
As time goes by: Lessons on aging from the birds and the bees
While changing over the calendar from 2024 to 2025, it’s only natural that thoughts turn to the passage of time and the advancement of years. Aging and lifespan are sources of endless fascination, anxiety, and study. Why do we age? Might we find ways to extend lifespan, or to prolong wellness? Much of what we have learned about these weighty questions comes from studies of humans and of targeted research models (lab mice, fruit flies, and a few others). But the critters outside our windows provide intriguing opportunities for gaining additional insights.
Among mammals, larger species generally live longer. Humans with good access to modern health care have life expectancies in the range of 80+ years. Our pet dogs and cats might live a dozen years or so, whereas anyone choosing to adopt a mouse or hamster must be prepared for a lifespan just 20-25% as long. It turns out, though, that the natural world offers some rather different patterns of longevity. I will highlight two groups in particular: birds and insects.
Birds, like mammals, have lifespans that generally increase with species body size. Also like mammals, birds as a group are uniformly “warm blooded.” One might expect that the high rates of metabolism needed to sustain those warm bodies would exert similar patterns of wear and tear in birds as in mammals, translating into similar lifespans. And yet, birds substantially outlive mammals of similar size. Out on Midway Island in the Pacific, Wisdom the Laysan albatross, weighing in about like a mid-sized cat, made headlines recently by returning to breed at age 73. Closer to home, a 15-gram indigo bunting was captured in Ohio 13 years after it was initially marked; that’s five or six times as long as a similar-sized mouse would live. Even tiny ruby throated hummingbirds, which migrate annually between North and Central America, may return year after year to your feeder; they have lived longer than nine years in the wild. No shrew could match that record.
The long lifespans of birds are intriguing—but insects are where things really get interesting. Across the diversity of insects, adult lifespan (usually measured in the laboratory, but sometimes in the wild) ranges from hours to years. Interesting variations can occur even within a single species. In bumblebees, for example, the queens—females responsible for founding a colony and laying eggs—develop during summer and are fertilized by males during the subsequent few weeks. Those fertilized queens survive overwinter, then re-emerge the following spring to establish new colonies; they die a few months later, having lived for about a year. In contrast, male bumblebees (drones, which develop from unfertilized eggs) often are not produced until mid-summer. Their only job is to find and fertilize virgin queens, after which they die, having accomplished their mission in just one or two months of life. Honeybees provide an even more dramatic model. There, the female workers live just a few weeks in summer, whereas queens, which are genetically identical to workers but are fed a special “royal” diet and don’t leave the hive to forage, can live 20 times as long, up to five years.
Monarch butterflies provide another example of a species with variation in lifespan. Monarchs that develop in Ohio fly south to Mexico for the winter, then return to the southern US the following spring. They lay their eggs and die, having lived for 6-8 months. Those eggs develop into adults that fly a portion of the remaining journey back to Ohio, but after just a few weeks they lay their eggs and die. That happens again, and then again, so that the monarchs departing from Ohio in late summer are about four generations removed from the ones that left the year before. Of those four generations, one— the one that flies south to Mexico—lives several times as long as the others.
Two big questions arise from these patterns. The first is whether birds and insects actually exhibit signs of aging as they get older; do they suffer cognitive or physical decline? The short answer appears to be yes, at least in some cases. Birds do have a notable ability to regrow neurons in parts of their brains, which may forestall certain aspects of aging. However, older birds of at least some species have diminished visual acuity, immune function, and reproductive success. Likewise, there is evidence that some insects lose capacities as they age, including diminished vision, learning, and flight performance. For both birds and insects, we still have a lot to learn about the consequences of aging, especially for animals living in the wild.
The second question concerns the mechanisms responsible for aging. Why, in general, do animals age, and by what cellular or molecular mechanisms does aging occur? There isn’t space in this essay to address those important questions, including the roles of telomeres, anti-oxidants, and other pathways that promote or delay aging. But we can see hints that studies of birds and insects offer intriguing models for exploring those mechanisms. For example, birds achieve their long lives despite having blood sugar levels several times as high as in mammals. Could studies of birds offer insights into how to mitigate the damaging effects of high blood sugar seen in aging humans? Environmental factors also can influence lifespan. For example, a lot of insects, including overwintering bumblebee queens and monarch butterflies, enter a period of dormancy, when their metabolism is suppressed and they don’t feed. Could those animals offer clues to how we might induce “suspended animation” that prolongs life? And what accounts for the long lives of honeybee queens? One idea is that their special diet induces changes to gut bacteria that somehow promote longevity. Can humans tap into that phenomenon?
When we think about lessons we might learn from the birds and the bees, we might not immediately think about lifespan and aging. But many cellular mechanisms operate in common across a wide spectrum of animal life; the fundamental things apply, one might say. With the calendar turning to a new year, I offer a resolution to appreciate and enjoy the time that we have. For me, that includes taking pleasure and amazement in the beauty and diversity of our fellow creatures and all that we can learn from them. On that you can rely.
Article and photo contributed by Dr. David L. Goldstein, Emeritus Professor, Department of Biological Sciences, Wright State University.