U. MELBOURNE (AUS) — Male fairy-wrens use the pitch of their songs to broadcast their body size, new research shows.
The study led by University of Melbourne researcher Michelle Hall, is the first to show that the larger the male fairy wren, the lower the pitch of his song.
“This is the first time we have been able to show that song pitch indicates body size in song birds,” says study leader Michelle Hall from the University of Melbourne’s department of zoology.
“We found the bigger males sang certain song types at a lower pitch than smaller males,” says researcher Michelle Hall. (Credit: Michelle Hall/U. Melbourne)
The study, which began when Hall was at the Max Planck Institute for Ornithology in Germany, was published yesterday in the journal PLOS ONE.
Reliable communication about body size between animals is particularly important when communicating with mates or rivals. For example the bigger the rival is, the more likely it is to win in a fight so a song pitch indicating a large size may deter rivals.
“Surprisingly, there is very little evidence that the pitch of calls indicates body size differences within species, except in frogs,” she says. “In birds in particular, there has been no evidence that the pitch of songs indicated the size of the singer until now.”
The study involved measuring the leg length, which is a good indicator of overall body size, of 45 adult male purple-crowned fairy-wrens. It finds there was a correlation between the lowest song pitches and male size.
“We found the bigger males sang certain song types at a lower pitch than smaller males,” she says.
Purple-crowned fairy-wrens are creek-dwelling birds from northern Australia and, like their close relatives the blue wrens, males sing trill songs after the calls of certain predators, a context that seems to attract the attention of females.
Males have a repertoire of trill song variants, and it is the low-pitched variants that indicate the size of the singer.
Hall shows that it may be the complexity of birdsong that has obscured the relationship between body size and song frequency in the past.
“Birds can have large repertoires of song types spanning a wide frequency range, and some birds even shift the pitch of their songs down in aggressive contexts,” she says. “Focusing on the lowest pitches that males were able to sing was the key to finding the correlation with body size.”
The study was conducted at Mornington Wildlife Sanctuary in collaboration with Anne Peters of Monash University and Sjouke Kingma of University of East Anglia, and funded by the German Max Planck Institute for Ornithology.
Source: University of Melbourne