Sunday, January 27, 2019
In findings published earlier this month in Ecological Applications, scientists from the University of Washington and Center for Ecosystem Sentinels examine the reason for the plummeting numbers of female Magellanic penguins, Spheniscus magellanicus, that have been reported at the birds’ breeding sites in South America over the past twenty years and more. Wikinews caught up with postdoctoral researcher and study co-author Natasha Gownaris to learn more.
In a press release, Gownaris said, “Two decades ago, there were about 1.5 adult male Magellanic penguins for every adult female at Punta Tombo[…] Today, it’s approaching three males for every female.” The findings suggested a disparity in the death rate of juvenile and adult penguins, rather than differences in chick survival, account for this difference.
Punta Tombo is one of the annual breeding sites for the species; it is in Argentina. The penguins travel thousands of miles each year to reach these sites.
The work involved building population models out of over thirty years of data collected by tagging individual penguins. Findings also suggested 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.
According to the data, since 1987, overall population of Magellanic penguins in Punta Tombo at one of their annual breeding sites in Argentina has declined 40%, while the male-to-female ratio has greatly increased.
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, 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.
The researchers noted implications for penguin conservation: Gownaris remarked, “Over the years, this team has helped preserve the land and waters around breeding colonies like Punta Tombo[…] 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.”
Gownaris answered a series of questions for our correspondent.
((Wikinews)) What prompted your curiosity about Magellanic penguins?
Natasha Gownaris: I’ve wanted to be a marine scientist since I was a child, when I would collect sand crabs (Emerita talpoida) from local beaches in New York. I studied fish as a graduate student, but I have a pair of adopted parrots and I am generally fascinated by birds. Plus, penguins eat fish! Studying penguins seemed like a great way to merge my love for the ocean and my love for birds. Penguins and other seabirds are also important to study because they tell us something about the health of the ocean ecosystems they feed in, similar to the use of canaries to test air quality in coal mines. Unfortunately, the decline of many seabird species worldwide is yet another warning sign of the negative and widespread impacts humans are having on the ocean.
((WN)) How did you approach putting together such a large-scale study?
NG: This study started in 1982, long before my joining the lab in March of 2016. Dr. Dee Boersma began this study as a response to a Japanese company’s interest in harvesting penguins for their skin, meat, and oil. Although the project has evolved over time, Dr. Boersma had the foresight to start banding chicks in 1983 and to set up a standard protocol that we follow each year. Since then, over 44,000 chicks have been banded at Punta Tombo. We’ve been able to follow some individuals for 30+ years, collecting detailed information on things like how often they breed and how many mates they’ve had.
((WN)) How much time did you end up spending in Argentina? What was it like at the breeding site?
NG: Members of the Boersma lab and volunteers spend approximately six months each year at Punta Tombo. I was fortunate enough to spend nearly four months at the colony between 2015 and 2017. It’s an incredible, otherworldly place. Magellanic penguins nest in burrows or bushes, and some areas of the colony are so dense with burrows that you feel like you’re on a different planet. The colony has declined by over 40% since the study started…so I can’t even imagine what it was like in the 1980s. My favorite time of the day is around 8PM, when (hopefully fat) penguins are returning to the colony en masse after a foraging trip. They are also most vocal in the morning and evening, making their characteristic braying sound— the related African penguin earned the name “jackass penguin” because they sound a bit like donkeys. The colony is also full of other beautiful and interesting creatures, including a llama-like species called the guanaco and an ostrich-like species called the rhea.
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I was fortunate enough to spend nearly four months at the colony between 2015 and 2017. It’s an incredible, otherworldly place. |
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((WN)) Do you have any theories on why more female juveniles die at sea? You mention starvation; what might be the causes of that, and are there other possible explanations you can think of?
NG: We are not yet certain why females are more likely to die, but we think it must be related to their smaller body size. Because the mortality is most uneven in juveniles, higher mortality doesn’t seem to be related to greater costs of breeding for females than for males. Female Magellanic penguins are about 17% lighter than males and have smaller bills. We think that, because of this size difference, females have a lower storage capacity, can’t dive as deep, and can’t take as wide a range of prey as males — all disadvantages when faced with limited and unpredictable food resources. These disadvantages hit juvenile females even harder, as juveniles are still learning how to forage and often travel further than adults do in the non-breeding season. Counts of carcasses in the species’ migration range support starvation as the main cause of female-biased mortality; while oiled carcasses have a sex ratio of 1:1, females outnumber males in carcasses of starved birds. The only other possibility is that females are moving to other colonies at higher rates than are males, but this species is known to almost always return to its natal colony to breed.
((WN)) You suggest conservation efforts should look at protection of feeding grounds. What sort of measures do you think might be beneficial?
NG: Because penguins migrate such long distances over the non-breeding season, a mixture of tools (including no-take marine protected areas and traditional fisheries management tools, like catch limits) is likely to be needed. Although there is currently some spatial protection surrounding the species’ breeding colony, this protection does not extend to their migratory route. And, of course, everyone can contribute to penguin conservation by reducing their plastic waste, making more sustainable food choices, and reducing their carbon footprint.
((WN)) What do you think might be causing pressure on food sources for the penguins?
NG: The two main threats to the food sources of this colony are climate change, which cause shifts in primary productivity and fish stocks, and fisheries. Fisheries compete with penguins for fish species such as hake and anchovy.
((WN)) Have you noticed differences in behavior among the penguins as the ratios become increasingly skewed?
NG: In a separate study currently under review, we have shown that aggression between males of Magellanic penguins is higher when the sex ratio at the colony is more skewed towards males. We also showed that nearly all females at the colony breed but that, over time, fewer and fewer males find mates. Single male penguins sometimes intrude [on] nests of mated pairs and interrupt the incubation of eggs or feeding of chicks, leading to mortality. In some cases, they will even attack and kill chicks.
((WN)) Your release mentioned sexing the penguins was problematic; how did you achieve it with confidence?
NG: We have some methods of sexing penguins that we feel confident about — using genetics or measures of cloaca size around egg laying, for example. However, these methods are time intensive, so we have also developed visual cues for sex penguins (bill size, behavior, forehead shape). We looked at individuals that had been sexed using both a certain method (e.g. genetics) and visual methods to calculate how often we got it right based on visual cues alone and found that we have very high accuracy. We also used statistical tools to help to deal with uncertainty in the sex of some individuals.
((WN)) How well can you extrapolate population trends at Punta Tombo based on the birds you tagged? More broadly, how well do you think this work represents global populations?
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everyone can contribute to penguin conservation by reducing their plastic waste, making more sustainable food choices, and reducing their carbon footprint |
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NG: It is likely that females have higher mortality than males at other colonies of this species and in other penguin species. We unfortunately do not have enough information from other colonies of this species (e.g. sex ratio and population trends) for an accurate global assessment of population trends. We do know that some colonies of the species are growing but that, at the global level, the species is still in decline.
((WN)) In your opinion, for how much longer are penguin populations sustainable without intervention?
NG: This is nearly impossible to answer without more information on other colonies of the species, but the Punta Tombo colony is declining rapidly. We estimate declines of at least 43% since 1987 from our annual surveys at the colony, but it is likely that actual declines are higher because of the increasingly skewed sex ratio.
((WN)) What are your next plans moving forward with your work?
NG: We are currently studying the sex ratio in Magellanic penguin chicks (at hatching and at fledging) to determine how this influences the sex ratio in adults. There are two priorities moving forward — 1) estimating sex ratio at other colonies of this species and determining whether females are more likely to leave Punta Tombo for other colonies than are males and 2) determining the mechanisms underlying lower female survival, e.g. by studying the foraging behavior and diet of males and females and the individual characteristics (like body size) that correlate with survival.