Some of you may have heard the news recently about the seventy-year-old albatross that hatched another chick. It got me thinking about the life span of our feathered friends. I have wondered for example if it is the same bald eagle I have been seeing during the spring and fall migration in the same tree on the shoreline of Lake Metigoshe, or the wrens in our birdhouse are the same birds as last year. We may have a tendency to think that some of these birds are the same ones, but that is probably not accurate.
Birds face many threats to their survival. Mortality is generally high among the young but stays roughly the same through adulthood. Song sparrows for example, have been found to have about a 25% chance of making it through the first year, and they seldom die from old age.
No doubt winters can be difficult for the permanent residents in our area. Although we might envy our migratory birds from spending their winters in warmer climates, their lives are far from easy. One study that looked at the mortality of a species of warbler found that the birds had roughly a 50% chance of living through a year.
There is a general rule of thumb that the larger the bird, the longer the lifespan. Smaller birds such as warblers, for example, may only live a couple years. But there are some other factors to consider. Birds that reach adulthood quickly and have more offspring tend to have shorter lifespans. Also ground nesting birds tend to have shorter lifespans than those that nest above the ground.
I did run across a list of some bird longevity records from Stanford University. Records for wild bird longevity gives us some insight into the lifespan of some of our more common birds. I will list a few here, but remember these are the oldest of the old, and the data may be limited. Plus, the average lifespan of course would be much shorter. The record for house wrens was 7 years. It was 9 years for ruby-throated hummingbirds, and 10 years for killdeers, black-capped chickadee 12 years, and robins 13 years.
The record for blue jays is 16 years, American crow 14 years, red wing blackbirds 15 years, mourning dove 19 years. Red-tailed hawk and bald eagle 21 years, and great blue heron 23 years.
Those life spans give us some indication of what the longevity might be some of our more common birds. But we will probably still wonder if the birds we see this year are the same ones from previous years.
-Chuck Lura
