Figure 1 - uploaded by Christina N. Zdenek
Content may be subject to copyright.
spectrogram of three Palm cockatoo calls. (a) Hello, (b) Whistle A and (c) Whistle B. spectrograms were prepared using RavenPro v. 1.3 (charif et al. 2010).
Source publication
The ability to identify individuals within a population is often essential for a detailed understanding of the ecology and conservation of a species. However, some species, including large parrots, are notoriously difficult to catch and mark for individual identification. Palm cockatoos (Probosciger aterrimus) are a large, poorly understood species...
Contexts in source publication
Context 1
... call samples with high signal-to-noise ratio and no interference from other calling birds were used for analysis. Three different call types (the Hello call, Whistle A and Whistle B; see Figure 1) were sampled sufficiently often from three to six birds of each sex (except the Hello call in females) to be included in each analysis. The threshold for inclusion into the analysis was 6-10 samples of each call type per individual. ...
Context 2
... better account for individual differences in the spectrographic contour line of Whistle A (e.g. Figure 1 vs. Figure 2), we used the on-screen cursor in RavenPro to make two additional manual measurements: trough frequency (the frequency at the trough of the call) and ridge1 frequency (the frequency at the top of the first ridge of the call) (see Figure 2). ...
Citations
... Signaling individual identity information in learned vocalizations could instead reflect a more fixed aspect of vocal communication systems, such as developmental constraints or genetic encoding of receivers' perceptual abilities. Future work could also address the stability of individual identity information encoding in learned contact calls across different social contexts, given that some vocal learning species exhibit rapid convergence or divergence that appears conditional on the social context [36][37][38][39], and in others, individual vocal signatures [92] or individually-distinctive repertoires of shared contact calls appear to change over time [93]. ...
Animals can actively encode different types of identity information in learned communication signals, such as group membership or individual identity. The social environments in which animals interact may favor different types of information, but whether identity information conveyed in learned signals is robust or responsive to social disruption over short evolutionary timescales is not well understood. We inferred the type of identity information that was most salient in vocal signals by combining computational tools, including supervised machine learning, with a conceptual framework of “hierarchical mapping”, or patterns of relative acoustic convergence across social scales. We used populations of a vocal learning species as a natural experiment to test whether the type of identity information emphasized in learned vocalizations changed in populations that experienced the social disruption of introduction into new parts of the world. We compared the social scales with the most salient identity information among native and introduced range monk parakeet (Myiopsitta monachus) calls recorded in Uruguay and the United States, respectively. We also evaluated whether the identity information emphasized in introduced range calls changed over time. To place our findings in an evolutionary context, we compared our results with another parrot species that exhibits well-established and distinctive regional vocal dialects that are consistent with signaling group identity. We found that both native and introduced range monk parakeet calls displayed the strongest convergence at the individual scale and minimal convergence within sites. We did not identify changes in the strength of acoustic convergence within sites over time in the introduced range calls. These results indicate that the individual identity information in learned vocalizations did not change over short evolutionary timescales in populations that experienced the social disruption of introduction. Our findings point to exciting new research directions about the robustness or responsiveness of communication systems over different evolutionary timescales.
... Furthermore, selection for individually recognizable (i.e. "signature") calls could drive diversification of vocal signals that are used in individual-specific social interactions (for examples of this in parrots, see Wanker et al. 1998, Cortopassi and Bradbury 2006, Wanker and Fischer 2001, Berg et al. 2011, Zdenek et al. 2017, Smith-Vidaurre et al. 2019, which may be complex on islands, where the social neighborhood includes parakeets from across the entire island. Diversifying selection might be expected to be stronger on more easily perceived call features (i.e. ...
Learned vocalizations play a key role in parrot social dynamics and vocal dialects have been documented for several mainland species, but to date no studies of geographically structured call variation in parrot species have examined the role of isolation on islands. In a study of the Brown-throated Parakeet (Eupsittula pertinax), which inhabits 5 small Caribbean islands as well as the adjacent mainland, we found that the contact calls of island and mainland parakeets show divergence in vocal characters as well as in call variability. We assessed call variation using 3 approaches: frequency measurements, spectrogram cross-correlation (SPCC) analyses, and call duration measurements. Island parakeets’ calls were longer and had lower mean frequencies, and calls from different islands were distinguishable from each other as well as from mainland calls using measures derived from the SPCCs. In addition, we measured call variability at 2 different levels—within-location and within-individual. We found calls to be more variable for island parakeets for SPCC and duration measures, but less variable for frequency measures. The observed call differentiation among locations may be due to drift, whereas the lower frequency of island calls could either be a response to the windy environment on the islands or a consequence of the island subspecies’ larger body sizes. We also hypothesize that the isolation of parakeet populations on small islands may have resulted in reduced selection for local call convergence, allowing island parakeets to produce more variable calls. We suggest that due to poor signal transmission in the windy island environment, selective pressures may favor variability in more easily perceived call features (like call duration) rather than more subtle features, like frequency shifts. Experimental tests are required to determine whether observed call patterns translate into similarly structured patterns in the responses to vocal variants.
... Several bird species display vocal distinctiveness in different call types. For example, the parrotlets (Forpus conspicillatus) have distinctiveness in contact calls (Wanker et al. 1998), California towhees (Pipilo crissalis) and white-eared groundsparrows (Melozone leucotis) in duets (Benedict and McEntee 2009;Sandoval et al. 2016), palm cockatoos (Probosciger aterrimus) in their hello and whistle calls (Zdenek et al. 2018) and common cuckoos (Cuculus canorus) in their advertising calls (Lei et al. 2005;Jung et al. 2014;Zsebők et al. 2017). All of these call types are mainly used for territorial maintenance and mating purposes. ...
... This further supports our idea that different calls have encoded individuality in different parameters (Supplementary Table 1). Vocal distinctiveness is found in many avian species (Walcott et al. 1999;Favaro et al. 2016;González-García et al. 2017), particularly those that are noted to be highly vocal (Wanker et al. 1998;Schwing et al. 2012;Zdenek et al. 2018). Environmental, developmental and genetic factors are likely involved in the distinctiveness of vocalizations (McGregor 1993;Suthers 1994). ...
The Asian koel (Eudynamys scolopacea) is a well-known brood parasitic bird that visits Pakistan every summer from India. This species produces at least five loud call types that are presumed to be used in territorial and mating behaviour. We noticed vocal differences among individuals in the wild and hypothesised that Asian koels produce individually distinct vocalizations. To test this, we recorded type 1 cooee calls, coe calls, type 1 coegh calls, type 2 coegh call and wurroo calls from 46 adult birds in the wild, and measured 15 different acoustic parameters, both spectral and temporal, for each vocalization type. We also measured the Potential of Individual Coding (PIC). Parameters having PIC values ≥1.1 were further analysed through stepwise cross-validated discriminant function analysis (DFA). The DFA accurately categorised 86.5% of the type 1 cooee calls, 95.7% of coe calls, 91.5% of the type 1 coegh calls, 82.2% of type 2 coegh calls and 83.3% of wurroo calls to the individuals from which these calls were recorded. Thus, consistent with our hypothesis, our results indicate that Asian koels produce individually distinct calls.
... Galeotti and Pavan 1991;González-García et al. 2017), others, like ours, have not been successful in re-identifying birds over multiple years (e.g. Zdenek et al. 2017). Some studies have found that successful re-identification declines gradually over time. ...
Acoustic monitoring of birds is developing rapidly as equipment, methods and analyses improve. However, most population monitoring studies still utilise traditional techniques like mark-recapture or line transects. Previous researchers used vocal recordings of male European nightjars, Caprimulgus europaeus, to identify individuals, finding that four acoustic parameters correctly assigned 98.5% of calls to individuals. We tested their methods on a population of European nightjars recorded over two successive breeding seasons and found that percentage of males correctly classified within a season reached a maximum of 73.5%, rising to 75% if full-length calls and 13 acoustic parameters were used. We tested whether males could be re-identified over a two-year period and found that only 20% of calls were assigned to the same putative territorial individuals, despite separate ringing data showing that males can maintain site fidelity for up to eight years. Our results indicate that the characteristics of male nightjar vocalisations may alter over time. We therefore recommend that vocal discrimination be used in conjunction with existing monitoring techniques when surveying for population monitoring, that as many call parameters as possible are used and that recording for automated presence/absence surveys takes place over a short time-frame.
... However, other studies have failed to find this stability (e.g. Feher et al. 2009;Kipper and Kiefer 2010;Zdenek et al. 2017). For example, DFA correctly assigned 59% of female White-throated Magpie-jays (Calocitta formosa) begging calls to individual females, but this correct rate declined sharply to less than 20% for some individuals when using recordings made over 7 days within the same season (Ellis 2008). ...
Numerous studies have identified individually distinctive vocal characteristics and call consistency in different bird species. If these vocal characteristics are to be utilised as non-invasive markers for monitoring purposes, then they must remain stable over time. Three recent studies have shown that it is possible to identify individual male Common Cuckoos (Cuculus canorus) based on vocal characteristics, but whether these characteristics are stable over the duration of a breeding season remains unknown. We recorded 1032 syllables from 30 male Common Cuckoos in a Northeast Asian population. We banded six of these males and made repeated recordings of their cu-coo advertisement call across a 19-day period of the breeding season in China. We used three methods to identify individuals: discriminant function analyses (DFA), correlation analysis (CA) and spectrographic cross-correlation (SPCC). We also used repeatability analysis to test whether call consistency (the number of syllables in each calling bout) was repeatable within individuals. Based on the same-day recordings, calls from the same male were more similar in their characteristics than compared to those of different males, and yielded correct rates of classifying individuals of 93.6% (SPCC), 90.8% (DFA), and 71.5% (CA). However, these rates declined to 40.5% (SPCC), 40.7% (DFA) and 27% (CA) when using recordings over the 19-day period. Call consistency was repeatable within individuals across two successive calling bouts, but this individual repeatability disappeared when several (more than two) calling bouts from the same day or bouts from the different days of the study were included in the analyses. Declines in the correct rate of identifying individual male cuckoos and call consistency in this study raise concerns that individual male cuckoo calls may be more variable than previously thought.
The stability of measurement parameters over the years is essential in long-term
monitoring of populations. The goal of this study was to evaluate the variation of
selected acoustic parameters in male Tawny Owl territorial calls. A total of ten
sites were monitored in low mountains mostly covered by deciduous forests.
The owl calls were recorded from February to July and in one case in
September. Three acoustic parameters were analysed: the duration of the first
and third notes and the total duration of the call. The third note showed the
lowest coefficient of variation (10.4%) over the years. This parameter also
showed the lowest range between minimum and maximum values. All parame-
ters had higher inter-individual than intra-individual variation. The stability of the
parameters was analysed in two males between two years. All parameters
showed significant differences in one male. The total duration of the call was
also different for the second male. Individual recognition based on the duration
of notes is therefore not a suitable method for long-term monitoring. These find-
ings may help in selecting appropriate parameters for individual recognition and
a more detailed view of the stability of acoustic parameters.
The rarity of tool manufacture in wild parrots is surprising because they share key life-history traits with advanced tool-using species, including large brains, complex sociality and prolonged parental care. When it does occur, tool manufacture in parrots tends to be innovative, spontaneous and individually variable, but most cases have been in captivity. In the wild, only palm cockatoos (Probosciger aterrimus) have been observed using tools regularly. However, they are unusual because they use tools to enhance their displays rather than for foraging or self-maintenance. Males in northern Australia make two types of tool from sticks and seed pods, which they tap rhythmically against a tree during display. We analysed 256 sound tools retrieved from 70 display trees. Drumsticks (89% of tools) were used more often than seed pod tools; most males manufactured only drumsticks, but some made both types. Individual males differed significantly in the design of their drumsticks including the length, width and mass but we found no evidence that neighbours copied each other. We discuss the highly individualized preferences for sound tool design in context of the behavioural predispositions behind the rarity of tool manufacture in wild parrots.
Use of species‐specific field methods may be required for taxa that are inherently difficult to survey, for example species with cryptic camouflage or secretive behaviour. However, these methods often require more manual effort and therefore cost. Passive acoustic monitoring (PAM) is now an established tool to reduce manual effort to monitor species and analysis of spectrograms provides the means to discriminate individuals by call characteristics. At night, male Eurasian Woodcock Scolopax rusticola make distinct, audible ‘roding’ displays above the tree canopy to advertise to females. Studying this behaviour at an individual level whilst using PAM presents opportunities to improve monitoring methods of this cryptic, Red Listed species. This study evaluates the potential use of vocal individuality measurements in distinguishing Woodcock individuals and interpreting spatial and temporal patterns in their roding displays across woodland sites. Woodcock roding calls were recorded from woodland fragments across two regions comprising 20 sites. A random forest classifier was applied to reduce the time needed to find and manually verify calls. Principal component analysis (PCA) and hierarchical clustering algorithms were used on call measurements, describing duration and frequency differences in calls. When clusters formed, they were used to qualitatively assess supposed individual spatial and temporal variation in roding behaviour. The variance of dimensionally reduced measurements was used to interpret local Woodcock abundance and changes over time. Supposed individuals used many sites within a region, and many sites were used by multiple birds. However, sites showed clusters of calls from supposed individuals in different proportions. It was difficult to discriminate individuals using PCA with more than six birds as the degree of call overlap increased. Though the call measurement variance is associated with number of call events, it may provide a suitable method for representing population size without call count bias.
Animal vocalisations can signify diverse behavioural contexts, knowledge of which can be applied in bioacoustic monitoring programs. Australia’s endemic black cockatoos (Calyptorhynchus sp., family Cacatuidae) are highly vocal species that are threatened in many locations. In this study, we describe the nest‐associated vocal behaviours of two endangered subspecies of black cockatoo, the south‐eastern red‐tailed black cockatoo, C. banksii graptogyne and the Kangaroo Island glossy black cockatoo, C. lathami halmaturinus . Breeding success is limiting their recoveries and nest monitoring is challenging, but vocal recordings might provide valuable long‐term information hard to obtain otherwise. We recorded daily vocal activity at wild nests of both cockatoos using autonomous sound recorders. Combined with behavioural observations and video footage, we identified vocalisations characteristic of six behavioural contexts at nests: birds in flight, while perched, during begging (adult females), during courtship displays (adult males), when entering or sitting near to the nest hollow entrance (adult females), and from nestlings. Linear discriminant analysis on 12 acoustic measurements correctly classified 58.4% of calls of the red‐tailed black cockatoo (n = 907 calls from eight nests) and 62.9% of calls of the glossy black cockatoo (n = 1632 calls from 11 nests). In both subspecies, the female nest call and nestling calls are the most conspicuous vocal indicators of active nesting, and therefore should be considered for their bioacoustic potential. Other adult vocalisations indicate a range of behavioural contexts that could be informative for monitoring nesting behaviour, and its association to habitat features, in these endangered subspecies.
