You Are What You Eat
Today a neat new study was published demonstrating that it is possible to determine what a penguin was eating from its bones. The article appeared in Journal of Avian Biology, and was written by two of my favorite penguin collaborators, Dr. Daniel Thomas and Dr. Ewan Fordyce (recent winner of the Hutton Medal) and their colleague Keith Gordon. They applied a method called Raman spectroscopy to measure the chemical composition of penguin bones from museums in New Zealand. Raman is a cool technique. Basically, they blast the bones with a low-powered laser, and the way energy is scattered back gives a good estimate of what elements are prevalent in the bone. Raman spectroscopy is really useful because it does not damage the bone. Other methods for determining chemical composition usually require a bit of bone to be vaporized, which many museums don’t want to see happen.
So what does this have to do with penguin diet? Well, there is an old saying: You are what you eat! It is true at the finest scales. Different species of penguins like to eat fish, squid, or krill. These prey have different concentrations of elements in their bodies due to the different ways the metabolize food and pull oxygen from the water. Krill are very rich in the element fluoride, which they tend to concentrate in their hard carapace. You may be familiar with fluoride as a key ingredient in toothpaste! It is actually toxic, which is why it helps fight the bacteria that cause cavities. However, it is not dangerous at very low concentrations. Our toothpaste has only a tiny, tiny fraction of fluoride, enough to zap a microbe but not enough to hurt us. Fluoride in toothpaste also alters the mineralogy of our tooth enamel, making it harder and less susceptible to dissolving when contacted by acids (like those in soda). Penguins digest their prey in such a way that most of the fluoride stays in the bones or carapaces and gets passed away harmlessly. They do keep some though – think of it like shrimp flavored toothpaste for animals without teeth.
In the new study, the Raman data showed a big difference in the bones of krill-loving penguins compared to fish-loving penguins. Two species that eat large quantities of krill, the Emperor Penguin and the Adélie Penguin, showed higher spectra bands than the other four species included in the study (Humboldt, Little Blue, Yellow-eyed, and Fiordland Penguins), which eat almost no krill. This proves the method works, and it give penguin scientists a new tool to look at how feeding patterns have changed in penguins over time. Actually, there are other ways to reveal diet from long-passed penguins too, including isotopes in eggs and guano (penguin poop).
With all these techniques, it is possible to look at old museum specimens from one hundred years ago or more to see if the diet of penguins has changed along with the growth of fisheries or changes in climate. Indeed, some of this work is already going on. We will return to the topic later.
Reference: Thomas, D.T., R.E. Fordyce and K.C. Gordon. In Press 2013. Evidence for a krill-rich diet from non-destructive analyses of penguin bone. Journal of Avian Biology 44.