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Bird plumage more than decoration

By Kelly Foss

Researchers at Memorial University have discovered the elaborate feather ornaments of some birds do more than just make a pretty face. Conventional theory was that long feather appendages primarily aid in the attraction of a mate. However, Sampath Seneviratne, a PhD candidate in the Department of Biology, has discovered that similar to a cat’s whiskers, there is a link between this decorative plumage and a bird’s ability to navigate in dark and cluttered environments.

Over two summers, Mr. Seneviratne and his supervisor, Dr. Ian Jones, have tested that theory on the auklet. This nocturnal family of birds is made up of five species which display a varying amount of facial ornamentation including bizarre facial plumes derived from contour feathers and filoplumes, and nests in tiny rock crevices on the volcanic Aleutian and Kuril Islands on the edge of the North Pacific.

In order to determine whether or not there was a correlation, the pair caught a large number of birds in their Alaskan breeding colonies and carefully taped the forehead crest and superorbital plumes down. The birds were then exposed to a test chamber – a light-proof maze that simulated their natural breeding crevices.

Their resulting exploratory behaviour was recorded on an infrared digital camcorder. Each bird was tested three times in the chamber, in random order: once with the feathers taped down, once with the feathers free and once with the feathers free, but with tape attached to the bird’s head in the same position as in the first test. The latter “sham” test was used to determine if the tape alone would prove to be enough of a distraction to affect the behaviour of the birds.

The prediction was that if the whiskered auklets, the most decorated of the auklet family, used the feather ornaments as a sensory device to avoid obstacles, they would bump their heads against the barriers of the chamber more frequently once the feathers were temporarily “eliminated.”

“We found there was 275 per cent increase in head bumps when the crest was cancelled out and this showed that they primarily use this crest as an immediate clutter detection device, much like a blind man uses a cane,” said Mr. Seneviratne. “In addition, the longer crested birds had more difficulty navigating in the chamber in the absence of the crest than the shorter crested birds.”

They believe this is the first empirical evidence for a possibly widespread but overlooked mechanosensory function of elaborate feather ornaments in birds. Much of the research for this study was done in the summer of 2006. In 2007 Mr. Seneviratne returned to the same area to test his theory on other closely related species of auklets – the least and crested auklets. Of these, the least auklet has no crest at all, and for this experiment the pair gave the birds a faux crest by gluing feathers to it taken from the whiskered auklet.

“We wanted to see how they reacted,” said Mr. Seneviratne. “It was much like putting a collar on a cat. They didn’t freak out but the analysis showed they didn’t know how to use it. We determined they did not have any significant reductions in the number of head bumps using the artificial crest. So it proved the validity of our previous experiment.”

Mr. Seneviratne is now looking these trait expressions across all bird species to see if there is a correlation between habitat selection and these types of trait expressions in birds in general.