What aspect of a male’s song is important to a female songbird? | @GrrlScientist
Female songbirds choose mates based on their songs, and this study provides some insights into what aspects of song they use to identify a “quality” male
When a female chooses a mate, she is looking for a male who possesses a set of characters that makes him attractive. In songbirds, one of the primary characters that females use to choose a mate is the quality of his song. But many songbirds learn their songs from older males, which points to the familiar and longstanding “nature versus nurture” debate: does quality result from growing up in a good environment or it is based solely upon having good genes? And hand-in-hand with that argument comes another question: what aspect of a male’s song is important to a female songbird?
Just what do females want?
Like a male peacock’s huge, colorful tail (or like an expensive red sportscar), ornaments that reflect a male’s quality are necessarily costly to the male in ways that test his survival (or credit rating), thereby creating an honest signal that reflects his overall quality as a mate (ref). Males who overcome this “handicap” long enough to breed are reliably of higher quality than are males who lack these expensive ornaments — or who do not survive long enough to breed.
But when it comes to mate choice, what, exactly, is “quality”?
“‘Quality’ is determined by genetic and environmental factors”, write the authors in their paper, which was published today in the Proceedings of the Royal Society B.
But how genetics and environment influence each other are poorly known.
“[S]urprisingly there is very limited evidence if, and how, genetic aspects of male quality are reflected in song”, write the authors.
The research team, based at the University of Antwerp, designed an elegant little study that examines how genes and environment influence birdsong. They did this by altering the genetic variability of a domesticated songbird, the canary, by comparing outbred canaries to inbred canaries resulting from brother-sister pairings.
Domestic canaries are an ideal animal for these studies because song in canaries is linked to genetics — some breeds of domesticated canaries are better singers than others — and to environment — fledgling canaries learn their songs from older males during a specific time period in their lives.
Inbreeding is reflected in song phonetics
To do this work, the researchers studied 19 pairs of domestic male canaries that they raised to adulthood. All of the study males were either first or second-hatched (because hatch order affects size). Half were outbred whilst the other half were inbred, and individuals were assigned to an inbred-outbred pair according to similar weights at fledging.
Because canaries learn their songs, all inbred-outbred pairs were placed with an older unrelated, outbred male canary who acted as their song tutor for the duration of the youngsters’ song development phase (which lasts from 40 to 240 days after hatching in canaries).
This video provides an example of what one breed of domestic canary (a Spanish Timbrado, in this case) sounds like when it sings:
After the youngsters reached adulthood, the researchers recorded songs produced by each individual for three consecutive hours. Four song parameters were analyzed and compared between individuals for each inbred-outbred pair of canaries:
- song length, including pauses
- song complexity, including the number of unique syllables in each song bout
- song learning, particularly the similarity of the song to the tutor’s song, and how much of it was learned from the tutor
- song phonetics, particularly how many different sounds were used to create each song syllable
Comparisons for each inbred-outbred pair of male canaries showed no differences for the first three of the four analyzed song parameters, indicating that inbreeding status had no role in the birds’ ability to learn and produce their tutor’s songs. However, the analysis revealed that inbreeding status strongly influenced the canaries’ song phonetics — the amplitude (in dB), mean frequency (in kHz), entropy (uniformity and width of the power spectrum so that pure tones had large negative values) and frequency modulation (FM) of their songs (Figure 1):
As you can see in the above data analyses, inbred canaries sang “out of tune”: individual notes were less pure than those sung by outbred birds, and were produced at different frequencies — and the longer the syllable, the more “out of tune” it was.
But these were a series of data analyses — what happens in real life, when a female canary is paired with either an inbred and an outbred male?
Females paired with inbred males produced fewer and smaller eggs
Basically, female canaries didn’t much like inbred male canaries.
The researchers found that outbred female canaries who were paired with an inbred male produced significantly lighter clutches when compared to outbred females who were paired with an outbred male. Not only were individual eggs lighter, but females produced fewer eggs when compared to outbred females paired with outbred males — and these effects was independent of the weights of both the male and the female parents.
In essence, this study suggests that the inbreeding status of a male songbird is reflected in his song phonetics, which females are capable of hearing — even when the males grow up in the same environment. Further, females use song phonetics to choose a mate with “good genes” (i.e.; greater heterozygosity/less inbreeding).
Personally, I think this study presents a powerful argument in support of the value of birdsong for identifying species — particularly for identifying new or cryptic species.
Raïssa A. de Boer, Marcel Eens and Wendt Müler (2016). ‘Out of tune’: consequences of inbreeding on bird song, Proceedings of the Royal Society B: Biological Sciences 20161142, published online on 27 July 2016 before print 10.1098/rspb.2016.1142
Amotz Zahavi (1975). Mate selection — a selection for a handicap, Journal of Theoretical Biology, 53(1):205–214 | doi:10.1016/0022–5193(75)90111–3
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Originally published at Forbes on 27 July 2016.