Research article

# Incubation behaviour in a double-nesting alpine bird *Alectoris graeca saxatilis*: similar nest attendance by males and females

Ariane Bernard-Laurent<fnref n="1" />, Guillelme Astruc<fnref n="2" />, Meïli Baragatti<fnref n="3" />, Claire Anceau<fnref n="1" />, Thierry Faivre<fnref n="4" /> and Jean-Louis Laurent<fnref n="5" />

Correspondence: Ariane Bernard-Laurent (abernardlaurent@wanadoo.fr)

Journal of Avian Biology
2025: e03484

doi: 10.1002/jav.03484

Subject Editor: Kristal Cain

Editor-in-Chief: Jan-Åke Nilsson

Accepted 18 August 2025

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In birds with double-nesting and uniparental incubation, such as the rock partridge *Alectoris graeca saxatilis*, the male incubates one clutch, while the female incubates the other. A previous study found no significant difference in hatching and predation rates on Alpine rock partridge nests incubated by each sex. We therefore hypothesized that the incubation rhythms of both sexes would be similar. To test this, we monitored the incubation patterns of 40 nests incubated by females and 41 nests incubated by males in the French Alps between 2011 and 2020. Temperature loggers were installed within and outside the nests to record internal and ambient temperatures at 3-min intervals. Incubation recess timing and duration were inferred from the analysis of temperature curves. We employed statistical modelling to assess the effects of the incubating bird's sex, minimum ambient temperature, incubation day, clutch size, and recess rank on various incubation parameters. The timing, total duration, and number of recesses, as well as nest temperature, were found to be similar between the sexes. On average, birds took 2.5 recesses per day, with each recess lasting approximately 75 min. Overall nest attendance was ≈ 88%. Recesses occurred throughout the day, with a peak after sunrise and a second, less pronounced peak before sunset. Nocturnal recesses were rare and resulted from disturbances to the incubating bird. Modelling results indicated only slight differences in the mean recess duration between the sexes throughout the incubation period. Further analysis showed that both sexes adjusted their incubation rhythms in a similar manner in response to the progress of incubation and to daily minimum temperatures. Cold temperatures may compel parents to spend more time foraging to meet their energy needs. Rock partridges exhibited lower nest attendance compared to grouse species inhabiting cold environments, likely due to their relatively lower body reserves.

Keywords: *Alectoris graeca saxatilis*, double-nesting, French Alps, galliforms, sex-specific incubation behaviour, temperature data logger, uniparental incubation

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<footnote n="1">¹DRAS OFB, French Agency for Biodiversity, Gap, France</footnote>

<footnote n="2">²CEFE, University Montpellier, CNRS, EPHE-PSL University, IRD, Montpellier, France</footnote>

<footnote n="3">³MISTEA, University Montpellier, INRAE, Institut Agro, Montpellier, France</footnote>

<footnote n="4">⁴French Agency for Biodiversity, Avrieux, France</footnote>

<footnote n="5">⁵Independent Researcher, Grasse, France</footnote>
Introduction

Incubation is crucial in birds for maintaining the tempera-
tures necessary for embryo development, usually through
direct contact and heat provided by the parent. This process
is energetically costly and forms a significant component of
the avian reproductive cycle (Williams 1996, Thomson et al.
1998, Tinbergen and Williams 2002, Nord and Williams
2015). Previous studies on reproductive costs and life his-
tory trade-offs in birds have highlighted the fitness conse-
quences of incubation behaviour, which can influence nest
success and/or survival and future population productivity
(Walsburg 1983, Visser and Lessels 2001, Reid et al. 2002,
Carter et al. 2014). As a result, incubation behaviour may
be subject to strong selective pressures (Marasco and Spencer
2015).

Birds have evolved a variety of incubation strategies to
optimize embryo development in response to variable envi-
ronmental conditions. Skutch (1957) identified five main
categories of incubation patterns, based on the presence of an
incubating adult and its activity rhythm: incubation by both
parents, by one parent alone, by more than two birds at a
single nest, by birds of other species, and incubation without
animal heat. Excluding bird species that do not incubate, this
classification can be simplified into two primary incubation
strategies: biparental, where both partners share incubation
duties, and uniparental, where only one parent incubates
(Deeming 2002). In ancestral birds, both sexes shared incu-
bation, a pattern that remains predominant, albeit with vary-
ing levels of involvement from each sex (Skutch 1957).

Incubation behaviours are likely shaped by selective pres-
sures related to parental energy balance, embryo development,
and minimising predation risk to both parents and offspring
(Tulp and Schekkerman 2006, Coates and Delehanty 2008).
These behaviours are further influenced by factors such as
body size, age, sex, nest insulation, weather conditions, and
food availability in the nesting habitat (Afton and Paulus
1992, Wiebe and Martin 2000, Tulp and Schekkerman 2006).

Shared parental incubation, the most common pattern,
offers the advantage of providing continuous protection from
predators and ensuring eggs are incubated at optimal temper-
ature (Webb 1987). In species where only one sex incubates
the clutch, incubation is periodically interrupted, requiring
the incubating parent to carefully manage its time to reduce
predation risk. This involves balancing energy intake (feed-
ing) and heat requirements for embryo development (Drent
1975, Afton 1980, Deeming 2002).

This study focuses on the ‘double-clutch system’, where
a female lays two clutches in succession at the start of the
breeding season. This system is characterized by uniparen-
tal incubation in both nests, with the first clutch incubated
by the male and the second by the female. Double-clutching
(also known as double-nesting) has been observed in
monogamous species, where both parents contribute to rais-
ing both broods, as well as in polyandrous and ambisexual
polygamous species, where sequential polygyny and poly-
andry occur simultaneously, and individuals may switch

partners between clutches. This reproductive strategy has
been reported in several species, including some galliforms
such as the red-legged partridge *Alectoris rufa* (Green 1984,
Casas et al. 2009), the rock partridge *Alectoris graeca saxatilis*
(Bernard-Laurent et al. 2017), and the northern bobwhite
*Colinus virginianus* (Curtis et al. 1993, Burger et al. 1995). It
has also been observed in certain Charadriiform species, such
as the Temminck's stint *Calidris temminckii* (Hildén 1975),
the little stint *C. minuta* (Hildén 1983, Tulp et al. 2002),
and the mountain plover *Charadrius montanus* (Graul 1975).
The present study investigates the incubation behaviour of
radio-marked rock partridges, a mountain galliform species
in which pairs remain together during egg-laying and where
uniparental incubation has previously been documented
(Bernard-Laurent et al. 2017). Incubation patterns in dou-
ble-clutch bird species have rarely been assessed according to
the sex of the bird, and this is the first time such patterns have
been quantified for a species of the genus *Alectoris*. A previous
study indicated similar predation rates for nests incubated by
either female or male rock partridges (Bernard-Laurent et al.
2024), suggesting that both sexes may exhibit similar incuba-
tion strategies. Validating this hypothesis would support our
earlier findings and confirm the importance of double-nest-
ing and uniparental incubation as a key demographic mecha-
nism. To test this hypothesis, we monitored the incubation
rhythms of nests incubated exclusively by male and by female
birds using temperature data loggers.

Several factors could influence the incubation behaviour.
Since nest attendance is largely determined by the thermo-
regulatory requirements of developing embryos, ambient
temperature is commonly regarded as a key factor shaping
incubation rhythms (Drent 1975, Afton 1980, Conway and
Martin 2000, Coe et al. 2015, Carroll et al. 2018).

The effects of ambient temperature on incubation behav-
iour can vary between species, as demonstrated in the compar-
ative study of northern bobwhite and scaled quail *Callipepla
squamata* by Carroll et al. (2018), but also among populations
within the same species (Diez-Méndez et al. 2021). These
effects may also vary considerably depending on the specific
environmental context. We assume that, in environments
characterized by extreme temperature fluctuations, such as
arid regions, nest departures would generally occur during
cooler hours in the early morning or before dusk, as a strategy
to avoid egg overheating, as described in sandgrouse (fam-
ily Pteroclidae) species (Mougeot et al. 2014). Conversely,
in some cold environments, incubating parents may take
recesses in the middle of the day to minimize clutch exposure
to low ambient temperatures and reduce the energetic cost
of reheating the eggs, a pattern observed in some uniparental
Arctic-breeding shorebirds (Cantar and Montgomerie 1985,
Tulp and Schekkerman 2006).

Incubation behaviour may also be shaped by predation
risk. To minimize the chance of attracting predators, recesses
should ideally be consolidated into a single off-bout and
timed to occur during the safest periods of the day, avoiding
early morning and twilight hours when predator activity is
highest.
Additionally, time allocation during incubation may be influenced by the energetic demands of the incubating parent, particularly in females that have already invested heavily in producing two clutches. In alpine environments, this energetic constraint may result in recesses occurring at dawn and dusk, enabling parents to forage before and after the long, cold nights of continuous incubation.

To compare these hypotheses for each sex, we analysed the incubation rhythms of the birds using several temporal parameters measured daily. If females are in a less favourable body condition than males, we expect to observe sex differences in recess frequency, recess duration, and the timing of the first recess of the day.

Secondly, we examined the relationships between the key parameters of incubation rhythms and potential influencing factors, such as environmental conditions and temporal variables, both individually and in interaction with sex.

Lastly, in the discussion, we will compare the rock partridge's incubation rhythm with that of other galliforms living in mountainous or cold environments under similar climatic conditions, highlighting the unique aspects of the rock partridge's incubation behaviour.

# Material and methods

## Study species and area

The rock partridge has traditionally been regarded as socially monogamous (Del Hoyo et al. 1994). However, recent observations of radiotagged individuals in our study area provide evidence of polyandrous behaviour (Bernard-Laurent A., unpubl.). This ground-nesting species is of conservation concern and is currently listed as Near Threatened by the IUCN (BirdLife International 2021). Since the 1960s, its populations have declined significantly across most of its range, with particularly steep declines observed in the Alps (Bernard-Laurent and De Franceschi 1994, Griffin 2011).

The rock partridge, which is distributed throughout southern Europe, is a monomorphic species, with both males and females contributing to nest incubation and chick rearing (Bernard-Laurent et al. 2017). In our study area, the laying period extended from late April to early July, while incubation took place from late May to early August (Bernard-Laurent et al. 2017). The average incubation period for a clutch was 25–26 days.

Double-clutching was a common reproductive strategy in this species, with 64% of 85 radio-tagged paired males incubating a clutch during the breeding seasons from 2012 to 2020. The proportion of incubating males varied considerably between years, ranging from 33 to 88% (Bernard-Laurent A., unpubl.). When both of the female's successive clutches remain intact, incubation begins synchronously for both members of the pair, but only after the second clutch has been completed. If, however, the second clutch is destroyed during laying, the female typically lays a third clutch, resulting in asynchronous incubation relative to the male's clutch (Bernard-Laurent et al. 2017).

We studied incubation behaviour over a 110 km² area in the Dévoluy Massif and adjacent mountains in the southwestern French Alps (44°41′N, 5°56′E), from May to August during the 2011–2020 breeding seasons. The nesting habitat of the rock partridge consists of a mosaic of shrublands, grasslands, and rocky terrain located between 1400 and 2100 m a.s.l.

Climatic conditions in the study area are highly variable both seasonally and annually, influenced by a combination of oceanic, Mediterranean, and alpine weather patterns. Summers are generally warm, while winters are cold and snowy. The average annual precipitation is 1072 mm (1981–2010), based on data from the Météo-France weather station in Saint-Étienne-en-Dévoluy (1300 m a.s.l.). During the breeding seasons from 2011 to 2020, the average daily temperatures were 5.0°C in May, 8.2°C in June, and 10.5°C in July.

## Nest searching

Incubation behaviour was investigated through radio-tracking of partridges during the breeding season. Details of the capture methods, as well as the procedures used to determine the age and sex of captured individuals, are provided in Canonne et al. (2023). Birds were equipped with VHF radio collar transmitters (model RI-D2M, Holohil Systems Ltd, Canada), with transmitter weight adjusted to the size of each bird, ranging from 9 to 14 g.

Telemetry data from incubating individuals were used to locate all nests, except for five that were discovered opportunistically during the egg-laying period. When incubation was suspected, nests were located with great care to minimise disturbance to the incubating parent. Each nest's location was recorded with a hand-held GPS device to an accuracy of 3–5 m, allowing for reliable relocation the following morning when nest monitoring began. Most nests were identified within the first five days of incubation through regular monitoring (every 2–3 days) of each paired bird's radio signal.

## Monitoring of temperatures inside and outside of the nest

To minimise disturbance, temperature data loggers were used to remotely monitor nest fate and incubation behaviour throughout the incubation period. The loggers (25 mm in diameter, 15 mm thick, 0.2°C accuracy; model: Tidbit V2 Temp, Ets PROSENSOR, France) provided detailed information on incubation recesses as well as the timing of clutch loss or hatching. This non-invasive method reduced the frequency of nest visits, thereby lowering the risk of disturbance and associated predation.

At each nest site, two data loggers were deployed: one placed directly under the eggs within the nest cup to record incubation temperatures, and the other positioned 1–3 m away under vegetation to measure ambient temperature. Both loggers recorded temperature every 3 min throughout the incubation period. Installation was carried out with particular care (the upper surface of the logger inside the nest was positioned just below the top of the eggs). Loggers were typically installed one or two days after nest discovery, during
the first observed morning recess of the incubating parent, which was tracked via telemetry. Full clutch size was recorded at the same time.

In the early stages of the study, some internal loggers were lost due to removal by mesocarnivores or became unreadable due to improper placement (partridges reject foreign objects in close contact with their bodies). To address this, each internal logger was secured with a 10 cm thread attached to a peg placed outside the nest cavity. This method ensured successful retrieval of all nest-cup loggers and did not appear to affect parental behaviour.

By installing the data loggers during a single visit, nests could be monitored without the need for further direct observation until hatching or nest failure occurred. Nests were only approached again if telemetry data indicated that the incubating bird had moved away from the nest site, suggesting a possible failure. In such cases, the continuous temperature recordings enabled precise identification of the time of failure. The nest contents were then examined to determine the cause of failure such as predation of eggs or the adult, egg trampling, or abandonment, following the classification used by Bernard-Laurent et al. (2024). Whether the outcome was hatching or failure, the data loggers were retrieved promptly once the nesting attempt had concluded.

## Analyses of temperature recordings

Temperature data recorded by the loggers were downloaded using HOBOware® software, ver. 3.7, from Onset Computer Corporation (www.onsetcomp.com>products>software >hoboware). Each time an incubating partridge left the nest, nest-cup temperature dropped rapidly to match ambient conditions. As such, analysing fluctuations in nest temperature allowed us to examine incubation patterns, specifically the timing, frequency, and duration of recesses during daylight hours.

Temperature series for each individual were examined manually. Recesses, defined as periods during which the eggs were left unattended, were identified based on distinct temperature patterns: a sharp decline in nest temperature, followed by a steep rise indicating the bird's return. The duration of each recess was measured as the time between the onset of the temperature drop and the beginning of the subsequent increase. Data from one to two days before hatching were excluded due to erratic temperature variations that prevented reliable interpretation.

To avoid misclassifying movements made by the incubating bird (e.g. egg repositioning) as recesses, we applied a threshold: temperature drops of less than 1.5°C were not considered true recesses. This threshold was adjusted according to ambient temperature conditions. Because spontaneous and disturbance-induced diurnal recesses were indistinguishable, both types were included in the analysis.

In addition to identifying daily incubation behaviour, temperature profiles enabled detection of the precise timing of nest depredation, abandonment, or hatching. A final sharp drop in nest temperature, with no subsequent return to baseline incubation levels, marked the definitive departure of the

incubating bird, either due to predation, abandonment, or post-hatching departure with chicks.

Due to their placement within the nest cup, the temperatures recorded by the loggers were slightly lower than the actual egg temperatures during incubation. The exact difference between logger-recorded temperatures and true egg temperatures was not known. Consequently, for the purposes of interpretation, we assumed that temperature variations recorded by the loggers were proportional to changes in egg temperature, an approach consistent with that adopted in other studies using nest temperature loggers (Novoa et al. 2003, Camfield and Martin 2009, Legagneux et al. 2011).

## Components of incubation rhythms

Time was expressed in minutes relative to the hour of sunrise in Grenoble (data source: https://www.ephemeride.com/calendrier/solaire/19/horaires-du-soleil.html).

To characterise the incubation rhythm for each nest and each monitored day, we defined several parameters:

* FRST: the start time of the first diurnal recess,

* TRD: total recess duration, i.e. the cumulative amount of time spent off the nest during the diurnal phase,

* MRD: mean recess duration, calculated as TRD divided by the number of recesses per day (RNo),

* RNo: number of recesses during the diurnal phase,

* Nest T°: nest cup temperature at the time the bird departed for a diurnal recess,

* RR: rank of the recess within the day,

* RD: duration of each single recess.

In addition to the sex of the incubating bird, we also included a range of biological, temporal, and environmental covariates considered potentially relevant for modelling incubation parameters:

* T° min: minimum daily temperature in °C measured by the logger placed outside the nest,

* Incubation day: progress of the incubation of a nest expressed in days,

* Clutch size: number of eggs in the complete clutch counted after the start of incubation,

* Rank of the recess: rank of a diurnal recess for each monitoring day.

## Dataset

A total of 88 tagged incubating birds were monitored during the breeding seasons from 2011 to 2020, including 31 tagged pairs. Among these, nine complete pairs were found incubating separate nests. The sample size of complete tagged pairs was too small to allow for a comparison of incubation rhythms between partners within each pair. Therefore, incubation rhythms were analyzed by comparing all monitored incubating males with all monitored incubating females.

Due to the loss of some loggers, temperature data were collected from 81 nests (40 females, 41 males), covering a
total of 1142 monitoring days (605 for females and 537 for males). During this period, 2977 recesses were recorded, of which 2900 were diurnal, with 1551 attributed to females and 1426 to males.

Most incubating birds were observed during only one breeding season. However, incubation rhythms were monitored across two consecutive years for seven females and four males, and for one male across three consecutive years.

## Statistical analyses

In the following analysis, a nest is defined by a unique combination of bird identity and year. To compare the frequency of day and night recesses between sexes in incubating birds, we used a $\chi^2$ test of independence. When the null hypothesis was not rejected, a power analysis was conducted using the *pwr.chisq.test* function from the 'pwr' package (ver. 1.3) in R (www.r-project.org).

The mean values of the components of the birds' incubation behaviour, i.e. the total recesses duration (TRD), the mean recess duration (MRD), the number of recesses per day (RNo), the temperature in the nest (Nest T°) at the time the bird left the nest and the start time of the first recess (FRST), were calculated by averaging the daily values observed for each sex over the entire monitoring period. To test the null hypothesis of no difference between sexes, we used a permutation test. For a given nest, we cannot assume that the observations are independent over time. Therefore, the classical Student's t-test cannot be used and we compared the means values between sexes using a permutation test. To preserve the structure of the dataset and to be consistent, we permuted the data by nest: for a given nest, the sex was randomly permuted. The difference in means between sexes observed was compared to the distribution of the 9999 differences in means obtained after permutation. We considered the null hypothesis (no difference in means between males and females) acceptable if the proportion of differences in means between sexes exceeding the difference in observed mean (two tailed p-value) was greater than 0.05.

In a next step, we examined the relationships between four response variables characterising the daily incubation rhythm (total recess duration, mean recess duration, number of recesses, and single recess duration) and several potentially relevant covariates listed in the section 'Components of incubation rhythms'. We used linear mixed models for all analyses, except for the modelling of the number of recesses, for which we applied a generalized linear mixed model with a Poisson distribution. For this latter model, the set of explanatory variables was reduced, and overdispersion was assessed. For the modelling analysis of the first three response variables, we used a dataset comprising 1142 monitoring days. For the analysis of recess duration, we used a dataset of 2888 recesses, after excluding 12 considered as outliers. In all models, the nest was considered as a random effect (random intercept). For each of the four response variables, the full model included all possible relevant covariates as well as biologically relevant interactions with the sex of the incubating bird. A log(y) transformation was used for the TRD, RD, and MRD

response variables to obtain Gaussian residuals. Hypotheses about the residuals were tested graphically. A backward stepwise procedure was used from each full model, to select the best fixed effects structure. We also tested whether the random intercept (the nest) was significant. The 'lme4' library, ver. 1.1-36 (Bates et al. 2015) was used for all models.

If the sex of the bird was not validated as a significant explanatory variable of the final model, we calculated the power of a test between the final model considered and the same model with sex as an additional variable. This power was calculated using the 'powerSim' command from the 'simr' library and considering a 1% difference between the sexes in the mean value of the parameter.

All analyses were performed using the R software, ver. 4.4.1, and a significance level of 5%.

## Results

### Daily distribution of recess start times: comparison between sexes

We found that 97.4% (2900/2977) of recesses occurred during the day, with similar proportions for males and females (97.3% (1387/1426) versus 97.5% (1513/1551), $\chi^2=0.1396$, df=1, p=0.71; $\chi^2$ power calculation w=0.1, n=2977, df=1, sig. level=0.01, power=0.998; Fig. 1).

Recesses occurred throughout the day, with a higher frequency in the early morning, peaking between 30 and 15 min before sunrise. After a relative decrease at midday, a second period of significant activity was observed in the afternoon (Fig. 1). Going forward, when comparing the activity rhythms of incubating birds between sexes, only the diurnal period will be considered, and the term 'diurnal' will no longer be used before the names of the components of the incubation rhythm.

### Parameters of incubation rhythm: comparison between sexes

Nest attendance by males and females, measured as the proportion of time a bird spent on the nest each day, estimated by the ratio of mean TRD to the duration of the day, was 87.9%.

The distributions of the five incubation rhythm parameters were highly similar between sexes (Fig. 2). Statistical comparisons of the mean values of these parameters showed no significant differences between males and females (Table 1).

### Relationships between incubation rhythm parameters and various covariates

#### Total recess duration (TRD) modelling

Of the four fixed effects and three interactions with sex that could explain the variation in TRD for each nest, only one explanatory variable, the minimum daily temperature, was retained in the final model (Table 2a). The hypothesis that the final model with and without the random effect were equivalent was rejected ($\chi^2=92.17$, df=1, Pr($>\chi^2$) < 0.001).
<figure><img src="image_3.png" /><figcaption>Figure 1. Distribution of rock partridge recess start times (n = 3029) by time of day (diurnal versus nocturnal phases) and sex of the incubating bird, in the French Alps study area from 2011 to 2020. Sunrise time is set to 0.</figcaption></figure>

Therefore, the model with the random effect was retained, emphasizing the variability between nests. No significant differences were detected based on the sex of the incubating bird, nor its interactions with incubation day, clutch size, or daily minimum temperature. The observed power to detect a 1% difference in TRD between incubating males and females, calculated by comparing the final model with a model including sex as an additional variable, was 100.0% (CI 95%: 96.38–100.0). This model predicted a decrease in TRD of 48 min when the daily minimum temperature increased from –3 to 21°C (Fig. 3).

### Mean recess duration (MRD) modelling

Of the four fixed effects and three interactions with sex likely to explain the variation in MRD for each nest, two explanatory variables, sex and incubation day, and their interaction were retained in the final model (Table 2b). The hypothesis of equivalence between the final model with and without the random effect was rejected ($\chi^2 = 188.17$, df = 1, Pr($>\chi^2$) < 0.001). Therefore the final model with the random effect was retained, highlighting variability between nests.

The interaction revealed small differences between the sexes. The model predicted a decrease in MRD for both sexes throughout the incubation period. However, this decrease started at a higher level for females than for males at the beginning of incubation, with a greater mean decrease of 34 and 18 min, respectively, after 25 days of incubation (Fig. 3).

### Recesses number (RNo) modelling

Of the three fixed effects and two interactions that could explain the variation in the RNo for each nest, two explanatory variables were retained in the best model: incubation day and minimum daily temperature (T°min) (Table 2c). The hypothesis of equivalence between the final model with and without the random effect was rejected ($\chi^2 = 23.25$, df = 1, Pr($>\chi^2$) < 0.001). Therefore, the final model with the random effect was retained, highlighting the variability between nests. No significant differences were detected based on the sex of the incubating bird. The observed power to detect a 1% difference in RNo between incubating males and females, calculated by comparing the final model with a model including sex as an additional variable, was 100.0% (CI 95%: 99.6–100.0). The beta estimate for ‘incubation day’ predicted an increase in the diurnal RNo by approximately 0.8 as incubation day progressed from 1 to 25. The beta estimate for T°min predicted a decrease in RNo by approximately 1 as T°min increased from 1 to 25°C (Fig. 3).

### Recess duration (RD) modelling

Of the two fixed effects and their interaction that could explain the variation in RD, one explanatory variable, the rank of the recess, was retained in the final model (Table 2d). The hypothesis of equivalence between the final model with and without the random effect was rejected ($\chi^2 = 45.26$, df = 1, Pr($>\chi^2$) < 0.001). Therefore, the final model with
<figure><img src="image_4.png" /><figcaption>Figure 2. Sex-specific distribution of incubation rhythm components in rock partridges, based on data collected in the French Alps study area from 2011 to 2020. Only diurnal recesses were included in the analysis.</figcaption></figure>

the random effect was retained, emphasizing the variability
between nests. No significant differences were found based
on the sex of the incubating bird. The observed power to
detect a 1% difference in RD between incubating males
and females, calculated by comparing the final model with
a model including sex as an additional variable, was 100.0%
(CI 95%: 99.6–100.0). The beta estimate for recess rank
(RR) predicted a decrease in RD of approximately 13 min as
rank increased from 1 to 5 (Fig. 3).

Discussion

Comparison of incubation rhythms between sexes

The daily timing of recesses and the parameters describing
incubation rhythms showed no statistical differences between
the sexes. As expected, male and female rock partridges
exhibited very similar incubation patterns. A slight difference
between the sexes was revealed through modelling, which
showed an interaction effect of sex with incubation day on

the response variable mean recess duration (MRD). At the
start of the incubation period, MRD was slightly longer in
females than in males, but this difference diminished as incu-
bation progressed (Fig. 3). This suggests that females may
have higher food requirements than males at the beginning of
the incubation period, possibly due to the energy expenditure
associated with egg-laying.

The overall convergence of incubation rhythms between
the sexes may be explained by the small weight dimorphism
observed (13.4%; Bernard-Laurent A., unpubl.), suggest-
ing similar energy requirements during incubation. This
assumes that the pre-incubation weight gain of females was
nearly sufficient to meet their energy needs for laying. This
hypothesis is supported by Afton and Paulus (1992), who
found that in waterfowl, energy requirements for incubation
are partly met by lipid and protein reserves accumulated dur-
ing the pre-laying period. Unfortunately, our study design
did not allow us to investigate the influence of the incubat-
ing bird's body condition on the incubation rhythm, as the
partridges were only weighed at capture – months or even
<table><caption>Table 1. Mean values of the components of the diurnal incubation rhythm in rock partridges, by sex of the incubating bird, in the French Alps study area from 2011 to 2020. The components include the start time of the first diurnal recess (FRST), total recess duration (TRD), mean recess duration (MRD), number of recesses per day (RNo), and nest temperature (Nest T°). Mean differences between sexes were compared using permutation tests. The *p* value represents the proportion of 9999 random sex permutations (by nest) in which the mean differences between males and females exceeded the observed difference (two-tailed test). Sample size (n) is the number of recesses used in the analyses.</caption><thead><tr><th></th><th>FRST (in min)<br>mean ± SE<br>range (n)</th><th>TRD (in min)<br>mean ± SE<br>range(n)</th><th>MRD (in min)<br>mean ± SE<br>range(n)</th><th>RNo<br>mean ± SE<br>range(n)</th><th>Nest T° (in °C)<br>mean ± SE<br>range(n)</th></tr></thead><tbody><tr><td>All birds</td><td>83 ± 5<br>(-88, 772)<br>(1142)</td><td>174 ± 2<br>(30, 520)<br>(1142)</td><td>75 ± 1<br>(15, 465)<br>(1142)</td><td>2.54 ± 0.03<br>(1, 8)<br>(1142)</td><td>29.6 ± 0.1<br>(12.4, 40.6)<br>(2899)</td></tr><tr><td>Males</td><td>79 ± 7<br>(-88, 772)<br>(537)</td><td>177 ± 3<br>(30, 520)<br>(537)</td><td>74 ± 2<br>(20, 360)<br>(537)</td><td>2.58 ± 0.04<br>(1, 8)<br>(537)</td><td>28.7 ± 0.1<br>(12.4, 40.4)<br>(1386)</td></tr><tr><td>Females</td><td>87 ± 6<br>(-87, 753)<br>(605)</td><td>172 ± 3<br>(33, 465)<br>(605)</td><td>75 ± 2<br>(15, 465)<br>(605)</td><td>2.50 ± 0.04<br>(1, 6)<br>(605)</td><td>30.3 ± 0.1<br>(14.0, 40.6)<br>(1513)</td></tr><tr><td>p</td><td>0.66</td><td>0.59</td><td>0.82</td><td>0.55</td><td>0.13</td></tr></tbody></table>

years before nesting. The similar incubation patterns of males and females are consistent with comparable nest survival and hatching success between the sexes, as demonstrated in a previous study on nest survival in the same population

(Bernard-Laurent et al. 2024). These results highlight the significant contribution of male incubation and, by extension, of double-nesting behaviour when it is predominant, to the demographic performance of rock partridge populations.

<table><caption>Table 2. Modelling of diurnal recess parameters of rock partridges in the study area of the French Alps from 2011 to 2020. Statistics of the covariates were selected by backward stepwise ANOVA.</caption><tbody><tr><td colspan="5"><b>a. Total recess duration (TRD). Number of monitoring days=1142</b></td></tr><tr><td>Full model</td><td colspan="4">lmer((log TRD) ~ sex + incubation day + clutch size + T°min + sex: incubation day + sex: clutch size + sex: T°min + (1|nest))</td></tr><tr><td>Final model</td><td colspan="4">lmer((log TRD) ~ T°min + (1|nest))</td></tr><tr><td>Fixed effects:</td><td>Estimate</td><td>95% CI</td><td>t value</td><td>Pr(&gt;|t|)</td></tr><tr><td>(Intercept)</td><td>5.193</td><td>5.108, 5.278</td><td>117.20</td><td>&lt; 0.001</td></tr><tr><td>T°min</td><td>-0.013</td><td>-0.02, -0.005</td><td>-3.72</td><td>0.001</td></tr><tr><td colspan="5"><b>b. Mean recess duration (MRD). Number of monitoring days=1142</b></td></tr><tr><td>Full model</td><td colspan="4">lmer((log MRD) ~ sex + incubation day + clutch size + T°min + sex: incubation day + sex: clutch size + sex: T°min + (1|nest))</td></tr><tr><td>Final model</td><td colspan="4">lmer((log MRD) ~ sex + incubation day + sex: incubation day + (1|nest))</td></tr><tr><td>Fixed effects:</td><td>Estimate</td><td>95% CI</td><td>t value</td><td>Pr(&gt;|t|)</td></tr><tr><td>(Intercept)</td><td>4.4770</td><td>4.3767, 4.5792</td><td>87.319</td><td>&lt; 0.001</td></tr><tr><td>Sex male</td><td>-0.1521</td><td>-0.2958, -0.0098</td><td>-2.099</td><td>0.037</td></tr><tr><td>Incubation day</td><td>-0.0207</td><td>-0.0258, -0.0155</td><td>-7.874</td><td>&lt; 0.001</td></tr><tr><td>Sex: incubation day</td><td>0.0089</td><td>0.0013, 0.0166</td><td>2.302</td><td>0.021</td></tr><tr><td colspan="5"><b>c. Recess number per day (RNo). Number of monitoring days=1142. * = reduced variables</b></td></tr><tr><td>Full model</td><td colspan="4">glmer (RNo ~ sex + incubation day* + T°min* + sex: incubation day* + sex: T°min* + (1|nest), family='Poisson')</td></tr><tr><td>Final model</td><td colspan="4">glmer (RNo ~ incubation day* + T°min* + (1|nest))</td></tr><tr><td>Fixed effects:</td><td>Estimate</td><td>95% CI</td><td>z value</td><td>Pr(&gt;|z|)</td></tr><tr><td>(Intercept)</td><td>0.9280</td><td>0.7972, 1.0565</td><td>14.065</td><td>&lt; 0.001</td></tr><tr><td>Incubation day*</td><td>0.0788</td><td>0.0400, 0.1178</td><td>3.981</td><td>&lt; 0.001</td></tr><tr><td>T° min*</td><td>-0.0654</td><td>-0.1064, -0.0244</td><td>-3.135</td><td>0.002</td></tr><tr><td colspan="5"><b>d. Recess duration (RD). Recesses number=2888</b></td></tr><tr><td>Full model</td><td colspan="4">lmer (RD ~ sex + RR + sex: RR + (1|nest))</td></tr><tr><td>Final model</td><td colspan="4">lmer (RD ~ RR + (1|nest))</td></tr><tr><td>Fixed effects:</td><td>Estimate</td><td>95% CI</td><td>t value</td><td>Pr(&gt;|t|)</td></tr><tr><td>(Intercept)</td><td>4.2211</td><td>4.1555, 4.2865</td><td>127.128</td><td>&lt; 0.001</td></tr><tr><td>Recess rank (RR)</td><td>-0.0558</td><td>-0.0758, -0.0358</td><td>-5.506</td><td>&lt; 0.001</td></tr></tbody></table>
<figure><img src="image_5.png" /><figcaption>Figure 3. Model predictions of incubation rhythm response variables in rock partridges as a function of minimum temperature (°C), incubation day, and recess rank, using data from the French Alps (2011–2020). Shaded grey lines indicate 95% confidence intervals.</figcaption></figure>

This reproductive system enables us to understand how pop-
ulations recover from periodic catastrophic declines due to
climatic events (Bernard-Laurent and Léonard 2000). Similar
incubation behaviour between males and females was also
observed in two uniparental ground-nesting birds: the north-
ern bobwhite (Burnam et al. 2012) and the mountain plo-
ver *Charadrius montanus* (Skrade and Dinsmore 2012). The
comparable incubation sharing between males and females
in these species and the rock partridge is consistent with the
persistence of uniparental incubation over time.

Incubation rhythms over time

Temporal parameters influenced incubation behaviour at both
the level of the incubation period and the incubation day. We
found that TRD was not influenced by the covariate incuba-
tion day, meaning the daily time spent by parents on self-maint-
tenance activities did not vary across the incubation period.
However, parents adjusted the partitioning of recess time by
varying the number and duration of recesses as incubation
progressed. Specifically, for both sexes, MRD became shorter
over time, while RNo increased throughout the incubation
period (Fig. 3). Similar patterns have been reported in previ-
ous studies of ground-nesting birds, which also found that
the duration of nest recesses decreases with increasing clutch
age. Examples include natural hybrids between red-legged
partridges and rock partridges (Bernard-Laurent and Laurent
1991), northern bobwhites (Burnam et al. 2012), and other
precocial species such as ducks (Legagneux et al. 2011). These
changes in incubation behaviour are likely related to embryo
development: as incubation progresses, parents reduce the
length of recesses to prevent the eggs from cooling for too
long in the later stages, but they also leave the nest more often
to feed. Shorter recesses in the late stages of incubation help
minimize drops in mean egg temperature, thus reducing the
energetic cost associated with rewarming cold eggs (Williams
1996, Hainsworth and Voss 2002). Additionally, they help
moderate temperature fluctuations, which are beneficial for
embryo development, as embryos require higher thermal sta-
bility as they grow (Webb 1987). The increase in the number
of recesses indicates that parents compensate for the shorter
recess durations to meet their energetic needs as hatching
approaches. This suggests that the parents may lack sufficient
body reserves to reduce the time spent outside the nest in the
later stages of incubation.

At the level of the incubation day, the duration of daily recesses tended to decrease as recess rank increased from 1 to 5. This likely reflects hunger physiology: following an overnight fast, the incubating bird forages longer once daylight is sufficient to restore its energy reserves.

Incubation rhythms and ambient temperature

Rock partridges nest on the ground and breed in subalpine
areas with large diurnal temperature variations, making them
particularly interesting for studying how incubating birds
respond to thermal changes throughout the incubation period,
especially to cold temperatures typical of alpine environments.
Modelling showed that TRD and RNo were influenced by
the minimum ambient temperature, regardless of sex. TRD
tended to increase on colder days, primarily due to an increase
in the number of recesses, which aligns with our prediction.

These results suggest that the rock partridge, a species
known for its high sensitivity to adverse weather conditions
in the Alps (Bernard-Laurent and Léonard 2000) and lim-
ited body reserves (Boos et al. 2009, Bernard-Laurent 2011),
likely compensates for increased energetic demands at low
temperatures by increasing the number of recesses. This sup-
ports the notion that incubation is a dynamic period, during
which behavioural flexibility allows parents to adjust to vary-
ing environmental conditions, as previously reported in the
white-tailed ptarmigan Lagopus leucurus (Wiebe and Martin
2000) and several passerine species (Cooper and Voss 2013).

Similar behavioural adaptations to environmental condi-
tions have also been observed in several uniparental shorebirds
(Cantar and Montgomerie 1985, Tulp and Schekkerman
2006), suggesting that such flexibility in incubation strate-
gies may be widespread across avian taxa. In Arctic-breeding
shorebirds, for example, total daily recess duration increased
on colder days, as observed in the rock partridge, but this

was primarily achieved by extending the average duration
of recesses (Tulp and Schekkerman 2006), rather than by
increasing their number, as seen in the rock partridge.

The influence of ambient temperature on incubation
behaviour has also been demonstrated in the horned lark
Eremophila alpestris, an alpine-breeding passerine subject
to strong thermal constraints (Camfield and Martin 2009,
MacDonald et al. 2014). While horned larks appear capable
of maintaining high levels of parental investment even under
cold conditions (Camfield and Martin 2009), the exception-
ally harsh weather in 2010 seems to have pushed them to the
limits of their coping capacity, forcing a trade-off between
survival and reproductive success (MacDonald et al. 2014).

Prolonged periods of low temperatures can significantly
increase energy requirements of birds, leading to increased
foraging activity and reduced incubation attendance. If the
parent spends too much time away from the nest, it could
negatively affect hatchability and offspring condition (Olsen
1989), ultimately reducing reproductive output.

We observed that, at the end of a recess, temperatures
in rock partridge nests were often well below the presumed
threshold for continued embryonic development (25–27°C)
(Drent 1975, Webb 1987), occasionally dropping to very
low levels. For example, the lowest temperatures recorded in
rock partridge nests following normal recesses on cold days
were 7.3°C (on 16 July 2016) and 7.9°C (on 30 June 2017),
both in successful nests. Given that embryonic development
slows or ceases below approximately 26°C (Webb 1987), the
energetic costs incurred by parents to rewarm the eggs under
such conditions are likely substantial. Nevertheless, the suc-
cessful outcomes of these nests, despite suboptimal thermal
conditions, suggest that rock partridge embryos may exhibit
a relatively high resilience to low incubation temperatures.

To further explore this potential thermal tolerance, con-
trolled studies on captive rock partridges are needed. Such
experiments could help determine precise temperature
thresholds for embryonic development and hatchability, pro-
viding valuable insights into the plasticity of their incubation
temperature regulation and potential adaptive responses to
thermal challenges.

Clutch size

In our study area, female rock partridges incubated signifi-
cantly smaller clutches, averaging 9.3 eggs, compared to
males, which incubated an average of 10.7 eggs (Bernard-
Laurent et al. 2018). This difference likely reduces the ener-
getic cost of incubation for females. However, we found that
clutch size did not significantly influence incubation behav-
iour, as no significant relationship was detected between
clutch size and incubation parameters. This result contrasts
with the general pattern observed in other precocial bird spe-
cies, where nest attendance tends to increase with clutch size
(Thomson et al. 1998, Deeming 2002, Hartman et al. 2023).
Our findings suggest that both male and female rock par-
tridges are capable of successfully incubating a wide range
of clutch sizes (7–15 eggs in our sample), without apparent
adjustments in incubation behaviour.
## Comparison of overall incubation rhythms between rock partridges and grouse

Nocturnal incubation of the clutch is continuous. However, the recorded nocturnal recesses, which accounted for only 2.7% of the total number of recesses, were primarily the result of disturbances caused by either nest predators or non-predatory wildlife, as indicated by camera traps placed around a sample of 58 out of 81 nests. For the purposes of our study, only diurnal recesses were analysed, including both spontaneous recesses and those triggered by daytime disturbances from wildlife or cattle. Although spontaneous and disturbance-induced recesses may follow different patterns, we were unable to distinguish between them and therefore could not analyze potential differences. Therefore, the incubation rhythms described here reflect the natural conditions experienced by rock partridges at our study site, which is characterized by a high presence of both wildlife and livestock.

Diurnal recess timing showed a significant number of recesses throughout the day, with a primary peak occurring early in the morning after sunrise and a secondary, less pronounced peak in the late afternoon before sunset. This timing, marked by two diurnal peaks in recess activity during early morning and evening, aligns with patterns observed in mountain grouse (family Phasianidae) species, albeit with a slight difference: in grouse, recesses tend to be more precisely timed around sunrise and sunset (Storaas and Wegge 1997, Summers et al. 2009, for black grouse and capercaillie). We also observed a decrease in the duration of rock partridge recesses as their rank increased, suggesting a behavioural adjustment aimed at progressively meeting the bird's nutritional needs throughout the day. The early morning peak in recesses likely represents a hunger response: after fasting overnight, the incubating bird needs to forage extensively once there is sufficient light to replenish its energy reserves, despite the higher risk of egg cooling during the colder early morning hours. While recesses at dawn and dusk may allow the incubating bird to maintain a steady metabolism before the overnight fast, two recesses per day appeared insufficient on some days to meet the metabolic demands of the incubating partridge. On 46% of the incubation days, birds took at least three recesses during the day. Taking recesses during the day does not seem to pose a significant predation risk for incubating rock partridges. The parents exhibit anti-predator behaviour at two key stages: first, by selecting well-concealed nest sites before incubation (Bernard-Laurent et al. 2018), which helps prevent detection by visual predators when the bird is away from the nest; and second, by quickly flying away from the nest when initiating a recess. Based on direct observations and photos from camera traps placed near some nests, we found that returns to the nest often involved a combination of flying to the vicinity of the nest followed by a short walk (1-3 m) to reach the nest. In our study (Bernard-Laurent et al. 2024), no depredation by avian egg predators occurred, suggesting that these inconspicuous movements to and from the nest may effectively reduce predation risk.

A comparison of incubation rhythms between rock partridges and grouse species inhabiting cold environments reveals notable differences in nest attendance patterns. In our study, the total time spent off the nest per day, measured as TRD, averaged approximately 3 h for both sexes: 172 min for females and 177 min for males. The mean duration of each recess was relatively long, exceeding 1 h on average for both males (74 min) and females (75 min).

In contrast, females of grouse species in colder climates tend to take a similar number of daily recesses as rock partridges, but each recess is typically shorter in duration. For instance, the following values have been reported in various grouse species for TRD, MRD, and RNo:

* Willow grouse *Lagopus lagopus* in Norway: TRD = 65.1 ± 26.7 min, MRD = 19.2 ± 10.3 min, RN₀ = 3.4 ± 1.1 (Erikstad 1986);

* Capercaillie *Tetrao urogallus* in Norway: TRD = 66 min, MRD = 27 min, RN₀ = 2.4 (Storaas and Wegge 1997);

* Black grouse *T. tetrix* in Norway: TRD = 84 min, MRD = 20 min, RN₀ = 4.0 (Storaas and Wegge 1997);

* Capercaillie in Scotland: TRD = 53 ± 10 min, MRD = 24 ± 5 min, RN₀ = 2 ± 0.2 (Summers et al. 2009);

* White-tailed ptarmigan in Canada: TRD = 77.8 ± 31.6 min, MRD = 19.6 ± 6.7 min, RN₀ = 3.07 ± 1.1 (Wiebe and Martin 1997);

* Spruce grouse *Dendragapus canadensis*: no data available for TRD, MRD = 26.4 ± 0.8 min, RN₀ = 3 (range 2–4) (Naylor et al. 1988).

Therefore, due to their longer recess durations, rock partridges exhibit lower overall nest attendance compared to grouse species living in cold environments. We propose that the combination of limited nutrient reserves in incubating rock partridges and the high energetic demands of thermoregulating numerous eggs by a single parent may have favoured the evolution of longer recesses and relatively short nest attendance, in contrast to other species living in cold environnement such as grouse.

Incubation patterns recorded in eight natural hybrids between rock and red-legged partridges were intermediate, with a TRD averaging 105 ± 4.4 min and a MRD of 43.0 ± 18.8 min (Bernard-Laurent and Laurent 1991). These findings highlight that rock partridges in the Alps take notably longer recesses compared to grouse species. This difference is unlikely to be explained by body size, as both smaller and larger tetraonid species typically exhibit higher nest attendance than rock partridges. A more plausible explanation lies in the greater energetic reserves of grouse, which enable them to sustain longer periods of continuous incubation. This strategy may allow them to accelerate embryonic development while reducing predation risk through higher nest attendance (Wiebe and Martin 1997). In contrast, rock partridges, which have relatively low body reserves (Boos et al. 2009, Bernard-Laurent 2011), are likely more constrained by energy depletion, necessitating more frequent foraging to meet their metabolic demands. Given that some rock partridge populations inhabit Mediterranean regions, it remains
an open question whether individuals incubating in these milder climates spend less time away from the nest compared to their alpine counterparts.

Considering the trade-off between two conflicting selec-
tive pressures, the survival of future offspring and the survival
of the incubating parent and its clutch, relatively low nest
attendance could potentially entail significant costs. These
include increased thermoregulatory demands associated with
rewarming the eggs after extended recesses, as eggs cool more
rapidly than they warm (Drent 1975), as well as prolonged
exposure of both eggs and parents to predation during forag-
ing absences.

However, in our study, these risks appeared to be moder-
ate. Specifically, the number of incubating birds lost during
a foraging recess was relatively low, with only 10% of the
39 recorded nest failures attributed to this cause (Bernard-
Laurent et al. 2024). Moreover, predation events on eggs were
not observed during parental recesses, but rather occurred
primarily following nest attacks at dusk, dawn, or during the
night (Bernard-Laurent et al. 2024).

Nest monitoring with temperature data loggers

The use of temperature loggers allowed for a detailed quanti-
fication of incubation behaviour patterns, which would have
been difficult to achieve through direct visual observations,
especially given the cryptic nature of rock partridge nests
located in rocky crags. Various remote monitoring methods
have been developed to study incubation rhythms, depend-
ing on the ecology of the target species (see Afton and Paulus
1992, Smith et al. 2015, for a description of older and newer
devices). In our study, small temperature loggers placed inside
and outside the nest proved particularly effective for contin-
uously tracking the timing and duration of recesses. Since
the nest was only approached once to install the loggers, this
method minimized disturbance, making it especially suit-
able for a species of conservation concern. A limitation of the
device is that it does not provide the absolute temperature of
the eggs, but it is well suited for detecting temperature fluc-
tuations within the nest during recesses. In line with previous
studies documenting incubation patterns in other precocial
ground-nesting species (Novoa et al. 2003, Hartman and
Oring 2006, Legagneux et al. 2011, Mougeot et al. 2014,
Moreau et al. 2018), we found no evidence that the place-
ment of a temperature logger during recesses affected nesting
success.

Conclusion

Our study reveals that incubating male rock partridges
exhibit very similar nest attendance to females, providing
valuable insights into incubation patterns in an uncommon
avian parental care system. These findings contribute to a bet-
ter understanding of the species' behaviour, which is crucial
for its conservation. While we have made significant progress,
some complex factors influencing incubation patterns were
not explored here. These may include weather parameters,

the body condition and age of the parents, clutch rank (first
versus second or third clutches), the year of observation, nest
predator abundance, and the availability of food resources
near the nest site (Wiebe and Martin 2000). Future research
should investigate these factors to refine our understanding
of sex-specific investment in incubation behaviour and its
impact on reproductive success. Additionally, exploring the
physiological and behavioural limits of incubation tempera-
ture regulation in the context of climate change, where more
frequent and severe weather events are expected, should be
a priority. Lastly, our nest monitoring data on the timing
of incubation could be valuable for mitigating the effects of
human disturbances, such as grazing or outdoor activities, on
reproductive success.

*Acknowledgements* – We are deeply grateful to everyone who contributed to the challenging fieldwork, particularly P. Bouvet, M. Guillot, E. Millet-Delpech, B. Rochedy, J. P. Serres, and S. Tangis from the 'Office National de la Chasse et de la Faune Sauvage' (known since 2020 as the French Office for Biodiversity). We also extend our thanks to those among them who assisted with processing the temperature data from the loggers.

*Funding* – The study was part-funded by two European funds: the Fond Européen de Développement Régional (FEDER) during a four-year period from May 2011 to May 2015 and the Programme Interrégional du massif des Alpes – Fonds Européen de Développement Régional (POIA-FEDER) in the three-year period 2016 to 2018 (https://www.europe-en-france.gouv.fr/fr/fonds-eurospeens/fonds-europeen-de-developpement-regional-FEDER).

Author contributions

**Ariane Bernard-Laurent:** Conceptualization (lead); Data curation (lead); Funding acquisition (lead); Investigation (equal); Methodology (equal); Writing – original draft (equal); Writing – review and editing (equal). **Guillelme Astruc:** Data curation (equal); Investigation (equal). **Meili Baragatti:** Formal analysis (equal). **Claire Anceau:** Investigation (equal). **Thierry Faivre:** Investigation (equal); **Jean-Louis Laurent:** Formal analysis (equal).

Data availability statement

Data are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.hmgqnk9xb (Bernard-Laurent et al. 2025).

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