Survival of the Biggest – How Humans Are Sowing the Seeds for Bigger Beaks

After graduating with a degree in Biology last summer, I knew that I wanted to do something that would keep me surrounded by the exciting world of science. Despite this, a career in research didn’t particularly appeal to me, so I decided that instead I want to spread the fascinating work of scientists to as many people as possible. I am now completing a masters course in Science Communication at the University of Sheffield, and for my first blog post I thought I would explore a concept that is fundamental to all of nature; natural selection.

Charles Darwin photographed in 1878. Photograph: Print Collector/Getty Images

As one of Britain’s most influential scientists, Charles Darwin is a household name for the majority of people alive today, becoming famous for describing how evolution occurs through his theory of natural selection. He observed that members of the same species varied from individual to individual, and that certain individuals lived for longer than others due to there being some kind of struggle for survival. If you think about it this is true in humans, as we all have different characteristics and physical traits, and this is known as natural variation.

Every living entity has the same ultimate goal; to get their own heritable material into the next generation, and for those that survive longer there is a greater chance of producing offspring that contain their own heritable material. Therefore Darwin realised that over time, the individuals who are best suited to the environment in which they live will survive for longer and pass on this material, which is why he called it ‘survival of the fittest’. He wrote about this theory in his book ‘On the Origin of Species’, stating in it that for “the advancement of all organic beings…let the strongest live and the weakest die.”

One thing that Darwin didn’t understand was how specific traits were passed from an individual to its offspring, which is an essential part of his theory of natural selection. Thanks to technological advancements, we now know about the vehicle in which particular characteristics are transferred from one generation to the next. This transportation device is called DNA, and it is responsible for the way we look, behave and many vital bodily functions, essentially acting as a set of body instructions. All organisms contain DNA, which is formed from a number of different genes, each accounting for a different physical feature or bodily function.


Beaky Birds

In modern day studies on evolution, sections of DNA can be analysed to determine what specific characteristics they are responsible for. Furthermore, specific genes can be compared between individuals to identify particular traits that are changing over time due to natural selection. This is what scientists did in a recent study which looked at evolution in birds, finding that great tits in the UK are currently evolving longer beaks. Beak size in birds, in the same way as a trait such as height in humans, is not controlled by a single gene, but is instead determined by the effects of a number of genes. One of the most interesting aspects of the study is that the scientists also analysed the DNA of a population of great tits in the Netherlands, however beak size in those birds wasn’t changing at all.

UK great tits have significantly longer beaks than their Dutch counterparts.

This begs the question; why have the beaks of great tits in the UK been getting longer, but the beaks of Dutch great tits haven’t? In addition, what advantage do birds with longer beaks gain over those with smaller beaks, with ‘survival of the fittest’ leading to more and more great tits possessing longer beaks? It turns out that birds with longer beaks are more successful at reproduction than birds with shorter beaks, because the longer the beak of the parent, the more likely it is for their chicks to fly the nest. As chicks inherit the genes that control beak size from their parents, longer beaks spread throughout the population due to their success at breeding.

But this still doesn’t tell us specifically how the birds with longer beaks rear more offspring. Well here’s the interesting part; it is believed that the ongoing beak lengthening in the UK population of great tits is down to the British public’s love affair with feeding these birds. According to the British Trust for Ornithology, in the UK we spend an estimated £200 million on wild bird food every year! This astonishing amount of money equates to double that spent on the same thing by the rest of mainland Europe, and it means that around 50% of UK gardens have bird feeders. It just so happens that great tits are particularly common visitors to these bird feeders, and the study found that birds with longer beaks visited garden feeders more often than those with shorter beaks. When I sat down with Jon Slate, one of the scientists responsible for the research, he told me; “One possible explanation is that great tits in the UK with the longer beaks are better able to extract food from bird feeders.” The fact that great tits with longer beaks attended the feeders more frequently suggests that they are better equipped to extract seeds from them.


Are Humans Giving Rise to Evolution?

It’s important to stress that this hasn’t been proved yet, however the amazing thing about this theory is that is demonstrates how human interference can actually lead to the birds adapting to the feeders. Over time the great tits may have been evolving longer beaks in response to the food provided in garden feeders, as longer beaks mean more food. Birds who are able to access more food will generally be in a better condition, meaning they will be able to produce more young and outperform others with smaller beaks.

You may be wondering, as I was, if these beaky birds suffer any negative side effects from their long mouths. Jon Slate told me there’s no evidence that they’re a bad thing, saying; “All species have to adapt to the environment that they’re in. Man is obviously changing the environment massively and rapidly all over the world, and most species are attempting to adapt to that.” Although great tits are some of the most common attendees of garden feeders, this research got me thinking whether there are other bird species that are evolving longer beaks. It turns out that this is probably true, and in other garden goers such as black caps there is evidence that beaks are getting longer in response to feeders.

So just how quickly are UK great tits experiencing this change? In the population studied for this research, the average beak size has been increasing by 0.004mm each year. Although this sounds like an extremely small amount, over a 100-year timeframe this equates to a 0.4mm increase, and considering that great tit beaks are only 13mm long on average it represents a significant size increase. Evolution is often believed to take place over long periods of time, so I think it’s amazing that this research shows how natural selection can operate on such short timescales. What’s more, the way in which these birds are adapting to garden feeders demonstrates that small, insignificant human behaviours could potentially shape the way that animals evolve in the future.


Study Referenced:

Bosse, M., Spurgin, L. G., Laine, V. N., Cole, E. F., Firth, J. A., Gienapp, P., Gosler, A. G., McMahon, K., Poissant, J., Verhagen, I., Groenen, M. A. M., van Oers, K., Sheldon, B. C., Visser, M. E., Slate, J., 2017. Recent natural selection causes adaptive evolution of an avian polygenic trait. Science, Volume 358, pp. 365-368.