# Effects of weather and colony size on water collection in honey bee, Apis mellifera, colonies

Pierre Le Bivic, Cedric Alaux, Camille Gay, Cyril Vidau, Yves Le Conte, Luc

P Belzunces, Maryline Pioz

► To cite this version:

Pierre Le Bivic, Cedric Alaux, Camille Gay, Cyril Vidau, Yves Le Conte, et al. Effects of weather and colony size on water collection in honey bee, Apis mellifera, colonies. Animal Behaviour, 2025, 227, pp.123271. 10.1016/j.anbehav.2025.123271. hal-05213526

HAL Id: hal-05213526

https://hal.science/hal-05213526v1

Submitted on 18 Aug 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
specific behaviour called evaporative cooling wherein water is
collected from the environment by foragers and then spread over
the combs to be evaporated (Stabentheiner et al., 2021, 2022).
However, considering the ongoing climate change, the perfor-
mance of evaporative cooling is likely to be challenged by the
projected increase in the frequency and magnitude of concurrent
heat waves and droughts (IPCC, 2023), coupled with a decrease in
the availability of water during the dry season (Konapala et al.,
2020; Kumar et al., 2014). Honey bees are insects of global socio-
cultural (Crane, 1999), economic (Chauzat et al., 2013) and
ecological (Hung et al., 2018) importance. Therefore, investigating
the mechanism by which honey bee water collection behaviour is
affected by ecological factors (i.e. weather and colony size) is
important to better predict their response to the aforementioned
extreme weather events and to provide insights into the pattern of
collective response that underlies the ecological success of euso-
cial insects.

Honey bees collect water not only for thermoregulatory purposes, but also to obtain micronutrients (Bonoan et al., 2017, 2018; Khan et al., 2021) and to keep bees hydrated, either through larval food production (Lindauer, 1955) or by diluting stored honey (Butler, 1940; Haydak, 1970) when nectar is limited. As water is stored only transiently and in small amounts in the crop of the bees or, more rarely, in the comb cells in response to extreme brood nest hyperthermia (Ostwald et al., 2016; Park, 1923), honey bees collect water on a 'just-in-time' basis depending on the needs of the colony. Consequently, colony water collection can be triggered by a highly concentrated sugar solution in the bee's crop when the colony is experiencing a negative water budget, for example after a period of confinement because of rainy days (Kiechle, 1961; Lindauer, 1954; Seeley, 1995), or by rising environmental temperatures (Bordier et al., 2017; Lensky, 1964; Stabentheiner et al., 2021). Regarding the frequency of colony water needs, Lindauer (1955) recorded the number of daily visits of a honey bee colony to a watering place between early April and mid-September. He found that the bees collected water almost daily, although the number of daily visits dropped sharply in September, indicating that the colony's water needs go beyond thermoregulation.

The organization of water economy in honey bees is based on a
division of labour with specialized bees (Robinson et al., 1984).
Water foragers collect water outside the colony, whilst water re-
ceivers manage the water resource within the colony (Kühnholz &
Seeley, 1997; Ostwald et al., 2016). Water foragers have a lower
sucrose response threshold than nectar or pollen foragers (Pankiw
& Page Jr, 2000), depending on their genetic patriline (Kryger
et al., 2000), and they represent a small fraction of the colony
population, which is typically less than 1% of the workers (Seeley,
1995). In recruiting more water foragers, they perform waggle and
tremble dances (Kühnholz & Seeley, 1997), and each water forager
can carry a load of approximately 30–60 µL of water, with the load
decreasing with ambient temperature (presumably for flight
optimization) (Kovac et al., 2010, 2018; Louw & Hadley, 1985;
Visscher et al., 1996). The distance that foragers will travel to
collect water depends on the availability of water sources in the
vicinity of the colony. In an environment with water sources close
to colonies, Gary et al. (1979) showed that most foragers collected
water within 500 m of their colony with a mean flight distance of
89 m and a maximum of 2.3 km. In a desert environment, Visscher
et al. (1996) found that foragers could collect water up to 2 km
from their colony. Nevertheless, they pointed out that this 2 km
distance did not necessarily reflect the maximum distance that
water foragers could travel. Considering that the foragers reach the
water source with an empty crop, the energy for the return flight is
only provided by the body's energy reserves, thereby limiting their

foraging radius around the colony (Visscher et al., 1996). Finally,
similar to nectar and pollen foraging, water foraging is expected to
increase with temperature and solar radiation and decrease with
relative humidity and wind (Clarke & Robert, 2018; Karbassioon
et al., 2023; Ngo et al., 2021). However, water foraging can occur
at lower ambient temperatures compared with nectar and pollen
foraging. Chilcott and Seeley (2018) observed honey bees foraging
for water at ambient temperatures just over 4 °C. This behaviour
can be explained by the need to dilute honey stores in winter.
Within the colony, water receivers are middle-aged adult bees
(between 10 and 25 days old) that perform tasks related to water
distribution and colony thermoregulation, such as cell inspection
to deposit water in overheated cells; distribution of water to their
nestmates; tongue lashing and ventilation (Kühnholz & Seeley,
1997). Water receivers play an important role in the regulation
of water collection, informing inactive foragers of the colony's
water needs by begging, as well as stopping colony water collec-
tion by refusing to unload water foragers (Kühnholz & Seeley,
1997; Ostwald et al., 2016).

Therefore, the water economy in honey bees is a self-organized
system regulated by a negative feedback loop: Water foragers
sense the colony's need for water through their own thirst and
through more frequent requests from in-hive bees, and water
collection is stopped when foragers are no longer able to unload
their forage (Ostwald et al., 2016). However, the effects of
ecological factors (i.e. weather and colony size) on colony water
requirements remains poorly understood. Some authors have
estimated that a colony collects 20–25 litres of water per year
(Seeley, 1995; Weipple, 1928), whereas others have stated that it
can be as much as 4 litres per week (Farrar, 1973). Therefore, col-
ony water requirements are highly variable and should depend on
weather and environmental conditions (e.g. nectar flow and its
sugar concentration) as well as colony size (Park, 1923). To our
knowledge, this topic has never been studied. Thus, in this study,
the factors influencing water collection at the colony level and
whether there is a thermal threshold that triggers a sharp increase
in water collection for thermoregulatory purposes were investi-
gated. In addressing this issue, the amount of water collected daily
by colonies placed under semifield conditions during spring,
summer and autumn was monitored. Colony water collection was
expected to increase with population factors (i.e. the number of
adult bees and brood cells), solar radiation and temperature (for
brood thermoregulation). Then, whether a temperature break-
point can affect colony water collection for thermoregulatory
purposes was investigated. According to Stabentheiner et al.
(2021), the water-cooled comb surface area increases sharply
from 29-30 °C. Thus, we hypothesized that colony water collection
would sharply increase from this temperature threshold. Finally,
whether weather and population factors affected the proportion of
water foragers in the colony was investigated. The proportion of
water foragers was expected to increase with temperature but not
with population factors because the genetic dependence of this
behaviour would keep the proportion of water foragers in a colony
roughly stable at around 1%.

METHODS

Experimental Set-up

This study was conducted at the INRAE (France's National
Research Institute for Agriculture, Food and Environment)
research centre of Avignon (France) from September 2020 to
October 2021. A semifield design was selected to control water
collection by the colonies and to avoid any external supply via
nectar or other water sources. The trials lasted 5 consecutive days,
during which two colonies were placed in a tunnel covered with an insect-proof net (high-density polyethylene, 920 µm × 920 µm openings, Diatex France), each in a separate compartment (8 m × 8 m). Wherever possible, different colonies were used for each trial. A pair of colonies included a large colony (3–9 frames of brood in a 10-frame Dadant hive, i.e. L50 cm × 143 cm × H31 cm) and a smaller one (3–5 frames of brood in a six-frame Dadant hive, i.e. L50 cm × 128 cm × H31 cm) to obtain a variation in colony size.

Colonies were provided by a beekeeper and selected from his apiaries. Colony size was initially selected on the basis of the number of brood frames and bee density to ensure (where possible) a difference in size between the two colonies for each trial. Then, colony size (i.e. number of adults and brood cells) was assessed more accurately during the trials using the ColEval method (Hernandez et al., 2020). Consequently, a gradient of colony size was obtained to make predictions about daily colony water collection. Colony water collection was monitored in spring (late April to early June 2021), summer (late June to August 2021) and autumn (late September to October 2020 and 2021), with a total of five trials per season (i.e. 10 colonies per season, with six colonies used two times in two different seasons in 2021).

Throughout the experiment, the colonies were fed ad libitum with pollen (chestnut, Castanea sativa Mill., dominance) and sugar paste (Apimel 1 kg, Apitec). Chestnut pollen was selected because of its availability in the experimental area and its good nutritional quality (Di Pasquale et al., 2013). Waterers (such as siphon drinkers) were installed in each compartment to measure the amount of water collected by the colonies. They consisted of a laboratory wash bottle (1 litre) turned upside down over a saucer (ø 14 cm), with a hole (approximately 1 cm) in the centre of the cap to allow water to go through. To keep the wash bottle upright, it rested on wooden sticks placed on a plant saucer, and the whole thing was strapped to the saucer. Queen excluder segments were placed in the plant saucer to allow the bees to collect the water without drowning. Based on a preliminary study, colonies were placed under the tunnel 2 days before the start of the monitoring to allow colonies to familiarize themselves with the waterers.

## Data Collection

### Colony water collection

In measuring foraging activity, water foragers were counted hourly each day before weighing the waterer (i.e. between 0700 hours and 2000 hours in spring and summer and between 0900 hours and 1900 hours in autumn because of the shorter day length). All bees collecting water (i.e. with submerged proboscis and pulsating abdomen) were counted during a period of 30 s. This period was selected on the basis of preliminary observations (see Results) to avoid counting the same bee twice during each 30 s count. Three consecutive 30 s counts were made per hour to account for the differences observed amongst the waves of foragers arriving at the waterer.

Then, colony water collection was recorded hourly each day immediately after the water foragers were counted. The 5-day trials were only scheduled when the weather forecast was favourable (i.e. no rain and average wind speed <20 km/h) to ensure that all the planned counts and weighs could be performed. In assessing water collection, two waterers were placed in each compartment: one that enabled water collection (free waterer) and the other to measure evaporation (control waterer surrounded by an insect-proof net). Colony water collection (W) was estimated by taking the difference in weight between two hourly weighing sessions of the free waterer ($m_{t-1} - m_t$) and subtracting the evaporation (e) measured from the control waterer, which is expressed in equation (1).

$$W = (m_{t-1} - m_t) - e \quad (1)$$

An OHAUS NVT6201 portable scale (0.1 g accuracy) was used for weighing. Daily colony water collection (i.e. between 0700 hours and 2000 hours in spring and summer and between 0900 hours and 1900 hours in autumn) was determined on the basis of the cumulative amount of water collected by colonies at each hour of the same day.

### Collection of weather and population variables

Three weather variables associated with foraging activity were monitored to investigate their influence on daily water collection, including temperature (°C), relative humidity (% RH) and global solar radiation (W/m²), which is the sum of direct, diffuse and reflected solar radiations (Clarke & Robert, 2018; Karbassioon et al., 2023; Ngo et al., 2021). Temperature was recorded every 15 min in each tunnel compartment (using a PLUG&TRACK button-cell temperature data logger with a 0.1 °C resolution), whilst relative humidity and global solar radiation were recorded outside the tunnel at the INRAE weather station located near the experimental site (~150 m away). Relative humidity was recorded hourly, while global solar radiation was recorded daily (cumulative daily values). The data were retrieved from the INRAE CLIMATIK platform (Delannoy et al., 2022).

Three population variables were collected using the ColEval method (Hernandez et al., 2020), including the number of adult bees, the number of open brood cells (i.e. eggs and larvae) and the number of capped brood cells (i.e. pupae). The ColEval method enables the assessment of honey bee colony population, which is inspired by the 'Liebefeld method' (Dainat et al., 2020; Imdorf et al., 1987). In addition, this method is based on the percentage of area occupied by adult bees, open brood and capped brood. Colonies were assessed three times during the 5-day experimental period (i.e. at the beginning, middle and end of the period), and missing data between two ColEval assessments were imputed using the mean of the ColEval assessments taken on the previous day and the next day.

## Statistical Analysis

On 28 September 2020, one observation was removed before statistical analyses because the colony did not collect water on the first sampling day and no bee was recorded at the waterer. On 7 October 2020, one additional observation was removed before modelling the proportion of water foragers in the colonies (which was estimated from the daily maximum number of foragers recorded during the counts). This colony had collected 5.5 ml of water during that day, but no water foragers were recorded at the waterer during the hourly counts.

### Identification of a temperature breakpoint in daily water collection

Piecewise regression was used to investigate the structural break in the relationship between daily colony water collection and temperature (sample size: N = 145). The following model (equation 2) was fitted to estimate the breakpoint (Bolker, 2008):

$$y_i = \begin{cases} \alpha + \beta_1 x_i + e_i & \text{for } x_i < s \\ (\alpha + \beta_1 s) + \beta_2(x_i - s) + e_i & \text{for } x_i > s \end{cases} \quad (2)$$

where $y_i$ is the value of the dependent variable (herein referred to as the daily colony water collection) for the i-th observation; $x_i$ is the corresponding value of the independent variable (i.e. temperature); $\alpha$ is the intercept; $s$ is the breakpoint; $\beta_1$ is the slope of the first line of the regression; $\beta_2$ is the difference in slopes (i.e. $\beta_1 + \beta_2$
gives the slope of the second line of the regression), and *e*ᵢ is the
additive error assumed to be independent with a constant vari-
ance. The intercept and breakpoint parameters were included as
random effects to allow them to vary amongst colonies.

Two piecewise regressions were fitted with either the daily mean temperature (hourly mean temperatures from 0000 hours to 2300 hours) or daily maximum temperature as independent variables. The second-order Akaike Information Criterion (AICc) was used to perform model selection. Finally, a Chow test (Chow, 1960) was performed to confirm the structural change from the estimated breakpoint in the relationship between daily colony water collection and temperature.

Weather and population factors affecting daily colony water
collection and the proportion of water foragers

The breakpoints estimated for each colony from the previously
selected piecewise mixed-effect regression were used as temper-
ature thresholds to investigate the effects of weather and popu-
lation factors on daily colony water collection below (N = 91) and
above (N = 54) the temperature thresholds. Linear mixed-effect
models (LMMs) were used for this purpose.

A generalized additive mixed-model (GAMM) was also fitted to a binomial distribution with a logit link to investigate the relationship between the proportion of water foragers and the weather and population factors (N = 144). The daily proportion of water foragers in a colony was estimated as the ratio of the daily maximum number of foragers counted at the waterer (recorded during the 30 s counting sessions) to the estimated number of adult bees in the colony. The daily maximum number of foragers counted at the waterer was used to get as close as possible to the total part of the colony population that can be involved in water collection. However, this proportion should be considered the minimum, as we cannot know the exact proportion of foragers in the colony: Foragers returning to the colony or remaining in the hive during the counts were not included in this proportion.

The selection process of LMMs and GAMM was in accordance with the recommendations of Zuur et al. (2009), that is using a top-down strategy from full models (or beyond optimal models) that included as many explanatory variables as possible in the fixed component. The independent variables were initially standardized to have a mean of zero and a standard deviation of one. Then, a threshold-based preselection of the independent variables to be included in the full models was used to avoid collinearity, and highly correlated variables (Pearson correlation coefficient |r| > 0.7) were tested in separate models (Dormann et al., 2013). Depending on their collinearity, the variables that could be included in the fixed component of the full models included the daily mean temperature, daily maximum temperature, daily minimum relative humidity and daily global solar radiation for weather factors, as well as the number of adult bees, open brood cells and capped brood cells for population factors. For LMMs, two-way interactions were investigated between temperature and the number of adult bees, as well as amongst temperature, relative humidity and global solar radiation. Our results are expressed in terms of daily water collection, and the sampling periods in our study (i.e. the period of time between the first and last weighing on each day of observation) could vary because of perturbed weather (showers or wind) or data collectors. Thus, the effect of sampling periods on daily colony water collection measurements in LMMs was assessed. To do this, the ratio of sampling periods to daily day lengths (i.e. the period of time between sunrise and sunset) was used and included as a fixed effect in the full models. For LMMs and GAMM, colony identity was included as a random

intercept. Model selection was performed using AICc, and the
model with the lowest AICc was selected as the best model.

Multicollinearity was checked for LMMs using the variance inflation factor (VIF) with a threshold of 3 (Zuur et al., 2009). By contrast, concurvity was checked for GAMM. Concurvity is a non-parametric analogue of multicollinearity with values ranging from 0 (no identifiability problem) to 1 (complete lack of identifiability). A threshold of 0.8 was selected for high concurvity. For LMMs, influential observations were assessed using the Cook's distance with a cutoff of 0.5. Some observations influenced the estimated coefficients of LMMs; thus, we choose to present the results of the LMMs fitted with all the data, and the results of the LMMs selected without these influential observations are shown in the Supplementary Material. Models selected by AICc were validated by graphically checking the assumptions of normality and homoscedasticity of the residuals.

Finally, the coefficient of determination (R²) of the models and the semipartial R² (part R²) were estimated to attribute the proportion of observed variance explained by the LMMs and by each independent variable. R² estimates the proportion of variance explained by the model, either by the fixed part (marginal R² or R²<sub>m</sub>) or by the fixed and random parts (conditional R² or R²<sub>c</sub>), whereas part R² estimates the variance explained by each independent variable or the combination of independent variables relative to the total variance in the dependent variable (Stoffel et al., 2021). Considering that the proportion of variance explained by the random part is given by R²<sub>c</sub>, only the marginal part R² (part R²<sub>m</sub>) is shown in the results. For all statistical tests used in our data analysis, the statistical significance level was set at α = 0.05.

Software and packages

Statistical analysis was performed using R software v4.0.2 (R Core Team, 2020). Sunrise and sunset times were obtained using the package suncalc v0.5.1 (Thieurmel & Elmarhraoui, 2022). Piecewise regressions were fitted, and the 95% confidence intervals (95% CI) for the breakpoints were computed, using the package nlme v3.1-161 (Pinheiro et al., 2022). The Chow test was computed using the package strucchange v1.5-3 (Zeileis et al., 2002). GAMM was fitted and concurvity was computed using the packages gamm4 v0.2-6 (Wood & Scheipl, 2022) and mgcv v1.8-42 (Wood, 2017), respectively. LMMs were fitted, and the 95% CI of their coefficients were computed, using the package lme4 v1.1-31 (Bates et al., 2015). *P* was obtained using the package lmerTest v3.1-3 (Kuznetsova et al., 2017), and AICc was calculated using the package MuMln v1.43.17 (Barton, 2020). Finally, R² and part-R² were calculated using the package partR2 v0.9.1 (Stoffel et al., 2021). The graphical validation of VIFs and LMMs was obtained using the package performance v0.10.1 (Lüdecke et al., 2021).

Ethical Note

Honey bees are not covered by the European Union legislation on the welfare of animals used for scientific purposes (Directive 2010/63/EU). However, in accordance with the Council for International Organisations of Medical Sciences guidelines for research involving animals, and considering the fact that our experimental design does not allow the use of floral resources, we took care to provide the best living conditions for honey bee colonies (Bayne et al., 2010). The data collection was purely observational, and the experiments were conducted with care to ensure the welfare of the colonies by providing pollen, sugar and water ad libitum. At the end of the experiments, the colonies were returned to an environment suitable for meeting their needs.
# RESULTS

## Hourly and Daily Colony Water Collection by Season

Data were obtained for a total of 73 days using 24 colonies, some of which were used two times over two seasons in 2021 (colony sizes are shown in Fig. A1). The sampling periods averaged (± SD) 82% ± 5% of the total day length. A moderate positive correlation (with 95% CI in brackets) was found between hourly water collection and temperature (Pearson correlation coefficient *r* = 0.60, 95% CI [0.56; 0.63], *df* = 1628, *P* < 0.001). Preliminary observations showed that the mean (± SD) of the foraging time of water collectors was 33 ± 3 s at approximately 30 °C and 47 ± 10.5 s at approximately 20 °C. The highest hourly water collection by colonies was observed in the afternoon, between 1500 hours and 1700 hours, when it was the hottest. The highest hourly water collection averaged (± SD) 43 ± 45, 84 ± 39, and 20 ± 18 ml for large colonies in spring, summer and autumn respectively, and 25 ± 16, 39 ± 29, and 13 ± 5 ml for small colonies (Fig. A2).

The average (± SD) daily water collection was 401 ± 278, 639 ± 259, and 123 ± 82 ml for large colonies in spring, summer and autumn, respectively, and 202 ± 72, 320 ± 166, and 102 ± 55 ml for small colonies (Fig. A3). A maximum value of 1390 ml was observed in summer (13 August 2021) for a colony of 15 890 adult bees and 12 200 brood cells at a daily mean temperature of 30.3 °C.

## Weather and Population Factors Affecting Daily Colony Water Collection

Above a daily mean temperature of 22.3 °C (95% CI [21.0; 23.6]) or a daily maximum temperature of 31.5 °C (95% CI [30.0; 33.1]), the daily colony water collection increased sharply (Chow tests: *F* = 3.39, *P* = 0.04; *F* = 3.60, *P* = 0.03, respectively; Fig. 1, Table A1).

When we investigated the effects of weather and population factors on daily colony water collection, the daily colony water collection was most strongly associated with population factors

below the daily mean temperature threshold (i.e. the number of adult bees and open brood cells; Table 1, Fig. A4) and with the number of adult bees and weather factors above this threshold (i.e. daily maximum temperature and cumulative global solar radiation; Table 2, Fig. A5). The results without influential observations (Table A2) are shown in Table A3. At high ambient temperatures (i.e. above the daily mean temperature threshold), little evidence supported a two-way interaction between the daily maximum temperature and the number of bees. In addition, the effects of daily maximum temperature and cumulative global solar radiation were dependent on the daily minimum relative humidity, indicating that their effects on daily colony water collection increased with the decrease of relative humidity (Fig. 2).

Regarding the proportion of observed variance explained by weather and population factors (Fig. 3 and Table A4), the combined population factors, namely the number of adult bees and open brood cells, accounted for 64% and 45% of the observed variance in daily colony water collection below and above the daily mean temperature threshold, respectively, compared with 9% and 24%

<caption>**Table 1**</caption>

Effects of weather and colony size on daily colony water collection below the temperature threshold

<table><thead><tr><th>Term</th><th>Coefficient</th><th>95% CI</th><th>t</th><th>df</th><th>P</th></tr></thead><tbody><tr><td>(Intercept)</td><td>182.07</td><td>155.83; 208.36</td><td>13.16</td><td>15.19</td><td>&lt;0.001</td></tr><tr><td>Tmean</td><td>14.49</td><td>-3.36; 34.94</td><td>1.56</td><td>83.36</td><td>0.123</td></tr><tr><td>GR</td><td>29.89</td><td>14.25; 45.82</td><td>3.66</td><td>84.87</td><td>&lt;0.001</td></tr><tr><td>Bees</td><td>79.04</td><td>53.58; 104.25</td><td>5.95</td><td>22.91</td><td>&lt;0.001</td></tr><tr><td>OB</td><td>41.28</td><td>19.01; 63.26</td><td>3.55</td><td>50.60</td><td>0.001</td></tr><tr><td>σ<sub>colony</sub></td><td>57.55</td><td>34.59; 78.81</td><td></td><td></td><td></td></tr><tr><td>σ<sub>residual</sub></td><td>45.06</td><td>37.95; 53.23</td><td></td><td></td><td></td></tr><tr><td>R<sup>2</sup><sub>m</sub></td><td>0.70</td><td>0.59; 0.82</td><td></td><td></td><td></td></tr><tr><td>R<sup>2</sup><sub>c</sub></td><td>0.89</td><td>0.83; 0.93</td><td></td><td></td><td></td></tr></tbody></table>

The results of the LMM fitted to investigate the effects of weather and colony size below the inflection point in daily colony water collection are shown. Tmean (°C): daily mean temperature; GR (W/m²): daily global solar radiation; Bees and OB: the number of adult honey bees and open brood cells in the colony, respectively; σ<sub>colony</sub> and σ<sub>residual</sub>: the standard deviation for colony level and data level errors, respectively. The coefficient of determination (R²) estimates the proportion of variance explained by the model, either by the fixed part (R²<sub>m</sub>) or by the fixed and random parts (R²<sub>c</sub>).

<caption>**Table 2**</caption>

Effects of weather and colony size on daily colony water collection above the temperature threshold

<table><thead><tr><th>Term</th><th>Coefficient</th><th>95% CI</th><th>t</th><th>df</th><th>P</th></tr></thead><tbody><tr><td>(Intercept)</td><td>497.32</td><td>437.55; 556.00</td><td>15.80</td><td>11.29</td><td>&lt;0.001</td></tr><tr><td>Tmax</td><td>165.36</td><td>133.47; 198.28</td><td>9.42</td><td>42.51</td><td>&lt;0.001</td></tr><tr><td>RHmin</td><td>12.82</td><td>-28.88; 54.21</td><td>0.56</td><td>44.79</td><td>0.576</td></tr><tr><td>GR</td><td>125.21</td><td>83.23; 165.51</td><td>5.65</td><td>42.52</td><td>&lt;0.001</td></tr><tr><td>Bees</td><td>178.39</td><td>121.77; 232.96</td><td>5.94</td><td>19.67</td><td>&lt;0.001</td></tr><tr><td>OB</td><td>63.65</td><td>23.10; 100.55</td><td>3.20</td><td>42.42</td><td>0.003</td></tr><tr><td>Tmax × Bees</td><td>32.37</td><td>-3.18; 70.54</td><td>1.66</td><td>39.18</td><td>0.106</td></tr><tr><td>Tmax × RHmin</td><td>-45.14</td><td>-76.95; -15.29</td><td>-2.75</td><td>38.91</td><td>0.009</td></tr><tr><td>GR × RHmin</td><td>-50.79</td><td>-74.92; -25.65</td><td>-3.83</td><td>37.44</td><td>&lt;0.001</td></tr><tr><td>σ<sub>colony</sub></td><td>99.19</td><td>51.87; 148.07</td><td></td><td></td><td></td></tr><tr><td>σ<sub>residual</sub></td><td>81.13</td><td>60.78; 94.86</td><td></td><td></td><td></td></tr><tr><td>R<sup>2</sup><sub>m</sub></td><td>0.79</td><td>0.69; 0.90</td><td></td><td></td><td></td></tr><tr><td>R<sup>2</sup><sub>c</sub></td><td>0.92</td><td>0.86; 0.96</td><td></td><td></td><td></td></tr></tbody></table>

The results of the LMM fitted to investigate the effects of weather and colony size above the inflection point in daily colony water collection are shown. Tmax (°C): daily maximum temperature; GR (W/m²): daily global solar radiation; RHmin (%): daily minimum relative humidity; Bees and OB: the number of adult honey bees and open brood cells in the colony, respectively; σ<sub>colony</sub> and σ<sub>residual</sub>: the standard deviation for colony level and data level errors, respectively. The coefficient of determination (R²) estimates the proportion of variance explained by the model, either by the fixed part (R²<sub>m</sub>) or by the fixed and random parts (R²<sub>c</sub>).

<figure><img src="image_2.png" /><figcaption>**Figure 1.** Structural break in daily colony water collection as a function of temperature. The predictions are shown using the daily mean temperature (Tmean) as the independent variable. The grey dots indicate the observed value, and the red lines indicate the predicted values.</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>**Figure 2.** Predicted changes in daily colony water collection as a function of weather factors when colonies were under high ambient temperatures. The plots indicate the observed values (grey dots) and predictions (with 95% confidence intervals) of daily colony water collection as a function of the (a) daily maximum temperature (Tmax) and (c) daily global solar radiation (GR), respectively, at three levels of the daily minimum relative humidity (RHmin). Conversely, plots (b) and (d) indicate the predictions of daily colony water collection as a function of the daily minimum relative humidity (RHmin) at three levels of either daily maximum temperature (Tmax) or daily global solar radiation (GR). The three levels of the moderator variable are the mean and plus or minus one standard deviation thereof (−1SD and +1SD), and all other covariates are held at their means.</figcaption></figure>

for the combined weather factors, namely temperature and global solar radiation. Observing the factors individually, the number of adult bees accounted for about 40% of the observed variance in daily colony water collection below and above the daily mean temperature threshold. Other factors included the number of open brood cells, which accounted for 19% of the observed variance in daily colony water collection below the temperature threshold, and the daily maximum temperature, which accounted for 23% of the observed variance above the temperature threshold.

## Weather and Population Factors Affecting the Proportion of Water Foragers

With regard to the effect of colony size on the proportion of water foragers (Figs. A6, A7 and Fig. 4), when all other explanatory variables were held at their means, the predicted proportion of water foragers in the colony decreased (from about 0.30% to 0.13%) with the number of bees in the colony up to about 13 000 adult

bees and then remained roughly stable, whilst the proportion of water foragers showed a linear increase with the number of open brood cells. By contrast, with regard to the effect of daily maximum temperature, the predicted proportion of water foragers remained roughly stable (about 0.13%) up to 30 °C before increasing sharply above this temperature.

## DISCUSSION

This study aimed to investigate the effects of weather and colony size on the water collection behaviour of honey bees. A semifield design was selected to avoid alternative water supplies (especially via nectar). Although these are experimental conditions, they may be close to those found under natural conditions after the end of a honey flow, when nectar resources are no longer available to the colonies. Our results indicated that the amount of water collected by the colonies varied throughout the day and with seasons. Daytime water collection peaks in the
<figure><img src="image_4.png" /><figcaption>**Figure 3.** Proportion of variance explained by weather and colony size on the daily colony water collection. The semipartial coefficients of determination (Part-R²<sub>m</sub>) for the main effects, the interaction terms (‘:’ ) and the combinations (‘+’ ) of weather and population factors of the LMMs fitted (a) below and (b) above the temperature breakpoint in daily colony water collection are shown. Tmean and Tmax (°C): daily mean and maximum temperature, respectively; GR (W/m²): daily global solar radiation; RHmin (%): daily minimum relative humidity; Bees and OB: the number of adult bees and the number of open brood cells in the colony, respectively.</figcaption></figure>

afternoon when temperatures are the highest, regardless of the
season. The daily colony water collection by seasons ranged from
around 87 ml to 1 litre in spring, from 145 ml to 1.4 litres in
summer and from 5 ml to 300 ml in autumn. For honey bee health
purposes, Hegić and Bubalo (2006) tested, under natural condi-
tions, a waterer with a water reserve that was not in the open to
avoid Nosema contamination. They estimated the daily water
collection of colonies from the end of July to the end of
September and found that 60–230 ml of water was collected per
day (an average of 120 ml per day). However, we remain cautious
about comparing our results with theirs, as the experimental
designs are quite different. In addition, no evidence that supports
the fact that the colonies did not have access to water from
sources other than the waterers they provided was found in their
study. Even if this were not the case, the discrepancy between our
summer observations and theirs could be due to differences in
weather or colony size. Alternatively, it could indicate that nectar
was an important source of water for their colonies. Our results
show that colony water requirements can be very high, more
than 1 litre per day, and beekeepers should pay special attention
to this resource in their colony management, especially during
periods of high colony water demand (i.e. spring and summer)
and low nectar flow.

In this study, the water collection of colonies in winter was not
investigated. At this time of year, the water needs of bees can only
be met by metabolic water, by condensation inside the hive or by

water collected outside the hive in the close proximity to the
colony. Toomemaa et al. (2013) estimated that the amount of water
resulting from condensation in winter, in hives with clusters of
about 13 200 adult bees, averaged 445 ml during the period from
November to March in Estonia. However, foragers can be seen
collecting water outside the colony in winter. Chilcott and Seeley
(2018) recorded the number of foragers from three colonies
visiting a waterhole in January and February in Scotland. Over
27 days of monitoring, they observed active foraging for water 80%
of the time (i.e. 22 days), with temperatures mostly below 10 °C
and dropping to slightly above 4 °C. At the waterhole, an average
daily maximum of five foraging bees (ranging from 1 to 21) from
three colonies was observed. As the foragers also brought back
pollen, as well as in the absence of nectar, the water collected at
the waterhole was probably used to dilute honey stores and pro-
duce food for the larvae. Therefore, even in winter, the colony can
collect small amounts of water outside to consume its honey stores
and, if pollen is available, to ensure renewal of the colony
population.

Apart from the individual physiological water needs, colonies
use water to maintain colony thermal homeostasis in response to
high ambient temperatures (Bordier et al., 2017). Stabentheiner
et al. (2021) reported the gradual set of thermoregulatory behav-
iours of honey bees in response to high ambient temperatures,
each occurring at a specific ambient temperature threshold: wing
fanning (24–25 °C), evaporative cooling, either by spreading water
<figure><img src="image_5.png" /><figcaption>**Figure 4.** Marginal effects of weather and colony size on the daily proportion of water foragers (%) in colonies. The effects of (a) the number of adult honey bees and (b) the number of open brood cells in a colony, as well as (c) the daily maximum temperature (Tmax), are shown. Grey dots are the observed values, and the red lines and shaded areas are the predicted values with 95% confidence intervals. All other covariates are held at their means.</figcaption></figure>

droplets in the cells of the comb (29-30 °C) or by evaporating water droplets by stretching them between the mandibles, which is known as tongue lashing (31 °C), and bee density reduction on the combs (whose minimum is reached at 34-36 °C). Finally, a thermoregulatory behaviour known as 'heat shielding', which consists of heat absorption and dissipation by the bee's body, was observed (Starks & Gilley, 1999). Stabentheiner et al. (2021) found that the surface area of the brood cooled by water droplets increased sharply above 29-30 °C. Therefore, we tested the hypothesis that there may be a thermal threshold that triggers water collection for colony thermoregulation. Using the daily maximum temperature as the independent variable, evidence that supports an ambient temperature threshold at 31.5 °C (95% CI [30.0; 33.1]), or 30.3 °C (95% CI [28.6; 31.9]), if the extreme observation of 1.4 litres was excluded, was found. Our estimated breakpoint is close to the values of 29-30 °C observed by Stabentheiner et al. (2021), at which colonies begin to use water to cool the brood in response to high ambient temperatures. Thus, we assume that the increase in daily water collection above the temperature threshold was for thermoregulatory purposes. At our local scale, in Avignon (France), the average number of days per year above or equal to the thresholds estimated in this study increased by 31% for daily mean temperatures and by 52% for daily maximum temperatures in the period 2010–2020 compared with the period 1990–2000. For the recorded maximum summer temperature, the mean (± SD) accounted for 38.3 ± 2.3 °C for the period 2010–2020 compared with 36.1 ± 0.8 °C for the period 1990–2000. This trend is expected to continue in the coming decades without radical reductions in greenhouse gas emissions. Therefore, the temperature thresholds estimated in our study can help beekeepers in managing the water supply to their colonies, thereby mitigating the effects of high temperatures (e.g. brood overheating) and reducing colony losses (Sibaja Leyton et al., 2025).

Regarding the effects of weather and population factors on daily colony water collection, our results indicated that the number of adult bees in a colony alone accounted for about 40% of the observed variance. Daily colony water collection also increased with the number of open brood cells. This is caused by the high water content of the larval food, which can make up to 70% in the jelly given to worker larvae (Wang et al., 2015). In fact, when a colony is not rearing brood, water collection decreases significantly (Lindauer, 1955). With regard to weather factors, our results indicated that temperature and global solar radiation were positively associated with daily colony water collection. Furthermore, at high ambient temperatures (i.e. when the ambient temperature was above the daily mean temperature threshold), their effect was sensitive to relative humidity, such that drier air increased colony water collection. These results can be first explained by the fact that honey bee body water loss increases with temperature and decreases with hygrometry (Abou-Shaara et al., 2012; Atmowidjojo et al., 1997). Thus, an increase in water collection could sustain the physiological water needs of bees in response to dehydration. Then, high ambient temperatures combined with drier air could also negatively affect nest hygrometry. Consequently, the colony might increase water collection in order to maintain the required level of hygrometry (around 70%) in the brood area to prevent the desiccation of eggs and larvae (Ellis et al., 2008; Li et al., 2016). It is also notable that active bees within the colony are endothermic (Stabentheiner et al., 2003), and that resting bees may be weakly endothermic (Kovac et al., 2007). As a result, the temperature in the hive may also increase with the number of bees, except for the brood temperature, which remains at an average of 34.5 °C due to thermoregulation (Cook et al., 2022; Godeau et al., 2023; Smith et al., 2017). However, no evidence was provided by our data that the effect of temperature on the daily colony water collection was dependent on colony size.
Based on our results, we can expect that the concurrent heat waves and droughts caused by climate change (IPCC, 2023) will greatly increase the water requirements of managed and free-living colonies for physiological and thermoregulatory purposes. These extreme climatic events will put high pressure on the availability of environmental water sources, including nectar production (Day Briggs & Anderson, 2024; Martén-Rodríguez et al., 2025). Furthermore, sugar concentration in nectar should also increase with global warming (Martén-Rodríguez et al., 2025). Therefore, this could also negatively affect small wild bees, which rarely drink water alone and are more dependent on the water content of nectar than larger bees because of their low metabolic water production (Willmer, 1988).

The proportion of water foragers in the colony was also investigated in this study. This proportion was estimated using the daily maximum number of foragers derived from 30 s counts at the waterer. Therefore, foragers returning to the colony or remaining in the hive during this period were not included in this proportion. In addition, counts were made hourly, so a larger number of water foragers at the waterers may have been missed. Irrespective of the season and colony size, the proportion of water foragers in the colonies averaged (± SD) 0.18% ± 0.09 with a maximum at 0.54%. Based on the studies by Kühnholz and Seeley (1997) and Ostwald et al. (2016), the former observed up to 12 water foragers in a colony of approximately 4000 bees (representing 0.30% of the colony population), and the latter observed up to 19 water foragers in a colony of approximately 3000 bees (i.e. 0.63% of the colony population), both of which are close to our results.

In our study, the proportion of water foragers decreased as the number of bees in the colony increased up to a threshold of about 13,000 adult bees. After that threshold, the proportion of water foragers remained roughly constant at 0.13%. In contrast, the proportion of water foragers increased with the number of open brood cells (Fig. 4). Therefore, our results indicate that colony size affects the proportion of water foragers, with a smaller proportion of water foragers in large colonies than in small ones. If a colony may invest more in the number of individuals recruited to increase the collection of a given resource, the foraging activity of each individual may also increase. These two components of foraging effort are known as the ‘number versus effort problem’ (Schmid-Hempel et al., 1993; Ydenberg & Schmid-Hempel, 1994). For example, nectar foragers from large colonies have been shown to be more active than those from small colonies in some contexts (Eckert et al., 1994; Wolf & Schmid-Hempel, 1990). Thus, in our study, water foragers in colonies with more than 13,000 adult bees can bring back more water, either by making more trips or by bringing back larger loads, than those from colonies below this colony size threshold. This increased foraging activity could be due to a higher worker specialization in large colonies compared with small ones. In fact, group size shapes the structure and organization of insect colonies, and the level of division of labour is positively related to group size (Dornhaus et al., 2012). Thus, the increase in group size could lead to an increase in specialization at the colony level (e.g. an increase in the number of water foragers) and at the individual level (e.g. an increase in individual foraging activity) (Jeanson & Weidenmüller, 2014). Furthermore, conducting further studies is warranted to confirm whether colony status, particularly colony size, influences water foraging effort with regard to the time spent foraging, the number of trips made or the load of water brought back to the colony by each forager. Regarding the relationship between the predicted proportion of water foragers and daily maximum temperature, the proportion of water foragers increased sharply at around 30 °C, which is consistent with the

temperature threshold that we estimated using piecewise regression. Bordier et al. (2017) found that the proportion of returning water foragers doubled during simulated five-day heat waves at 37 °C, with no change in nectar and pollen foraging efforts. However, they observed a decrease in the rate of empty bees returning to the colony. These bees might have a high response threshold to sucrose and could not find nectar with a sugar concentration sufficient for them (Pankiw & Page Jr, 2000). To explain this difference, the authors indicated that heat stress could lower the sucrose response threshold of the bees.

Finally, the methods we used did not allow us to obtain a high level of accuracy in determining the number of adult bees or the number of water foragers per colony. However, despite these limitations, our results are consistent with those of previous studies.

## Conclusion

The results of this study indicated that the amount of water collected daily by colonies can be substantial, especially in spring and summer, and that honey bees start using water to maintain colony thermal homeostasis from a daily mean temperature of 22.3 °C or a daily maximum temperature of 31.5 °C. In the context of climate change, which is characterized by an increase in the frequency and magnitude of concurrent heat waves and droughts in many regions (IPCC, 2023), our results may help beekeepers in managing their colonies with regard to water supply. Providing colonies with clean water can also help the beekeepers in addressing health and social concerns. Firstly, the consumption, by bees and larvae, of water collected from the environment raises questions about their exposure to chemicals and the transmission of pathogens that could be found in the water (Johnson & Pettis, 2014; MacInnis et al., 2021; Samson-Robert et al., 2014). Secondly, the apiaries located in residential areas or near livestock can be a source of conflict between beekeepers and other stakeholders because of the nuisance caused by bees collecting water from private homes (e.g. swimming pools) or livestock water troughs. Therefore, beekeepers must consider this resource when managing their colonies and, where possible, ensure a sustainable access to clean water for their colonies, at least during periods of high water demand (i.e. spring and summer). A deeper understanding of water fluxes at the bee and colony levels as well as the factors that determine the choice of water sources by water foragers would help to identify periods at risk for water collection and improve water supply in apiaries under ongoing climate change.

## Author Contributions

**Pierre Le Bivic:** Writing – original draft, Visualization, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
**Cedric Alaux:** Writing – review & editing.
**Camille Gay:** Writing – review & editing, Investigation, Data curation.
**Cyril Vidau:** Supervision, Investigation, Funding acquisition.
**Yves Le Conte:** Writing – review & editing.
**Luc P. Belzunces:** Writing – review & editing, Supervision, Funding acquisition.
**Maryline Pioz:** Writing – review & editing, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Conceptualization.

## Data Availability

The data set used in this study is available in the Supplementary Material.
**Declaration of Interest**

The authors declare no conflicts of interest.

**Acknowledgments**

The authors thank Stan Chabert for his statistical advice and suggestions, Bernard Vaissière for his review and constructive feedback on our manuscript and Antoine Sudan for providing the honey bee colonies. The authors are also thankful for Benjamin Basso, Julie Fourrier, Coline Kouchner, Alban Maisonnasse, Guillaume Kairo and Robin Buisson for their technical assistance. The authors are grateful to the four anonymous referees for their constructive comments, which improved the manuscript. This work was supported, in part, by grants from the European Agricultural Guarantee Fund as part of the French National Apiculture Program (FranceAgriMer agreement number 20-01 R).

**Supplementary Material**

Supplementary material associated with this article is available at https://doi.org/10.1016/j.anbehav.2025.123271.

**References**

Abou-Shaara, H. F., Al-Ghamdi, A. A., & Mohamed, A. A. (2012). Tolerance of two honey bee races to various temperature and relative humidity gradients. *Environmental and Experimental Biology, 10* (4), 133–138.

Atmowidjojo, A. H., Wheeler, D. E., Erickson, E. H., & Cohen, A. C. (1997). Temperature tolerance and water balance in feral and domestic honey bees, *Apis mellifera* L. Comparative Biochemistry and Physiology Part A: Physiology, 118(4), 1399–1403. https://doi.org/10.1016/S0300-9629(97)00031-5

Barton, K. (2020). MuMln: Multi-model inference. https://CRAN.R-project.org/package=MuMln.

Bates, D., Mahler, M., Bolker, B., & Walker, S. (2015). Fitting linear mixed-effects models using lme4. *Journal of Statistical Software*, 67(1). https://doi.org/10.18637/jss.v067.i01

Bayne, K., Morris, T. H., & France, M. P. (2010). Legislation and oversight of the conduct of research using animals: A global overview. In R. Hubrecht, & J. Kirkwood (Eds.), *The UFAW handbook on the care and management of laboratory and other research animals* (1st ed., pp. 107–123). Wiley. https://doi.org/10.1002/9781444318777.ch8

Beshers, S. N., & Fewell, J. H. (2001). Models of division of labor in social insects. *Annual Review of Entomology*, 46(1), 413–440. https://doi.org/10.1146/annurev.ento.46.1.413

Bolker, B. M. (2008). *Ecological Models and Data in R*. Princeton University Press.

Bonabeau, E., Theraulaz, G., & Deneubourg, J.-L. (1996). Quantitative study of the fixed threshold model for the regulation of division of labour in insect societies. *Proceedings of the Royal Society of London. Series B: Biological Sciences*, 263 (1376), 1565–1569. https://doi.org/10.1098/rspb.1996.0229

Bonoan, R. E., O'Connor, L. D., & Starks, P. T. (2018). Seasonality of honey bee (*Apis mellifera*) micronutrient supplementation and environmental limitation. *Journal of Insect Physiology*, 107, 23–28. https://doi.org/10.1016/j.jinsphys.2018.02.002

Bonoan, R. E., Tai, T. M., Tagle Rodriguez, M., Feller, L., Daddario, S. R., Czaja, R. A., O'Connor, L. D., Georgiana, B., & Starks, P. T. (2017). Seasonality of salt foraging in honey bees (*Apis mellifera*). *Ecological Entomology*, 42(2), 195–201. https://doi.org/10.1111/een.12375

Bordier, C., Dechatre, H., Suchail, S., Peruzzi, M., Soubeyrand, S., Pioz, M., Pélissier, M., Crauser, D., Conte, Y. L., & Alaux, C. (2017). Colony adaptive response to simulated heat waves and consequences at the individual level in honeybees (*Apis mellifera*). *Scientific Reports*, 7(1), 3760. https://doi.org/10.1038/s41598-017-03944-x

Butler, C. G. (1940). The choice of drinking water by the honeybee. *Journal of Experimental Biology*, 17(3), 253–261. https://doi.org/10.1242/jeb.17.3.253

Chauzat, M.-P., Cauquil, L., Roy, L., Franco, S., Hendrikx, P., & Ribière-Chabert, M. (2013). Demographics of the European apicultural industry. *PLoS One*, 8(11), Article e79018. https://doi.org/10.1371/journal.pone.0079018

Chilcott, A., & Seeley, T. (2018). Cold flying foragers: Honeybees in Scotland seek water in winter. *American Bee Journal*, 158(1), 75–77.

Chow, G. C. (1960). Tests of equality between sets of coefficients in two linear regressions. *Econometrica*, 28(3), 591. https://doi.org/10.2307/1910133

Clarke, D., & Robert, D. (2018). Predictive modelling of honey bee foraging activity using local weather conditions. *Apidologie*, 49(3), 386–396. https://doi.org/10.1007/s13592-018-0565-3

Cook, D., Tarlinton, B., McGree, J. M., Blackler, A., & Hauxwell, C. (2022). Temperature sensing and honey bee colony strength. *Journal of Economic Entomology*, 115(3), 715–723. https://doi.org/10.1093/jee/toac034

Crane, E. (1999). *The world history of beekeeping and honey hunting* (1st ed.). Routledge.

Dainat, B., Dietemann, V., Imdorf, A., & Charrière, J.-D. (2020). A scientific note on the 'Liebefeld Method' to estimate honey bee colony strength: Its history, use, and translation. *Apidologie*, 51(3), 422–427. https://doi.org/10.1007/s13592-019-00728-2

Day Briggs, S., & Anderson, J. T. (2024). The effect of global change on the expression and evolution of floral traits. *Annals of Botany*, 135(1–2), 9–24. https://doi.org/10.1093/aob/mca057

Delannoy, D., Maury, O., & Décome, J. (2022). CLIMATIK : système d'information pour les données du réseau agroclimatique INRAE (Version V1). Recherche Data Gouv. https://doi.org/10.57745/AJNXEN

Di Pasquale, G., Salignon, M., Le Conte, Y., Belzunces, L. P., Decourtye, A., Kretschmar, A., Suchail, S., Brunet, J.-L., & Alaux, C. (2013). Influence of pollen nutrition on honey bee health: Do pollen quality and diversity matter? *PLoS One*, 8(8), Article e72016. https://doi.org/10.1371/journal.pone.0072016

Dormann, C. F., Elith, J., Bacher, S., Buchmann, P., Carl, G., Carré, G., Marquéz, J. R. G., Gruber, B., Lafourcade, B., Leitão, P. J., Münkemüller, T., McClean, C., Osborne, P. E., Reineking, B., Schröder, B., Skidmore, A. K., Zurell, D., & Lautenbach, S. (2013). Collinearity: A review of methods to deal with it and a simulation study evaluating their performance. *Ecography*, 36(1), 27–46. https://doi.org/10.1111/j.1600-0587.2012.07348.x

Dornhaus, A., Powell, S., & Bengston, S. (2012). Group size and its effects on collective organization. *Annual Review of Entomology*, 57(1), 123–141. https://doi.org/10.1146/annurev-ento-120710-100604

Duarte, A., Weissing, F. J., Pen, I., & Keller, L. (2011). An evolutionary perspective on self-organized division of labor in social insects. *Annual Review of Ecology, Evolution, and Systematics*, 42(1), 91–110. https://doi.org/10.1146/annurev-econsys-102710-145017

Eckert, C. D., Winston, M. L., & Ydenberg, R. C. (1994). The relationship between population size, amount of brood, and individual foraging behaviour in the honey bee, *Apis mellifera* L. *Oecologia*, 97(2), 248–255. https://doi.org/10.1007/BF00323157

Ellis, M. B., Nicolson, S. W., Crewe, R. M., & Dietemann, V. (2008). Hygropreference and brood care in the honeybee (*Apis mellifera*). *Journal of Insect Physiology*, 54 (12), 1516–1521. https://doi.org/10.1016/j.jinsphys.2008.08.011

Farrar, C. L. (1973). Productive management of honey bee colonies. *American Bee Journal*, 113, 416–417.

Gary, N. E., Witherell, P. C., & Lorenzen, K. (1979). Distribution of honeybees during water collection. *Journal of Apicultural Research*, 18(1), 26–29. https://doi.org/10.1080/00218839.1979.11099938

Godeau, U., Pioz, M., Martin, O., Rüger, C., Crauser, D., Le Conte, Y., Henry, M., & Alaux, C. (2023). Brood thermoregulation effectiveness is positively linked to the amount of brood but not to the number of bees in honeybee colonies. *Peer Community Journal*, 3(e42). https://doi.org/10.24072/pcjournal.270

Groh, C., Tautz, J., & Rössler, W. (2004). Synaptic organization in the adult honey bee brain is influenced by brood-temperature control during pupal development. *Proceedings of the National Academy of Sciences*, 101(12), 4268–4273. https://doi.org/10.1073/pnas.0404077310

Haydak, M. H. (1970). Honey bee nutrition. *Annual Review of Entomology*, 15(1), 143–156. https://doi.org/10.1146/annurev.en.15.010170.001043

Hegić, G., & Bubalo, D. (2006). Hygienic water supply for the bees. *Journal of Central European Agriculture*, 7(4), 743–752.

Hernandez, J., Maisonnasse, A., Cousin, M., Beri, C., Le Quintrec, C., Bouetard, A., Castex, D., Decante, D., Servel, E., Buchwalder, G., Brunet, F., Fesch-Destrella, E., de Bellescze, K., Kairo, G., Frontero, L., Pédehontaa-Hiaa, M., Buisson, R., Pouderoux, T., Aebi, A., & Kretschmar, A. (2020). Coleval: Honeybee colony structure evaluation for field surveys. *Insects*, 11(1), 41. https://doi.org/10.3390/insects11010041

Hung, K.-L. J., Kingston, J. M., Albrecht, M., Holway, D. A., & Kohn, J. R. (2018). The worldwide importance of honey bees as pollinators in natural habitats. *Proceedings of the Royal Society B: Biological Sciences*, 285(1870), Article 20172140. https://doi.org/10.1098/rspb.2017.2140

Imdorf, A., Buehlmann, G., Gerig, L., Kilchenmann, V., & Wille, H. (1987). Überprüfung der schätz methode zur ermittlung der brutfläche und der anzahl arbeiterinnen in freifliegenden bienenvölkern. *Apidologie*, 18(2), 137–146. https://doi.org/10.1051/apido:19870204

IPCC. (2023). Climate change 2023: Synthesis report. Contribution of working groups I, II and III to the sixth assessment report of the intergovernmental panel on climate change, 184 https://doi.org/10.59327/IPCC/AR6-9789291691647.

Jeanson, R., & Weidenmüller, A. (2014). Interindividual variability in social insects—Proximate causes and ultimate consequences. *Biological Reviews*, 89 (3), 671–687. https://doi.org/10.1111/brv.12074

Johnson, J. D., & Pettis, J. S. (2014). A survey of imidacloprid levels in water sources potentially frequented by honeybees (*Apis mellifera*) in the eastern USA. *Water, Air, & Soil Pollution*, 225(11), 2127. https://doi.org/10.1007/s11270-014-2127-2

Jones, J. C., Helliwell, P., Beekman, M., Maleszka, R., & Oldroyd, B. P. (2005). The effects of rearing temperature on developmental stability and learning and
memory in the honey bee, *Apis mellifera*. Journal of Comparative Physiology, **191** (12), 1121–1129. https://doi.org/10.1007/s00359-005-0035-z

Jones, J. C., & Oldroyd, B. P. (2006). Nest thermoregulation in social insects. *Advances in Insect Physiology, **33***, 153–191. https://doi.org/10.1016/S0065-2806(06)33003-2

Kühnholz, S., & Seeley, T. D. (1997). The control of water collection in honey bee colonies. *Behavioral Ecology and Sociobiology, **41**(6), 407–422. https://doi.org/10.1007/s002650050402

Karbassioon, A., Yearlsey, J., Dirilgen, T., Hodge, D., Stout, J. C., & Stanley, D. A. (2023). Responses in honeybee and bumblebee activity to changes in weather conditions. *Oecologia, **201***, 689–701. https://doi.org/10.1007/s00442-023-05332-x

Khan, K. A., Ghramh, H. A., Ahmad, Z., El-Niweiri, M. A. A., & Mohammed, M. E. A. (2021). Honey bee (*Apis mellifera*) preference towards micronutrients and their impact on bee colonies. *Saudi Journal of Biological Sciences, **28**(6), 3362–3366. https://doi.org/10.1016/j.sjbs.2021.02.084

Kiechle, H. (1961). Die soziale regulation der wassersammeltätigkeit im bienenstaat und deren physiologische grundlage. *Zeitschrift Für Vergleichende Physiologie, **45***, 154–192. https://doi.org/10.1007/BF00297763

Konapala, G., Mishra, A. K., Wada, Y., & Mann, M. E. (2020). Climate change will affect global water availability through compounding changes in seasonal precipitation and evaporation. *Nature Communications, **11**(1), 3044. https://doi.org/10.1038/s41467-020-16757-w

Kovac, H., Käfer, H., & Stabentheiner, A. (2018). The energetics and thermoregulation of water collecting honeybees. *Journal of Comparative Physiology, **204** (9–10), 783–790. https://doi.org/10.1007/s00359-018-1278-9

Kovac, H., Stabentheiner, A., Hetz, S. K., Petz, M., & Crailsheim, K. (2007). Respiration of resting honeybees. *Journal of Insect Physiology, **53**(12), 1250–1261. https://doi.org/10.1016/j.jinsphys.2007.06.019

Kovac, H., Stabentheiner, A., & Schmaranzer, S. (2010). Thermoregulation of water foraging honeybees—balancing of endothermic activity with radiative heat gain and functional requirements. *Journal of Insect Physiology, **56**(12), 1834–1845. https://doi.org/10.1016/j.jinsphys.2010.08.002

Kryger, P., Kryger, U., & Moritz, R. F. A. (2000). Genotypic variability for the tasks of water collecting and scenting in a honey bee colony. *Ethology, **106**(9), 769–779. https://doi.org/10.1046/j.1439-0310.2000.00571.x

Kumar, S., Lawrence, D. M., Dirmeyer, P. A., & Sheffield, J. (2014). Less reliable water availability in the 21st century climate projections. *Earth's Future, **2**(3), 152–160. https://doi.org/10.1002/clt.130000159

Kuznetsova, A., Brockhoff, P. B., & Christensen, R. H. B. (2017). ImerTest package: Tests in linear mixed effects models. *Journal of Statistical Software, **82**(13), 1–26. https://doi.org/10.18637/jss.v082.i13

Lüdecke, D., Ben-Shachar, M., Patil, I., Waggoner, P., & Makowski, D. (2021). performance: An R package for assessment, comparison and testing of statistical models. *Journal of Open Source Software, **6**(60), 3139. https://doi.org/10.21105/joss.03139

Lensky, Y. (1964). Comportement d'une colonie d'abeilles à des températures extrêmes. *Journal of Insect Physiology, **10**(1), 1–12. https://doi.org/10.1016/0022-1910(64)90090-3

Li, Z., Huang, Z. Y., Sharma, D. B., Xue, Y., Wang, Z., & Ren, B. (2016). Drone and worker brood microclimates are regulated differentially in honey bees, *Apis mellifera*. *PLoS One, **11**(2), Article e0148740. https://doi.org/10.1371/journal.pone.0148740

Lindauer, M. (1954). *Temperaturregulierung und wasserhaushalt im bienenstaat.* Zeitschrift für vergleichende Physiologie, **36**, 391–432. https://doi.org/10.1007/BF00345028

Lindauer, M. (1955). The water economy and temperature regulation of the honeybee colony. *Bee World, **36**(5), 81–92. https://doi.org/10.1080/0055772X.1955.11094876

Louw, G. N., & Hadley, N. F. (1985). Water economy of the honeybee: A stoichio-metric accounting. *Journal of Experimental Zoology, **235**(1), 147–150. https://doi.org/10.1002/jez.1402350118

MacInnis, C. I., Keddie, B. A., & Pernal, S. F. (2021). Honey bees with a drinking problem: Potential routes of *Nosema ceranae* spore transmission. *Parasitology, **149**(5), 1–8. https://doi.org/10.1017/S0031182021001827

Martén-Rodríguez, S., Cristobal-Pérez, E. J., de Santiago-Hernández, M. H., Huerta-Ramos, G., Clemente-Martínez, L., Krupnick, G., Taylor, O., Lopezaraiza-Mikel, M., Balvino-Olvera, F. J., Sentés-Aguilar, E. M., Díaz-Infante, S., Jaimes, A. A., Novais, S., Cortés-Flores, J., Lobo-Segura, J., Fuchs, E. J., Delgado-Carrillo, O., Ruiz-Mercado, I., Sáyago-Lorenzana, R., ... Quesada, M. (2025). Untangling the complexity of climate change effects on plant reproductive traits and pollinators: A systematic global synthesis. *Global Change Biology, **31**(2), Article e70081. https://doi.org/10.1111/gcb.70081

Ngo, T. N., Rustia, D. J. A., Yang, E.-C., & Lin, T.-T. (2021). Automated monitoring and analyses of honey bee pollen foraging behavior using a deep learning-based imaging system. *Computers and Electronics in Agriculture, **187***, Article 106239. https://doi.org/10.1016/j.compag.2021.106239

Ostwald, M. M., Smith, M. L., & Seeley, T. D. (2016). The behavioral regulation of thirst, water collection and water storage in honey bee colonies. *Journal of Experimental Biology, **219**(14), 2156–2165. https://doi.org/10.1242/jeb.139824

Pankiw, T., & Page Jr, R. E. (2000). Response thresholds to sucrose predict foraging division of labor in honeybees. *Behavioral Ecology and Sociobiology, **47**(4), 265–267. https://doi.org/10.1007/s002650050664

Park, W. (1923). Water stored by bees. American Bee Journal, **63**, 348–349.

Perez, R., & Aron, S. (2020). Adaptations to thermal stress in social insects: Recent advances and future directions. *Biological Reviews, **95**(6), 1535–1553. https://doi.org/10.1111/brv.12628

Pinheiro, J., Bates, D., DebRoy, S., Sarkar, D., & R Core Team. (2022). nlme: linear and nonlinear mixed effects models. https://CRAN.R-project.org/package=nlme

R Core Team. (2020). *R: a language and environment for statistical computing*. R Foundation for Statistical Computing. https://www.R-project.org/.

Robinson, G. E., Underwood, B. A., & Henderson, C. E. (1984). A highly specialized water-collecting honey bee. *Apidologie, **15**(3), 355–358. https://doi.org/10.1051/apid:19840307

Samson-Robert, O., Labrie, G., Chagnon, M., & Fournier, V. (2014). Neonicotinoid-contaminated puddles of water represent a risk of intoxication for honey bees. *PLoS One, **9**(12), Article e108443. https://doi.org/10.1371/journal.pone.0108443

Schmid-Hempel, P., Winston, M. L., & Ydenberg, R. C. (1993). Invitation paper (C. P. Alexander fund): Foraging of individual workers in relation to colony state in the social hymenoptera. *Canadian Entomologist, **125**(1), 129–160. https://doi.org/10.4039/Ent125129-1

Seeley, T. D. (1995). *The wisdom of the hive: The social physiology of honey bee colonies*. Harvard University Press.

Sibaja Leyton, M., Lattorff, H. M. G., Kiatoko, N., & Requier, F. (2025). Climate effects on honey bees can be mitigated by beekeeping management in Kenya. *Journal of Environmental Management, **374***, Article 123879. https://doi.org/10.1016/j.jenvman.2024.123879

Smith, M. L., Koenig, P. A., & Peters, J. M. (2017). The cues of colony size: How honey bees sense that their colony is large enough to begin to invest in reproduction. *Journal of Experimental Biology, **220**(9), 1597–1605. https://doi.org/10.1242/jeb.150342

Stabentheiner, A., Kovac, H., & Brodschneider, R. (2010). Honeybee colony thermoregulation – regulatory mechanisms and contribution of individuals in dependence on age, location and thermal stress. *PLoS One, **5**(1), Article e8967. https://doi.org/10.1371/journal.pone.0008967

Stabentheiner, A., Kovac, H., Mandl, M., & Käfer, H. (2021). Coping with the cold and fighting the heat: Thermal homeostasis of a superorganism, the honeybee colony. *Journal of Comparative Physiology, A*. https://doi.org/10.1007/s00359-021-01464-8

Stabentheiner, A., Nagy, J. M., Kovac, H., Käfer, H., Petrocelli, I., & Turillazzi, S. (2022). Effect of climate on strategies of nest and body temperature regulation in paper wasps, *Polistes biglumis* and *Polistes gallicus*. *Scientific Reports, **12**(1), 3372. https://doi.org/10.1038/s41598-022-07279-0

Stabentheiner, A., Vollmann, J., Kovac, H., & Crailsheim, K. (2003). Oxygen consumption and body temperature of active and resting honeybees. *Journal of Insect Physiology, **49**(9), 881–889. https://doi.org/10.1016/S0022-1910(03)00148-3

Starks, P. T., & Gilley, D. C. (1999). Heat shielding: A novel method of colonial thermoregulation in honey bees. *Naturwissenschaften, **86**(9), 438–440. https://doi.org/10.1007/s001140050648

Stoffel, M. A., Nakagawa, S., & Schielzeth, H. (2021). partR2: partitioning R² in generalized linear mixed models. *PeerJ, **9***, Article e11414. https://doi.org/10.7717/peerj.11414

Thieurmel, B., & Elmarhraoui, A. (2022). suncalc: Compute sun position, sunlight phases, moon position and lunar phase. https://CRAN.R-project.org/package=suncalc.

Toomemaa, K., Martin, A.-J., Mänd, M., & Williams, I. H. (2013). Determining the amount of water condensed above and below the winter cluster of honey bees in a north european climate. *Journal of Apicultural Research, **52**(2), 81–87. https://doi.org/10.3896/IBRA.1.52.2.17

Visscher, P. K., Crailsheim, K., & Sherman, G. (1996). How do honey bees (*Apis mellifera*) fuel their water foraging flights? *Journal of Insect Physiology, **42** (11–12), 1089–1094. https://doi.org/10.1016/S0022-1910(96)00058-3

Wang, Y., Ma, L., Zhang, W., Cui, X., Wang, H., & Xu, B. (2015). Comparison of the nutrient composition of royal jelly and worker jelly of honey bees (*Apis mellifera*). *Apidologie, **47**(1), 48–56. https://doi.org/10.1007/s13592-015-0374-x

Weipple, T. (1928). Futterverbrauch und arbeitsleistung eines bienenvolkes im laufe einesjahres. *Archiv Für Bienenkunde, **9***, 70–79.

Willmer, P. G. (1988). The role of insect water balance in pollination ecology: *Xylocopa* and *Calotropis*. *Oecologia, **76**(3), 430–438. https://doi.org/10.1007/BF00377039

Wolf, T. J., & Schmid-Hempel, P. (1990). On the integration of individual foraging strategies with colony ergonomics in social insects: Nectar-collection in honeybees. *Behavioral Ecology and Sociobiology, **27**(2), 103–111. https://doi.org/10.1007/BF00168453

Wood, S. N. (2017). *Generalized additive models: An introduction with R (2nd ed.). Chapman and Hall/CRC.*

Wood, S. N., & Scheipl, F. (2022). gamm4: generalized additive mixed models using 'mgcv' and 'lme4'. https://CRAN.R-project.org/package=gamm4.

Ydenberg, R., & Schmid-Hempel, P. (1994). Modeling social insect foraging. *Trends in Ecology & Evolution, **9**(12), 491–493. https://doi.org/10.1016/0169-5347(94)90321-2

Zeileis, A., Leisch, F., Hornik, K., & Kleiber, C. (2002). strucchange: an R package for testing for structural change in linear regression models. *Journal of Statistical Software, **7**(2), https://doi.org/10.18637/jss.v007.i02

Zuur, A. F., Ieno, E. N., Walker, N., Saveliev, A. A., & Smith, G. M. (2009). *Mixed effects models and extensions in ecology with R*. New York: Springer. https://doi.org/10.1007/978-0-387-87458-6
# Appendix

<table><caption>**Table A1**
Temperature breakpoints in daily colony water collection.</caption><thead><tr><th rowspan="2">Model</th><th colspan="3">Coefficients ± 95% CI</th><th rowspan="2">s</th><th rowspan="2">AICc</th><th rowspan="2">ΔAICc</th><th rowspan="2">Model rank</th></tr><tr><th>β<sub>0</sub></th><th>β<sub>1</sub></th><th>β<sub>2</sub></th></tr></thead><tbody><tr><td>Null</td><td>313.60 (±42.14)</td><td></td><td></td><td></td><td>2026</td><td>251</td><td>5</td></tr><tr><td>Tmax a)</td><td>57.78 (±328.61)</td><td>5.42 (±12.94)</td><td>48.46 (±9.84)</td><td>28.46 (±1.57)</td><td>1818</td><td>43</td><td>4</td></tr><tr><td>b)</td><td>-23.58 (±215.83)</td><td>8.83 (±8.10)</td><td>74.65 (±15.58)</td><td>31.53 (±1.56)</td><td>1803</td><td>28</td><td>3</td></tr><tr><td>Tmean a)</td><td>-134.51 (±212.00)</td><td>19.97 (±11.53)</td><td>77.21 (±16.61)</td><td>23.00 (±1.39)</td><td>1792</td><td>17</td><td>2</td></tr><tr><td>b)</td><td><strong>78.96 (±187.24)</strong></td><td><strong>6.97 (±10.35)</strong></td><td><strong>89.99 (±15.81)</strong></td><td><strong>22.30 (±1.26)</strong></td><td><strong>1775</strong></td><td><strong>0</strong></td><td><strong>1</strong></td></tr></tbody></table>

Piecewise mixed-effect regression coefficients with the parameter s in (a) fixed effects only or (b) in fixed and random effects. These models are compared with the null model (i.e. a model without structure). The estimated coefficients are as follows: β₀, the intercept; β₁, the slope of the first line; β₂, the difference in slopes (β₁ + β₂ gives the slope of the second line); s, the temperature breakpoint. Delta (Δ) AICc: AICc value minus the lowest AICc; model rank: model ranking by increasing the AICc value. The model from which the temperature thresholds were used to investigate the effects of weather and colony size on daily colony water collection is shown in boldface.

<table><caption>**Table A2**
Influential observations in the LMMs used to investigate the effects of weather and colony size on daily colony water collection</caption><thead><tr><th>Model</th><th>Date</th><th>Colony</th><th>Water</th><th>Bees</th><th>OB</th><th>Tmean</th><th>RHmin</th><th>GR</th></tr></thead><tbody><tr><td rowspan="6">i)</td><td><strong>3 May 2021</strong></td><td><strong>12</strong></td><td><strong>584</strong></td><td><strong>20 860</strong></td><td><strong>14 800</strong></td><td><strong>15.0</strong></td><td><strong>24</strong></td><td><strong>7736</strong></td></tr><tr><td>4 May 2021</td><td>12</td><td>391</td><td>20 650</td><td>14 000</td><td>15.7</td><td>32</td><td>7231</td></tr><tr><td>5 May 2021</td><td>12</td><td>371</td><td>20 440</td><td>13 200</td><td>18.0</td><td>32</td><td>6842</td></tr><tr><td>6 May 2021</td><td>12</td><td>250</td><td>19 495</td><td>12 900</td><td>16.6</td><td>35</td><td>5933</td></tr><tr><td>7 May 2021</td><td>12</td><td>321</td><td>18 550</td><td>12 600</td><td>20.6</td><td>24</td><td>6789</td></tr><tr><td><strong>24 May 2021</strong></td><td><strong>16</strong></td><td><strong>702</strong></td><td><strong>25 480</strong></td><td><strong>9200</strong></td><td><strong>17.8</strong></td><td><strong>36</strong></td><td><strong>5183</strong></td></tr><tr><td rowspan="6">ii)</td><td>25 May 2021</td><td>16</td><td>639</td><td>25 620</td><td>9300</td><td>18.4</td><td>26</td><td>8431</td></tr><tr><td>26 May 2021</td><td>16</td><td>674</td><td>25 760</td><td>9400</td><td>19.2</td><td>18</td><td>8047</td></tr><tr><td>9 August 2021</td><td>20</td><td>779</td><td>14 070</td><td>2800</td><td>24.1</td><td>21</td><td>7456</td></tr><tr><td>10 August 2021</td><td>20</td><td>670</td><td>14 385</td><td>3600</td><td>26.4</td><td>26</td><td>6925</td></tr><tr><td>11 August 2021</td><td>20</td><td>1068</td><td>14 700</td><td>4400</td><td>28.3</td><td>20</td><td>7147</td></tr><tr><td>12 August 2021</td><td>20</td><td>884</td><td>15 295</td><td>5200</td><td>28</td><td>26</td><td>6000</td></tr><tr><td></td><td><strong>13 August 2021</strong></td><td><strong>20</strong></td><td><strong>1390</strong></td><td><strong>15 890</strong></td><td><strong>6000</strong></td><td><strong>30.3</strong></td><td><strong>26</strong></td><td><strong>6925</strong></td></tr></tbody></table>

The observations identified by Cook's distance as influencing the coefficients of the LMMs fitted (i) below and (ii) above the temperature breakpoint in daily colony water collection are shown in boldface. Colony: colony ID; water (ml): the daily colony water collection; bees and OB: the number of adult honey bees and open brood cells in the colony; Tmean (°C), the daily mean temperature; RHmin (%): the daily minimum relative humidity; GR (W/m²): the daily global solar radiation.

<table><caption>**Table A3**
Effects of weather and colony size on daily colony water collection (models selected without influential observations)</caption><thead><tr><th>Model</th><th>Term</th><th>Coefficient</th><th>95% CI</th><th>t</th><th>df</th><th>P</th></tr></thead><tbody><tr><td rowspan="8">i)</td><td>(Intercept)</td><td>180.27</td><td>155.95; 204.58</td><td>14.08</td><td>16.08</td><td>&lt;0.001</td></tr><tr><td>Tmean</td><td>25.37</td><td>9.57; 42.24</td><td>3.03</td><td>82.35</td><td>0.003</td></tr><tr><td>GR</td><td>28.62</td><td>15.39; 42.41</td><td>4.09</td><td>81.61</td><td>&lt;0.001</td></tr><tr><td>Bees</td><td>65.56</td><td>42.27; 88.69</td><td>5.36</td><td>28.55</td><td>&lt;0.001</td></tr><tr><td>OB</td><td>32.79</td><td>13.65; 51.90</td><td>3.24</td><td>56.70</td><td>0.002</td></tr><tr><td>Tmean × Bee</td><td>15.54</td><td>-0.35; 31.75</td><td>1.86</td><td>82.32</td><td>0.067</td></tr><tr><td>σ<sub>colony</sub></td><td>53.67</td><td>33.67; 72.95</td><td></td><td></td><td></td></tr><tr><td>σ<sub>residual</sub></td><td>36.28</td><td>30.25; 42.57</td><td></td><td></td><td></td></tr><tr><td rowspan="8">ii)</td><td>(Intercept)</td><td>486.98</td><td>430.90; 542.20</td><td>16.59</td><td>11.45</td><td>&lt;0.001</td></tr><tr><td>Tmax</td><td>144.37</td><td>115.11; 174.00</td><td>9.09</td><td>40.80</td><td>&lt;0.001</td></tr><tr><td>RHmin</td><td>-4.22</td><td>-41.60; 33.02</td><td>-0.21</td><td>44.33</td><td>0.836</td></tr><tr><td>GR</td><td>111.17</td><td>74.01; 146.62</td><td>5.76</td><td>41.92</td><td>&lt;0.001</td></tr><tr><td>Bees</td><td>153.22</td><td>100.01; 203.72</td><td>5.57</td><td>18.66</td><td>&lt;0.001</td></tr><tr><td>OB</td><td>65.09</td><td>29.99; 97.15</td><td>3.77</td><td>41.74</td><td>0.001</td></tr><tr><td>Tmax × RHmin</td><td>-46.93</td><td>-74.47; -20.85</td><td>-3.30</td><td>38.70</td><td>0.002</td></tr><tr><td>GR × RHmin</td><td>-45.47</td><td>-66.23; -23.55</td><td>-4.02</td><td>37.32</td><td>&lt;0.001</td></tr><tr><td></td><td>σ<sub>colony</sub></td><td>94.45</td><td>52.15; 139.95</td><td></td><td></td><td></td></tr><tr><td></td><td>σ<sub>residual</sub></td><td>69.80</td><td>52.74; 82.53</td><td></td><td></td><td></td></tr></tbody></table>

The results of LMMs selected without influential observations and fitted (i) below and (ii) above the inflection point in daily colony water collection. Tmean and Tmax (°C): daily mean and maximum temperature, respectively; GR (W/m²): daily global solar radiation; RHmin (%): daily minimum relative humidity; Bees and OB: number of adult honey bees and open brood cells in the colony, respectively; σ<sub>colony</sub> and σ<sub>residual</sub>: the standard deviation for colony level and data level errors, respectively.
<table><caption>**Table A4**
Proportion of variance explained by weather and colony size in daily colony water collection</caption><thead><tr><th>Model</th><th>Term</th><th>Part R<sup>2</sup><sub>m</sub></th><th>95% CI</th><th>df</th></tr></thead><tbody><tr><td rowspan="6">i)</td><td>Tmean</td><td>0.02</td><td>0.00; 0.25</td><td>4</td></tr><tr><td>GR</td><td>0.05</td><td>0.00; 0.27</td><td>4</td></tr><tr><td>Bees</td><td>0.41</td><td>0.24; 0.57</td><td>4</td></tr><tr><td>OB</td><td>0.19</td><td>0.00; 0.38</td><td>4</td></tr><tr><td>Tmean + GR</td><td>0.09</td><td>0.00; 0.30</td><td>3</td></tr><tr><td>Bees + OB</td><td>0.64</td><td>0.52; 0.76</td><td>3</td></tr><tr><td rowspan="7">ii)</td><td>Tmax × Bees</td><td>0.00</td><td>0.00; 0.28</td><td>8</td></tr><tr><td>Tmax × RHmin</td><td>0.02</td><td>0.00; 0.30</td><td>8</td></tr><tr><td>GR × RHmin</td><td>0.02</td><td>0.00; 0.29</td><td>8</td></tr><tr><td>Tmax</td><td>0.23</td><td>0.03; 0.45</td><td>4</td></tr><tr><td>GR</td><td>0.04</td><td>0.00; 0.30</td><td>4</td></tr><tr><td>Bees</td><td>0.44</td><td>0.28; 0.62</td><td>4</td></tr><tr><td>OB</td><td>0.02</td><td>0.00; 0.29</td><td>4</td></tr><tr><td></td><td>Tmax + GR</td><td>0.24</td><td>0.04; 0.46</td><td>3</td></tr><tr><td></td><td>Bees + OB</td><td>0.45</td><td>0.29; 0.62</td><td>3</td></tr></tbody></table>

The semipartial coefficients of determination (Part-R²_m) for the main effects, the interaction terms (‘×’) and the combinations (‘+’) of weather and population factors of the LMMs fitted (i) below and (ii) above the inflection point in daily colony water collection. Tmean and Tmax (°C): daily mean and maximum temperature, respectively; GR (W/m²): daily global solar radiation; RHmin (%): daily minimum relative humidity; Bees and OB: the number of adult honey bees and open brood cells in the colony, respectively.