As I approach that golden age of retirement my birding hobby causes me to look to the avian world for guidance. Do birds retire and perhaps seek that perfect habitat where food and water are plentiful and the temperature ideal all year long? Do they give up those long migrations and the work of nesting and breeding? Do they recreate with other aging birds, have more time for song, or perhaps help with raising of the grand and great-grand chicks? Birds, I know do not crave a large nest egg; for them that just signifies the nefarious work of a parasitic cowbird and means another large mouth to feed. (See earlier post “Birds Behaving Badly / Brood Parasites”, 8/22/2015) In short, is there a golden age for birds?
There seems to be two distinct approaches to this issue in humans; those who want to keep working or must work until they die in the saddle, and those who crave and can afford the free-time of retirement. You can’t explore these issues for birds until you figure out how to determine the bird’s age, and they don’t make that easy.
Bird size is not a reliable dating tool, nor is bird song. Some have observed that second year males often have weird or incomplete versions of the adult song, but you can’t rely on it for dating. Early dating by plumage is straight forward, using natal down and the rapid progression to juvenile plumage, which is usually duller than the adult’s and often spotted or striped. But by late summer, fall, or early winter, depending on the species, the “first winter” plumage develops which is usually very similar to the adult.
Judging the age of adult birds then becomes much more difficult. The annual or biannual molt makes the shabby and worn out feathers all new again, like repairing the wrinkles of age. Wouldn’t a yearly face-lift or tummy tuck be great? Luckily some birds, gulls in particular, have a yearly progression of plumages allowing first year, second, third, and adult age designations. Learning these variations is difficult and requires a good guidebook or an experienced colleague.
Another dating technique is called skulling. One can observe the air cavities in the bird’s skull by wetting and separating the feathers. The maturing skull apparently goes through a specific and progressive pattern of pneumatization and maturation, visible through the bird’s thin skin. This is obviously a tool for ornithologists–don’t try this at home. That leaves banding, the most definitive technique in determining the birds age, but again a technique for the experts. These basic facts are now known: birds in the cooler temperate zones live shorter lives than those in the tropics, rural birds live longer than urban birds, large birds live longer than small birds, and young, inexperienced juveniles have the highest mortality rate of all.
I was surprised to learn that the annual mortality of passerines was 70% in the temperate zones. The longevity record for the Bald Eagle and Osprey is 22 years, 16 years for a Northern Cardinal, and 7 years for a House Wren. But these were the lucky ones. Message to birds: avoid risky juvenile capers, leave the city and head to the tropics and stay there, and don’t volunteer to be a canary in a coal mine or a clay pigeon.
D.J. Holmes and others, writing in “Experimental Gerontology”, has noted that birds have relatively longer life spans compared to similar sized mammals, especially given their warm body temperatures, rapid heart rates, high glucose levels, and high metabolic rates. These are usually harbingers of rapid aging, but not so with birds. Some seabirds in particular age very slowly and actually increase their reproductive activity with age. Apparently birds have evolved specific adaptations to offset the cell damage caused by oxidative and glycosylative compounds, mechanisms not found in mammals. Is there a hidden “Fountain of Youth” under all those feathers?
So it turns out that birds do not retire and enter a life of leisure but rather press on or even increase their activity and fecundity with age. That is until they just drop, fly into a window, or are snatched away by a more agile hawk or owl. I’m sorry to learn this, but maybe we humans can adapt some of their techniques for staying young. Life in the tropics sounds good, so I for one will become a “snow bird” and head south this winter. I’m also interested in those avian chemical adaptations. Maybe there’s an investment opportunity lurking here.