Energy Cost of Heavy Peacock Plumages: Is it worth it?

Summary: Peacocks were tested to see if their feathers present a disadvantage in respect to their ability to fly even though it is an obvious sexual advantage in attracting peafowls. Tests were conducted on this question and results show that in fact, their heavy plumages do not present much of a disadvantage to peacock flight.

Peacocks are one of the most famous examples used to describe the definition of sexual selection. Their grand and colorful tail feathers attract peafowls who use these tails as an indicator for a mate with good health. However, these colorful feathers that drag behind the peacock are heavy and for a long time, researchers have hypothesized that these birds have a physical disadvantage when flying as their plumages take up the energy that could potentially be used to fly longer or escape from predators faster.

However, recent research on this topic by Graham N. Askew with assistance from professors at Loughborough University, tested to see if this hypothesis was valid. Two groups of peacocks from the UK population of captive bred-birds were observed using high speed video cameras. One group was in its natural state with their full plumages while the other group was made of peacocks whose plumages were removed. Data on the energy expenditure and aerodynamics of these two groups revealed that there wasn’t much of a difference in their ability to fly. The total energy that is required for take-off was slightly higher in those with the plumage but not significant enough to support the old hypothesis. The power required to generate the same velocity was not significantly different between the two groups either.

To ensure that flight muscles weren’t exerting more energy (in the group with the plumage) to allow the bird to fly just as fast as it would without the train of feathers, researchers also checked the mechanical power output of the flight muscles but there was no evidence for this hypothesis. Based on the data and the observations of how these two groups take-off for flight, it is understood that the drag force on the plumage is dependent on the flight velocity and the angle at which the plumage is when the bird takes off. The drag force (the force of the plumage feathers weighing down the bird) was calculated to be only 0.12-0.15 Newtons. This force increases the parasite power (the power required to overcome the force of drag) which is only 0.1% of the total power required for flight. This shows how insignificant the slight increase in the power needed to take off, is, in birds with the plumage. 

Despite these studies, it cannot be confirmed that the sexual advantage that peacocks have with their plumages is not a disadvantage. In respect to flight and escaping predators, there is now evidence to support the claim that heavy plumages are not a drag, however, in other respects these ornaments may be a disadvantage to these birds.

Citation:

Askew, Graham N. 2014. The elaborate plumage in peacocks is not such a drag. The Journal of Experimental Biology 217: 3237-3241