Birds do a variety of behaviors to keep warm, avoid predators, mate, and find food. In my observations, I watched the Black-bellied Whistling Duck, or Dendrocygna autumnalis. This bird is a type of waterfowl native to parts of Mexico and South America, although they can be seen in the southern United States during the summer (“Black-bellied Whistling-Duck”). The Black-bellied Whistling Duck is brown with a grey head and a black underbelly. Its feet and beak are pink. The Whistling Duck gets its name from the whistling noise it makes. I observed flock of these birds at around 4:30 pm on a rainy cold day in Herman Park. The temperature outside was about 40°F, and the rain was very light.
The flock of ducks I observed numbered about ten, and they were walking along the path by the large pond in Herman Park. The behavior I thought was interesting happened a few times during my time observing these ducks. First, a duck would get a little taller in stance, and hold its wings out to the side. Then it would flap its wings, put them down, and ruffle its feathers a little as its wings shifted back into place. I took the picture below while observing the initial states of this behavior. You can see the raised wings of the Whistling Duck right before it folds them in and ruffles its feathers.
Black-bellied whistling ducks. Photo by Clare Randolph.
This behavior could have a lot of explanations. From my observations, it looked as though the ducks were trying to keep warm by doing this behavior. The individual would do the behavior and then sit for a while and look as though it were huddling into itself. When I did further research, I found that many birds have been observed doing this behavior, and that it has been explained as a way to deal with the cold by trapping warm air inside the ruffled feathers (Desmond, 1956).
Carr and Lima, in an article from 2011, discuss how this behavior of fluffing feathers makes it harder for birds to take off or get away from predators quickly. It is stated in this paper that many warming behaviors in birds decrease the speed with which the bird can escape an attack (Carr, 2011). The Whistling Duck must have been unconsciously weighing the trade-offs of the cold weather and the risk of predation. In this specific situation, the birds must have been cold enough and felt safe enough that they were comfortable taking the slight risk of slowing their escape time down in order to keep warm. From my observations, the birds did not look very threatened where they were foraging, so they were probably more concerned with staying warm.
Alternate explanations for the behavior of the Whistling Ducks ruffling their feathers might be that the birds were doing a mating ritual, or that they could have been warning potential predators that they have seen the predators. If the ducks had been doing a mating ritual, then the behavior would have been directed towards other individuals, and would have potentially been followed by mating. However, when I observed these behaviors, the birds that were doing it were usually a little separated from the group, and did not direct their ruffling towards the group. Moreover, I saw no mating while I was observing the group of ducks. Also, it is unlikely that the birds were warning potential predators that they had been seen because if that were true the birds would probably have flown away from the potential predator. I believe that keeping warm is the most logical explanation for the behavior I observed because I was able to find other descriptions of very similar behaviors that have been explained as behaviors used by birds to keep warm. If I it were a warm day and I observed the same birds and did not see this behavior, I could more solidly conclude that this behavior is for keeping warm.
I would speculate that feather fluffing is an adaptive behavior because a lot of birds appear to possess this same mechanism of staying warm. The two studies I have cited which talk about this behavior discuss the behavior existing in Dark Eyed Juncos, a large variety of sparrows, and birds as an entire class. The observation that multiple species across a single class have this behavior indicates that the behavior is adaptive. The ancestral individual who possessed the genes for this behavior may have reproduced better than its counterparts because it was able to stay warmer during cold weather, and it is now such a successful behavior that it has become part of a lot of bird species. This is what Dawkins would describe as a successful gene, one that is able to make copies of itself in many different species (Dawkins, 1989). Without looking at the specific genes that elicit the feather ruffling behavior in Black-bellied Whistling birds, however, I cannot say for sure that it is the same genes that control feather ruffling in other birds.
Ultimately, I believe this behavior in Black-bellied Whistling Ducks is used to try to keep individuals warm. Whether this behavior is adaptive or not needs to be researched further before the adaptability of the trait can be stated conclusively. The behavior is likely to be adaptive though because it has been observed in many different species of birds.
References:
“Black-bellied Whistling-Duck” All About Birds. Cornell Lab of Ornithology, Retrieved 02 Feb. 2014. http://www.allaboutbirds.org/guide/black-bellied_whistling-duck/id
Carr, Jennie M., and Steven L. Lima. (2011) Heat-conserving Postures Hinder Escape: A Thermoregulation–predation Trade-off in Wintering Birds. Behavioral Ecology 23 (2): 434-41. doi: 10.1093/beheco/arr208
Dawkins, Richard. The Selfish Gene. 30th Anniversary Edition. Oxford: Oxford University Press, 2006.
Desmond, Morris. (1956) The Feather Postures of Birds and the Problem of the Origin of Social Signals. Behavior 9 (2/3): 75-113. http://www.jstor.org/stable/4532841
Tags: birds, predation, thermoregulation