Bird song is frequently studied as a way to learn about the evolution and honesty of signaling in the field of animal communication.
Male birds sing to achieve two main goals: to attract mates and defend their territories.
This signal has many different components that vary between species such as the bird’s repertoire size, song types, trill rates, and frequency bandwidths.
These characteristics have been studied to determine performance levels in individual birds to see what the male uses to convey a honest representation of his fitness.
Henrik Brumm, from the Max Planck Institute, recently did a study researching if the amplitude of a bird’s song (nightingales and zebra finches in particular) signaled the bird’s fitness by relaying information about the bird’s body size.
He assumed that, since song amplitude is related to the air pressure the bird can create in its air sacs by using their abdominal muscles, vocal amplitude should be an honest signal of body size (which would have a direct relationship with muscle size).
After studying both captive and wild nightingales and zebra finches, he determined that, in fact, vocal amplitude did not relate to the bird’s body size and thus would not serve as an honest signal.
What he did find though, was the fact that smaller and lighter males produced higher maximum amplitudes in their song, which indicates that this signal was more related to the male’s singing effort (Brumm 2009).
I found this study to be particularly interesting because many other articles stress the emphasis of studying song amplitude as a means of measuring fitness and the difficulty of measuring it accurately.
Goncalo Cardozo et al. discussed amplitude as “the best currency to infer performance,” but also emphasized that many signals in bird song can work together to give the whole picture of his fitness (2007).
So maybe song amplitude in the nightingales and zebra finches that Brumm studied had other mechanisms to relay their performance levels, instead of just relying on amplitude to get the message across.
Rather than limiting our focus to one characteristic of bird song, we should in the future study these features in conjunction with each other to gain a deeper insight to the honest signaling systems that male birds use.
Brumm H (2009) Song amplitude and body size in birds. Behav Ecol Sociobiol 63:1157-1165.
Cardoso GC, Atwell JW, Ketterson ED, and TD Price (2007) Inferring performance in the songs of dark-eyed juncos (Junco hyemalis). Behav Ecol 18: 1051-1057.
Links to the papers:
Brumm 2009;
Cardoso et al. 2007
Posted by Christine Rega (3)
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ReplyDeleteI was surprised by the study results! It seemed like a great question with an obvious yes answer of correlation to bird fitness and size with amplitude. Maybe it really is distinguishable when a bird puts effort and strength into his song. Its quite funny the way the world works out with the smallest and lightest birds producing the most amplitude.
ReplyDeleteI am particularly interested in the honor system among birds, i had trouble believing it upon my first reading of the book. How can these small birds, not even human uphold to such a code? Is it really more work to bluff your way through a song? I believe a bird can lie about its size, strength and gathering capabilities. It simply does not. So youre absolutely right about the next direction and pathway of any future experiments!
Commented by Amanda Lee
This article surprised me. It has been reiterated that bird have evolved honest signals because it is too energetically costly to have "fake" signals or false advertising. Now are these signals from these two birds a form of false advertising because the high amplitude of the song didn't correlate to the bird's size. Was the amplitude of the songs correlated with any specific characteristics of the birds-maybe the fitness of the bird overall? It would be interesting to find out more. Do you think it is possibly that these birds are bluffing their fitness?
ReplyDeleteAlso is it the higher the amplitude of the song, the more attractive to females and the more respect given by males? Is the non-relatedness of amplitude and body size true for all of the songs sang by these species?
Posted by Tiffany Mallet
Hi Tiffany,
ReplyDeleteIt really surprised me too! Maybe song amplitude really doesn't take that much energy to increase as we originally thought. I would love to see a study researching the physiology of raising the volume of song and how that impact's the birds body. Brumm did cite another paper of his that he worked on with Slater, saying that zebra finches could regulate their song amplitude depending on the distance between the male and the receiver. So maybe amplitude is just the mechanism of which the signal travels rather than the signal itself?
Maybe females also pay more attention to the song type that the male is singing, rather than how loud he is singing it. But I do remember reading somewhere that female birds on average do prefer louder songs- maybe that was unique for the studied species. Good question though!
Responded to by Christine Rega