In a video first, researchers have captured footage of a bird couple arguing over parental duties.
While there are any number of videos showing animals appearing to squabble over many issues, this is the first time that researchers have evidence it is an actual vocal exchange leading to an agreement.
Perceived lack of fairness appears to be at the root of most arguments, including bird tiffs, apparently. The recorded bickering birds were a pair of zebra finches that were both spending much of their time taking care of their eggs and chicks.
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"In species with bi-parental care, individuals adjust their workload to that of their partner to either compensate or match its investment. Communication within a pair might be crucial for achieving this adjustment," Ingrid Boucaud of the Université de Lyon/Saint-Etienne and her colleagues wrote in a paper published in the Biological Journal of the Linnean Society.
Zebra finch parents follow a routine. Whenever one leaves their duties at the nest to hunt, forage or do other things, the two birds engage in a "structured call duet." No one yet knows what the birds are communicating to each other, but this vocal exchange tends to follow a certain predictable pattern.
Boucaud and her team disrupted the shared parenting by capturing males while they were foraging and keeping them away from the nest for an extra hour. In the meantime, the females sat at their respective nests, and waited.
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When they released the males and they returned to their nests, the females appeared to really let the males have it. What was usually a slow and regularly patterned vocalization became more anguished sounding and fast paced. The videotaped female zebra finch also pecked her partner's head a few times.
He, in turn, fired back with his own vocalizations, with the two communicating with each other far more rapidly than usual.
The researchers report that the rapid vocal exchanges "were associated with an increased haste of the partners to take turns incubating and foraging. Females also spent less time incubating during their subsequent shift."
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Furthermore, the length of the "arguments" seemed to predict what happened next. If the late-arriving male called just a couple of times, the females would take a lengthier (up to an hour) foraging nest break. If the vocal exchanges involved more calls, she would return to the nest in less than thirty minutes.
"Taken together," Boucaud and her team wrote, "these results suggest that acoustic communication may play a role in the negotiation of parental care between breeding partners."
While it's important not to anthropomorphize the behavior of birds or any other non-human, it does appear that heated verbal exchanges evolved, at least in part among humans and certain birds, to facilitate compromise and agreements over important matters, like parental care.