EPOW - Ecology Picture of the Week

Explanation:   Can you find two striped wrens in this photo?  They are Band-backed Wrens.  Like tiny striped tigers hiding in a thicket, these birds nearly vanish among the stripes and shadows of this large cactus, here in northwestern Ecuador.

Band-backed Wrens occur in the humid forests and woodlands of South America west of the Andes Mountains along the Pacific slope down to sea level.  Band-backed Wrens often nest at the base of palm fronds and lianas where their cryptic coloration helps hide them well.  

Interestingly, in Ecuador, just to the south they are replaced by the similarly-appearing Fasciated Wren (Campylorhynchus fasciatus), which is nearly a sibling species (looks nearly identical) in parapatry (their ranges adjoin but do not overlap).  Band-backed Wrens, however, select for more humid and closed forests and occur in pairs and small groups creeping in dense foliage, whereas Fasciated Wrens occur in more arid and open environments and occur in larger groups of 6-8 birds and often forage on the open ground.  

Band-backed Wrens tend to be more brown whereas Fasciated Wrens, in the more arid habitats, are grayer overall.  This may be another example of Gloger's Rule in ecology, which we explored previously with Brown Falcons of Australia.  This rule states that sometimes species or subspecies that occur in more humid or warmer environments tend to be more darkly colored than those found in more arid or cooler environments.  

Vocalizations of Fasciated Wrens are similar to those of Band-backed Wrens (both give a loud scratchy song and harsh "chak" calls).  This also suggests perhaps a recent common ancestry of both species that somehow underwent parapatric speciation along an environmental gradient of humidity-aridity.  

Information:  Ridgely, R. S., and P. J. Greenfield. 2001. The birds of Ecuador. Volume II field guide. Cornell University Press, Ithaca, New York. 740 pp. (pp. 588-589)