# Crocodile mothers' response to hatching calls

Naïs Caron Delbosc, Nicolas Boyer, Nicolas Mathevon, Nicolas Grimault

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Naïs Caron Delbosc, Nicolas Boyer, Nicolas Mathevon, Nicolas Grimault. Crocodile mothers' response to hatching calls. Animal Behaviour, 2025, 220, pp.123040. 10.1016/j.anbehav.2024.11.018. hal-04942512

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Crocodile mothers' response to hatching calls

Naïs Caron Delbosc<fnref n="1" />,<fnref n="2" />*, Nicolas Boyer<fnref n="1" />, Nicolas Mathevon<fnref n="1" />,<fnref n="3" />,<fnref n="4" />,<fnref n="5" /> & Nicolas Grimault<fnref n="2" />,<fnref n="5" />

<footnote n="1">¹ENES Bioacoustics Research Lab, CRNL, CNRS, Inserm, University of Saint-Etienne, Saint-Etienne, France.</footnote>

<footnote n="2">²Équipe Cognition Auditive et Psychoacoustique / CRNL, CNRS, Inserm, University Lyon 1, Bron, France.</footnote>

<footnote n="3">³Institut Universitaire de France.</footnote>

<footnote n="4">⁴École Pratique des Hautes Études, CHArt Lab, PSL University, Paris, France.</footnote>

<footnote n="5">⁵These authors jointly supervised this work.</footnote>

<footnote>*Author for correspondence (nais.caron.delbosc@gmail.com)</footnote>
In animal species with parental care, caregivers' investment is often driven by solicitation signals emitted by the young. Previous studies, particularly in birds and mammals, show that parents modulate their response to these signals according to characteristics such as their intensity and number per unit of time. In crocodilians, mature embryos still in the egg emit hatching calls perceived by other embryos and by the adult guarding the nest. These calls help to synchronize hatching within the nest and encourage the adult to dig the nest and help the young to hatch. However, the embryos do not start calling all at once, and it can take several hours or even days after embryos have started to vocalize before the adult digs the nest. When and why does the crocodile parent decide to respond to the hatching calls of its offspring? Here we show that Nile crocodile mothers only start digging their nests if the hatching calls are emitted in a sustained manner by the offspring. While females react with head and body orientation movements to isolated calls, only continuous bursts of calls lasting several tens of seconds induce digging behaviour. This high response threshold on the part of the mothers probably limits the untimely digging up of eggs that may not have reached full maturity, thus avoiding damaging them, and is likely to favour the synchronization of offspring hatching. Overall, this study suggests that parental response to juvenile solicitations is not necessarily linearly correlated with the quantity of begging signals received, but may require that those exceed a sufficient threshold.

KEYWORDS: Maternal care, Acoustic communication, Parent-offspring communication
Parental care is vital for offspring survival in many animal species (Clutton-Brock, 1991; Royle et al., 2012). Parent-offspring interactions are based on exchanges of information-carrying signals that enable the young to solicit caregivers, which in turn provide an appropriate response (Berlin & Clark, 1998; Evans, 1992; Godfray, 1991; Godfray & Johnstone, 2000; Kilner & Johnstone, 1997; Mathevon, 2023). These solicitation signals usually carry static information about the identity of the sender (species, individual; Charrier et al., 2003; Charrier, Mathevon, Hassnaoui, et al., 2002; Charrier, Mathevon, & Jouventin, 2002; Colombelli-Négrel et al., 2012; Leonard, 1997) and dynamic information about its immediate needs (hunger, distress; Budden & Wright, 2001; Leonard & Horn, 1998; Trivers, 1974; Wright & Leonard, 2007). Caregivers use this information to adjust their response and the quantity and quality of their investment (Godfray & Johnstone, 2000; Wright & Leonard, 2007). In some oviparous vertebrates (turtles, crocodiles, birds), these parent-offspring communication begin as early as in the egg, when embryos are able to vocalize and communicate through the eggshell (Jorgewich-Cohen et al., 2022; Kostoglou et al., 2021; Lacroix et al., 2022). These pre-hatching vocalizations have particularly important roles when they signal imminent hatching. They can induce physiological changes in parents preparing them to raise their brood (Saino & Fasola, 1996), play a role in how parents will accept to care for the young and thus constitute a barrier to nest parasitism (Colombelli-Négrel et al., 2012), or induce hatching assistance behaviours (Vergne & Mathevon, 2008). In crocodilians, mature embryos vocalize shortly before hatching. In response to these vocalizations, the parent digs up the eggs and helps the young to hatch by taking them in its mouth and cracking their shells. Here we examine how these vocal signals drive this parental behaviour.
Crocodilians are archosaurs, a monophyletic group that includes pterosaurs, dinosaurs and birds (Grigg & Kirshner, 2015). The female crocodile selects an egg-laying site - usually the same one year after year - and lays several dozen eggs at once in a nest that is either a mound of vegetation, or hole dug in generally sandy soil that she will cover with sand once laying is complete (Charruau et al., 2010; Grigg & Kirshner, 2015; Kofron, 1989; Kushlan & Mazzotti, 1989; Lang, 1987; Modha, 1967; Pooley, 1977; Pooley & Gans, 1976). The incubation period lasts 84 to 100 days after oviposition (Grigg & Kirshner, 2015; Pooley & Gans, 1976). Throughout this period, the female and sometimes the male remains on or near the nest to protect it from potential predators (Cott, 1971; Grigg & Kirshner, 2015; Hunt, 1969; Lang, 1987; Magnusson, 1980; Modha, 1967; Pooley, 1977; Surf et al., 2019). In at least eight crocodilian species, the male is involved in parental care (Lang, 1987; Reynolds et al., 2002; Toro, 1969). The aggressiveness with which the adult defends their nests increases as hatching approaches (Charruau & Hénaut, 2012; Cott, 1971; Grigg & Kirshner, 2015; Hunt & Watanabe, 1982; Kushlan & Kushlan, 1980; Lang, 1987). However, there are wide variations between parents: some hardly ever leave their nest, others visit only irregularly (Charruau & Hénaut, 2012; Cott, 1971; Grigg & Kirshner, 2015; Hunt, 1975; Kofron, 1989; Kushlan & Mazzotti, 1989; Kushlan & Simon, 1981; Lang, 1987; Magnusson, 1980; Modha, 1967; Pooley, 1977; Pooley & Gans, 1976). When the eggs hatch, the adult in charge of the nest digs up the eggs and takes them in its mouth to break the shell. It then brings the young to the water, either one by one or all at the same time, this behaviour presumably depending on the level of predation risk (Charruau & Hénaut, 2012; Cott, 1971; Hunt, 1975; Kushlan & Mazzotti, 1989; Lang, 1987; Modha, 1967; Pooley & Gans, 1976). After hatching, the adult(s) continue to protect their young for a period that varies
greatly depending on the species, from a few days to several years (Alonso Tabet,
2009; Charruau & Hénaut, 2012; Hunt & Watanabe, 1982; Kushlan & Mazzotti, 1989;
Lang, 1987; Magnusson, 1980; Modha, 1967; Pooley & Gans, 1976).

Among crocodilian acoustic signals, the calls emitted by mature embryos shortly
before or during hatching are of particular interest. Previous observations and
experimental work have established that these vocalizations synchronize hatching -
the young vocalize and hatch in response to the calls of their siblings - and induce
nest digging by the mother (Campbell, 1973; Charruau & Hénaut, 2012; Cott, 1971;
Hunt, 1975; Kushlan & Mazzotti, 1989; Kushlan & Simon, 1981; Modha, 1967;
Pooley & Gans, 1976; Surf et al., 2019; Vergne et al., 2006). Lang (1987) observed a
female mugger crocodile *Crocodylus palustris* in captivity opening her nest in
response to hatching calls emitted from one end of her enclosure. A similar
observation (Pooley, 1977) reported that a female Nile crocodile *Crocodylus niloticus*,
which had remained near her nest for 117 days, walked over to a loudspeaker in her
enclosure playing back hatching calls, and began digging here. The same female
used her jaws to pick up hatchlings previously introduced in the enclosure and
brought them to the water as if they had just hatched. In a controlled experiment in
which the effect of hatching calls was compared with that of non-biologically
significant sounds, Vergne & Mathevon (2008) demonstrated that playing back
hatching calls from a loudspeaker buried in place of the eggs at the nest site did
indeed elicit digging behaviour in female Nile crocodiles. In the same study,
playbacks of hatching calls near mature eggs caused the eggs to hatch. Other
observations report that mature embryos in the same nest increase their vocalization
frequency in the hours preceding excavation of the nest by the female (Cott, 1971;
Lee, 1968). It has also been found that young crocodiles are unable to emerge from
the nest on their own, making maternal assistance indispensable (Modha, 1967).

Moreover, both nests and young crocodiles are victims of numerous predators (mainly large lizards and birds), and parental protection is essential (Briggs-Gonzalez et al., 2017; Grigg & Kirshner, 2015; Khan et al., 2020; Rainwater et al., 1999; Somaweera et al., 2013). In the American alligator *Alligator mississippiensis*, one anecdote reports that half the eggs in a nest abandoned by the mother failed to hatch (Joanen, 1969). Similar observations have been made in the American crocodile *Crocodylus acutus* (Alonso Tabet, 2009; Charruau et al., 2010; Kushlan & Mazzotti, 1989). In the Nile crocodile, several reports mention that nests not excavated by females never hatch (Cott, 1971; Modha, 1967; Pooley & Gans, 1976). A study of the saltwater crocodile *Crocodylus porosus* found that eggs from a nest opened by the female all hatched successfully, whereas the young from an unexcavated nest all died, even though the young were vocalizing (Magnusson, 1980). Mature crocodilian embryos are apparently unable to free themselves from their nests (Kofron, 1989).

While it is therefore certain that parental assistance during the hatching of young crocodilians is both essential to their survival and driven by their hatching calls, none of the previous observations and experimental studies could determine precisely how much calling is necessary to induce the response of female crocodiles. In all studies where hatching calls were played from a loudspeaker, they were emitted in a continuous sequence. However, in a natural setting, mature embryos do not all vocalize strictly at the same time, and there are no reports of an adult crocodile digging and reburying its nest several times. Crocodile eggs are sensitive to manipulation - they must not be turned over, for example, as bird eggs can be (Deeming, 1989; Shaffer et al., 2014; Tullett & Deeming, 1987). Nest digging is probably a one-off event, carried out over a relatively short period of time. However,
we do not know to what extent the adult pays attention to the quantity of sound
signals coming from its clutch. Does it react as soon as the first vocalizations are
heard, at the risk of digging up eggs, some of which may not be quite ready to hatch?
Would it continue to dig if the hatching calls are emitted discontinuously, alternating
with periods of silence?

To explore the temporal dynamics of adult crocodilian response to hatching calls, we conducted playback experiments to test whether the response of Nile crocodile mothers to vocal solicitations from their young was gradual as a function of the quantity of calls heard. After burying a loudspeaker in place of mature eggs, we played succession of hatching calls of different duration separated by periods of silence, and observed the behavioural response of the mother guarding her nest. Our results show that female crocodiles have an interest in hatching calls even when played in low numbers, but decide to actively dig the nest only when these calls are played in a sustained manner.

METHODS

Location and tested animals

We worked with female Nile Crocodile *Crocodylus niloticus* (N=12). We conducted
the experiments when the eggs were mature in the nests, i.e. from July 7, 2022 to
July 14, 2022, (N=6 females) and from July 6, 2023 to July 14, 2023 (N=6 females).
Identifying individual females among hundreds was not possible, and a few
individuals may have been tested in both years.

To determine the maturity of the nests, zoo staff note the date of laying - it is easy to
observe a female crocodile laying eggs - and estimate the date of hatching by adding
3 months. We only tested females guarding their nests, i.e. females who, in the days preceding the experiments, remained almost motionless over their nest, moving only a few meters to take shelter from the sun or to cool off in the water near the nest.

## Acoustic stimuli

We used Nile crocodile hatching calls as acoustic stimuli. These calls had been recorded prior to the present study from mature eggs, and belong to the recording library of the ENES Bioacoustics Research laboratory. For the experiments in the present study, we prepared 7 different sequences, each lasting 10 minutes (Fig. 1b,c). Each sequence (S) presented an acoustic stimulus every 30 seconds, consisting of a succession of hatching calls (2-3 calls per second) whose duration varied between 0.5 second (1.67 % of the total duration of the sequence -S1) and 30 seconds (100 % of the total duration of the sequence -S7). The actual duration of hatching calls for the 7 sequences is shown in Table 1.

## Experiment

Prior to the experiment, one of us (NB) and one of the zoo staff descended into the crocodile area to remove the mother from her nest, and buried a handheld transceiver (Midland G7Pro, Kansas City, Missouri, United States) some 10 centimetres underground at the supposed location of the female's nest (Fig. 1a). During the experimental trials, the sound stimuli were sent by radio wave to this transceiver with a FoxPro Fusion loudspeaker (Lewistown, Pennsylvania, United States; see Fig. 2 for a complete description of the emission chain). We used this portable system because 1) for practical reasons, it was not possible to connect a
buried loudspeaker by cable to our transmitter system, 2) we had to use a small loudspeaker that was easy to bury, and 3) the distance between transmitter and receiver was too great (over 20 meters) to use a Bluetooth loudspeaker (the loudspeaker being buried, a Bluetooth connection would have been deficient anyway). The sound intensity measured at the receiver was equal to 81.2 ± 1.0 dB that leads to a sound intensity equal to 63.6 ± 1.1 dB at 1 cm above the ground surface the receiver being buried at 10 cm deep in the ground.

Female crocodiles were tested with the seven sound sequences, ordered from S1 to S7. The average duration between each sequence was 5 min 26 s ± 3 min 58 s. To prevent the female from damaging the loudspeaker, we stopped the experiment as soon as the female was actively digging the nest, i.e. sometimes before the sequence S7 was played back. We also stopped the experiment if the female left the nest to shelter from the sun (N=2 individuals; for details of what each tested female listened to, see Table S1).

## Analysis of behavioural reaction to stimuli

All experiments were filmed using a camcorder (JVC Everio, Kanagawa-ku, Yokohama, Japan) and a GoPro (Hero Session, San Mateo, California, United States). All observations were analysed after the experiments by viewing the videos. As illustrated in Fig. 3, we observed and measured three different female movements: body movements (head movements, body movements when the female moves forward or backward on the nest), movements involving the snout (when the female buries her snout in the nest or when she digs with her snout), digging the nest with the paws (videos examples of these behaviours are provided in electronic
supplementary materials with one video regrouping all these behaviours performed in sequence by one female: first the female turn her head, then moves forward, starts to dig with the paws and finally with the snout). We considered a new movement when the female starts moving again after a period of immobility of a minimal duration of 5 seconds.

## Statistical analysis

We performed Bayesian statistical analyses with R (v.4.1.2). Bayesian statistics are particularly suited to small sample sizes and offer intuitive interpretation by generating posterior probability distributions (Kruschke & Liddell, 2018). We modelled the probability of body movement, digging with the snout, digging with the paws, and digging duration, respectively using Bayesian mixed models, fit in Stan computational framework accessed with brms package (Bürkner, 2017). All models were based on four chains of 10,000 iterations with 5,000 warmup samples (Bernoulli distribution for probabilities and gamma distribution for digging duration). Default flat priors were kept for all models due to the difficulty of predicting the behaviour of the animals tested. Model convergence was checked using trace-plots. Fitted values and contrasts were reported using the median of posterior distributions and 95% credible intervals, reported in the text as 95% CIs. The existence of an effect and its certainty are represented by the proportion of posterior distribution that is positive (or negative). This posterior distribution ranges from 0 to 100% and correlates strongly with the frequentist p-value, meaning that p-values of 0.1, 0.05, 0.01 and 0.001 correspond approximately to a proportion of the posterior distribution that is positive (or negative) of 95%, 97.5%, 99.5% and 99.95% respectively (Makowski et al., 2019).
## Ethical note

The experiments were carried out at the “Crocoparc” zoo (Agadir, Morocco), in compliance with Moroccan regulations, under the supervision of zoo staff and under the ethical approval of the ENES laboratory (n° D 42-218-0901). 6 different female individuals were tested each year. We did not handle or trap any individuals as part of the study. Each year we took care to test different females once. All crocodiles tested in experiments returned to normal behaviours on their nest within 5 min after burying the loudspeaker. As the experiments took place in the park where the crocodiles are in semi-liberty, the crocodiles tested were free to leave the place where the stimulations were sent, which could only be heard a few metres away. Our experiments complied with the ASAB/ABS guidelines.

## RESULTS

Data show that female crocodiles only start digging their nests when they hear hatching cries emitted almost continuously (Fig. 3). Although mothers show interest in their young's vocalizations by moving around the nest as soon as they hear a few isolated calls, they do not dig the nest. The fitted probability of digging behaviour when hatching calls occupy less than 2% of the time (sequence S1) is 12.73 ± 6.21% (digging with paws) and 11.89 ± 5.53% (digging with snout). These probabilities rise to 56.01 ± 14.86% and 52.20 ± 13.44%, respectively, when hatching calls are played back continuously (sequence S7). The paragraphs below detail the behavioural responses observed and the differences according to the amount of hatching calls. The number of observed movements depending on the stimulus characteristics are
reported in Table S2. Fitted values and effects of the sound sequences on the
females' behavioural reaction are presented in Tables S3, S4.

Body movement

Female crocodiles responded to hatching calls with nest movements and head
movements in around 75% of trials for all stimuli S1 to S5 (Fig. 3a). Notably, the
probability of observing these simple movements in response to calls is higher than
when hatching calls are emitted for 100% of the trial time (comparison between S7
and S1: +44.00%, 95% CI [22.89, 62.35]; S2: +38.29%, 95% CI [18.60, 55.95]; S3:
+31.28%, 95% CI [8.58, 52.03]; S4: +37.15%, 95% CI [10.88, 60.21]; S5: +54.64%,
95% CI [27.58, 75.54]; S6: +27.22%, 95% CI [3.47, 49.95]). These behavioural
responses show that females perceive hatching calls even when they are emitted in
small amounts (from sequence S1).

Digging with snout

The probability of females responding to hatching calls by digging into the ground
with their snouts increases gradually from stimulus S1 to stimulus S7 (Fig 2b;
comparison between S7 and S1: +39.48%, 95% CI [16.51, 63.20]; S2: +37.58%,
95% CI [15.86, 60.10]; S3: +44.56%, 95% CI [20.97, 68.42]; S4: +38.84%, 95% CI
[13.34, 64.00]; S5: +35.21%, 95% CI [5.59, 62.43]; S6: +20.89%, 95% CI [-3.76,
44.89]; comparison between S6 and S1: +17.43%, 95% CI [-1.84, 46.13]; S2:
+15.53%, 95% CI [-3.37, 43.06]; S3: +22.17%, 95% CI [3.33, 51.89]; S4: +16.85%,
95% CI [-5.47, 46.29]; S5: +13.63%, 95% CI [-15.28, 44.21]).
## Digging with paws

The probability that the female responds to hatching calls by actively digging her nest with her paws is higher for S7 than for all other stimuli (Fig 2c; comparison with S1: +41.86%, 95% CI [17.78, 64.28]; S2: +39.22%, 95% CI [16.41, 61.33]; S3: +29.94%, 95% CI [6.11, 53.66]; S4: +31.58%, 95% CI [5.31, 57.27]; S5: +47.05%, 95% CI [19.13, 47.05]; S6: +31.59, 95% CI [7.84, 55.08]).

The time spent digging the nest (with paws or snout) also depends on the time during which the female hears hatching calls. While this time remains logically low in response to stimuli S1 to S5, it increases for stimuli S6 and S7 (Fig 3; comparison between S6 and S1: +2.15 s, 95% CI [-4.39, 13.14]; S2: +2.25 s, 95% CI [-4.07, 13.29]; S3: +4.41 s, 95% CI [-1.37, 15.27]; S4: +1.81 s, 95% CI [-5.66, 12.84]; S5: +4.32 s, 95% CI [-5.28, 15.39]; comparison between S7 and S1: +4.80 s, 95% CI [-2.32, 16.32]; S2: +4.87 s, 95% CI [-1.93, 16.50]; S3: +7.07 s, 95% CI [0.71, 18.54]; S4: +4.47 s, 95% CI [-3.42, 15.98]; S5: +6.93 s, 95% CI [-2.95, 18.78]). Fitted values and effects of the sound sequence on digging duration are presented in Tables S5 and S6.

## DISCUSSION

In this study, we show that nest digging by female Nile crocodiles depends on the temporal dynamics of the hatching calls she hears. The number of calls emitted from inside the nest by mature embryos, and by extension the number of eggs about to hatch, therefore represents crucial information for the female, driving her behavioural response. Isolated hatching calls are enough to mobilize the female's attention - an
attention that translates into movements towards the nest as soon as a small number
of hatching calls are heard - but it is only when these calls are heard continuously for
several tens of seconds that the female decides to dig with her legs or snout. These
results suggest that the female waits until all the eggs in the nest are ready to hatch
before opening the nest.

These results confirm that hatching calls are a key stimulus releasing maternal beha-
vior in crocodiles, and specifically digging behaviour (Lang, 1987; Pooley, 1977;
Vergne & Mathevon, 2008). They add to what was already known by showing that
the magnitude of this stimulus (the temporal duration during which the calls are emit-
ted) is a major factor modulating maternal behaviour. The production of hatching
calls has evolved as an effective solicitation strategy, fine-tuning the parent's nest-
digging behaviour. Without these calls, the female does not dig the nest. A small
amount of calling keeps the female alert, while continuous calling prompts her to take
action with her hatching young. These results underline the importance of acoustic
communication in crocodilians. In the wild, eggs and young crocodiles are heavily
predated, with low survival rates (Briggs-Gonzalez et al., 2017; Grigg & Kirshner,
2015; Khan et al., 2020; Rainwater et al., 1999; Somaweera et al., 2013). Parental
attention induced by the signals emitted by the young is probably an important factor
in their survival.

Other factors and stimuli may be involved in modulating digging behaviour. When
embryos break their shells, odours are certainly released (Lang, 1987). We currently
have no idea what role these odours may play in parental behaviour. It would also be
interesting to test whether the female perceives the vibrations of the substrate that
the movements of the hatching embryos inevitably provoke. It is possible that sticking
her snout into the ground may help the female to perceive the embryos' vocalizations
via ear-bone conduction. It is also possible that it facilitates the perception of ground vibrations produced by the embryos, as crocodilians have numerous extremely sensitive mechanoreceptors on the skin around the snout (Di-Poï & Milinkovitch, 2013; Leitch & Catania, 2012; Soares, 2007).

Does this link between stimulus (hatching cries) and behavioural response (nest digging) inform the cognitive processes involved? It is quite clear that the female digs only when she hears hatching calls, and stops as soon as the nest becomes silent again. This ON/OFF response suggests that the cognitive processes involved may be fairly unsophisticated. In any case, the female's all-or-nothing response is well adapted to the situation, since it would be dangerous for the survival of the embryos if the female dug her nest at the slightest cry. According to our observations and those of zoo staff, a female whose eggs have been removed after laying never digs her nest, either at the estimated time of hatching or in the weeks that follow, unless stimulated with a playback of hatching calls. Hatching calls are obligatory releasing factors.

The female crocodile's digging behaviour does not meet the definition of a fixed action pattern, which would imply that she continues to dig until she finds her eggs from the moment she starts digging (Lorenz & Tinbergen, 1938). Digging behaviour is more like a taxis, a term coined by Tinbergen to define stimulus-driven behaviour (Beer, 2020). The female digs only when she hears hatching calls. This probably explains why the hatching process could take hours or even days (Charruau & Hénaut, 2012; Kushlan & Mazzotti, 1989): until mature embryos vocalize continuously, the female will not dig them up. This behaviour is probably modulated by factors internal to the females, in particular their hormonal profile. An interesting experiment would be to measure the response of female crocodiles to hatching calls over the course of the
year, and particularly during the incubation period. In the present study, females were
tested at the end of the three-month incubation period, and it can be assumed that
females are particularly receptive to signals at this time. Observations by our re-
search group suggest that females remain highly receptive for weeks and months af-
terwards. It is likely that their motivation to respond diminishes afterwards.

On another note, the age of the female and her experience of reproduction are also
factors that should be evaluated. It may be hypothesized that an experienced female
would respond more adequately to sound stimuli from her offspring than a naïve fe-
male. At present, we have no information on this matter.

In our experimental protocol, we gradually increased the duration of the hatching call
sequence. It was difficult to design the experiment in any other way: if we had played
the stimuli in a random order among the females, some would have been stimulated
first with the long hatching call sequences and would have dug their nest immedi-
ately, which would have precluded testing them later with the short sequences. That
said, as the stimuli are always played in the same order, from sequences containing
few hatching calls to sequences containing many, a cumulative effect of the stimuli
cannot be ruled out. This effect is likely to work in two directions: increasing the fe-
male's motivation to dig (she would then dig in response to fewer cries than if she
had not heard the previous sequences - which seems unlikely in view of the experi-
mental results), or on the contrary decreasing her motivation to dig (following fatigue,
for example - crocodile mothers do not feed during the three-month incubation
period; Cott, 1971; Pooley & Gans, 1976). It is unlikely that these situations would
have led to a radically different conclusion. Perhaps the females would have respon-
ded a little better or a little less well to the stimuli played last, but in any case, it
seems certain that they would not have dug in the absence of calls.
Previous studies on various animal species show that offspring vocalize more when they need parental care. In a study on budgerigars *Melopsittacus undulates*, Berlin & Clark (1998) had already suggested that parents might interpret the high and constant frequencies of calls, typical of embryos close to hatching, as a signal indicating that the chick is ready to emerge from the egg and needs assistance hatching. In chickens, *Gallus gallus*, the rate of vocalizations also increases as hatching approaches, similar to crocodilians (Cott, 1971; Lee, 1968), and this increase in vocalizations could be an initial signal to the parents that the eggs are ready to hatch (Brua et al., 1996).

In conclusion, the present study shows that a parental response to infant vocalizations is not necessarily linearly correlated with the quantity of solicitation signals emitted by the young. In a bird's nest, a nestling usually expresses dynamic information quantitatively encoded in the signals it produces (e.g. intensity, spectral structure and number of begging calls). The parent responds to this information by providing appropriate care (e.g. feeding or hatching assistance; Berlin & Clark, 1998; Brua et al., 1996; Evans, 1992; Impekoven, 1973). Sometimes, it is the overall information coming from the nest that modulates the parental response (Mathevon & Charrier, 2004). In crocodilians, it is the information coming from the nest to which the parent pays attention. The information is therefore not encoded by a single individual, but by the whole clutch. The clutch's vocalizations therefore provide the crocodilian parent with information that is both static (only the calls of young crocodilians induce a parental response, Vergne & Mathevon, 2008) and dynamic (the quantity of calls). While the crocodilian parent perceives activity in the nest from the first call, it will wait until it detects sufficient vocal activity from the clutch to respond to its requests.
**Author Contributions**

N.C.D.: conceptualisation, data curation, formal analysis, investigation, methodology, validation, visualization, writing-original draft, writing-review and editing; N.B.: data curation, investigation, methodology; N.M. and N.G.: conceptualisation, funding acquisition, formal analysis, investigation, methodology, project administration, resources, supervision, validation, writing-review and editing.

**Data Availability**

Datasets, all original statistical codes and video examples will be available from the Zenodo Repository: DOI: 10.5281/zenodo.11198570

Additional information (sound file and tables) is provided in electronic supplementary material.

**Funding**

This research has been funded by the Labex CeLyA (PhD fundings to Naïs Caron Delbosc, Lyon Center of Acoustics ANR-10-LABX-60), the CNRS, the Institut universitaire de France (NM), and the University of Saint-Etienne. This publication was completed while NM was Visiting Miller Professor at the University of California, Berkeley (Miller Institute for Basic Research in Science).

**Declaration of Interest**

The authors declare no competing interests.
## Acknowledgments

The authors are grateful to "Crocoparc" zoo in Agadir, Morocco, for its long-term support.

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<table><caption>**Table 1.** Duration and percentage of time of the succession of hatching calls per 10-minute sequence.</caption><thead><tr><th>Sequence</th><th>S1</th><th>S2</th><th>S3</th><th>S4</th><th>S5</th><th>S6</th><th>S7</th></tr></thead><tbody><tr><td>Duration (s)</td><td>0.5</td><td>1</td><td>1.9</td><td>3.75</td><td>7.5</td><td>15</td><td>30</td></tr><tr><td>Percentage of the played back sequence with hatching calls (%)</td><td>1.67</td><td>3.33</td><td>6.33</td><td>12.5</td><td>25</td><td>50</td><td>100</td></tr></tbody></table>
<figure><img src="image_2.png" /><figcaption>**Figure 1.** Description of the experiment and stimuli. (a) Nile crocodile female digging with her paws in response to a playback of hatching calls. The loudspeaker has previously been buried in the nest. (b) Spectrogram and oscillogram of a sequence of hatching calls (2-3 calls/s). S1 and S4 are two examples of stimuli of different durations. (c) Females are tested with sound stimuli of varying duration, from 0.5</figcaption></figure>
second (S1) to 30 seconds (S7). Each sequence lasts 10 minutes, with one stimulus every 30 seconds. The stimuli thus correspond to a certain percentage of the total sequence duration (S1: 1.67%; S7: 100%).
<figure><img src="image_3.png" /><figcaption>**Figure 2.** Signal modification through the communication channel. From top to bottom, spectrogram of sequence S4 recorded at 5 cm from the loudspeaker, at 5 cm from the transceiver and at 5 cm above the sand surface where the transceiver is buried at a depth of 7 cm. The transmission of sound through the transceiver device adds a supplementary noise between 0.5 and 3.5 kHz. The sand also attenuates the sound propagation.</figcaption></figure>
<figure><img src="image_4.png" /></figure>

**Figure 3.** The behavioural response of female crocodiles depends on the duration of the hatching call stimulus. (a) Crocodile mothers react with simple body movements (head rotation, movement on the nest) when hatching calls are alternating with long periods of silence (from stimulus S1 -1.67% of the trial time with hatching calls- to stimulus S5 -25% of the trial time with hatching calls). (b)(c) Mothers dig the nest with their snout and paws when hatching calls are played for at least 50% of the trial (stimuli S6 and S7). Boxplots represent the probability of occurrence of each
movement for each sequence (fitted value of the median of the posterior distribution
with 95% CI; see Table S2 for the exact numbers of observed movements).
<figure><img src="image_5.png" /><figcaption>**Figure 4.** The duration of digging by crocodile mothers increases when hatching calls are present for at least 50% of the time. Boxplots represent the digging duration (fitted value of the median of the posterior distribution with 95% CI).</figcaption></figure>
Supplementary Material

<table><caption>**Table S1.** Number of sequences played-back to females.</caption><thead><tr><th>Year</th><th colspan="6">2022</th><th colspan="6">2023</th></tr></thead><tbody><tr><th>Female</th><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>8</td><td>9</td><td>10</td><td>11</td><td>12</td></tr><tr><th>Number</th><td>3</td><td>2</td><td>5</td><td>7</td><td>7</td><td>3</td><td>7</td><td>7</td><td>7</td><td>7</td><td>7</td><td>2</td></tr></tbody></table>
<table><caption>**Table S2.** Number of movements observed in response to acoustic stimuli for the different sequences.</caption><thead><tr><th></th><th>S1</th><th>S2</th><th>S3</th><th>S4</th><th>S5</th><th>S6</th><th>S7</th></tr></thead><tbody><tr><td>Body movement (N)</td><td>57</td><td>71</td><td>32</td><td>16</td><td>11</td><td>24</td><td>22</td></tr><tr><td>Digging movements with snout (N)</td><td>16</td><td>26</td><td>29</td><td>10</td><td>3</td><td>8</td><td>20</td></tr><tr><td>Digging movements with paws (N)</td><td>13</td><td>17</td><td>7</td><td>4</td><td>3</td><td>8</td><td>20</td></tr></tbody></table>
<table><caption>**Table S3.** Fitted values of probability (in %) for each behaviour during the 7 sound sequences. Fit: median fitted probability for all iterations of the bayesian model; Se: standard error; Lwr: value below which 2.5% of the fitted values are; Upr: value above which 2.5% of the fitted values are.</caption><thead><tr><th>Behaviour</th><th>Sequence</th><th>Fit</th><th>Se</th><th>Lwr</th><th>Upr</th></tr></thead><tbody><tr><td rowspan="7">Body movement</td><td>S1</td><td>78.19</td><td>7.34</td><td>60.74</td><td>90.19</td></tr><tr><td>S2</td><td>72.59</td><td>8.17</td><td>53.35</td><td>86.74</td></tr><tr><td>S3</td><td>65.22</td><td>10.48</td><td>43.33</td><td>83.62</td></tr><tr><td>S4</td><td>71.68</td><td>11.60</td><td>44.98</td><td>89.64</td></tr><tr><td>S5</td><td>89.89</td><td>7.31</td><td>64.71</td><td>98.32</td></tr><tr><td>S6</td><td>61.52</td><td>13.11</td><td>34.03</td><td>83.34</td></tr><tr><td>S7</td><td>33.06</td><td>10.93</td><td>14.81</td><td>57.11</td></tr><tr><td rowspan="7">Digging with paws</td><td>S1</td><td>12.73</td><td>6.21</td><td>3.89</td><td>30.45</td></tr><tr><td>S2</td><td>15.28</td><td>7.04</td><td>4.82</td><td>34.50</td></tr><tr><td>S3</td><td>24.44</td><td>10.67</td><td>7.83</td><td>49.72</td></tr><tr><td>S4</td><td>22.07</td><td>11.61</td><td>5.93</td><td>51.32</td></tr><tr><td>S5</td><td>6.72</td><td>5.50</td><td>0.88</td><td>29.16</td></tr><tr><td>S6</td><td>22.27</td><td>11.38</td><td>6.37</td><td>52.06</td></tr><tr><td>S7</td><td>56.01</td><td>14.86</td><td>26.37</td><td>82.24</td></tr><tr><td>Digging with snout</td><td>S1</td><td>11.89</td><td>5.53</td><td>3.93</td><td>26.36</td></tr></tbody></table>
<table><tr><td></td><td>S2</td><td>13.77</td><td>5.60</td><td>5.22</td><td>29.24</td></tr><tr><td></td><td>S3</td><td>6.88</td><td>3.80</td><td>1.93</td><td>18.50</td></tr><tr><td></td><td>S4</td><td>11.66</td><td>7.31</td><td>2.59</td><td>34.34</td></tr><tr><td></td><td>S5</td><td>14.92</td><td>10.15</td><td>2.67</td><td>45.69</td></tr><tr><td></td><td>S6</td><td>29.82</td><td>13.39</td><td>10.30</td><td>61.59</td></tr><tr><td></td><td>S7</td><td>52.20</td><td>13.44</td><td>27.25</td><td>77.85</td></tr></table>
<table><caption>**Table S4.** Effect of the sound sequence on the females' behavioural reaction. Median [95% CI] difference (in % of probability) between sequence from the first column and sequence from other columns (medians of posterior distribution (%), 95% CI and percentage of positive posterior distribution).</caption><thead><tr><th>Behaviour</th><th>Seq.</th><th>S1</th><th>S2</th><th>S3</th><th>S4</th><th>S5</th><th>S6</th><th>S7</th></tr></thead><tbody><tr><td rowspan="2">Body movement</td><td rowspan="2">S1</td><td></td><td>5.42 [-8.14, 20.06], 78.66 %</td><td>12.29 [-3.25, 30.12], 93.92 %</td><td>6.17 [-11.53, 28.91], 74.24 %</td><td>-10.62 [-28.16, 11.47], 12.55 %</td><td>16.21 [-4.44, 40.32], 93.3 %</td><td>44.00 [22.89, 62.35], 100 %</td></tr><tr><td></td><td>-5.42 [-20.06, 8.14], 21.34 %</td><td>6.86 [-7.29, 23.07], 82.47 %</td><td>0.97 [-18.02, 23.18], 53.64 %</td><td>-15.98 [-34.45, 5.38], 5.82 %</td><td>10.66 [-9.99, 34.46], 83.77 %</td><td>38.29 [18.60, 55.95], 100 %</td></tr><tr><td rowspan="2"></td><td rowspan="2">S2</td><td></td><td>-12.29 [-23.07, 30.12, 3.25], 6.08 %</td><td>-6.86 [-7.29], 17.53 %</td><td>-5.94 [-27.53, 17.42], 29.73 %</td><td>-22.91 [-44.42, -0.64], 2.21 %</td><td>3.84 [-20.08, 28.83], 61.78 %</td><td>31.28 [8.58, 52.03], 99.57 %</td></tr><tr><td></td><td>-6.17 [-28.91, 11.53], 18.02 %</td><td>-0.97 [-23.18, 17.42, 27.53], 42.93 %</td><td>5.94 [-17.42, 27.53], 42.93 %</td><td>-16.72 [-15.76, 35.87], 42.93 %</td><td>9.70 [-35.87, 35.87], 42.93 %</td><td>37.15 [10.88, 60.21], 42.93 %</td></tr></tbody></table>
<table><tr><td></td><td></td><td>25.76</td><td>46.36</td><td>70.27</td><td></td><td>6.98],</td><td>76.91</td><td>99.71</td></tr><tr><td></td><td></td><td>%</td><td>%</td><td>%</td><td></td><td>7.1 %</td><td>%</td><td>%</td></tr><tr><td>S5</td><td></td><td>10.62<br/>[-<br/>11.47,<br/>28.16],<br/>87.45<br/>%</td><td>15.98<br/>[-5.38,<br/>34.45],<br/>94.18<br/>%</td><td>22.91<br/>[0.64,<br/>44.42],<br/>97.79<br/>%</td><td>16.72<br/>[-6.98,<br/>42.93],<br/>92.9 %</td><td></td><td>26.63<br/>[0.69,<br/>54.33],<br/>97.73<br/>%</td><td>54.64<br/>[27.58,<br/>75.54],<br/>100 %</td></tr><tr><td>S6</td><td></td><td>-16.21<br/>[-<br/>40.32,<br/>4.44],<br/>6.70 %</td><td>-10.66<br/>[-<br/>34.46,<br/>9.99],<br/>16.23<br/>%</td><td>-3.84 [-<br/>28.83,<br/>20.08],<br/>38.22<br/>%</td><td>-9.70 [-<br/>35.87,<br/>15.76],<br/>23.09<br/>%</td><td>-26.63<br/>[-<br/>54.33,<br/>-0.69],<br/>2.27 %</td><td></td><td>27.22<br/>[3.47,<br/>49.45],<br/>98.73<br/>%</td></tr><tr><td>S7</td><td></td><td>-44.00<br/>[-<br/>62.35,<br/>-<br/>22.89],<br/>0 %</td><td>-38.29<br/>[-<br/>55.95,<br/>-<br/>18.60],<br/>0 %</td><td>-31.28<br/>[-<br/>52.03,<br/>-8.58],<br/>0.43 %</td><td>-37.15<br/>[-<br/>60.21,<br/>-<br/>10.88],<br/>0.29 %</td><td>-54.64<br/>[-<br/>75.54,<br/>-<br/>27.58],<br/>0 %</td><td>-27.22<br/>[-<br/>49.45,<br/>-3.47],<br/>1.27 %</td><td></td></tr><tr><td>Digging<br/>with paws</td><td>S1</td><td></td><td>-2.20 [-<br/>14.54,<br/>8.08],<br/>31.11</td><td>-10.85<br/>[-<br/>28.94,<br/>1.01],</td><td>-8.64 [-<br/>32.01,<br/>5.43],<br/>12.23</td><td>5.08 [-<br/>12.49,<br/>20.24],<br/>79.54</td><td>-8.84 [-<br/>32.77,<br/>5.94],<br/>12.61</td><td>-41.86<br/>[-<br/>64.28,<br/>-</td></tr></table>
<table><tr><td></td><td></td><td>%</td><td>3.76 %</td><td>%</td><td>%</td><td>%</td><td>17.78],<br>0 %</td></tr><tr><td>S2</td><td>2.20 [-<br>8.08,<br>14.54],<br>68.89<br>%</td><td></td><td>-8.41 [-<br>24.26,<br>2.19],<br>6.21 %</td><td>-6.27 [-<br>29.03,<br>8.45],<br>21.09<br>%</td><td>7.43 [-<br>9.34,<br>23.56],<br>87 %</td><td>-6.48 [-<br>29.62,<br>8.87],<br>20.89<br>%</td><td>-39.22<br>[-<br>61.33,<br>-<br>16.41],<br>0 %</td></tr><tr><td>S3</td><td>10.85 [-1.01,<br>28.94],<br>96.24<br>%</td><td>8.41 [-<br>2.19,<br>24.26],<br>93.79<br>%</td><td></td><td>1.89 [-<br>19.68,<br>21.26],<br>58.26<br>%</td><td>16.00 [-1.49,<br>37.67],<br>96.77<br>%</td><td>1.74 [-<br>21.01,<br>22.75],<br>57.34<br>%</td><td>-29.94<br>[-<br>53.66,<br>-6.11],<br>0.62 %</td></tr><tr><td>S4</td><td>8.64 [-<br>5.43,<br>32.01],<br>87.77<br>%</td><td>6.27 [-<br>8.45,<br>29.03],<br>78.91<br>%</td><td>-1.89 [-<br>21.26,<br>19.68],<br>41.74<br>%</td><td></td><td>13.70 [-5.02,<br>40.22],<br>94.07<br>%</td><td>-0.19 [-<br>23.90,<br>22.88],<br>49.31<br>%</td><td>-31.58<br>[-<br>57.27,<br>-5.31],<br>0.9 %</td></tr><tr><td>S5</td><td>-5.08 [-<br>20.24,<br>12.49],<br>20.46<br>%</td><td>-7.43 [-<br>23.56,<br>9.34],<br>13 %</td><td>-16.00 [-<br>37.67,<br>1.49],<br>3.23 %</td><td>-13.70 [-<br>40.22,<br>5.02],<br>5.93 %</td><td></td><td>-13.93 [-<br>41.63,<br>5.34],<br>6.65 %</td><td>-47.05<br>[-<br>72.43,<br>-<br>19.13],</td></tr></table>
<table><tbody><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>0.04 %</td></tr><tr><td></td><td>S6</td><td>8.84 [-5.94, 32.77], 87.39 %</td><td>6.48 [8.87, 29.62], 79.11 %</td><td>-1.74 [-22.75, 21.01], 42.66 %</td><td>0.19 [-22.88, 23.90], 50.69 %</td><td>13.93 [-5.34, 41.63], 93.35 %</td><td>-31.59 [-55.08, -7.84], 0.39 %</td></tr><tr><td></td><td>S7</td><td>41.86 [17.78, 64.28], 100 %</td><td>39.22 [16.41, 61.33], 100 %</td><td>29.94 [6.11, 53.66], 99.38 %</td><td>31.58 [5.31, 57.27], 99.10 %</td><td>47.05 [19.13, 47.05], 99.96 %</td><td>31.59 [7.84, 55.08], 99.61 %</td></tr><tr><td rowspan="3">Digging with snout</td><td></td><td></td><td></td><td></td><td></td><td></td><td>-39.48 [-63.20, -16.51], 0.01 %</td></tr><tr><td>S1</td><td>-1.65 [-14.05, 9.52], 37.01 %</td><td>4.61 [-5.20, 16.89], 84.29 %</td><td>0.04 [-19.19, 13.71], 50.2 %</td><td>-2.92 [-30.93, 13.19], 36.42 %</td><td>-17.43 [-46.13, 1.84], 4.03 %</td><td></td></tr><tr><td>S2</td><td>1.65 [-9.52, 14.05], 62.99 %</td><td>6.29 [-1.91, 18.56], 93.8 %</td><td>1.76 [-16.59, 15.90], 59.88 %</td><td>-1.19 [-28.06, 14.59], 44.62 %</td><td>-15.53 [-43.06, 3.37], 5.97 %</td><td>-37.58 [-60.10, -15.86], 0.01 %</td></tr></tbody></table>
<table><tr><td>S3</td><td>-4.61 [-16.89, 5.20], 15.71 %</td><td>-6.29 [-18.56, 1.91], 6.20 %</td><td>-4.44 [-24.60, 7.32], 22.34 %</td><td>-7.55 [-35.72, 6.17], 15.81 %</td><td>-22.17 [-51.89, -3.33], 0.74 %</td><td>-44.56 [-68.42, -20.97], 0 %</td></tr><tr><td>S4</td><td>-0.04 [-13.71, 19.19], 49.80 %</td><td>-1.76 [-15.90, 16.59], 40.12 %</td><td>4.44 [-7.32, 24.60], 77.66 %</td><td>-2.85 [-30.94, 17.88], 37.99 %</td><td>-16.85 [-46.29, 5.47], 6.91 %</td><td>-38.84 [-64.00, -13.34], 0.15 %</td></tr><tr><td>S5</td><td>2.92 [-13.19, 30.93], 63.58 %</td><td>1.19 [-14.59, 28.06], 55.38 %</td><td>7.55 [-6.17, 35.72], 84.19 %</td><td>2.85 [-17.88, 30.94], 62.01 %</td><td>-13.63 [-44.21, 15.28], 15.79 %</td><td>-35.21 [-62.43, -5.59], 1.03 %</td></tr><tr><td>S6</td><td>17.43 [-1.84, 46.13], 95.97 %</td><td>15.53 [-3.37, 43.06], 94.03 %</td><td>22.17 [-3.33, 51.89], 99.26 %</td><td>16.85 [-5.47, 46.29], 93.09 %</td><td>13.63 [-15.28, 44.21], 84.21 %</td><td>-20.89 [-44.89, 3.76], 4.82 %</td></tr></table>
<table><tr><td></td><td></td><td>39.48</td><td>37.58</td><td>44.56</td><td>38.84</td><td>35.21</td><td>20.89</td><td></td></tr><tr><td></td><td>S7</td><td>[16.51, 63.20], 99.99</td><td>[15.86, 60.10], 99.99</td><td>[20.97, 68.42], 100 %</td><td>[13.34, 64.00], 99.85</td><td>[5.59, 62.43], 98.77</td><td>[-3.76, 44.89], 95.18</td><td></td></tr><tr><td></td><td></td><td>%</td><td>%</td><td></td><td>%</td><td>%</td><td>%</td><td></td></tr></table>
<table><caption>**Table S5.** Fitted values of digging duration (in s) for the 7 sound sequences. Fit: median fitted probability for all iterations of the bayesian model; Se: standard error; Lwr: value below which 2.5% of the fitted values are; Upr: value above which 2.5% of the fitted values are.</caption><thead><tr><th></th><th>Sequence</th><th>Fit</th><th>Se</th><th>Lwr</th><th>Upr</th></tr></thead><tbody><tr><td rowspan="7">Digging duration (s)</td><td>S1</td><td>9.68</td><td>2.01</td><td>6.31</td><td>15.02</td></tr><tr><td>S2</td><td>9.65</td><td>1.88</td><td>6.29</td><td>14.51</td></tr><tr><td>S3</td><td>7.44</td><td>1.45</td><td>4.88</td><td>11.31</td></tr><tr><td>S4</td><td>10.03</td><td>2.43</td><td>6.14</td><td>16.83</td></tr><tr><td>S5</td><td>7.43</td><td>2.74</td><td>3.68</td><td>16.69</td></tr><tr><td>S6</td><td>11.88</td><td>3.42</td><td>6.82</td><td>23.02</td></tr><tr><td>S7</td><td>14.55</td><td>3.57</td><td>9.08</td><td>26.24</td></tr></tbody></table>
<table><caption>**Table S6.** Effect of the sound sequence on digging duration. Median [95% CI] difference (in % of probability) between sequence from the first column and sequence from other columns (medians of posterior distribution (%), 95% CI and percentage of positive posterior distribution).</caption><thead><tr><th>Digging duration (s)</th><th>Sequence</th><th>S1</th><th>S2</th><th>S3</th><th>S4</th><th>S5</th><th>S6</th><th>S7</th></tr></thead><tbody><tr><td rowspan="3"></td><td rowspan="3">S1</td><td></td><td>0.07 [-3.63, 4.19], 51.67 %</td><td>2.22 [-1.05, 6.52], 90.73 %</td><td>-0.32 [-5.93, 4.31], 44.5 %</td><td>2.19 [-6.08, 7.48], 76.08 %</td><td>2.15 [-13.14, 4.39], 27.21 %</td><td>-4.80 [-16.32, 2.32], 9.24 %</td></tr><tr><td></td><td>-0.07 [-4.19, 3.63], 48.33 %</td><td>2.16 [-0.47, 5.39], 94.57 %</td><td>-0.40 [-5.57, 3.52], 42.29 %</td><td>2.13 [-5.93, 6.81], 76.2 %</td><td>-2.25 [-13.29, 4.07], 25.81 %</td><td>-4.87 [-16.50, 1.93], 8.24 %</td></tr><tr><td></td><td>S3</td><td>-2.22 [-6.52, 1.05], 9.27 %</td><td>-2.16 [-5.39, 0.47], 5.43 %</td><td>-2.56 [-7.97, 0.94], 8.06 %</td><td>0.01 [-8.12, 3.98], 50.14 %</td><td>-4.41 [-15.27, 1.37], 7.29 %</td><td>-7.07 [-18.54, -0.71], 1.44 %</td></tr></tbody></table>
<table><tr><td></td><td></td><td>0.32 [-4.31, 5.93], 55.50 %</td><td>0.40 [-3.52, 5.57], 57.71 %</td><td>2.56 [-0.94, 7.97], 91.94 %</td><td>2.52 [-5.57, 8.61], 78.77 %</td><td>-1.81 [-12.84, 5.66], 31.58 %</td><td>-4.47 [-15.98, 3.42], 13.09 %</td></tr><tr><td>S4</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>-2.19 [-7.48, 6.08], 23.92 %</td><td>-2.13 [-6.81, 5.93], 23.8 %</td><td>-0.01 [-3.98, 8.12], 49.86 %</td><td>-2.52 [-8.61, 5.57], 21.23 %</td><td>-4.32 [-15.39, 5.28], 15.23 %</td><td>-6.93 [-18.78, 2.95], 7.07 %</td></tr><tr><td>S5</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>2.15 [-4.39, 13.14], 72.79 %</td><td>2.25 [-4.07, 13.29], 74.19 %</td><td>4.41 [-1.37, 15.27], 92.71 %</td><td>1.81 [-5.66, 12.84], 68.42 %</td><td>4.32 [-5.28, 15.39], 84.77 %</td><td>-2.62 [-10.43, 4.97], 21.67 %</td></tr><tr><td>S6</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>4.80 [-2.32, 16.32], 90.76 %</td><td>4.87 [-1.93, 16.50], 91.76 %</td><td>7.07 [0.71, 18.54], 98.56 %</td><td>4.47 [-3.42, 15.98], 86.91 %</td><td>6.93 [-2.95, 18.78], 92.93 %</td><td>2.62 [-4.97, 10.43], 78.33 %</td></tr><tr><td>S7</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></table>