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. 2012 May 8;22(9):801-6.
doi: 10.1016/j.cub.2012.03.023. Epub 2012 Apr 19.

Long-term memory for affiliates in ravens

Markus Boeckle  1 , Thomas Bugnyar
Affiliations

Long-term memory for affiliates in ravens

Markus Boeckle et al. Curr Biol. .

Abstract

Complex social life requires individuals to recognize and remember group members and, within those, to distinguish affiliates from nonaffiliates. Whereas long-term individual recognition has been demonstrated in some nonhuman animals, memory for the relationship valence to former group members has received little attention. Here we show that adult, pair-housed ravens not only respond differently to the playback of calls from previous group members and unfamiliar conspecifics but also discriminate between familiar birds according to the relationship valence they had to those subjects up to three years ago as subadult nonbreeders. The birds' distinction between familiar and unfamiliar individuals is reflected mainly in the number of calls, whereas their differentiation according to relationship valence is reflected in call modulation only. As compared to their response to affiliates, ravens responded to nonaffiliates by increasing chaotic parts of the vocalization and lowering formant spacing, potentially exaggerating the perceived impression of body size. Our findings indicate that ravens remember relationship qualities to former group members even after long periods of separation, confirming that their sophisticated social knowledge as nonbreeders is maintained into the territorial breeding stage.

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Figures

Figure 1
Figure 1
Example Oscillogram and Spectrogram of a Stimulus Call Amplitude modulation is best seen in the oscillogram; low frequency and noisiness are best seen in the spectrogram. (Spectrogram settings: fast Fourier transform with Gaussian window shape; window length 0.003 s; dynamic range 40 dB.) For details on stimulus presentation and experimental setup, see Table S3 and Figure S1.
Figure 2
Figure 2
Differences between Playback Categories in Component 5 of Call Parameters Analysis of call parameters shows that ravens react different to affiliate, nonaffiliate, and unfamiliar individuals. Error bars indicate the standard error of the estimates. ∗∗p ≤ 0.05; ∗∗∗p ≤ 0.001. See also Tables S1 and S2.
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