## 3 Results and Discussion
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multirow{2}{*}{**Sibling Contact Regime**} & \multirow{2}{*}{**Hatched Eggs (\(\omega\))**} & \multicolumn{6}{c}{**In incubation Length (Days)**} \\ \cline{3-10}  & & **Mean** & **Variance** & **CV (\%)** & **Skewness (g.)** & **Kurtosis (g.)** & **Min** & **Max** \\ \hline Without contact & 34 & 23.50 \({}^{\text{a}}\) & 0.318 \({}^{\text{c}}\) & 2.40 & \(-\)0.807 & 1.958 & 22.00 & 24.50 \\ Contact during incubation phase (1–20 days) & 33 & 23.02 \({}^{\text{b}}\) & 0.523 \({}^{\text{a}}\) & 3.14 & 0.406 & \(-\)0.599 & 22.00 & 24.50 \\ Contact during hatching phase & 36 & 23.06 \({}^{\text{b}}\) & 0.097 \({}^{\text{b}}\) & 1.35 & \(-\)0.071 & \(-\)0.281 & 22.50 & 23.50 \\
[21 days-hachting] & 35 & 22.74 \({}^{\text{c}}\) & 0.358 \({}^{\text{b}}\) & 2.63 & 0.036 & \(-\)1.129 & 22.00 & 24.00 \\ Total & 138 & 23.08 & 0.387 & 2.69 & \(-\)0.016 & \(-\)0.246 & 22.00 & 24.50 \\ \(p\)-Value & & \(<\)0.001 & \(-\)0.01 & & & & & \\ \hline \hline \end{tabular}  
* \({}^{\text{a}}\)–\({}^{\text{c}}\) Means in the same column with different superscript letters are significantly different (\(p<0.05\)); \({}^{\text{A}}\)–\({}^{\text{D}}\) variances in the same column with different superscript letters are significantly different (\(p<0.01\)).  
\end{table} 
Table 4: Effects of sibling eggs contact regime during the incubation process on incubation length and hatching synchrony of red-legged partridge eggs. Figure 1: Hatching spread of red-legged partridge eggs according to the sibling eggs contact regime during the incubation process: (**a**) without contact; (**b**) contact during incubation phase (1–20 days); (**c**) contact during hatching phase (21 days–hatching); (**d**) permanent contact (1 day–hatching). of the eggs during the hatching phase of the artificial incubation shortens its duration and increases hatching synchrony. In other poultry species, it has been reported that proximity or contact among eggs during the hatching period of the artificial incubation affects the time of hatch, accelerating it in Japanese quail (_Coturnix japonica_) [35] and Bobwhite quail [30]. In precocial birds, the contact among eggs favors hatching synchronization, reducing its dispersion, through mechanisms that involve inter-embryonic communication. Thus, embryos that are close to hatching emit more stimuli than those that are in a less advanced state of development [36]. The sources of stimulation are various, but those produced by the embryos themselves, when they are close to hatching, are clicks, sounds of embryo body movements, and breakage of the shell, as well as vocalizations [14]. In fact, it has been studied in pheasants (_Phasianus colchicine_) and mallards (_Anas platyrhynchos_) that eggs in contact during the hatching phase synchronize hatching more intensely, which shows that contact of the eggs in the final phase is more effective [15], as occurred in the present study. In Japanese quail, it was found that almost all embryos emit clicks, with a maximum level in pipped eggs, that all eggs emit sounds of body movements, and that vocalizations occur to a lesser extent but increase as hatching approaches [14]. In the present investigation, the close physical contact between the eggs achieved thanks to the artificial nests used in both the incubation and the hatching phases contributed not only to the adequate transmission of the sounds emitted by the embryos, but also to the movements and clicks that led to the maximum possible hatching synchrony. The evolutionary explanation of the findings in this research is related to the fact that, in precocial birds, physical contact of the eggs in the nest favors communication between embryos, favoring synchronized hatching in a short period of time [15; 37]. This favors the female partridge promptly leaving the nest with the nidifugous chicks even if there are eggs left unhatched [13; 38], to avoid the risk of being predated, which would be increased by a dilation of the hatching time [8; 39].