Most people hear birds singing on a regular basis especially during the spring. In the past when I heard various bird calls I didn't think to deeply about them. I never thought of the songs as a means of communication. I also never considered the possibility that different bird calls were selected against for the most efficient means of communication. I looked at them from a human perspective rather than a birds.
After reading a paper written by Gail L. Patricelli, Marc I. Dantzker and Jack W. Bradbury I gained some insight into the differences in vocalizations birds make and the selective pressures that guide these differences. The authors of the paper set up an experiment to test the directionality of different calls that male red-winged black birds make. They made man made perches in the birds natural habitats. They surrounded the perches with three cameras pointed toward the center and eight different microphones in a circle around the perch. They then recorded different types of the red- winged black birds calls. The experimenters used the recordings they took to measure the directionality of the calls. Calls with higher frequencies are more focused in one direction while lower frequency calls are less focused.
They found that different calls have different levels of directionality. Calls used to alert fellow birds about danger were the least directional. While calls used during courtship were the most directional. The experimenters believe that the calls are selected against for the most effective communication for the specific scenario. The alert calls are the least directional because the bird wants to warn the most other birds it can in the area. The courtship calls are the most directional because the bird doesn't want other birds eaves dropping and stealing it's potential mate. The experiment suggests that the directionality of the calls are related to the message the bird wants to send.
Posted by: Charles Carville 10/19/10
It makes a lot of sense evolutionarily that certain calls are more directional and others have a broader range depending on what the signal is. However, I don't quite understand the setup of the experiment. Were the researchers recording wild birds that landed on the perch? Did they do anything to coax them to the perch?
ReplyDelete-Alex Sprague
Its fascinating that birds have the ability to recognize call directionality and that they are able to eavesdrop! Do you know anything about the call directionality for territorial calls?
ReplyDeletePosted by: Sara Weaver
If calls are selected for efficient and effective communication, what other song traits could you see being selected for or against? I can think of magnitude (you might not want to let the neighbors know you're courting somebody, and a quiet alarm call helps no one) but what do you think of originality? While it might suggest intelligence, I wonder if it is selected against because it makes it difficult to register it as a species song, or a courtship song, or whatever it is serving as.
ReplyDelete-Alice Trei
The experimenters set up the perches in the birds territory. And waited for the wild birds to land on them. As for the originality of songs being selected against I couldn't find anything on the internet. In my opinion the originality of songs would be a good thing as long as the songs were still recognizable as the same species.
ReplyDelete-Charles Carville