Natural Selection in Your Backyard

Have you ever had a bird feeder or put out bird seed in your yard to attract birds? Watching birds outside our homes can be a popular year-round activity for a lot of us. But behind this seemingly simple activity lies something significant. By attracting birds to your backyard, you might actually be impacting how these birds are evolving!

A 2017 study by a group of scientists from the Netherlands and the United Kingdom (U.K.) studied two populations of great tits, a small bird similar to a chickadee that you might see in your backyard. These are popular birds to study. They live in many places, there’s a lot of them, and they’re very eager to use backyard feeders!

The study investigated how differences in the two populations’ genotypes (genetic makeup) translated into differences in their phenotypes (observable traits). For example, a bird’s beak size is part of its phenotype.

The study revealed fascinating correlations (links) between beak sizes and bird feeders. Let’s look at this study in more detail. Then let’s look at how these little birds might be a great example of natural selection.

What did the study find about the size of the bird’s beaks?

The scientists found that, on average, the beaks of birds living in the U.K. were about half a millimetre longer than the beaks of birds living in the Netherlands.

In fact, since 1970, the beak sizes of the U.K. birds have increased by about a tenth of a millimeter. This may not seem like a lot, but when a great tit’s beak is only about 13 mm long, even a small difference can be quite noticeable!

But why would the U.K. birds have longer beaks? Studies have shown that around half of U.K households feed birds in their gardens. The U.K. also spends about twice as much on birdseed and birdfeeders than other areas of Europe. According to this most recent study, the changes in the great tit could reflect the fact that over the past few decades, more and more people are getting bird feeders.

What does this mean for great tit evolution?

A gene variant is an alteration to the DNA nucleotide sequence that causes a change in a phenotype. The scientists monitored birds with electronic tracking devices and found that the birds with the gene variant for a longer beak tended to visit bird feeders more than those birds with a gene variant for a shorter beak. This is a prime example of natural selection in which specific genetic traits allow birds to better adapt to their environment and have better survival and reproductive success. The idea is, if birds have a longer beak they are better able to access the food in the bird feeders. And indeed, the birds with the gene variant for longer beaks went on to be more successful in raising their chicks to fledgling. This means that over time, the genetic variants have resulted in birds who visit bird feeders having slightly longer beaks. This trait is carried on over generations of great tits.

Did you know?

Great tits are increasingly killing birds and eating their brains - and climate change may be to blame.

This isn’t the first study to look at the evolution of beak characteristics. In the 1830s, on his famous visit to the Galapagos Islands Charles Darwin discovered that beak shape varied among species of finches. He found that each beak helped the birds acquire a specific type of food. This is thought to have been one of the key inspirations for his theory of evolution.

Summing up...

Natural selection is happening all around us, sometimes in places we don’t expect it! So, the next time you put out bird seed in your backyard and watch the birds at your feeder, remember that small evolutionary changes are happening around you - even in your own backyards!