Migration has critical impacts on life trajectories by shaping mortality and reproductive outcomes. These findings are important for our knowledge on the biology of aging.
A team of scientists based at several universities and other institutions in France report that pink flamingos, Phoenicopterus roseus, may provide important insights into one of the big questions about aging: why do some individuals age more slowly than others?
The scientists have been working on a long-term tagging-and-tracking field study of wild flamingos, a very tall wading bird species that lives in the Camargue region of France. In this species, some individuals, known as “residents”, live in the Camargue for their entire lives whilst others, known as “migrants”, leave to spend the winter in Italy, Spain or North Africa.
Over the span of 44 years, the researchers have found that, based on their life history strategies, these distinct groups of flamingos do not age at the same rate.
Previously, many scientists thought aging was rare in wild animals.
“For many years, scientists believed aging was rare in wild populations, since most individuals were thought to die from environmental challenges before aging could occur,” said the study’s senior co-author, conservation biologist Jocelyn Champagnon, a senior researcher at Tour du Valat, a research institute dedicated to the conservation of Mediterranean wetlands.
Unexpectedly, the study revealed that migration – a life history strategy in a variety of animals – actually does affect aging.
“Long-term studies now show that aging is widespread – in birds, mammals, and even insects – and many of these species migrate,” Dr Champagnon explained in email. “Our results suggest that migration decisions can influence aging across species. However, to our knowledge, this has not yet been demonstrated in migratory mammals.”
The Camargue is a coastal marshland in southern France (Figure 1C) located south of the city of Arles, between the Mediterranean Sea and the two arms of the Rhône river delta. The eastern arm of this river is known as the Grand Rhône; the western, the Petit Rhône.
Amongst the Carmargue flamingos, some individuals are residents whilst others are migratory, and a small number of individuals pursue a mixed strategy, migrating in some years and staying put in others.
In their study, Dr Champagnon and collaborators found that, at the beginning of their adult life, resident flamingos fare better: they have a higher survival rate and enjoy higher reproductive success than migrants. But at what cost?
“Our study shows that resident flamingos live longer on average (33.1 years) than migratory flamingos (25.4 years),” Dr Champagnon noted in email.
But according to the study’s findings, resident flamingos age much more rapidly than do migratory flamingos. With 40% greater aging, their ability to reproduce decreases and their risk of death increases faster than amongst migratory flamingos.
“Residents live intensely at first, but pay for this pace later on. Migrants, on the other hand, seem to age more slowly.”
As you can see (green; Figure 2), migratory flamingos do pay a high price – higher mortality and lower reproduction rates – for their seasonal jaunts in their youth but they do appear to compensate by aging more slowly after reaching maturity. Thus, the onset of the aging process occurs earlier in residents (20.4 years on average) than in migrants (21.9 years).
“[S]ome flamingos switch strategies. For the purpose of our study, we defined three categories: resident, migratory, and ‘mixed strategy’ individuals (those that do not consistently fit either pattern),” Dr Champagnon pointed out in email. “Flamingos with a mixed strategy showed an intermediate life expectancy of 30.8 years.”
This is probably linked to a compromise between performance when young and health in old age.
Dr Champagnon was most surprised by the contrast in aging rate between migratory and resident flamingos.
“The most striking result was that migratory flamingos age more slowly than residents,” Dr Champagnon told me in email. “This matches theoretical predictions, but it was still surprising to see it so clearly. In many bird species, migration is often seen as a strategy used by less dominant individuals. While residents can reproduce more often early in life, this comes at a cost: higher mortality and reduced reproductive success later on. Migrants, on the other hand, may trade off some early reproduction for better survival later in life.”
This study and its findings are very unusual because this field work has been ongoing for 44 years so far.
“That’s the whole point of having continued this study over the long term. Initiated in 1977 in the Camargue by tagging flamingos with rings that can be read from a distance with a telescope, this program still allows us to observe flamingos tagged that year,” Dr Champagnon said.
“This is a unique dataset that is proving invaluable for understanding of the mechanisms of aging in animal populations.”
“Overall, we find strong support for the ‘early benefits to residents’ hypothesis: Residents exhibit higher early-life demographic performances, with lower basal mortality and higher breeding probability than migrants. Lower mortality among young adults also allows residents to achieve longer adult lifespan compared to migrants,” Dr Champagnon summarized. “However, residents possibly bear the cost of their early-life advantages in advanced age, exhibiting both accelerated reproductive and actuarial senescence relative to migrants. Our study provides one of the few pieces of evidence of the demographic impacts that migration can have on senescence in a long-lived vertebrate.”
With their long lifespan – some flamingos live to be more than 50 years old! – and behavioral diversity, flamingos are more than just an iconic animal of the Camargue. They also provide an ideal model for understanding aging more generally in animals.
“Our study demonstrates that migration strategies have a strong impact on senescence, and potentially on population dynamics,” Dr Champagnon concluded in email. “We show that migration has critical impacts on life trajectories, shaping the mortality and reproduction outcomes. These results are important for our knowledge on the biology of aging.”
Want to help? This study was made possible thanks to more than 40 years of marking individual flamingos. Anyone interested in supporting this work is encouraged to “adopt a flamingo”.
Source:
Hugo Cayuela, Sébastien Roques, Antoine Arnaud, Christophe Germain, Arnaud Béchet, and Jocelyn Champagnon (2025). Migration shapes senescence in a long-lived bird, Proceedings of the National Academy of Sciences | doi:10.1073/pnas.242288212
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