Fascinating research out of Cornell that has some troubling implications given the pervasiveness of some pollutants in the environment.
Researcher Sara DeLeon, working on her Ph.D. at Cornell University, looked at blood samples of Song Sparrows and Black-capped Chickadees and discovered that presence of PCB (polychlorinated biphenyls) disrupts how these species sing their songs. The birds come in contact with the toxins when they ingest contaminated insects, and the study found that the chemicals appear to mimic hormones in the bird’s brains and interfere with the parts of the brain that affect song and song structure.
The species in question were excellent indicators of the effects of this type of pollution. Both Black-capped Chickadees and Song Sparrows feed primarily on insects while feeding nestlings, not only consuming the toxins themselves but passing them to their young. Both species are mostly non-migratory and common in the study area, a stretch of the Hudson River in upstate New York. Between 1947 and the late 70s – when PCBs were finally banned – General Electric manufacturing plants in the area dumped more than 1 million pounds of PCBs directly into the Hudson River. The Hudson River drainage contains high PCB levels even now, nearly 40 years later.
How did DeLeon determine the structural differences in the songs of these birds? At the Guardian, Grrlscientist explains:
Black-capped chickadees sing a “species identity signal” that consists of two notes; one high note (“fee”) and lower note (“bee”). Dominant high-quality male black-capped chickadees produce songs with consistent glissando and interval ratios (listen here) throughout their singing bouts. In contrast, male black-capped chickadees with higher levels of PCBs sang a song that varied in the glissando ratio of the higher “fee” note (listen here).
Computer analysis of specific characters of the male black-capped chickadee “species identity signal” songs revealed that individuals with higher levels of PCB exposure produced songs with more variable glissando ratios (data not show here, but can be viewed at this link).
Song sparrow songs also showed distinct effects (data not shown here,but can be viewed at this link).
Song sparrows sing long, complex songs with trills. The sonograms revealed that song sparrows with higher levels of PCBs had longer trills in their songs. (listen here; and compare to normal song sparrow song (listen here.) Longer trills in a song sparrow’s song indicates a higher quality male.
For more information on DeLeon and her extraordinary work, see the video below.