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Magellanic Penguin - Spheniscus magellanicus
Magellanic Penguin - Spheniscus magellanicus

[Image: Magellanic-penguins-on-beach-front-view_zpsa40b3104.jpg]

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Sphenisciformes
Family: Spheniscidae
Genus: Spheniscus
Species: Spheniscus magellanicus

[Image: 220px-Biomap_Sphenisus_Magellanicus_zps707622eb.png]
Distribution (in red)

The Magellanic Penguin (Spheniscus magellanicus) is a South American penguin, breeding in coastal Argentina, Chile and the Falkland Islands, with some migrating to Brazil where they are occasionally seen as far north as Rio de Janeiro. It is the most numerous of the Spheniscus penguins. Its nearest relatives are the African, the Humboldt and the Galápagos Penguins. The Magellanic penguin was named after Portuguese explorer Ferdinand Magellan, who spotted the birds in 1520.

[Image: Magellanic-penguin-portrait_zps0586d08b.jpg]

Magellanic Penguins are medium-sized penguins which grow to be 61–76 cm (24–30 in) tall and weigh between 2.7 kg and 6.5 kg (5.9-14.3 lbs). The males are larger than the females, and the weight of both drops while the parents nurture their young.
Adults have black backs and white abdomens. There are two black bands between the head and the breast, with the lower band shaped in an inverted horseshoe. The head is black with a broad white border that runs from behind the eye, around the black ear-coverts and chin, and joins at the throat. Chicks and younger penguins have grey-blue backs, with a more faded grey-blue colour on their chest. Magellanic Penguins can live up to 25 years in the wild, but as much as 30 years in captivity.
Young birds usually have a blotched pattern on their feet, which fades as they age. By the time these birds reach about ten years of age, their feet usually become all black.
Like other species of penguins, the Magellanic Penguin has very rigid wings used to "fly" or cruise under water.

Magellanic Penguins feed in the water, preying on cuttlefish, squid, krill, and other crustaceans, and ingest sea water with their prey. Their salt-excreting gland rids the salt from their bodies.

[Image: Magellanic-penguin-at-nest-with-egg_zpsa360a58a.jpg]

Magellanic Penguins travel in large flocks when hunting for food. In the breeding season, these birds gather in large nesting colonies at the coasts of Argentina, southern Chile, and the Falkland Islands, which have a density of 20 nests per 100 square meters. One of the largest of these colonies is located at Punta Tombo. Nests are built under bushes or in burrows. Two eggs are laid. Incubation lasts 39–42 days, a task which the parents share in 10-15 day shifts. The chicks are cared for by both parents for 29 days and are fed every two to three days. Normally, both are raised through adulthood, though occasionally only one chick is raised.
Magellanic Penguins mate with the same partner year after year. The male reclaims his burrow from the previous year and waits to reconnect with his female partner. The females are able to recognize their mates through their call alone.

[Image: Magellanic-penguin-with-chicks-at-burrow...837083.jpg]

Status in the wild 
Millions of these penguins still live on the coasts of Argentina and Chile, but the species is classified as a "threatened species", primarily due to the vulnerability of large breeding colonies to oil spills, which kill 20,000 adults and 22,000 juveniles every year off the coast of Argentina. To help the fight against the oil spills, zoo representatives from all over the world come and adopt the hatchlings, and breed them there. The decline of fish populations is also responsible, as well as predators such as sea lions and Giant Petrels, which prey on the chicks
Climate change has displaced fish populations, so Magellanic penguins must swim an extra 25 miles (40 km) further from the nest for fish. While the penguins are swimming an extra 50 miles (80.4 km), their mates are sitting on a nest and starving. A colony being tracked by University of Washington professor P. Dee Boersma, about 1,000 miles (1,609 km) south of Buenos Aires, has fallen by more than 20 percent in the past 22 years, leaving 200,000 breeding pairs. Some younger penguins are now moving their breeding colonies north to be closer to fish, but, in some cases, this is putting them on private, unprotected lands. As a result of these changes, some penguins are known to have been lost or confused. At present, 12 of 17 penguin species are experiencing rapid population declines.

[Image: Magellanic-penguin-swimming_zps3ad03a09.jpg]
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  • Claudiu Constantin Nicolaescu
Magellanic Penguins Devour 2 Million Tons of Seafood Yearly

Becky Oskin, Staff Writer
Date: 13 June 2013 Time: 08:45 AM ET 

[Image: magellanic-penguin-100910-02_zpsf524b49f.jpg] 
A braying Magellanic penguin from the colony at Punta Tombo, Argentina.

South American Magellanic penguins gobble down 1.5 million tons of silverside fish, squid and small, oily fish such as sprat every year. If all of the world's 1.3 million Magellanic penguins are as voracious as their Patagonian counterparts, then the black-and-white birds may be bolting down 2 million tons of seafood every year, according to a study published Dec. 12, 2012, in the journal PLOS ONE. The study adds to increasing evidence that seabirds consume larger quantities of food than previously estimated, the authors report.

Wiggle loggers tracked diving penguins from four colonies in Argentina to determine how much prey they captured. Wiggles during dives indicate the number of prey nabbed by each penguin. The total haul was 87 percent more than the 820,000 tons of commercial catches for the same seafood species (sprat, squid, anchovy, etc.), reported.

How Much Is Too Much? Assessment of Prey Consumption by Magellanic Penguins in Patagonian Colonies
Juan E. Sala, Rory P. Wilson, Flavio Quintana

Penguins are major consumers in the southern oceans although quantification of this has been problematic. One suggestion proposes the use of points of inflection in diving profiles (‘wiggles’) for this, a method that has been validated for the estimation of prey consumption by Magellanic penguins (Spheniscus magellanicus) by Simeone and Wilson (2003). Following them, we used wiggles from 31 depth logger-equipped Magellanic penguins foraging from four Patagonian colonies; Punta Norte (PN), Bahía Bustamente (BB), Puerto Deseado (PD) and Puerto San Julián (PSJ), all located in Argentina between 42–49° S, to estimate the prey captured and calculate the catch per unit time (CPUT) for birds foraging during the early chick-rearing period. Numbers of prey caught and CPUT were significantly different between colonies. Birds from PD caught the highest number of prey per foraging trip, with CPUT values of 68±19 prey per hour underwater (almost two times greater than for the three remaining colonies). We modeled consumption from these data and calculate that the world Magellanic penguin population consumes about 2 million tons of prey per year. Possible errors in this calculation are discussed. Despite this, the analysis of wiggles seems a powerful and simple tool to begin to quantify prey consumption by Magellanic penguins, allowing comparison between different breeding sites. The total number of wiggles and/or CPUT do not reflect, by themselves, the availability of food for each colony, as the number of prey consumed by foraging trip is strongly associated with the energy content and wet mass of each colony-specific ‘prey type’. Individuals consuming more profitable prey could be optimizing the time spent underwater, thereby optimizing the energy expenditure associated with the dives.
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  • Claudiu Constantin Nicolaescu
Climate change is 'killing Argentina's Magellanic penguin chicks'

Matt McGrath
By Matt McGrath
Environment correspondent, BBC News
30 January 2014 Last updated at 01:49 

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Magellanic penguin chicks huddle together for warmth in Punta Tombo, Argentina

Penguin chicks in Argentina are dying as a direct consequence of climate change, according to new research.

Drenching rainstorms and extreme heat are killing the young birds in significant numbers.

The study, conducted over 27 years, looked at climate impacts on the world's biggest colony of Magellanic penguins, which live on the arid Punta Tombo peninsula.

The research has been published in the journal Plos One.

About 200,000 pairs of these penguins make their nests on the peninsula every year.

They reside there, in desert-like conditions, from September until February to hatch their young.

However, the life of a newborn chick is perilous, to say the least.

Downy death

They are too big for their parents to sit on top of and keep warm, but too young to have waterproof feathers.

As a result, they are particularly vulnerable to rainstorms. If they get drenched they usually die, despite the attentions of their despairing parents.

They can also succumb to extreme heat, as they cannot cool off in the water like the others.

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The chicks are often too big for their parents to be able to keep them warm

The new analysis of data from Punta Tombo indicates that climate change is having an increasing impact on the chicks.

While on average, around 40% of the youngsters that die every year succumb to starvation, changes in the climate killed an average of 7%. Warming 'killing penguin chicks'

"Climate variability in the form of increased rainfall and temperature extremes, however, has increased in the last 50 years and kills many chicks in some years," the authors write in the report.

In two years it was the most common cause, accounting for half the dead chicks in one year, and 43% in another.

"It's the first long-term study to show climate change having a major impact on chick survival and reproductive success," said lead author Prof Dee Boersma, from the University of Washington.

The number of storms at the breeding site in the first two weeks of December, when the chicks are less than 25 days old, has increased between 1983 and 2010.

"Penguins live in the desert and what's really happening with these rain storms - they are turning their nests into swimming pools and they really don't like to be wet," said Prof Boersma.

Problems with ice

As well as more downpours, the researchers believe that altered fish behaviour is contributing to the rising numbers of deaths.

Over the 27-year period, the penguin parents have arrived at the breeding site later and later in the year, probably because the fish they eat are arriving later too.

The scientists say that the later in the year that the eggs are hatched, the more likely it is the chicks will still be at the vulnerable, downy stage Warming 'killing penguin chicks'when the storms arrive in November and December.

"The birds are coming back later and on average laying their eggs three days later than they did a decade ago, so they have a shorter breeding season and that cuts down the amount of time they have to raise their chicks," said Prof Boersma.

This year, though, the problem was heat, with several days over 30C.

In the longer term, the outlook for this species in the face of a changing climate is not good, say the researchers.

"We're going to see years where almost no chicks survive if climate change makes storms bigger and more frequent during vulnerable times of the breeding season as climatologists predict," said co-author, Dr Ginger Rebstock, also from the University of Washington.

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The chicks' down isn't waterproof and they can succumb to extremes

In a separate study, also published in Plos One, researchers found that changes in sea-ice were having an impact on Adelie penguins in the Ross Sea area of Antarctica.

The authors found that under normal conditions, the penguins were successful at finding food at relatively low sea-ice concentrations and should be able to cope with predicted future changes.

However, the researchers say that these penguins will have significant problems coping with infrequent, extreme environmental events such as the presence of giant icebergs.

"Our work shows that Adelie penguins could cope with less sea-ice around their summer breeding grounds," said lead author Dr Amelie Lescroel from the French National Centre for Scientific Research (CNRS).

"However, we also showed that extreme environmental events, such as the calving of giant icebergs, can dramatically modify the relationship between Adelie penguins and sea ice."

"If the frequency of such extreme events increases, then it will become very hard to predict how penguin populations will buffer future sea ice changes."

Magellanic penguins

[Image: _72608777_12108714863_2d20584216_b_zps7da57ed1.jpg]
  • Found predominantly in Argentina, Chile and the Falkland Islands

  • Medium-sized birds that stand about 35cm tall and weigh around 5kg

  • Males of species have a distinct vocalisation - they bray like donkeys

  • More than 17 penguin species are recognised, all south of the equator

Climate Change Increases Reproductive Failure in Magellanic Penguins

P. Dee Boersma, Ginger A. Rebstock
Published: January 29, 2014DOI: 10.1371/journal.pone.0085602

Climate change is causing more frequent and intense storms, and climate models predict this trend will continue, potentially affecting wildlife populations. Since 1960 the number of days with >20 mm of rain increased near Punta Tombo, Argentina. Between 1983 and 2010 we followed 3496 known-age Magellanic penguin (Spheniscus magellanicus) chicks at Punta Tombo to determine how weather impacted their survival. In two years, rain was the most common cause of death killing 50% and 43% of chicks. In 26 years starvation killed the most chicks. Starvation and predation were present in all years. Chicks died in storms in 13 of 28 years and in 16 of 233 storms. Storm mortality was additive; there was no relationship between the number of chicks killed in storms and the numbers that starved (P = 0.75) or that were eaten (P = 0.39). However, when more chicks died in storms, fewer chicks fledged (P = 0.05, R2 = 0.14). More chicks died when rainfall was higher and air temperature lower. Most chicks died from storms when they were 9–23 days old; the oldest chick killed in a storm was 41 days old. Storms with heavier rainfall killed older chicks as well as more chicks. Chicks up to 70 days old were killed by heat. Burrow nests mitigated storm mortality (N = 1063). The age span of chicks in the colony at any given time increased because the synchrony of egg laying decreased since 1983, lengthening the time when chicks are vulnerable to storms. Climate change that increases the frequency and intensity of storms results in more reproductive failure of Magellanic penguins, a pattern likely to apply to many species breeding in the region. Climate variability has already lowered reproductive success of Magellanic penguins and is likely undermining the resilience of many other species. 
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  • Claudiu Constantin Nicolaescu
After a bad winter in the ocean, female Magellanic penguins suffer most, study shows

November 7, 2018 by James Urton, University of Washington

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A 2002 satellite view of the Río de la Plata, which forms at the confluence of the the Paraná River and the Paraguay River. The Río de la Plata drains a basin of more than 1.2 million square miles, the second-largest in South America after the Amazon basin. Credit: Jacques Descloitres/MODISRapid Response Team/NASA/GSFC

Every autumn in the Southern Hemisphere, Magellanic penguins leave their coastal nesting sites in South America. For adults, their summer task—breeding, or at least trying to—is complete. Newly fledged chicks and adults gradually head out to sea to spend the winter feeding. They won't return to land until spring.

Yet life for these birds when they winter offshore is largely a mystery to the scientists who study Magellanic penguins—and who advocate for their conservation amid declining population numbers.

"The winter period is something of a black box for us in terms of understanding Magellanic penguins," said Ginger Rebstock, a University of Washington research scientist. "We know the least amount about this part of their year."

But research by Rebstock and P. Dee Boersma, a UW professor of biology and founder of the Center for Ecosystem Sentinels, is starting to pry open that black box and discover how Magellanic penguins from one nesting site, Punta Tombo in Argentina, fare during the winter months. In a paper published Aug. 9 in the journal Marine Ecology Progress Series, they report that the Río de la Plata—which drains South America's second-largest river system after the Amazon—strongly influences oceanographic conditions in the Magellanic penguins' winter feeding waters. Those oceanographic features, they report, show up in the body conditions of Magellanic penguin females, but not males, when the penguins return to their nesting grounds in spring.

[Image: 1-afterabadwin.jpg]
An adult Magellanic penguin and two chicks. Credit: Dee Boersma/Center for Ecosystem Sentinels

"Researchers only get to study the penguins up close—monitor their biology, their health, their population numbers—for the one time in the year that they come to nesting sites like Punta Tombo to breed," said Rebstock. "Until now, we have not really known how conditions out in the ocean, where they spend the entire winter, affect them."

Magellanic penguins are believed to swim hundreds of miles in winter to feed on fish such as anchovy and sardines. For penguins originating at Punta Tombo, this could mean swimming more than 1,000 miles north along the coast up to southern Brazil. They generally stay along the continental shelf in waters usually no more than about 650 feet deep. To understand the oceanographic dynamics in this region, Rebstock turned her attention to space. She analyzed 30 years of weekly sea-surface temperature data, which National Oceanic and Atmospheric Administration satellites collected for those South American coastal waters from 1982 to 2012. Data show that geographic features of coastal South America are responsible for key variations in ocean conditions.

For example, her analysis revealed that the Río de la Plata, which enters the ocean between Argentina and Uruguay, is the primary driver of oceanographic conditions in the penguins' winter feeding waters. The river discharges silt, microbes and nutrients into the ocean as a plume, which disperses in different directions based on prevailing winds. Strong winds from the southwest, for example, can spread the plume north along hundreds of miles of Brazilian coastline. If winds are weaker, the plume stays near the mouth of the Río de la Plata.

Rebstock then analyzed whether variations in these oceanographic features—such as a strong, dispersed plume or a weak, localized plume—were associated with the body condition of penguins at the time of their arrival at Punta Tombo. Boersma and her team have collected information on the health and state of individual penguins when they arrive Punta Tombo for more than three decades. According to their data, the body conditions of male Magellanic penguins weren't correlated with the extent of the plume. But Rebstock found that female penguins arrived back at Punta Tombo earlier, and in healthier body condition, if the Río de la Plata plume was weaker in winter. This may indicate that the plume affects how hard Magellanic penguins must work to find food.

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A summer scene at the Magellanic penguin colony at Punta Tombo in Argentina. Credit: Dee Boersma/Center for Ecosystem Sentinels

"We believe that the Río de la Plata plume carries a great deal of nutrients into the coastal waters, making them very productive feeding grounds for the penguins," said Rebstock. "But winds will affect where the plume is distributed and how far penguins will have to go to reach it."

A weaker plume may keep the penguins' prey closer together and closer to breeding colonies, increasing an individual penguin's odds of catching fish. Magellanic penguins also are mainly visual hunters. A stronger plume that clings to the coast may obstruct visibility for the birds by making waters more turbid, said Rebstock.

The size and disposition of the plume may affect females more than males because male Magellanic penguins tend to be larger, which allows them to dive deeper. This may give males a slight edge in catching food, especially in difficult conditions, said Rebstock.

"What we would like to do next is test some of these hypotheses by tracking male and female Magellanic penguins during the winter months, to see if they are feeding in the same locations and see how successful they are at obtaining food in different conditions," said Rebstock.

For researchers like Rebstock, that may be the next black box to open. But it will also pose a logistical challenge. Researchers have tried to track Magellanic penguins during winter using satellite tags, but the penguins are very effective at taking them off.

Journal Reference:
GA Rebstock et al, Oceanographic conditions in wintering grounds affect arrival date and body condition in breeding female Magellanic penguins, Marine Ecology Progress Series (2018). DOI: 10.3354/meps12668

ABSTRACT: Overwintering conditions often impact an individual animal’s breeding performance in the following season. These so-called carry-over effects have been demonstrated in birds, including penguins. We studied carry-over effects in Magellanic penguins Spheniscus magellanicus, a species of conservation concern, breeding at Punta Tombo, Argentina, and wintering from northern Argentina to southern Brazil. We characterized oceanographic conditions in the penguins’ wintering grounds from 1982 to 2012 using principal component analysis on weekly sea surface temperature (SST) anomalies. The first principal component represented a weak Rio de la Plata plume and warm SST. The Rio de la Plata plume carries cool, productive, low-salinity water north from the river mouth through the penguins’ wintering area. The plume is stronger (extends farther north) when winds blow from the southwest than when winds blow from the northeast. When the Rio de la Plata plume was weak in late winter, females arrived earlier to breed and were in better condition, likely because prey was concentrated in a smaller plume area closer to Punta Tombo. Females that arrived earlier laid eggs earlier, and females laid larger eggs when they arrived earlier and were in better condition. In contrast, body condition of breeding males did not vary with winter conditions. The effects on individual females varied, likely reflecting in part individual foraging ability. A weaker Rio de la Plata plume probably increased prey encounter rates closer to breeding colonies in winter, directly and indirectly improving female body condition, increasing egg size, and resulting in earlier arrival and egg laying.
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  • Claudiu Constantin Nicolaescu
The number of single male Magellanic penguins is rising at this breeding colony—here's why

January 3, 2019 by James Urton, University of Washington

[Image: thenumberofs.jpg]
A young Magellanic penguin male. On average, males at Punta Tombo don’t breed until age 7 and, with the increasingly skewed sex ratio, fewer and fewer males are finding mates each breeding season. Credit: Natasha Gownaris

Like most of their stout-bodied, flippered kin, Magellanic penguins spend much of their lives in the ocean. From late autumn through winter and into spring in the Southern Hemisphere, these South American penguins swim off the coast of southern Brazil, Uruguay and northern Argentina in search of anchovies, sardines and squid.

But as spring turns to summer, they swim thousands of miles south and congregate in big coastal colonies. There, males and females pair off, breed and attempt to rear one or two newly hatched chicks. One of the largest breeding colonies for Magellanic penguins is at Punta Tombo in Argentina, where University of Washington biology professor P. Dee Boersma and her team at the Center for Ecosystem Sentinels have studied the penguins since 1982. They have documented a population decline at Punta Tombo of more than 40 percent since 1987, along with a rising male-to-female ratio, and have spent years trying to pinpoint its cause.

In a paper published Jan. 2 in the journal Ecological Applications, Boersma and UW postdoctoral researcher Natasha Gownaris report that juvenile females are more likely to die at sea, which has caused a skewed sex ratio of nearly three males to every female, as well as population decline. Their study incorporated more than 30 years of population data collected by UW researchers—including banding and studying individual penguins—into models of population dynamics. Boersma and Gownaris' models show that juveniles have much lower survival rates than adults in all years, a common phenomenon in seabirds. In addition, among both juveniles and adults, females are less likely to survive than males, but this sex bias is much larger among juveniles. Adult females seem to fare worst in years when overall survival is low, suggesting they are more vulnerable than males to disruptions in the food supply during the nonbreeding season.

"From a conservation standpoint, this study shows us how important it is to try to protect the places where these penguins feed throughout the year, both in the breeding season and the nonbreeding season," said Gownaris. "It all comes down to food for this species."

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A Magellanic penguin mated pair mutually preening. Credit: Natasha Gownaris

This study relied on year-to-year surveys of penguins that had been fitted with stainless-steel bands marked with a unique five-digit number. Between 1983 and 2010, Boersma and her team banded 44,374 chicks at Punta Tombo, tracking generations of Magellanic penguin families. Only 3,296 of these individuals survived and were seen again at the colony. In 57 percent of cases, researchers also noted the sex of the individual—no easy task in a species where males and females look so much alike. Each Southern Hemisphere summer, which corresponds to winter in the Northern Hemisphere, researchers noted which individuals returned to Punta Tombo, and gathered information such as body condition and breeding success.

The 3,296 penguins that returned are a small fraction of the hundreds of thousands who came to Punta Tombo over the three-decade survey period. But information about the banded birds helped Gownaris and Boersma learn about the entire population. Gownaris compared the results from her models of banded birds to annual survey data collected throughout the colony. These comparisons allowed her to see whether trends in the banded birds were also seen in the larger population.

One of these trends is an increasingly skewed sex ratio and more single male penguins.

"Two decades ago, there were about 1.5 adult male Magellanic penguins for every adult female at Punta Tombo," said Gownaris. "Today, it's approaching three males for every female."

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A Magellanic penguin parent feeding its chicks as its mate looks on. Credit: Natasha Gownaris

Both the survey data and population models indicated that adult sex ratios were skewed because fewer females than males returned to the colony each spring for the breeding season. The surveys of banded penguins showed an average return rate for juvenile males of just 17 percent, and 12 percent for juvenile females. Gownaris' models of the whole population indicated that male juveniles had an average return rate about 33.3 percentage points higher than females. Adult Magellanic penguins had much higher return rates than juveniles, and though females still lagged behind males, the gap was not as large as in juveniles. About 89 percent of adult males returned each year, as did 85 percent of females.

Though this may seem like a small difference, the bias in survival accumulates over time. By the time a cohort of penguins reaches age 25, there are about six males for every female.

Other groups have analyzed Magellanic penguin corpses that washed up off the coast of southern Brazil in winter. Their studies also indicate that females are more likely to die of starvation than males—especially juvenile females.

Though male and female Magellanic penguins look similar, males are about 17 percent larger, and have longer and thicker bills. This may give males a significant advantage when foraging for food in the ocean—especially when oceanographic conditions make finding food in the winter more difficult, as the team showed in a paper published in August.

[Image: 3-thenumberofs.jpg]
A Magellanic penguin chick nearly ready to fledge, as shown by the small amount of down on its head, and leave for its first year at sea. Credit: Natasha Gownaris

Using population models, Gownaris showed that the higher mortality of females at Punta Tombo contributed to skewed sex ratios and consequent population declines at the site from 1990 to 2010. This contribution was much greater than that of variation in chick survival. The data also suggest that, due to the skewed sex ratio, the population may be declining faster than suggested by the population surveys that are typically used to calculate population trends in the colony.

"It makes sense that the worsening sex ratio is responsible for so much of the population decline at Punta Tombo based on what we know about penguin behavior," said Gownaris. "Magellanic penguins are serially monogamous—with one male pairing with one female each breeding season—and both parents working together to rear the chicks. So, having fewer females means you have fewer pairings each year overall."

Gownaris wants to survey other Magellanic penguin breeding colonies along the coast to see if they show similarly skewed sex ratios. She and Boersma hope that this information will help new conservation efforts.

"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."

Journal Reference:
N. J. Gownaris et al. Sex-biased survival contributes to population decline in a long-lived seabird, the Magellanic Penguin, Ecological Applications (2019). DOI: 10.1002/eap.1826

We developed a Hidden Markov mark–recapture model (R package marked) to examine sex‐specific demography in Magellanic Penguins (Spheniscus magellanicus). Our model was based on 33 yr of resightings at Punta Tombo, Argentina, where we banded ~44,000 chicks from 1983 to 2010. Because we sexed only 57% of individuals over their lifetime, we treated sex as an uncertain state in our model. Our goals were to provide insight into the population dynamics of this declining colony, to inform conservation of this species, and to highlight the importance of considering sex‐specific vital rates in demographic seabird studies. Like many other seabirds, Magellanic Penguins are long‐lived, serially monogamous, and exhibit obligate biparental care. We found that the non‐breeding‐season survival of females was lower than that of males and that the magnitude of this bias was highest for juveniles. Biases in survival accumulated as cohorts aged, leading to increasingly skewed sex ratios. The survival bias was greatest in years when overall survival was low, that is, females fared disproportionality worse when conditions were unfavorable. Our model‐estimated survival patterns are consistent with independent data on carcasses from the species’ non‐breeding grounds, showing that mortality is higher for juveniles than for adults and higher for females than for males. Juveniles may be less efficient foragers than adults are and, because of their smaller size, females may show less resilience to food scarcity than males. We used perturbation analysis of a population matrix model to determine the impact of sex‐biased survival on adult sex ratio and population growth rate at Punta Tombo. We found that adult sex ratio and population growth rate have the greatest proportional response, that is, elasticity, to female pre‐breeder and adult survival. Sex bias in juvenile survival (i.e., lower survival of females) made the greatest contribution to population declines from 1990 to 2009. Because starvation is a leading cause of morality in juveniles and adults, precautionary fisheries and spatial management in the region could help to slow population decline. Our data add to growing evidence that knowledge of sex‐specific demography and sex ratios are necessary for accurate assessment of seabird population trends.

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  • Claudiu Constantin Nicolaescu

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