult male Magellanic penguins for every adult female at Punta Tombo,” postdoctoral researcher and study co-author Natasha Gownaris said in a press release. “Today, it’s approaching three males for every female.” The findings showed that a disparity in the death rate of juvenile and adult penguins, not differences in chick survival, account for this difference.

The work involved building population models out of over thirty years of data collected by tagging individual penguins. Findings also suggested that the pronounced sex disparity might make population models used to predict survival among other birds with a more even gender balance inappropriate for use on Megallanic penguins.

The overall population of Magellanic penguins at one of their annual breeding sites in Argentina has declined 40% since 1987, and the male-to-female ratio has gone up a great deal.

Since 1983, the research team has been putting stainless steel bands on tens of thousands of chicks hatched at the Punta Tombo breeding site in Argentina and noting which juvenile and adult birds make it back to the site the next year and extrapolating how many lived and died. Among juveniles, there was a 17% survival rate for males and 12% for females. Among adults, it was 89% and 85%. These effects became compounded every year, reaching as high as six males to one female among older penguins.

These findings have implications for penguin conservation: “Over the years, this team has helped preserve the land and waters around breeding colonies like Punta Tombo,” said Gownaris. “But now we’re starting to understand that, to help Magellanic penguins, you have to protect waters where they feed in winter, which are thousands of miles north from Punta Tombo.”

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