When drought grips the African savanna, an aging elephant matriarch leads her herd to water she remembers from decades past. In the cold Pacific, an older killer whale guides her pod to elusive salmon, sharing her catch when prey runs thin. And over the open ocean, a seasoned albatross traces vast, invisible routes it has refined over years, returning unerringly to feed its chick. 

Across land, sea, and sky, these animals deploy memory, skill, and experience accumulated over long lives. So what happens when such older individuals are selectively removed through hunting, fishing, or other human pressures? Researchers say the loss may not be immediately visible, but it is profound: The knowledge that underpins population survival begins to disappear.

For decades, conservation has focused on numbers: how many animals remain in a population. But a growing body of research suggests this lens is too narrow, and that the loss of older animals can reshape populations in ways that simple counts fail to capture. “Not all individuals contribute equally,” says Keller Kopf, a senior lecturer at Charles Darwin University in Australia. “Older animals play roles that are often invisible in simple population counts.”

“There has been mounting evidence for the knowledge, skills, and leadership roles that older individuals have within their societies.”

Scientists say older animals often play several critical roles in how populations function, broadly falling into three categories: ecological knowledge, reproduction, and immunity. They carry knowledge that guides survival, play outsized roles in producing the next generation, and possess stronger defenses against disease built up over time. Together, these qualities can make the difference between populations that endure and those that slowly fall apart. 

Conservation biology has long been concerned with population dynamics. To gauge the health of a population, scientists would estimate how many animals remained, how fast they reproduced, and how many could be removed without causing collapse. Shaped largely by wildlife management and fisheries science, this approach treated populations as interchangeable collections of individuals, where one animal could substitute for another so long as overall numbers held steady.

Research into the specific role of older animals has spanned decades and multiple fields, but it has remained largely disconnected from conservation biology. Studies have been “limited to quite siloed disciplines,” says Kopf. Now, as research on the importance of older animals accumulates — and declines among long-lived species make those findings harder to ignore — the silos are coming down.

“In recent years, there has been mounting evidence for the knowledge, skills, and leadership roles that older individuals have within their societies,” says Jennifer Smith, a behavioral ecologist at the University of Wisconsin Eau Claire.

Few animals make the case more clearly than elephants. For decades, wildlife managers and hunting authorities often treated older males as expendable — an idea reflected in trophy hunting guidelines that encouraged the selective take of mature bulls, on the assumption that they were past their reproductive prime and could be removed without harming populations. But research over the past decade has challenged that view. One study of elephants in Botswana found that younger bulls were significantly more likely to behave aggressively — toward vehicles, livestock, and other animals — when fewer older males were present. Older bulls appear to act as a kind of social buffer, helping younger elephants better assess risk, which lowers stress and aggression. Older males may also directly police disruptive behavior.

Older individuals have survived repeated exposure to disease, meaning they are more likely to pass on traits that confer resistance.

From elephants to bison to hippos, older, larger animals shape the ecosystems around them by depositing large amounts of dung that fertilize soil, dispersing seeds over long distances, or helping maintain open habitats by knocking down trees and clearing vegetation. Cut their lives short, and that future activity disappears. “Every time you shorten the life of one of those individuals, you’ve shortened the function that animal played,” Redmond says.

The challenge for conservationists is that hunters typically target individuals with the largest horns, the darkest manes, the most impressive tusks — traits that often signal age, experience, and dominance. In species like lions and leopards, that selectivity can have cascading effects. Removing an older male lion can trigger a takeover of his pride by younger males, which often involves the killing of his cubs so that their mothers return to breeding condition. 

In leopards, the consequences play out more quietly but no less significantly. Adult males each hold territories, and their presence pushes younger males to disperse in search of their own range and unrelated mates. “If you shoot adult male leopards, their territories are left bare, [and] young subadult males don’t have to disperse,” says Mona Schweizer, a biologist and trophy hunting expert at Pro Wildlife in Munich, Germany. Without that pressure to disperse, she says, younger males remain close to related females, increasing the risk of inbreeding.

If big cats offer a clear case study, whales represent something more dramatic: a global-scale experiment in removing older animals. During the 20th century, industrial whaling killed millions, targeting the largest individuals and thus stripping away those that may have held accumulated knowledge of migration routes and feeding grounds. “We did this incredible experiment with the whales without knowing that we were doing it,” says Mark Simmonds, director of science at OceanCare, a marine conservation group.

Studies of orcas and sperm whales show that older individuals, especially females, play central roles in guiding groups and sharing food, shaping the survival of entire social units. Scientists say that kind of social knowledge may also extend to how whales locate and use key habitats. When older animals are lost, that knowledge can disappear with them, “probably because there weren’t any individuals left who knew about these habitats and how to exploit them well,” says Simmonds. Recent research shows that gray whales and right whales have failed to return to former calving grounds in parts of the Mediterranean.

Even among freshwater fish, the role of older, larger fish has long been recognized but often overlooked in practice. Some species, like sturgeons, grow slowly and live very long, sometimes more than a century. Many large fish, including sturgeons, continue to grow throughout their lives. As they age, their reproductive output rises sharply: Larger, older females produce far more eggs, and often higher-quality eggs, than younger fish.

This has clear implications for management. Fishing often targets the largest individuals, removing those that contribute most to population stability. When these fish disappear, populations may lose their reproductive engine and long-term resilience. “If you manage for the oldest, largest fish, you are managing for healthy fish populations,” says Zeb Hogan, a fish biologist at the University of Nevada, Reno, and the Convention on Migratory Species Councillor for Freshwater Fish.

Beyond knowledge and reproduction, many older animals carry something less visible but equally important: immunity. Individuals that live longer have survived repeated exposure to disease, meaning they are more likely to carry, and pass on, traits that confer resistance. When those animals are removed, populations may lose some of that accumulated resilience, leaving them more vulnerable to future outbreaks. While clear examples of this phenomenon are still emerging, there is growing evidence that preserving such individuals can help populations better withstand disease over time, Christian Walzer, a professor of conservation medicine at the University of Veterinary Medicine Vienna, told the U.N. meeting in Brazil.

Researchers say the resolution adopted by the International Union for Conservation of Nature last year is useful because it reframes the conversation, from focusing on how many animals remain to how populations actually function. The move could spur research into how to protect older animals, and lead to changes in hunting regulations and fisheries management to avoid disproportionately removing older individuals. 

Conservation has long been wary of drawing parallels between humans and animals. Yet some researchers say the emerging science increasingly mirrors our own experience, showing that older animals pass on knowledge that helps others thrive, much like elders in human societies. “I think we all can relate to it because we see that in humans as well, how important experience is,” says Schweizer.