Last week I came across an interesting press release on a strange phenomenon: vocal 'naming' of parrot chicks by their mothers. At the time of that posting I hadn't come across the primary journal article, but a few commenters were kind enough to point me in the direction of this paper by Wanker et al, which described similar studies from the same lab in depth.
[Reference: Wanker et al. 2005. Vocal labeling of family members in spectacled parrotlets, Forpus conspicillatus. Animal Behavior. vol. 70 (1), pp. 111-118]
Parrots are highly social and intelligent animals who, although possessing of extremely different anatomical neural structures, display quite a few interesting mental faculties. In previous issues of Grey Matters, I've discussed at length the work of Irene Pepperberg with Alex, Wart, and other African Grey parrots. While much debate exists over the scope of Alex's naming, coding, counting, etc abilities, there is at least recognition at all levels that Alex isn't just straight mimicking. He has some ability to name and manipulate his environment, even if the extent to which he can is not precisely clear.
Hence why studies of this nature, where parrots are using vocal labels in their natural habitat, rather than a starkly artificial one, are quite important in understanding parrot intelligence. Vocal labeling has been found and reported on before in other species. For example, the vervet monkey has been shown by Cheney & Seyfarth to give various warning calls, which vary depending on the type of threat (one call to climb up a tree, a different call to stay on the ground, etc). Vervet monkeys live in cooperative social settings, much like parrots, and other social animals like dolphin also seem to have labels for individuals.
The aforementioned study by Wanker et al. investigated whether spectacled parrotlets used different acoustic signals to refer to, and call to, specific members of their social cohort.
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Spectacled parrotlets give specific calls (the "contact call") when they are out of sight of one another and want to make contact. This has been observed in captivity and the wild (Authors note: Pepper certainly does this to me when I leave the room.) In previous studies, Wanker et al found that these birds respond differently depending on the source of the call: their mate, siblings, or non-related members of the social group. In the current paper, the researchers assembled a group of birds (10-25 birds) which had established pairs, new pairs, and unpaired birds with some juveniles. They then recorded contact calls of these individuals, as well as observed their social interactions every 10 minutes during 60-90 minute observation sessions.
At the beginning of the recording sessions, two birds which had been socializing for 30 min were separated from view of each other but still within earshot. Calls were recorded up to 1.5 hours following, and recorded at least 20 contact calls per trial. Calls were then digitized. The authors experimented with playback of the recorded calls to examine the reaction it would have on the birds (ie, would they call out themselves during periods of silence?).
During the playback experiments, the researchers induced interaction with a specific family member and a target bird and recording the calls elicited when they were separated. Then in a trial session, they played back the specific family member's call as well as calls attributed to other family members. The target bird was much more likely to respond to the correct family member's call (pre-recorded label) when in the presence of that family member, as opposed to a different family member.
Wanker et al also analyzed the acoustic properties of the vocal 'labels' (represented in the figure below), and found that they were unique and consistent for a conspecific over time. The figure below refers to one parrots' (Eddi) vocal labels for three different family members (Renee, Ustenov, and Uvo; represented in columns, Renee is a,d,g).
Take home message? Spectacled parrotlets may be able to vocally label individuals in their family with unique and consistent calls, which suggests they have some form of mental representation of individuals in their environment as well as utilization of arbitrary sounds with underlying meaning in certain contexts.
The otherwise excellent Language Log labels this study rather unfairly an "insane piece of glottobabble about animals with language behaviors", although the linked article carefully points out that they are not talking about the equivalent of human names. Maybe someone should set them straight? :)
(Or should "my dog knows his name" be replaced by "my dog responds to a unique call sign", since dogs don't use human names either?)
You've got to watch out for the linguistics/Speech and Hearing Science folks out there- they cling dearly to the assumption that no creature other humans have language. Anything that even comes close to that is taken like a personal attack.
You should have read the things they said about Koko, and about the released Orangutan who taught her offspring the sign language she had learned in captivity.
But yeah- they're usually cool until then!