Incubation Behavior of the Western Reef Heron (Egretta gularis) in Eastern Saudi Arabia: Adaptations to Extreme Thermal Conditions

Abstract

The Western Reef Heron (Egretta gularis) has a wide geographic distribution, ranging from the coasts of West Africa to Southwest Asia, including the Arabian Peninsula. Despite this extensive range, detailed information on its incubation behavior remains scarce. To address this gap, we investigated the 24 h incubation behavior of Western Reef Herons on Al-Fanateer Island, Eastern Saudi Arabia, during early summer-a period characterized by pronounced diurnal fluctuations in ambient temperature. Using trail cameras and temperature loggers, we found that adults maintained nearly continuous attendance at the nest throughout the day, with incubation coverage exceeding 97% across all two-hour intervals. A slight reduction in nest attendance was observed during nighttime (lowest at 86.8% between 20:00-21:59). Incubating adults exhibited behavioral plasticity in response to ambient temperature: a sitting posture was predominant during cooler periods, while a shading posture was more frequent during peak heat. Incubating adults also adjusted their orientation with the solar angle, actively avoiding southern and western exposures during the hottest parts of the day. Despite substantial variation in ambient temperature, the temperature beneath the clutch ranged from 29.4 to 37.8 °C, which may indicate effective thermoregulation. These findings suggest that a combination of near-continuous nest attendance, posture adjustment, and solar orientation avoidance allows Western Reef Herons to mitigate thermal stress and maintain optimal conditions for embryo and chick development. We recommend long-term monitoring of incubation behavior in this species to further evaluate its adaptability to environmental changes, particularly those driven by climate variability.

Keywords: harsh environment; incubation posture; nest attendance; thermoregulation.

Figure 1

Map of Al-Fanateer Island, Eastern Saudi Arabia, showing the locations of Western Reef Heron nests marked by red dots. The red circle shows the geographical location of the study area. Map created using QGIS v. 3.40, an open-source software (QGIS Development Team, 2022).

Figure 2

(A) Mean ambient temperature (±SE) recorded by camera-integrated data loggers positioned ~1.5 m from each nest (open triangles, n = 7 nests) and mean of temperature (±SE) recorded beneath the clutch by Thermochron iButton data loggers (filled circles, n = 7 nests). (B) Percentage of time spent by Western Reef Herons attending their nests in relation to ambient temperatures across the two-hour intervals (n = 7).

Figure 3

Top left: Incubation postures (%) of Western Reef Herons during two-hour intervals (n = 7 nests); shading posture: filled circles; sitting posture: open triangles; standing posture: open squares. Top right: shading posture, where the parent shades the eggs/chicks by drooping its wings over the nest without making full body contact. Bottom left: sitting posture, where the parent maintains full body contact with the eggs/chicks while sitting tightly on the nest. Bottom right: standing posture, where the parent stands on the nest without any physical contact with the eggs/chicks.

Figure 4

Orientation of incubating adult Western Reef Herons (%), recorded over two-hour intervals (n = 7 nests). (A) Proportion of individuals oriented toward east and west. (B) Proportion oriented towards north and south. Values are presented as means ± standard error (SE).