Why collect feathers?

Feathers can store a lot of information about the bird they have come from. As feathers grow very slowly and don’t change, they store this information for a long time, which we as researchers can use to find out about the history of a bird.

Feathers are particularly useful as they are made out of keratin - very similar to the keratin that our hair and fingernails are made out of. This means that they store elements like carbon and nitrogen, and their stable isotopes, which we can use to trace where that bird has come from.

Stable isotopes: you are what you eat

To combat the illegal wild-harvest of native Australian parrots, we used the feathers collected by citizen scientists in the Feather Forensics project to see if we could distinguish between captive and wild parrots using the chemical makeup of their feathers.

Feathers hold a lot of information about a bird, from it’s species, age, sex, and health. When we look closer at a feather to the molecular structure, we can identify the bird’s diet. Within the molecular structure, there are different forms of the same element called stable isotopes. Stable isotopes are different forms of elements which are chemically similar, but have different masses. This difference in mass cause stable isotopes to exist in an environment in predictable ways, and are unique to that particular environment. Therefore, they can act as an “environmental fingerprint”. As a bird eats and drinks and uses these elements as building blocks to grow, the environmental fingerprint is transferred to the bird. Stable isotopes are essentially “you are what you eat”: the stable isotopes in the diet reflects the stable isotopes in an animal, such as in a bird’s feather.

For example, carbon-12 (6 neutrons and 6 protons) is the most common stable carbon isotope. The less common and heavier isotope, carbon-13 (7 neutrons and 6 protons), can increase in an environment through a number of mechanisms in the carbon cycle, such as how the plants photosynthesise. Some plants, such as corn, millet, and sugarcane (which have what is called a C4 photosynthetic pathway) accumulate more of the heaver carbon-13 isotope than plants like wheat, rice, and barley (C3 photosynthetic pathway).

Another commonly used stable isotope is nitrogen. The large majority of nitrogen is the stable nitrogen-14 isotope (7 neutrons and 7 protons), while the remaining is nitrogen-15 (8 neutrons and 7 protons). While the nitrogen cycle is complex, the heaver stable nitrogen-15 isotope generally increases with an animal’s position in the food chain. For example, a carnivore would have more nitrogen-15 in its tissues than a herbivore.

A schematic from Lüdecke et al. (2022), showing how carbon-13 (δ13C) and nitrogen-15 (δ15N) varies within an ecosystem. Plants with a C3 photosynthetic pathway (most trees and shrubs) have less of the heavy stable carbon-13 isotope than plants with a C4 photosynthetic pathway, which are generally grasses. The heavier stable nitrogen-15 isotope increaes up the food chain, where carnivores have higher nitrogen-15 than herbivores.

In the lab

Once we recieve the feathers, we first sort through all the submissions. We identify feathers to species, and look for any other information we can get from them, such as identifying juveniles or sick birds. From here, we can select which feathers are suitable for the research project.

Once we’ve chosen the appropriate feathers, we wash them in ordinary washing detergent to remove the surface dirt. Then, we wash them in a chemical bath, which removes the oil the birds use to keep their feathers waterproof.

To clean off the layer of lipids which keep a feather waterproof, we washed the feathers in multiple detergent and chemical baths.

Once the feathers are clean and dry, we cut and measure out half a gram of the feather vane (the colourful parts, removing the quill). This goes into a tiny capsule made of tin, where it is ready to go in a mass spectrometer. In the mass spectrometer, the feather sample is combusted, and then separates and measures each isotope according to its weight. The final reading is the proportion of the heavier isotope to the lighter isotope (the stable isotope ratio, written as δ13C and δ15N). These are the feather measurements which we can then use to see if a bird is from captivity or from the wild.

Measuring stable isotopes in parrot feathers

Why collect feathers?

Stable isotopes: you are what you eat

In the lab

Further reading