Features
Birds of a Feather Dine Together
Award-winning biologist discovers that songbird's feather colour may be determined by what it eats
BY RACHELLE COOPER
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| Prof. Ryan Norris's research earned him a young investigator award from the American Ornithologists' Union. Photo by Martin Schwalbe |
For a songbird called the American redstart, its feather colour may not be determined by its physical condition, as many scientists believed, but by the food it eats while it grows new feathers, Prof. Ryan Norris, Integrative Biology, has found.
By collecting single feathers from more than 200 different American redstart songbirds, Norris and his colleagues at Queen's University and the Smithsonian Institution were able to determine where the birds had moulted, what condition the birds were in and the brightness of their feathers. These three pieces of information allowed Norris to test competing hypotheses of whether feather colour is dependent on condition or diet. His research was recently published in Biology Letters.
“What we found was, the condition wasn't related to the feather colour,” he says. “We found evidence that the amount or type of carotenoids (antioxidant fat-soluble molecules found in plants and animals) a bird gets from the food it eats offers the best explanation for variation in feather colour.”
This information provides important clues as to how species can develop, says Norris. “If the males from two populations look different because they eat different insects, then female birds may choose to mate only with males from their population, and over a longer time scale, it could actually lead to differentiation between populations.”
He sampled American redstart songbirds in the Caribbean and Central America. The migrating birds spend their summers anywhere from British Columbia to Newfoundland and south to Louisiana. After breeding in the north, they replace their feathers and fly south for the winter.
When feathers are being grown, they carry unique hydrogen isotope values, depending on the bird's latitude at the time. These values arise from variations in precipitation and are then transferred all the way up the food chain from plants to insects to animals. Looking at the ratio of heavy and light hydrogen isotopes in the feathers allowed Norris to estimate where the birds moulted in North America.
“The isotope value of where the bird grew its feathers doesn't change because, once the feather's grown, the chemical composition in that feather is fixed,” he says.
It's a lot easier to track where a bird has been by analyzing isotopes than by putting a band on it and trying to find it again, he adds.
Interestingly, the researchers found a relationship between the colour or brightness of the feather and where the bird had spent its summer in North America.
“Males that moulted at southerly latitudes were more likely to grow yellowish feathers, whereas males that moulted further north tended to have more orange-red feathers,” says Norris. “Redstarts moulting at lower latitudes may consume insects with lower carotenoid concentrations.”
The faint growth bars that appear on each feather also allowed Norris to estimate what condition the bird was in when it grew its feathers. “Every 24 hours, a bird lays down a light and a dark growth bar as it regrows its feathers,” he says. The width of those bars is related to how fast the feathers grew. If they grew quickly, the growth bars will be thin, which means the bird is in good physical condition. If the bars are wide, the bird grew them slowly because it was in poor condition.
Unlike the link between isotope values and feather colour, Norris found no relationship between the birds' condition and feather colour.
“The theory was that, if you're a bird in poor health, you have to use carotenoids for other things and therefore you can't use them to colour your feathers,” he says.
If that hypothesis were true, feather colour could be an “honest signal” for females to choose only mates in good condition. “Instead, in some birds, it looks like feather colour might not be an ‘honest signal.' It just tells you where the bird grew its feathers.”
Even though joining U of G this summer marks Norris's first position as an assistant professor, he's already well known within the ornithological community. In October, he was presented with the American Ornithologists' Union's (AOU) Ned K. Johnson Young Investigator Award at its annual meeting in Mexico. The award recognizes outstanding and promising work by AOU members who have received their doctorate within five years.
“It's a tremendous honour to be recognized for my research contributions at this early stage of my career, especially considering that the AOU is the largest and oldest ornithological organization in the world,” he says. “In honour of a great Canadian ornithologist who recently passed away,I will be donating half of my monetary award to the Jamie Smith Fund at the University of British Columbia to help establish a scholarship for students to attend field courses.”
Although his more recent research has focused on birds, Norris says he doesn't have an attachment to birds in particular. “What really fascinates me is migration more than anything else.”
That fascination began when Norris was an undergraduate at the University of Waterloo, where he studied a migratory grey wolf population in Algonquin Park. He went on to complete a master's degree at York University studying the effects of forest fragmentation on the mating system of hooded warblers. He started researching the American redstart while completing a PhD at Queen's University.
After finishing his dissertation, Norris was awarded both an Izaak Walton Killam Post-doctoral Fellowship and a Natural Sciences and Engineering Research Council fellowship at the University of British Columbia.
While at UBC, Norris began looking at how fisheries and climate change have influenced populations of marbled murrelets, small threatened seabirds that nest in old-growth trees. By reconstructing the murrelet's diet over the last 120 years, he is uncovering the effect of marine conditions on the bird.
“Before 1900, this bird fed almost exclusively on fish, but now, a significant amount of its diet includes marine invertebrates,” he says. “The results of this study suggest that only conserving nesting habitats of this species might not be enough. Recovery efforts need to focus on conditions at sea when they're not breeding.”
Norris has already integrated multiple and diverse fields in his research, including ecology, behaviour, population modelling and biogeochemistry, and says he's excited about expanding his multidis- ciplinary approach here at U of G.
When he's not doing field research, Norris, who lives in Guelph with his wife, Amy, spends most of his spare time fly fishing, hiking, canoeing and birding.