The question that I have been asked the second most often during my research (after “Do loons mate for life?”) is,”How long do loons live?”. On its face, this would seem an easy question to answer; one merely marks a loon and tracks it until death. For two reasons, the question is not so easy. First, loons live a long time, so a researcher must have considerable staying power to follow a loon throughout its life. Second, loons’ lifespans, like those of humans, are variable. Many loons die in their first year or at a young age. In order to determine maximum lifespan of a loon — which is truly what folks mean when they ask how long loons live — you need to track a large number of birds for a lengthy period.
Of course, we have studied hundreds of marked loons for over two decades, so we have learned a lot about survival patterns of the species. For example, we have learned that male loons have a higher rate of mortality than do females, and we have also determined statistically that loons senesce. In addition, as a consequence of capture efforts that began in 1991 and tireless monitoring since then, we now have a large set of study animals that are in their mid to late 20s. These ancient birds are listed below, the oldest at present being a male marked on Little Bearskin Lake in 1991, who is therefore at least 28 years old. (No male has held a territory and bred at less than 4 years of age.) Despite senescence, there seems a good chance that one or more of the loons listed in the table will cross the 30-year threshold in the next several years. However, most
individuals die well before they reach 20 years of age from disease, predation, or entanglement in fishing tackle. So….kudos to the senior loons listed in the table, which have survived all threats nature and humans have thrown at them to push towards the known age limit of the species!
While the table summarizes the oldest cohort of loons in the LP study area, it is the Bird Banding Laboratory in Patuxent, Maryland that maintains the official longevity records for all North American species, including loons. This makes sense, because the BBL provides metal bands that we place on birds’ legs and also receives many reports of banded birds that have been recovered or resighted, which can therefore provide information on age. If you scroll down to “common loon” in the BBL longevity database, you can see that age estimates follow a ratcheting process. That is, each year that passes permits known marked individuals to survive (or not) for another year. Therefore each year in which we have an oldest known loon that is still alive gives us a chance to extend the known longevity record by another year. If you scrutinize the BBL records for common loons, you see that we have been pushing the known lifespan of the species upwards for the past quarter century. In 1990, when almost no marking of loons had been done, the maximum known lifespan was 9 years; by 2000, the record had been extended to 14 years. Recently, the record listed by the BBL was listed at 25 years, based on the Little Bearskin male that I mentioned above.
But the longevity record listed by the BBL excludes data from a small cluster of lakes at the Seney National Wildlife Refuge, where loons were first marked in 1987, four years before our first birds were banded. It is on these lakes, not in our study area, where the oldest known loons live. At present the record for longevity is 35 years, held by a female banded at Seney as a territorial adult in 1989, at which point she was at least 5 years old. (No female has been observed to settle at an age of less than 5 years.) In addition, a male at Seney holds the distinction of being the oldest common loon whose age is known precisely. He was banded as a chick in 1987. Thus, he is exactly 32 years old. These are extremely old individuals. But since the age limit of common loons creeps upwards each year, it will be another 5-10 years before we have an accurate estimate of the maximum lifespan of the species.