Tail feather used in CSL experiment
Researchers shine a (very) bright light on duck feathers, revealing a sensitive technique for environmental monitoring.
Like the proverbial canary in a coal mine, birds of all kind can act as sentinels for toxic metals in the environment. Now agricultural and environmental scientists are discovering that birds – or more accurately their feathers – can reveal contamination at very low levels, giving us an even more sensitive monitoring tool.
Researchers have long known that like hair in humans, feathers can act as a sink for chemicals in the body. This in turn can contribute to the bird’s colour, which can act as a signal to other birds about its fitness as a potential mate.
Agriculture and Agri-Food Canada toxicologist Fardausi Akhter is part of a team that recently took a closer look at feathers, using x-ray fluorescence mapping at the Canadian Light Source synchrotron at the University of Saskatchewan. The technique measures the emission of fluorescent X-rays from material – in this case, a feather – that has been excited by being bombarded with high-energy X-rays.
In a proof of concept, Akhter and her team examined the level and distribution of zinc in feathers from lesser scaups, a type of diving duck common to the marshes of Canada. The ducks were fed high-zinc diets.
Micro-XRF map showing the distribution of zinc in feather microstructures
Learning where zinc goes
Peering at the feathers with the synchrotron, the researchers noticed zinc mostly accumulated in two feather microstructures – the barb and its barbules. Feathers have a narrow, hollow shaft bearing flat vanes formed of many parallel barbs. The barbs are in turn formed of even smaller structures called barbules.
Knowing exactly where metals end up can give researchers better insight into the biochemical processes in cells. Because feathers are increasingly used to measure biomarkers for wildlife health and environmental monitoring, such information is crucial to understanding how metals accumulate feathers in response to the birds’ dietary and environmental conditions.
The researchers also noticed similarities between the patterns of zinc distribution and melanosomes – that is, the more melanosomes, the more zinc. This shows the deposition of zinc within feather microstructures depends on the presence, distribution and density of melanosomes.
Melanosomes are organelles of melanin pigment granules that give tissues various colours. Zinc is one of a handful of elements that are essential in processing intermediate products that lead to melanin pigment synthesis in birds. Melanin produces deep auburn-like reds, browns and blacks, rather than the bright colours some birds display.
“Because of the presence of these metals in the feather, the bird is able to form melanin pigment molecules that contribute to these colours, which is very important for mating purposes,” says Akhter.
Technique reduces sample contamination
The researchers are particularly excited by the level of resolution possible using the synchrotron technique. “It’s powerful enough to detect lower concentrations of metals in natural environments. And we can see exactly where the zinc is, down to the barbule,” says Akhter.
And unlike traditional techniques that require the sample to be pulverized to see the quantity of a metal, the synchrotron technique leaves the feather intact. It also reduces the risk of sample contamination that comes from pulverizing feathers.
Akhter first started working on the project with Graham Fairhurst, a University of Saskatchewan avian ecophysiologist, when they were both working as postdocs supervised by Catherine Soos. Soos is a wildlife health specialist at Environment and Climate Change Canada, and adjunct professor at the University of Saskatchewan who researches the impacts of large-scale environmental changes on wildlife health.
Fairhurst said they chose to look at zinc because it’s nutritionally important, and it has a connection to melanin. Zinc can be found in the aquatic creatures and plants that ducks eat. It’s also an emergent pollutant from smelting and mining operations, and could be a health concern at high levels.
While the team doesn’t know what its findings might mean for a given metal’s impact on mating and other feather-based communication, Akhter says she would like to see more research into this.
“We’re going to see more pollution, so we need to pay attention to how it will affect birds mating and other behaviour,” she says.
Akhter and her fellow researchers are now using the same technique to examine other contaminants in birds. They are in the midst of a study measuring levels and distribution of multiple toxic metals – including cadmium and selenium – in the feathers of tree swallow nestlings in the oil sands region of Alberta. The goal is to compare them to tree swallow nestlings outside the oil sands.
Using synchrotron techniques to investigate feather structures at a scale of a thousandth of a millimetre, the team hopes to “learn more about potential physiological mechanisms associated with trace element deposition within feather microstructures,” says Soos.