Age-Advertisement and the Evolution of the Peacock's Train

The present article discusses the Age-Advertisement Theory in relation to the evolution of a peacock's train of feathers. In the journal article's introduction, Manning (1989) puts forth four main explanations that previous research have used to explain the evolution of such elaborate tails. The first explanation states that the sons of "choosy" females in a population with posses the "preferred type of elaborate tails and will in turn be preferred by the daughters of other "choosy" females in the population. The second explanation puts forth the Handicap principle in order to to try to illustrate the robustness and quality of a peacock's genes despite its large and inconvenient train of feathers. The third principle looks at the condition of the peacock's train of feathers that is dependent on parasite load--a large train of feathers therefore shows a low parasite load. Finally, the article introduces the Age-Advertisement Theory which states that a large train of feathers is indicative of age and overall genetic quality. In conclusion, the article was able to find a strong correlation between the age of a male peafowl and the actual number of feathers in the peacock's train (specifically the number of ocellus feathers). It was indeed concluded that this is an honest advertisement of age in peacocks.

Journal article:
          Manning J. T. (1989). Age-advertisement and the evolution of the peacock's train. Journal of Evolutionary Biology, 2, 379-384.

The Peacock's Complaint

I recently stumbled upon this cheesy, yet insightful, cartoon from Aesops Tales that does in fact seem to sum up a lot of what describes a peacock. In this cartoon the peacock complains that it has an unfortunately ugly voice in comparison to "insignificant" birds like the nightingail. The peacock then learns that each animal and more specifically, each bird, has something special about it that makes it unique. Although the peacock's voice can be annoying and a nuisance to some, it has a majestic train of feathers that no other bird can say they have. This brings me back to the first post I posted on this blog where I blogged on a video that discussed the presence of peacock's in Palos Verdes, CA where they were seen as either a giant nuisance or something beautiful to add the to the town's landscape. No matter how "annoying"people may say peacock's are, they are undeniably beautiful birds that have mesmerized many. 

The Peacock Problem: Does It Affect Predation?

Resent research has looked at the "peacock problem" or Costly Signaling Theory where the classic example is a peacock's long and eye-catching train of feathers. In this theory, the size, color and overall extravagance of the peacock's train of feathers is said to strongly indicate a male peafowl's overall gene quality. A peacock with a long train of feathers is more likely to be strong and resilient when it has such a large train of feathers because it can potentially hinder the peacock in catching the attention of potential predators. It also indicates that the peacock has used a large amount of metabolic-energy and resources in order to take care of such a large tail even though it is useless in every aspect of the peacock's life (with the exception of courtship and attracting mates of course). As Loyau et al. (2005) put it, "a high-quality tail is an honest signal of good genes because only those peacocks who are in good health and who have the traits required to survive and acquire abundant supplies of food can afford to waste their energy and resources to grow and maintain this showy and nutritionally costly ornament." But Gerhand Adam has questioned this "classic" example of the costly signaling theory and has stated that there is no empirical or sufficient evidence that is able to draw a correlation between the size of a peacock's train of feathers and its rate of mortality. A higher vulnerability to predation must be demonstrated in those peacocks with larger and more colorful tails. Furthermore, Adam goes onto say that the "peacock problem" in relation to a peacock's train of feathers is often based on assumptions and that there is not sufficient evidence that a peacock's train is indicative of a peacock's gene quality or overall ability to survive. Thus more research must be done in order to draw conclusive conclusions on the relationship between a peacock's tail and its ultimate survival value. 


Sources: Science 2.0: Explore the Revolution

Congo Peafowl

The Congo peacock, Africa's only only pheasant species, looks significantly different from the typical Indian peacock we often envision in our mind. While the Indian peacock has a long train of feathers that it uses to attract the opposite sex in mate selection, the Congo peacock has short yet equally as vibrant feathers on its back. The reason why the Congo peacock does not have the same beautifully majestic tail that the other two species of peafowl have is because it resides in the deep forest of central Africa where having a long train of feathers would be impractical and difficult to maneuver around with. Due to the fact that the male peacocks do not their typical train of feathers to distinguish themselves from their fellow peahens, one can tell a Congo peacock from a Congo peahen by its color. While Congo peahens are a mixture of green and a dull brown in order to more easily blend into their environment, the male peacocks are vivacious blue and have a crest. Furthermore, this species of peafowl is relatively shy compared to its ancestors and therefore might closely resemble early peafowl ancestors. Unfortunately, this particular species of peacock is endangered but the Species Survival Program has attempted to take control of the situation in order to deter the species declining population. 

Sources: San Diego Zoo

Peacock Eyespots

When one thinks of a peacock, the first thing that usually comes to mind is their eye-spotted colorful train of feathers. A single peacock feather has an "eyespot" that seems to serve a controversial function for the bird. Some research has shown that female peahens seemed to be particularly attracted to, and therefore more prone to chose peacocks, with a large number of eyespots on their train of feathers. But more recent research has shown otherwise. For instance Dakin, at the Queen's University in Canada, recently showed evidence that the number of eyespots a peacock had did not actually improve its chances of impressing a peahen. Furthermore, others have hypothesized that perhaps it isn't the number of eyespots a peacock has that illustrates a peacock's success in mating, but actually the size and elaboration of the peacock's train of feathers. In running a number of experiments where Dakin and Montgomerie manipulated the number of eyespots each peacock had by snipping them off, Dakin found through a series of experiments that most peacocks that were "eyespot-challenged" mated significantly less than those who were not. Ultimately, research has not shown to be conclusive in what function feather eyespots serve for peacocks and needs to be further researched in order to fully understand the mechanisms that underlie peacock mate selection.

Sources: Discovery News