Thursday, July 12, 2012

Wild Parrots Name Their Children

Wild pair of green-rumped parrotlets, Forpus passerinus, photographed in Venezuela. Male (left) and female (right). Image: screengrab.

People who live with parrots know that they can mimic their human care-givers as well as many of the common sounds in their environment. One parrot owner started receiving mysterious phantom phone calls. The phone would ring; but, no matter how quickly it would be answered, there was never anyone there. Then, one day, the mystery was solved. The owner had answered yet another phantom call when she happened to glance at the parrot. Much to her amazement, the phone rang again while it was still up to her ear. More suspiciously, the parrot's beak moved.

The parrot had learned to imitate the sound of a ringing phone so well that the owner could not tell the difference between the phone and the parrot. Now, before answering any phone calls, the owner checks in with the parrot first.

Although such mimicry is delightful, it does raise the question of what purpose does vocal mimicry serve for wild parrots?

One proposed hypothesis for parrots' remarkable ability to mimic sounds in their environment is to develop and maintain social cohesion. For example, several species of wild parrots studied to date demonstrate the ability to readily imitate their flock mates' calls. This ability is important for psittacines: when an individual parrot moves from one locale to another, it learns the calls of the local parrot flock as part of forming a social bond with those birds.

But research in spectacled parrotlets, Forpus conspicillatus, went further: this research showed that each parrot has its own signature call – a unique sound that is used only for recognising that particular individual (doi:10.1007/s002650050481). Basically, each parrot has its own name. Interestingly, similar to human culture, members of each parrot family have names that sound more like each other than like those for other parrot families. But how do young parrots acquire their special signature calls (their names)? Do they learn their names from their parents, or are they born knowing their names?

To answer to this question, Karl Berg, a graduate student in Neurobiology and Behavior at Cornell University in Ithaca, NY, assembled a team of researchers and studied a wild population of green-rumped parrotlets, Forpus passerinus, in Guarico, Venezuela. Because this particular population has been carefully documented for decades, it provided an excellent opportunity to study the social dynamics of wild parrots.

Slightly smaller than a domestic canary, green-rumped parrotlets are the smallest parrot species in the Americas. They are resident in open forest and scrubland throughout much of tropical South America, and they have small ranges. These tiny, mostly green, parrots are slightly sexually dimorphic cavity nesters, laying between five and seven eggs in a termite nest, in a tree cavity -- or in a hollow pipe.

To distinguish between the two hypotheses (social name learning versus biological name inheritance), Mr Berg and his team of researchers set up inconspicuous video cameras and audio recorders inside and outside 17 nest cavities in PVC pipes in 2007 and 2008. When the resident female parrotlet had completed her clutch, nine of those nests were swapped between unrelated birds that lived far enough apart that they did not come into any auditory contact with each other. (The other eight nests were controls that remained with their biological parents.)

The researchers then recorded and analyzed the sounds in each nest cavity (figure 1 a & b):

Figure 1. Least-squares regression of contact call similarities within pairs and within sibling groups of green-rumped parrotlet nests. (a, b). Dotted lines indicate confidence intervals. (a) r2 = 0.64, p < 0.02; (b) r2 = 0.62, p < 0.01.

The team found that each adult had its own unique contact call and that contact call was more similar to each bird's mate's call than to calls produced by adults at other nests.

They also recorded and analyzed the nestlings' contact calls (figure 1 c & d):

Figure 1 c & d. Least-squares regression of contact call similarities within pairs and within sibling groups of green-rumped parrotlet nests. (c, d) Mean canonical scores of nestlings as a function of canonical scores of siblings within nests (c) in 2007 and (d) in 2008. Dotted lines indicate confidence intervals. (c) r2 = 0.71, p < 0.02; (d) r2 = 0.37, p < 0.15.

As expected, the parrot nestlings' calls were more variable than those of the adults, but sibling parrots tended to show strong similarities in their contact call structure. Like their parents, nestling parrotlet calls were more similar to their siblings than to nestling calls at other nests (however, this finding was significant only in 2007).

But were the foster parents learning their adopted nestlings innate contact calls or were the nestlings learning calls that their parents assigned to them? The researchers had anticipated this question by recording the foster parents' calls prior to them hearing their adopted nestlings' calls. Spectrographic analysis showed that it was the parents who assigned signature calls -- names -- to the young parrots instead of the other way around. Further, all parrot nestlings adopted contact calls that were notably similar to those that their parents -- whether biological or foster -- vocalized to them in the first weeks of their lives. Taken together, these data indicate that nestling parrots learn their names from their parents and parrot names are the result of social learning rather than biological inheritance.

It's likely that parrots evolved the ability to mimic sounds for social reasons, although those precise reasons are still unknown. But since this ability allows families to recognise each other by voice, it is likely that such vocal recognition is important for restricting parental care to one's own fledglings after parrot families begin moving to communal foraging and roosting sites.

These findings have a number of interesting implications as well. For example, can parrots recall and distinguish particular individuals and identify family members, even after being separated for years? This also raises the possibility that parrots may have a concept of individuality and even of self awareness.

This video is a slide presentation of these findings:

Reposted from GrrlScientist

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