Gentoo penguins with high levels of hemoglobin in their blood have a clear advantage when diving and foraging, which in turn could have a positive effect on breeding success.
For most human observers, gentoo penguins are like two peas in a pod, but as is so often the case, it’s the inner values that make the difference. As with us humans, some penguins are in better shape than others, as indicated by the hemoglobin levels of their blood. And better fitness in penguins leads to more successful foraging and possibly to better breeding success – the result of a study by the Canadian-British research team published a few days ago in Marine Ecology Progress Series.
The researchers determined hemoglobin levels of 66 adult gentoo penguins from two colonies on the Falkland Islands to find out how their diving ability is related to their aerobic capacity. They were particularly interested in the length of time foraging penguins can stay near the seafloor where the largest and most energy-rich morsels can be found.
In order to measure the duration of the dives, the total time spent at sea and the vertical (dive) distance traveled, each of the 66 penguins was fitted with sensor tags. The evaluation and linking of the data with the hemoglobin values showed that penguins with higher hemoglobin levels dive more frequently at greater depths (more than 140 meters) and spend more time there. At the same time, longer and deeper dives do not mean that these penguins have to spend more time replenishing their oxygen reserves. Their foraging is therefore much more efficient and they find better and rarer food compared to other, less fit penguins, which saves energy and reduces competition.
The research team also determined the hematocrit value, the percentage of red blood cells in the blood. It can also be used as a factor for diving capacity because a higher hematocrit percentage can sometimes mean a higher level of hemoglobin in the blood, which in turn means a higher oxygen carrying capacity. However, a higher hematocrit does not necessarily mean a better dive – more red blood cells thicken the blood, resulting in less blood flow and forcing the heart to work harder to circulate the blood.
“Diving deep takes time and energy, and it’s useful only if the penguin can search and catch food at the bottom. We showed that penguins with higher aerobic capacities can spend more of their dive at depth than other penguins while still taking the same amount of time to recover,” explains Dr. Marie Auger-Méthé, associate professor at the Institute for the Oceans and Fisheries at the University of British Columbia and principal investigator.
The amount of hemoglobin – the protein in the red blood cells that transports oxygen to all parts of the body – therefore determines the quality and quantity of food that a penguin can capture. And the more efficient foraging is, the more energy a penguin has available for breeding, which can ultimately be crucial for breeding success.
After breeding is before breeding: In winter, after the exhausting breeding season, it is crucial for the penguins to replenish their energy reserves and prepare for the coming breeding season, which requires a lot of energy right from the start, when the nests have to be defended and the eggs are laid. A well-fed penguin lays its eggs earlier than its less fit conspecifics, which means a higher survival rate for its offspring.
“Animals attempt to time the birth of new offspring with an abundance of food in their environment for optimal nourishment while the chicks grow,” Sarah McComb-Turbitt said, a marine biologist at the Institute for the Oceans and Fisheries and first author of the study. “Penguins can also lay later in the season, delaying nesting until they have recovered from the harsh winter seas. The trade-off, however, is that late chicks will be smaller when winter comes again and have a lower chance of survival. Chicks from eggs laid early have a longer period of growth before winter, increasing their chances of fledging and growing into adulthood.”
Dr. Auger-Méthé stresses that this type of study is really important, “because while most research still tries to describe what a typical individual of a species does, we know that individuals vary drastically in their conditions, behaviour and reproduction. In some cases, there may not be a typical individual that represents the majority in a population. These differences can have a large effect on their resilience to human stressors, as some individuals may be hit harder than others.”
Human-induced stressors that can affect gentoo penguins include climate change, fishing, tourism, pollution, invasive species and industrial development.
“Pollution from shipping, oil spills and other maritime activities introduce contaminants that penguins ingest and carry,” says McComb-Turbitt. “Commercial fishing, particularly for squid and fish, is also a significant industry in the Falkland Islands. Overfishing could impact the food availability, and consequently, a penguin’s survival and ability to reproduce.”
In particular, overfishing in coastal waters can disproportionately affect penguins with lower aerobic capacity, as they are unable to reach prey in offshore waters.
However, gentoo penguins are very resilient and use their diving skills and foraging flexibility to adapt quickly to changes in their environment. The gentoo penguins of the Falkland Islands are genetically different from their Antarctic relatives, so future studies are essential for a better understanding of these fascinating animals.
Julia Hager, PolarJournal
Link to the study McComb-Turbitt SP, Crossin GT, Tierney M, Brickle P, Trathan P, Williams TD, Auger-Méthé M (2023) Diving efficiency at depth and pre-breeding foraging effort increase with haemoglobin levels in gentoo penguins. Mar Ecol Prog Ser 722:1-17. https://doi.org/10.3354/meps14441
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