Bird Song
If you've ever tried bird watching before you know that you often hear a bird before you see it. Over half of all bird species are in the order Passeriformes, more commonly known as passerines, and even more commonly known as songbirds.
If you hear a bird singing, it is most likely a male. Males sing both to attract mates and to defend their territories. Song is what is called a sexually-selected trait. Unlike natural selection where traits evolve to help a species survive, sexually-selected traits help individuals (usually the males) acquire mates. The classic example is the peacock's tail. It serves no function in keeping the male alive, but the ladies love it.
Photo by John Benson on Flickr
The same with bird song. Female birds are able to analyze a male's song to determine if he is a good candidate for a mate. If a bird is infected with a parasite and his song is affected, a female may choose not to pair up with him.
Song is a complicated trait and can be altered by many different factors. It can be difficult to isolate the effects of any one influence. To narrow the focus, I will be looking into performance-related aspects of song. These relate to energy demands and include things like:
- song rate - how fast is the bird singing?
- song amplitude - how loud is the bird singing?
- song consistency - how consistent is the bird from song to song?
- etc.
In general, previous studies I've found have shown that performance-related aspects are negatively affected by parasites (slower song rate, lower amplitude, inconsistency between songs) and I predict that white-crowned sparrows infected with avian malaria will show similar patterns.
The Cornell Lab of Ornithology is one of the best resources for all things "bird." Here's a great page from the Lab with different clips of some common North American birds: Songs & Calls
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