In the Biblical story of the Tower of Babel, God, angry with the early denizens of Sennar for trying to build a tower to the heavens, created a confusion of languages that effectively disabled human communication. Today, human land-use patterns may be confusing bird communication to similar effect.
In many avian species, males use melody to attract females and to defend their territory. Like kids who grow up listening to the same radio stations, male birds from the same neighborhood will share a similar repertoire. When a male bird challenges another, the two face off like rappers (although they croon the same song in their show of aggression).
Yet, in some areas, birds may no longer share the vocabulary required to effectively call one another out. Songbird habitat is increasingly fragmented. Areas of urbanization—where habitat is lost—act as anthropogenic barriers that divide the landscape and reduce the size of contiguous habitat patches. Large roads and agricultural fields can also act as barriers to animal movement. As a result, song-sharing behavior changes.
Paola Laiolo, a postdoctoral researcher in applied biology at the Doñana Biological Station in Seville, Spain, says that such behavioral changes “could be a good predictor [of fragmentation] in bird species that show this behavioral pattern—that are extremely habitat selective and sedentary.”
In a paper published in the December issue of the Journal of Applied Ecology, Laiolo and José Tella, also a postdoc at Doñana, examined the songs of Dupont’s larks living in fragmented habitats. Dupont’s larks are specialized sparrows that live exclusively in the flat, semi-desert steppelands of Spain and northern Africa.
The researchers found that in fragmented environments, neighboring larks—those living within the same habitat patch—share a greater amount of their repertoire than is shared between neighboring larks that live in pristine environments. This increase in common language is probably due to increased competition in interrupted areas. In smaller habitats, there is often an increased strain on resources; a lark that knows many of its neighbors’ songs has the weapons necessary to challenge them.
The paper’s authors suggest that habitat barriers prevent the dissemination of song types over distance. Imagine if there was no MTV and young people didn’t know the shared slang of the moment. The language required for aggressive men to levy insults at one another would be different from community to community. A scathing slur in one neighborhood might mean nothing in another. In a contiguous environment, birds that live some distance from one another still interact and learn songs from one another; there is a shared culture. In a fragmented environment, there is less exchange between birds living far apart.
Because song sharing is a cultural rather than genetic trait, it changes quickly in response to environmental stimulus. The study’s authors suggest that changes in song-sharing behavior could be early indicators of ecological disturbance.
Yet, Laiolo hesitates to suggest that changes in songbird communication could act as an early warning system.
“Many species actually use a mosaic of habitats,” she said. “In these cases it could be difficult to establish which habitat is good and which is not, and how deep is the barrier [between habitat fragments].”
Sandra Vehrencamp, an ornithologist from Cornell University’s Bioacoustic Research Program, agrees that a relationship between intensity of song-sharing behavior and habitat fragmentation is possible.
“If habitat fragmentation decreases dispersal distances and/or increases local densities of territorial birds,” she said via e-mail, it would validate the relationship.
Vehrencamp is also cautious about the application of this relationship to predict the intensity of habitat fragmentation.
“Whether this is a general result for song-learning birds,” she said, “depends on the details of the duration of the critical song-learning window and on the typical dispersal distances of each species, and whether they do or do not cross suboptimal habitat between patch fragments.”
Originally published December 8, 2005
