What if you could tell someone was already in a relationship simply by listening to them speak? Well, female pied flycatchers can! It may sound like a Disney movie plot, but the phenomenon has recently been reported in a new study published in Ethology.
As per the findings, male pied flycatchers change their songs after mating and moving to another territory to court a second female. Their songs become shorter, and they repeat syllables less often.
But how did the scientists find out? When researchers played songs from male birds — who had partners or mated recently — to female pied flycatchers, the females responded differently to songs from bachelor and mated males.
In short, when the female knew the song was coming from a bird who had already ‘paired’, they’d behave differently. And this isn’t just because of loyalty and romance.
A male’s mating status matters because, once mated, he may divide his time between two nests, leaving less time to help raise chicks.
The pied flycatcher (Ficedula hypoleuca) has a mating strategy known as polyterritoriality. After a first female lays eggs, a male may set up another territory several hundred metres away and court another female.
To see whether his song changes, ethologist Helene Lampe and her colleagues recorded 17 wild males twice — first when they were bachelors and again after they had mated and moved to a second territory.
When the males became polyterritorial, their songs became shorter, falling from about two seconds to roughly 1.7 seconds. They also repeated syllables less often.
Normally, a male tends to sing his syllables in an orderly pattern, often repeating one or two syllables from one song to the next. After mating, that repetition became less frequent.
This does not mean the males suddenly developed a bigger vocabulary or more complicated songs. The specific change the researchers found was less repetition and more switching between syllables.
One possibility has to do with other males. Earlier research found that male pied flycatchers repeated syllables less when a rival male was nearby, but not when a female was. The researchers suggest this change could be linked to territorial signalling or male-male interactions.
Another interesting possibility is that a shorter song helps the males stay undetected. Basically, females can recognise their mate’s song. So when he moves on to another female, playing around infidelity, the first mate may fly over and chase away another female approaching her partner.
Shorter songs possibly help them cheat in peace, without inconvenience, by reducing the chances of their first mate detecting them in another territory. But this remains a hypothesis: the new study did not test whether first females actually failed to detect or respond to shorter songs.
What the researchers did test was whether females responded differently to bachelor and mated males’ songs.
During the experiment, the researchers played recordings of bachelor and mated males to female pied flycatchers in large outdoor aviaries.
Twenty-one of 29 females visited more often the nest box beside the speaker playing a bachelor male’s song. And when researchers digitally altered the bachelor songs to resemble those of mated males, that preference disappeared.
This suggests that females were responding to specific song features associated with a male’s mating status.
There is an important distinction, though. The experiment measured nest-box visits, not whether females actually chose those males as mates, bred with them or avoided already-mated males in the wild.
So the findings suggest that females can pick up on song differences associated with whether a male is unmated or already paired. They do not show that a female hears a song and consciously thinks, “This male is taken.”
That is also why “cheating” belongs in quotation marks. Calling these males cheaters makes their behaviour sound deliberately deceptive. The study does not show that they are consciously trying to fool their first mate or a potential second mate.
As behavioural ecologist Stephen Nowicki of Duke University, who was not involved in the study, points out, the birds are not necessarily tiny schemers. Their behaviour can instead be understood as the result of natural selection favouring traits that increase reproductive success.
For females, however, those subtle changes in a male’s song could still be useful clues — not necessarily a clear “I’m taken” signal, but differences that appear to carry information about his mating status!
