Why do some birds live longer than others?

Why do some birds like the robin and chickadee only live a year or two, while other birds can live longer? That is so sad. ~ Anonymous

A definitive answer to the evolution of lifespan is still a mystery. Scientists believe that birds’ observable characteristics: such as their development, physiological properties, and behavior (like nest building) is a result of the expression of their genes and the influence of environmental factors.

Another theory on why some birds live longer than others is size. Because smaller birds tend to be more prone to predation and other dangers, their life may be cut short. The average lifespan of the littler bird is only a year or two while the bigger birds average around 25-50 years. There are a number of cases in which smaller animals within a given species live longer in captivity. For example it has been recorded that some captive House Sparrows lived for 23 years, and Northern Cardinals 22 years.

At what age a bird reaches sexual maturity might also influence longevity. While chickadees, sparrows, and goldfinches can mate at one year, crows, hawks, and eagles may take up to five years to reach sexual maturity.

Although life expectancy in birds might be correlated closely with size, further information is required. So in addition to collecting data directly by banding and recapturing birds more research needs to be done.

In fact one recent study already found that tropical birds, leading a slower life and expending less energy, tended to live longer than birds that had to survive harsh winters. The researchers traveled to Panama where they captured tropical birds and measured their basal metabolic rate (BMR) – the minimum amount of energy they expend at rest, solely to maintain their vital bodily functions.

They compared these measurements with the BMRs of temperate birds. They found that tropical birds used about 18 percent less energy, as measured by BMR, when compared with temperate birds.

The researchers also tested neotropical migrants – those birds that live in the tropics much of the year, but migrate north to temperate climates such as the United States and Canada to breed. Results showed these birds expended more energy than those species that live year-round in the tropics, but still used less energy than birds that were permanent residents in colder states like Michigan.

Scientists believe that tropical birds may have a slower pace of life because it fits with the rest of their life history. Tropical birds, compared to those from temperate regions, tend to live longer, and produce fewer offspring which develop slowly and mature relatively late in life.

Makes me glad I feed the hardy birds that choose to stay year-round in Michigan. As the temperatures dip and natural food sources may become covered with snow or locked in ice, I know that the supplemental food and water that I provide is more widely appreciated and has a bigger impact on the birds’ survival.

Source: Ohio State University (2007, May 23). Tropical Birds Have Slow Pace Of Life Compared To Northern Species, Study Finds. http://www.biosci.ohio-state.edu/~patches/publication/wiersma%20et%20al_2007_PNAS.pdf

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