Secrets of Birds' Sexual Signals RevealedScienceDaily (Jan. 19, 2011http://www.sciencedaily.com/releases/20 ... 101153.htm) — Patterned feathers, previously thought to be used only for camouflage in birds, can play an important role in attracting a mate and fending off rivals, a University of Melbourne study reveals.
Thanh-Lan Gluckman, co-author of the paper and Masters of Philosophy student from the Department of Zoology at the University of Melbourne, said this finding brought a new perspective to research in animal communication and evolution.
"The implication of this study is that feathers don't need to be bright and showy to be used in sexual signalling and hence this changes our understanding of animal communication," she said.
Hundreds of bird species such as Zebra Finches and Cuckoos have "barred" patterns on their feathers, which are made up of horizontal bars alternating dark and light pigmentation side by side.
"Since Darwin wrote of visual communication in birds, we have known that bright coloured feathers play a role in sexual signalling, for example to attract females. But the role of barred patterns as a communication signal has largely been overlooked," Gluckman said.
The study was a large-scale comparison of plumage of around 8900 bird species worldwide (90% of all bird species), and was conducted with former University of Melbourne lecturer Dr. Gonçalo Cardoso, now at the Research Centre in Biodiversity and Genetic Resources (CIBIO), Portugal.
The researchers compared barred plumage and other patterns on the body of males, females, and juvenile birds, to assess what they might be used for.
While the researchers found evidence that barred plumage is predominantly used as camouflage, they also found that barred plumage was much more likely to appear only in males, or only at sexual maturity, compared to other patterns.
"Furthermore, we found these differences on the front of the birds, which is an important area for communication during face-to-face interactions, not on their back, which is more useful for camouflage when running away or hiding from predators," she said.
"This is an exciting finding showing an elegant evolutionary solution to the needs of birds to camouflage as well as to signal to a potential mate or rival."
The study has been published in the Journal of Evolutionary Biology.
Plumage-Color Traits More Extreme Over TimeScienceDaily (May 17, 2010http://www.sciencedaily.com/releases/20 ... 111521.htm) — Ever since Darwin, researchers have tried to explain the enormous diversity of plumage colour traits in birds. Now researchers at the University of Gothenburg, Sweden, are adding something new to this particular field of research, which is so rich in tradition, by demonstrating how a bird can become red instead of yellow.
Sixteen years ago, Malte Andersson, a professor at the University of Gothenburg, published the book Sexual Selection, which analysed how animals use behavioural signals, colours and other ornamentation to compete for a mate. Based on, among other things, a famous experiment involving a long-tailed widowbird published in Nature in 1982, and is now a standard zoological work that has been cited in around 5,000 scientific articles and innumerable textbooks.
Next generation
The third generation of ecological researchers at the Department of Zoology at the University of Gothenburg are now publishing their findings in this field. Together with colleagues and project leader Staffan Andersson, postgraduate student Maria Prager has studied how sexual signals in widowbirds and bishops (Euplectes spp.) are produced and change during the evolutionary process.
Enormous range
In the past, the function of signals was much disputed but is now well-known: it has to do with attracting a mate for reproduction and deterring rivals. But why the animal kingdom displays such an enormous range of signals and traits has still not been explained. The African widowbirds and bishops are an excellent illustration of this phenomenon: despite being closely related and using classic avian signals -- elongated tail feathers and bright colours -- there is a fascinating amount of variation in the traits of these species.
More extreme
Maria Prager's thesis follows on from field studies that indicate a general pattern amongst these and many other birds: females prefer males with the longest tail feathers, while males with larger and redder colour signals are able to occupy larger breeding territories. Maria Prager's hypothesis was that the signals of widowbirds and bishops thus have become ever more extreme during evolution.
DNA-studies
A lack of fossil feathers means she has studied modern DNA in order to reconstruct the evolution of colours and plumage in the genealogical trees of these species. The results show that today's species of widowbirds and bishops are descended from birds with short tails and yellow colour signals.
Genetic imitations
The current red colour has evolved through several means: the birds store large amounts of yellow dietary pigments in their feathers, which produce a red hue, or they convert some of the dietary yellow pigment to red with the aid of an enzyme. As yellow widowbirds and bishops seem to lack this enzyme, colour diversification may be due in part to physiological or genetic limitations in some species.
Evolution of colour
Malte Andersson was a pioneer in work to test and further develop Darwin's concept that the reproductive success of males often depends on eye-catching ornamentation. Maria Prager's research now clarifies three new aspects of colour signalling: the pigment mechanisms behind colours, the development of colours in individuals, and the evolution of colour signals over time.
"Our combined research provides a unique and complete picture of colour evolution in birds, and there are few other animals for which we now have so much knowledge of the various aspects of these signals."
