Datos de investigación
Pre-hatching social interactions mediated by acoustic signals. Dynamics of click emission and hatching synchronization in birds
Autores:
Rapacioli, Melina
Publicador:
Consejo Nacional de Investigaciones Científicas y Técnicas
Fecha de depósito:
18/08/2025
Fecha de recolección:
2015/2024
Clasificación temática:
Resumen
The present paper analyzes the sounds emitted by pre-hatching chicks, focusing on those named as “clicks,” which are thought to mediate pre-hatching social interactions and hatching synchronization. Representative acoustic signals were analyzed under three incubation conditions: (1) isolated pre-hatching chicks (n=13), (2) pre-hatching chicks in contact with others of the same age (n=14), and (3) pre-hatching chicks in contact with other of different age (n=10 for each group: leader and follower). Customized MATLAB software was developed to (a) identify and isolate clicks from other recorded sounds, (b) represent them as temporal series of stochastic point processes, and (c) determine whether click emission dynamics resembled white noise or exhibited characteristics of informative signals. Mathematical methods were applied to analyze (a) temporal dynamics, (b) clustering patterns (via hierarchical clustering and log–log scaling), and (c) scaling properties (via power spectral density analysis) of clicks under each condition. The results reveal developmental-dependent changes in click temporal patterns. As hatching approaches, clicks evolve from isolated events to highly organized hierarchical clusters. Contacting chicks displayed greater temporal organization than isolated ones. Significantly, contact with more advanced chicks accelerated click dynamics in less developed embryos, while older embryos showed a slight delay, suggesting reciprocal social interactions. Spectral analysis revealed long-range correlations consistent with fractional Gaussian noise. These findings confirm that click sequences (a) exhibit physical characteristics of informative signals, (b) function as communication signals, and (c) align developmental processes among pre-hatching chicks. The study underscores the value of fractal analysis in describing physiological signals and expands our understanding of prenatal social interactions. The results suggest that acoustic signals may influence both hatching coordination and central nervous system development. This work provides insight into the evolutionary advantage of embryo communication and highlights the importance of studying how environmental disruptions may affect these critical prenatal processes.
Información Técnica
Fig 1. Characteristics of claps. A. Shows a 30-second-long segment of an audio signal made 32 hours before hatching. B. Magnification of the cluster indicated by the red box in Figure A. C. Fourier transform of the signal segment shown in Figure B. D. Spectrogram of the signal segment shown in B. Fig 2. Inspiratory and Expiratory clicks. A. Shows a 25-second-long segment of a signal recorded 7 hours before hatching. Red arrows: inspiratory clicks; black arrows expiratory clicks. B and D. Zoom of the red boxes, B and D, indicated in Figure A, corresponding to inspiratory and expiratory clicks respectively. C and E. Fourier transform corresponding to inspiratory and expiratory clicks respectively. Fig 3. Example of a call. A. Temporal record. B. Fourier transform. C. Spectrogram. Record obtained 7 hours before hatching. Fig 4. Movement noises. Shows an 8-second-long segment of a record obtained 30 minutes before hatching. The segment includes a regular succession of clicks (black arrows) and a set of fluctuations corresponding to body movements (red box). Fig 5. Variability in the click rate as a function of the pre-hatching time. Each point represents the mean ± standard deviation measured in 13 independents recordings. Slopes (rate of change in click rate) were calculated for four predefined pre-hatching time intervals: (a) from 34 to 15 pre-hatching hours, (b) from 15 to 10 pre-hatching hours, (c) from 10 to 6 pre-hatching hours, and (d) from 6 to 0 pre-hatching hours. For each interval, the slope is expressed as the median (interquartile range, IQR) of individual slopes. Statistical comparisons among the four intervals were performed using the Kruskal-Wallis test followed by Dunn’s post-hoc analysis. The results revealed statistically significant differences between successive intervals (p < 0.05), confirming that the rate of change in click emission differs significantly across the different phases of the pre-hatching period. Fig 6. Surrogate binary signals. Three-hundred-second-long binary signals were constructed from audio signals obtained at different pre-hatching times (17, 16, 15, 12, 11, 10, 7, 6, 5 pre-hatching h). The bars ("1s") indicate the temporal locations of clicks as a function of the time (s). Sub-series of "0s" between successive "1s", which, in these binary signals, appear as empty spaces, represent the lengths of the inter-click intervals. Fig 7. Hierarchical Cluster Analysis of binary signals. The figures represent dendrograms corresponding to binary signals obtained at different pre-hatching times (17 to 10 pre-hatching h). They reveal striking changes in the pattern of clusters organization during the pre-hatching stage. The height of the connectors (Π) represents inter-cluster intervals measured in s. The x axis represents the succession of clicks ordered by their time of appearance. Fig 8. Hierarchical Cluster Analysis of binary signals. The figures represent dendrograms corresponding to binary signals obtained at different pre-hatching times (7, 6 and 5 pre-hatching h). They illustrate the changes in the pattern of clusters organization during the pre-hatching stage. The height of the connectors (Π) represents the inter-cluster intervals measured in s. The x axis represents the succession of clicks ordered by their time of appearance. Fig 9. Bi-logarithmic plots of the number of click clusters as a function of the inter-cluster interval. Each plot shows the log–log relationship between the number of click clusters and the inter-cluster interval length, calculated at selected pre-hatching time points (17 to 5 pre-hatching hours). The data were derived from the dendrograms shown in Figures 7 and 8. The log-log plots show power law behaviors revealing the absence of a typical mean cluster size and that clicks are distributed in a continuous hierarchical set of clusters within clusters across scales. The figure shows that there is a typical variation in the clicks clustering as a function of the pre-hatching time. Detailed description in the text. Fig 10. Frequency analysis of the I-CI signals. A. Illustrates an example of an I-CI signal obtained from an audio recorded at 11 h pre-hatching h. The red line was obtained by a third order polynomial fitting. B. Autocorrelation function of the I-CI signal. The dotted lines indicate the 95% confidence interval. C. Fourier transform of the ACF. The slope of the line fitted by least squares linear regression is -β, where β is the scaling index of the process [33]. Table 1. Values of β (mean ± SD) estimated by PSD applied to I-CI signals and their corresponding surrogate signals at different pre-hatching h. Table 1. Shows values of β obtained from signals recorded at 20, 11, 6 and 2 pre-hatching h in chicks incubated in isolation. The values of β are significantly > 0.0. These results indicate that they have power spectra of the type 1/f(β) and that the signals behave as realizations of a fractional Gaussian noise (fGn). The values of β obtained from both kinds of surrogate signals correspond, as it was expected, to white noise processes. Table 2. Values of β (mean ± SD) estimated by PSD applied to ICI signals and their corresponding surrogate signals at different pre-hatching h Fig 11. Evolution of the click rate as a function of the pre-hatching time. Each point represents the mean ± standard deviation of 14 individuals (7 groups, each composed of 2 contacting chicks). The blue dotted line represents the evolution observed in clicks emitted by isolated pre-hatching chicks (Fig 5). Slopes (rate of change in click rate) were calculated for five predefined pre-hatching time intervals: (a) 34-15 pre-hatching hours (phh), (b) 15-10 phh, (c) 10-6 phh, (d) 6-0 phh, and (e) 10-0 phh. For each interval, the slope is expressed as the median (interquartile range, IQR) of individual slopes. Statistical comparisons between intervals were performed using the Kruskal-Wallis test followed by Dunn’s post-hoc analysis. Significant differences were found between 34-15 phh and 15-10 phh, and between 15-10 phh and 10-6 phh (p < 0.05), but not between 10-6 phh and 6-0 phh. Additionally, slopes from the contacting group were compared to those from isolated embryos (Fig 5) using Mann-Whitney U tests. Significant differences (p < 0.05) were found during the intervals 34-15 phh and 6-0 phh, indicated by asterisks. Fig 12. Bi-logarithmic plots of the number of clusters as a function of the inter-cluster interval length. The bi-logarithmic plots were obtained from dendrograms corresponding to 17, 16, 15, 12, 11, 10, 7, 6, 5 pre-hatching h. The plots show typical variations in the clicks clustering as a function of the pre-hatching time. Red circles: contacting pre-hatching chicks; Blue circles: isolated pre-hatching chicks. The dynamics of clicks clustering significantly differs between both groups. The changes in clustering dynamics observed in isolated chicks are anticipated in the groups of contacting chicks. See the description in the text. Fig. 13. Evolution of the click rate as a function of the pre-hatching time. Each point represents the mean ± standard deviation of 10 experiments (10 leader chicks and 10 follower chicks). The red dotted line represents the evolution observed in contacting pre-hatching chicks (Fig 11). Slopes (rate of change in click rate) were calculated for four predefined pre-hatching time intervals: (a) from 22 to 13 pre-hatching hours (phh), (b) from 13 to 9 phh, (c) from 9 to 7 phh, and (d) from 7 to 0 phh, for both leader and follower groups. In the leader litter, the slope for the 9–7 phh interval was significantly higher than all other intervals (p < 0.05, Kruskal-Wallis test with Dunn’s post-hoc). In the follower litter, the slope for the 13–9 phh interval was significantly higher than all other intervals (p < 0.05, Kruskal-Wallis test with Dunn’s post-hoc). Comparisons between leader and follower litters revealed significant differences in the slopes for the intervals 22–13 phh, 13–9 phh, and 9–7 phh (p < 0.05, Mann-Whitney U test), indicated by asterisks. Fig. 14. Evolution of the click rate as a function of the incubation time. A. Standard curve obtained by averaging the frequency of click emission of 14 independent experiments as a function of the incubation time. B. Shows the evolution of the click rate of the leader and follower litter (green lines). The reference curve (red dashed line) is also included. It is observed that the two asynchronous litters reciprocally influence each other. The leader litter undergoes a delay (horizontal red arrows) in respect to the reference curve and the follower litter shows an advance (horizontal green arrows) with respect to the reference. Arrowheads (upward and downward) indicate the onset of click emission for each individual recording, while arrows (upward and downward) indicate the hatching time, both color-coded according to group (follower, leader, or reference). Hatching time is defined here as the moment when the recording was interrupted due to intense noises produced by chick movements during hatching.
Palabras clave:
prenatal interactions,
hatching synchronization,
developmental programming
Alcance geográfico
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Datos de Investigación(SEDE CENTRAL)
Datos de Investigación de SEDE CENTRAL
Datos de Investigación de SEDE CENTRAL
Citación
Rapacioli, Melina; (2025): Pre-hatching social interactions mediated by acoustic signals. Dynamics of click emission and hatching synchronization in birds. Consejo Nacional de Investigaciones Científicas y Técnicas. (dataset). http://hdl.handle.net/11336/269161
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