Identification of vocal individuality in male cuckoos using different analytical techniques

Abstract

Background: Individuality in vocalizations may provide an effective tool for surveying populations of the Common Cuckoo (Cuculus canorus) but there remains few data on which technique to use to identify individuality. In this research, we compared the within-and between-individual variation in cuckoo calls using two different analytical methods, and discuss the feasibility of using call individuality to count male cuckoos within a population. Methods:We recorded vocalization from 13 males, and measured 15 spectro-temporal variables for each call. The majority of these call variables (n = 12) have greater variation between individuals than within individual. We first calculated the similarity (Pearson's R) for each paired calls in order to find a threshold that could distinguish calls emitted from the same or different males, and then counted the number of males based on this distinction. Second, we used the more widely accepted technique of discriminant function analysis (DFA) to identify individual male cuckoos, and compared the correct rate of classifying individuals between the two analytical methods.Results: Similarity of paired calls from the same male was significantly higher than from different males. Under a relatively broad threshold interval, we achieved a high (>90%) correct rate to distinguish calls and an accurate estimate of male numbers. Based on banded males (n = 3), we found the similarity of paired calls from different days was lower when compared with paired calls from the same day, but this change did not obscure individual identification, as similarity values of paired calls from different days were still larger than the threshold used to distinguish calls from the same or different males. DFA also yielded a high rate (91.9%) of correct classification of individuals. Conclusions:Our study suggests that identifying individual vocalizations can form the basis of an appropriate survey method for counting male cuckoos within a population, provided the performance of different analytical techniques are compared.

Components of variation in female common cuckoo calls

“…Here the phrase 'number of calls' refers to number of syllables in males, and the number of calling bouts in females. Male cuckoo calls consist of a repeated series of 'cu-coo' syllables (Møller et al, 2016a;Li et al, 2017) i.e. both 'cu' and 'coo' elements constitute a single syllable with several successive syllables constituting a bout.…”

“…These recordings were recorded in different locations, or at the same location on different days. Since common cuckoos are abundant in our study area (Li et al, 2017) we treated these 43 recordings as being derived from 43 different female individuals. To avoid pseudo-replication, we used a smaller data set only including six recordings (corresponding to six individual females) recorded from different locations, randomly selected from the original 43 recordings.…”

“…Male common cuckoos Cuculus canorous utter loud simple and stereotypic "cuck-ooo" calls during the breeding season. Temporal and frequency variables among different male cuckoo calls are sufficient to provide individual information (Jung et al, 2014;Li et al, 2017;Zsebok et al, 2017), which can be used to distinguish between neighbors and strangers (Moskat et al, 2017). Furthermore, there appears to be a high degree of consistency in the number of syllables in each bout produced by individual males (Møller et al, 2016a, b).…”

The function of three main call types in common cuckoo

“…For cuckoos, a well‐studied brood parasitic avian species, the temporal and frequency variables of male “cu‐coo” calls (Figure a) are well‐known (Lei, Zhao, Wang, Yin, & Payne, ). This call type is sufficient to provide individual information (Jung, Lee, & Yoo, ; Li, Xia, Lloyd, Li, & Zhang, ; Zsebök, Moskat, & Ban, ), which can be used to distinguish between neighbors and strangers (Moskát, Elek, Ban, Geltsch, & Hauber, ; Moskát et al, ): Male cuckoos show less aggressive response to familiar “ cu‐coo ” calls from neighbors than unfamiliar “ cu‐coo ” calls from strangers during playback experiments. Besides the characteristic and conspicuous two‐element “ cu‐coo ” calls, males can also utter a three‐element “ cu‐cu‐coo ” call (Figure b) which contains a repeat of the first element of the regular “ cu‐coo ” call (Lei et al, ; Payne, ).…”

“…For cuckoos, a well-studied brood parasitic avian species, the temporal and frequency variables of male "cu-coo" calls ( Figure 1a) are well-known (Lei, Zhao, Wang, Yin, & Payne, 2005). This call type is sufficient to provide individual information (Jung, Lee, & Yoo, 2014;Li, Xia, Lloyd, Li, & Zhang, 2017;Zsebök, Moskat, & Ban, 2017), which can be used to distinguish between neighbors and strangers (Moskát, Elek, Ban, Geltsch, & Hauber, 2017;Moskát et al, 2018):…”