The Smithsonian Institution is more than just a museum.  According to their own information they consist of a total of 18 museum’s and galleries as well as the National Zoo.  One of the organizations associated with the National Zoo is the Migratory Bird Center founded in 1991 with a goal of “fostering greater understanding, appreciation, and protection of the  grand phenomenon of bird migration“.

In a recent posting (Smithsonian Scientists Discover That Urban Songbirds Adjust Their Melodies to Adapt to Various Elements of City Life), Sarah Bloom Leeds describes the results of some research carried out by scientists at the Migratory Bird Center on how songbirds adapt their songs and calls in a noisy urban environment.

Birds use sound to communicate and their survival often depends on it.  Their songs, usually only given by the males during the breeding season, are used to find a mate and to define and defend territory.  Calls allow a bird to communicate with other birds, usually of the same species.  The alarm call, for instance, is an important way in which a bird seeing an approaching predator or other threat can quickly let all of their friends know.

In an urban environment, any person with a good sense of hearing knows how hard it can be to communicate over when noise levels are high.  We adapt by changing our voice – usually just raising the volume.  Birds, perhaps not surprisingly, have also learned to adapt their sounds to the noisy environment as well since their survival may depend on it.  The level of adaptation is, species dependent.

The article goes on to describe how some birds will raise the pitch of their songs where there is a significant (low-frequency) background noise level.  On the other hand they will lower their song frequency when reflections off of hard surfaces (e.g. buildings) distorts the sound, an effect more serious with higher frequency sound.  Apparently when both effects are present, many birds can have a much harder time adapting.

It’s a fascinating article on bird behaviour and adaptation.  The best part of Sarah’s post, however, are two sound recording links for a Carolina Wren from both an urban and a rural site.  You can clearly hear that the bird singing in the urban setting has a much smaller dynamic range: the lowest urban frequency is about 700 Hz higher than the lowest rural frequency while the highest urban frequency is about 1600 Hz lower than the highest rural frequency.

For those wanting to know more, there is a link to the original research published in 2011 that can be downloaded for free in either HTML or PDF format.