January 9, 2015
How do sparrows use crown color to communicate? Thanks to Allison Huysman for this guest student blog post. We are glad to learn that those white-stripes are important after all!
Birds and other animals communicate via signals including calls, behaviors, and physical characteristics. Some of these signals can be deceitful, while others are reliable and honest. Experiments can help determine if a signal is honest, meaning it will accurately reflect the health of the sender and other individuals can reliably use this information. A recent study by Zacahary M. Laubach and colleagues gave a closer look at the reliability of white crown plumage as a signal on White-crowned Sparrows. The bright colors we see on the birds in our own backyards may mean more than we think.
White-crowned Sparrows are small passerine birds that are mostly brown and gray except for a pronounced black and white striped pattern on the top of the head. Studies have suggested that the crown pattern may influence interactions between individuals. Males depend on acquiring a territory to attract a mate, so anything that influences communication and competition can have an important impact on survival. Laubach and colleagues set out to determine if white crowns really are brighter on stronger males and if other males use this information.
Using a decoy experiment, they found that territory-holding males respond more aggressively to decoys with more white on their crowns. They then changed the amount of white on live birds and found that “bluffers,” or those birds with artificially enhanced crowns, had higher levels of a stress hormone called corticosterone. Not only were males discriminating between different crown plumage, but it was also physiologically stressful for a male to have more white than his status would naturally allow. This means that only males who are really superior and stronger can afford to grow these whiter crowns.
Experiments like these show that not only are certain signals an indicator of an individual’s health, but it can also change the ways that individuals interact with one another! A status badge like a white crown can communicate valuable information like fighting ability and resource-holding potential. This is important for species like White-crowned Sparrows, which need to establish territories in order to have breeding success. This study reflects the ways in which many birds use badges as signals to communicate with each other while competing for valuable resources.
Read more about white-crowned sparrows here on the Cornell All About Birds page.
Laubach, Z.M., D.T. Blumstein, L.M. Romero, G. Sampson , and J. Foufopoulos. 2013. Are white-crowned sparrow badges reliable signals? Behav Ecol Sociobiol 67:481-492.