Research Paper

INTRODUCTION

The loss of coastal wetlands due to land development pressures and rising sea levels resulting from climate change has become a significant threat to waterbird populations (Galbraith et al. 2002, Davidson 2014). These wetlands play crucial roles as stopovers, feeding areas, and breeding grounds for numerous waterbird species (Galbraith et al. 2002, Catry et al. 2011). While the rate of natural wetland loss has slowed in Europe and North America, it remains high in Asia, particularly in densely populated regions like East Asia (Davidson 2014, Murray et al. 2014). This loss has led to a notable decline in waterbird populations along the East Asian-Australasian Flyway (Hua et al. 2015, Moores et al. 2016, Piersma et al. 2016, Santos et al. 2023).

In response to the extensive loss of natural wetlands, the restoration of wetland ecosystems and the evaluation of artificial wetlands as alternative habitats for waterbirds have gained increasing importance. Although artificial wetlands cannot fully replicate the functions of natural wetlands (Tourenq et al. 2001, Ma et al. 2004, Bellio et al. 2009, Li et al. 2013, Fan et al. 2021), they still provide habitat or temporary alternatives for certain waterbird species, helping to mitigate the impact of natural wetland loss (Sripanomyom et al. 2011, Strum et al. 2013, Li et al. 2013, Lei et al. 2018, Fan et al. 2021). Consequently, artificial wetlands are crucial in protecting waterbirds and wetland ecosystems.

Aquaculture ponds, commonly found in coastal areas, are a prevalent type of artificial wetland. Global aquaculture production has increased substantially, particularly in Southeast Asia, as fishing resources have declined (Luo et al. 2022). Aquaculture ponds not only contribute to food production but also provide valuable ecological functions as habitats for waterbirds (Kloskowski et al. 2009, Navedo et al. 2017, Jackson et al. 2020). For example, shrimp farms in Ecuador attract a diverse range of heron species for foraging (Cheek 2009), while catfish farms in North America are utilized by American coots (Fulica americana), diving ducks, and dabbling ducks (Feaga et al. 2015). Aquaculture ponds in Sumatra, Indonesia, have recorded 25 shorebird species (Iqbal et al. 2022), and abandoned shrimp farms in India offer suitable habitats for waterbirds (Sandilyan 2017).

Several environmental factors influence waterbird use of aquaculture ponds, including area, water depth, bank vegetation, and the species and size of cultured aquatic organisms (Froneman et al. 2001, Kloskowski et al. 2010, Sebastián-González and Green 2014, Feaga et al. 2015, Burr et al. 2020, Wang et al. 2020). Water depth, in particular, plays a key role in the waterbird utilization of aquaculture ponds. For instance, water depth in shrimp ponds affects the foraging behavior of waterbirds of different body sizes (Cheek 2009). Reduced water depth in aquaculture ponds can lead to increased waterbird density and species richness (Wang et al. 2020). Waterbird community was also correlated with water coverage in different ponds (Niu et al. 2013). Additionally, different management practices in various types of aquaculture ponds create different environmental conditions, attracting different bird species (Lu 2004, Yang 2006, Wang et al. 2020).

Many waterbird species engage in nocturnal foraging activities in addition to daytime feeding (Rojas et al. 1997, Merke and Mosbech 2008, Barbaree et al. 2015, Ntiamoa-Baidu et al. 1998, Urfi 2011) to meet energy demands and have adapted to foraging under poor lighting conditions (Katzir and Martin 1998, Robert and McNeil 1989, Rojas et al. 1997). Shorebirds, for example, adjust their foraging strategies based on lighting conditions, using either vision or touch to locate food (Robert and McNeil 1989). Moreover, studies have shown that some waterbirds utilize different habitats during the day and night (Dorr et al. 2004, Barbaree et al. 2015, Joo and Lee 2022). Geese and ducks, for instance, often rest in low disturbance habitats during the day and move to nearby wetlands for foraging at night (Parejo et al. 2019, McDuie et al. 2021). Therefore, evaluating waterbird habitat conservation should encompass daytime and nighttime activity areas and consider their habitat use patterns (Guillemain et al. 2002, Austin et al. 2016).

However, past studies of waterbirds in aquaculture ponds, including those conducted in Taiwan, focused primarily on daytime observations. As shorebirds and waterfowl are internationally important targets for waterbird conservation, and Taiwan's coastal aquaculture ponds are important habitats for these species (Lu 2004, Yang 2006), a better understanding is needed of how these species use aquaculture ponds at different times of day. The Black-crowned Night Heron (Nycticorax nycticorax), a widely distributed piscivorous bird, frequently inhabits aquaculture ponds and is known to be primarily active during the night (Taylor et al. 2010, Maccarone and Hamilton 2014). Therefore, this study aims to investigate changes in the abundance of different waterbird species in aquaculture ponds over time (day and night) and space (different aquaculture types) to assess the function of aquaculture ponds as waterbird habitats.

METHODS

Study site

Aquaculture ponds are extensively distributed in the southwestern coastal region of Taiwan, encompassing an area exceeding 40,000 hectares. According to the fish farming survey by the Fisheries Agency of Taiwan (Fisheries Agency 2022), the Cigu District in Tainan City held the largest aquaculture area in Taiwan, with 4724 hectares of aquaculture ponds recorded in 2022.

Notably, the Cigu District is also home to two important wetlands: the Zengwun Estuary Important Wetland and the Cigu Salt Pan Important Wetland. These wetlands serve as crucial habitats for numerous waterbird species, including the Black-faced Spoonbill (Platalea minor). Consequently, Cigu presents an excellent site for investigating the utilization of artificial wetlands by waterbirds. The study site is situated within the aquaculture ponds located between Shulin Stream and the Zengwun River in Cigu, Tainan City (Fig. 1). Among the various aquaculture areas, hard clams account for the largest coverage (30.0%), followed by milkfish (29.2%). Other areas with coverage exceeding 1% include abandoned ponds (5.0%), green grouper (4.1%), white shrimp (1.6%), tiger groupers (1.2%), and nursery ponds (1.1%).

Field survey

The aquaculture ponds in our study were classified into three types: fish/shrimp ponds, hard clam ponds, and abandoned ponds. Fish/shrimp ponds were utilized for cultivating milkfish, grouper, or white shrimp. These ponds, along with hard clam ponds, constituted the primary types of aquaculture in the study area, while abandoned ponds offered a semi-natural marsh environment. Field surveys were conducted ten times between October 2021 and November 2022, specifically in October, November, December 2021, January, February, March, May, July, September, and November 2022. Access to privately owned ponds was restricted, so we selected ponds that were accessible from the roadside and avoided selecting adjacent ponds if possible. However, due to the relatively low number and concentrated distribution of abandoned ponds, some selected ponds were adjacent. In 2021, 73 fishpond sites were surveyed, comprising 51 fish/shrimp ponds, 13 hard clam ponds, and 9 abandoned ponds. In 2022, 72 fishpond sites were surveyed, including 47 fish/shrimp ponds, 13 hard clam ponds, and 12 abandoned ponds. The variation in numbers is attributed to changes in land use in seven sites and the addition of six new sites. The average area of hard clam ponds was 1.95 ± 1.2 hectares, followed by fish/shrimp ponds at 0.58 ± 0.2 hectares and abandoned ponds at 0.57 ± 0.3 hectares.

Each survey round was carried out by a team of two experienced surveyors, who completed the surveys within two days. Surveyors recorded the bird species (or taxa), quantity, behavior (foraging/non-foraging), and water coverage (%) of each sampled pond. Water coverage was classified into four categories: low (0–30%), moderate (>30–60%), high (>60–90%), and full (>90%). To minimize disturbance to waterbirds, surveyors conducted daytime surveys from inside their vehicles using binoculars and telescopes between 10 a.m. and 4 p.m. Night surveys were conducted on the same day as the daytime surveys, from 6 p.m. to 10 p.m., using a handheld thermal imaging camera (FLIR T560 with a 6° lens). The thermal imaging camera provides temperature distribution images of organisms, which differ from naked-eye observations. Species identification solely based on thermal imaging is more challenging. Therefore, other features and clues such as habitat, behavior, sound, or telescopes with light sources (streetlights or moonlight) assisted in bird recognition. Waterbirds were classified into at least three groups: shorebirds, herons, and waterfowl. Birds were identified at the species level when clear features were observed. Throughout the survey, one observer vigilantly monitored the movement of waterbirds among the studied ponds to prevent duplicate counts. Simultaneously, the other thoroughly scanned the sampling pond using the equipment. In instances where no birds were detected, each pond was surveyed for a minimum of 1 minute during the day using binoculars and at least 2 minutes at night using a thermal imaging camera.

According to the intertidal zone map in 2017 (Construction and Planning Agency, Taiwan), the maximum area of the intertidal zone in the Cigu District was approximately 497 hectares. Considering the relatively small size of the intertidal zone along the coastal area of the Cigu District, it is assumed that waterbirds in aquaculture ponds seldom move to the nearby intertidal zone during low tides.

Data analysis and statistics

We employed generalized linear mixed models (GLMM) to examine the influence of time of day (day/night), pond type, and water coverage percentage on the density of waterbirds in aquaculture ponds. Specifically, our analysis focused on shorebirds, waterfowl, and the Black-crowned Night Heron. Shorebirds and waterfowl were chosen as target groups for waterbird conservation in the study area, while the Black-crowned Night Heron is known to cause losses in aquaculture fisheries. To facilitate analysis, waterbird density (ind. ha^-1) was logarithmically transformed using the formula log(x+1). Random effects were applied to account for pond number and month. Fixed effects included day/night, pond type, water coverage, and the interaction between day/night and pond type. The significance of factors was evaluated using ANOVA (type III), and post hoc comparisons were conducted using Tukey's HSD test in cases where significant differences were detected. The foraging ratio for each survey was calculated by dividing total number of feeding individuals across all study ponds by the total count. We performed Wilcoxon Sign-Rank tests to determine if there was a significant difference in foraging ratio of waterbirds during the day and at night. The statistical analysis was performed using R 3.6.0 (https://www.r-project.org/) software, with the lme4 package utilized for GLMM analysis, the car package for ANOVA (type III) testing, the emmeans package for post hoc comparisons, and stats for Wilcoxon Sign-Rank test. Finally, the results were visualized using the ggplo2 package.

RESULTS

Between October 2021 and November 2022, we conducted ten rounds of the day and nighttime surveys to assess waterbird populations in the sampled aquaculture ponds in Cigu. During the daytime surveys, we observed a total of 32 species and 6268 individuals of waterbirds from 10 families (Appendix 1). The most abundant shorebird species included the Black-winged Stilt (Himantopus himantopus), Pacific Golden-Plover (Pluvialis fulva), Long-toed Stint (Calidris subminuta), Little Ringed Plover (Charadrius dubius), and Kentish Plover (Charadrius alexandrinus). Notable waterfowl species included the Northern Shoveler (Spatula clypeata), Tufted Duck (Aythya fuligula), Eurasian Wigeon (Mareca penelope), and Green-winged Teal (Anas crecca). The most frequently observed heron species were the Little Egret (Egretta garzetta), Great Egret (Ardea alba), and Black-crowned Night Heron (N. nycticorax). Other species of importance included the Whiskered Tern (Chlidonias hybrida), Little Grebe (Tachybaptus ruficollis), and Black-faced Spoonbill (P. minor).

Shorebirds are primarily winter visitors, and their numbers peak in aquaculture ponds from October to March (Fig. 2a). Therefore, for subsequent analysis, we considered survey data from October 2021 to March 2022 and November 2022. The results indicated no significant difference in shorebird density between day and night (χ² = 1.92, p = 0.116, Table 1). The foraging ratio was similar during the day (50.8 ± 23.0%) and night (64.8 ± 26.0%) and did not exhibit a significant difference (p = 0.244, Wilcoxon Sign-Rank test). Shorebird density significantly differed among different types of aquaculture ponds (χ² = 13.54, p = 0.001, Table 1), with significantly higher densities in fish/shrimp ponds compared to abandoned ponds, while no significant difference was observed between hard clam ponds and the other two types (Fig. 3a). Furthermore, shorebird density significantly varied among aquaculture ponds with different water coverage (χ² = 191.8, p < 0.001, Table 1). The density of shorebirds in ponds with water coverage exceeding 90% was significantly lower than in other groups (Fig. 4a).

Waterfowl are predominantly wintering birds, and their numbers in aquaculture ponds are higher from November to March (Fig. 2b). Consequently, we included survey data from November 2021 to March 2022 and November 2022 for analysis. The density of waterfowl in aquaculture ponds was significantly influenced by the interaction between time (day/night) and pond type (χ² = 32.96, p < 0.001, Table 1). Irrespective of day or night, waterfowl density was significantly higher in abandoned ponds compared to fish/shrimp and hard clam ponds. Moreover, waterfowl density in abandoned ponds during the day was significantly higher than at night (Fig. 3b). The foraging ratio of waterfowl was significantly higher at night (43.1 ± 37.0%) than during the daytime (6.8 ± 14.5%) in the study ponds (p = 0.0278, Wilcoxon Sign-Rank test), indicating more frequent foraging activities during nocturnal hours. Significant differences in waterfowl density were also observed among aquaculture ponds with different water coverage (χ² = 21.32, p < 0.001, Table 1). Ponds with water coverage ranging from 60% to 90% exhibited significantly higher waterfowl densities than ponds with coverage below 30% and above 90%. However, waterfowl density in ponds with water coverage between 30% and 60% did not significantly differ from other groups (Fig. 4b).

The Black-crowned Night Heron is a commonly observed bird in Taiwan throughout the year (Fig. 2c). Hence, all ten surveys were included in the analysis. The density of Black-crowned Night Herons in aquaculture ponds was significantly influenced by the interaction between time (day/night) and pond type (χ ²= 66.34, p < 0.001, Table 1) but not by water coverage (χ² = 3.81, p = 0.283, Table 1). During the day, the density of Black-crowned Night Herons was significantly higher in abandoned ponds compared to other pond types. Conversely, during the night, fish/shrimp ponds exhibited the highest density of Black-crowned Night Herons, which was significantly greater than in hard clam ponds (Fig. 3c). The foraging ratio of Black-crowned Night Herons was significantly higher at night (88.2 ± 8.7%) than during the daytime (5.3 ± 9.2%) in the study ponds (p = 0.002, Wilcoxon Sign-Rank test), indicating more frequent foraging activities during nocturnal hours.

DISCUSSION

The results of this study provide valuable insights into the behavior and habitat preferences of shorebirds, waterfowl, and Black-crowned Night Herons in aquaculture ponds. The findings indicate that shorebirds remain active throughout the day, with no significant differences in density or foraging behavior between day and night. However, their density was influenced by the type of aquaculture pond and the extent of water coverage. Fish/shrimp ponds exhibited the highest shorebird densities among different pond types, while ponds with less than 90% water coverage have significantly higher shorebird densities. On the other hand, waterfowl density in abandoned ponds was consistently higher than in other pond types, irrespective of the time of day. During the day, waterfowl density in abandoned ponds is notably higher than at night. Furthermore, based on the counts of Black-crowned Night Herons in the sampling ponds during day and night across different seasons (Fig. 2c), a substantial number of these birds move from areas outside the sampling ponds to these locations at night, especially in around fish/shrimp ponds, where they engage in foraging activities.

Shorebirds

Our results suggest that shorebirds continue to forage in aquaculture ponds throughout the day when suitable conditions are present. Research shows shorebirds can forage at night (Burger and Gochfeld 1991, Dodd and Colwell 1998, Barbaree et al. 2015). Studies on the Black-tailed Godwit (Limosa limosa) indicate whether they forage at night depends on whether they have obtained enough energy during the day (Santiago-Quesada et al. 2014). If the food obtained during the day does not meet their daily energy expenditure (DEE), they will continue to forage at night to compensate for the deficit. Conversely, if their intake during the day has met their DEE, they will not forage at night. In this study, the average nighttime foraging ratio of shorebirds was 61.9%, implying that their intake during the day was insufficient to meet their DEE. This may be due to interference from fishing activities or poor quality of food resources in the sediment.

Fish farmers often drain the pond after harvesting to disinfect and sun-dry the pond, exposing the mudflats and shallow water environment and attracting shorebirds to forage. This is critical for shorebirds to utilize aquaculture ponds (Yang 2006, Huang and Hsueh 2014). The milkfish ponds in Cigu are sun-dried yearly, while the hard clam pond is sun-dried once every two to three years (Huang and Hsueh 2014), and the abandoned ponds are not managed for sun-drying. The shorebird density of fish/shrimp ponds, which are sun-dried more frequently, is the highest, while the density of abandoned ponds that are not sun-dried is the lowest. Therefore, sun-drying frequency may be the main cause of the difference in shorebird density among the three types of aquaculture ponds. In addition, most species of shorebirds prefer to utilize environments with sparse vegetation (Davis and Smith 1998, Andrei et al. 2008, Huang 2013). The dense vegetation in abandoned ponds, which lacks management, was also a disadvantage for shorebirds to utilize.

The shorebirds in aquaculture ponds are mostly medium and small-sized wading birds, which are greatly affected by the water depth of their habitat. During the cultivation process, the water coverage in fish ponds was typically greater than 90%. The lowest density of shorebirds was observed, reflecting the lack of shallow water environments that can be used for foraging under a full water level. After harvest, the water levels are dropped between 0–90% water coverage, exposing the damp mudflats containing benthic invertebrates, which provide food resources for shorebirds (Rocha et al. 2017, Fonseca and Navedo 2020). In this study, shorebirds densities were highest when water coverage was 30–90%. The shorebird density of ponds with a water coverage of 0-30% slightly decreases, possibly due to the decreasing food resources as the pond gradually dries up. A study found that the biomass of benthic invertebrates in ponds for shrimp cultivation decreased by 43% after three days of foraging by shorebirds, and the shorebird density decreased every day accordingly (Fonseca and Navedo 2020).

Waterfowl

In places where human activities during the day are highly disruptive, waterfowl often rest in safer habitats during the day and only move to forage habitats at night. For example, in the Suisun Marsh of California, during the duck hunting season, waterfowl hide in secluded shelters during the day and come out to forage in habitats with food resources at night (Casazza et al. 2012, McDuie et al. 2021). Studies in Spain have shown that waterfowl rest during the day in large reservoirs such as water reservoirs and forage in nearby rice paddies at night (Navedo et al. 2012, Parejo et al. 2019). The results of this study are similar to those of the above studies. In this study, the low foraging ratio of waterfowl during the day may be due to the frequent human activities in aquaculture environments.

Ponds are one of the preferred types of daytime habitats for waterfowl (Bengtsson et al. 2014). Lu (2004) found that abandoned ponds were preferred habitats for waterfowl compared to operational aquaculture ponds, salt ponds, and natural wetlands. This study also showed that abandoned ponds were the main type of aquaculture ponds used by waterfowl. The reason may be that abandoned aquaculture ponds are less frequented by fishermen and have dense vegetation, providing waterfowl with high levels of sheltered resting places.

The foraging activities of waterfowl in the aquaculture ponds increase at night. Still, the overall number significantly decreases, indicating that waterfowl fly to nearby wetlands of other types for foraging at night. The abandoned salt fields to the north of the study area and the grass swamps on the west side of the Cigu campus of Tainan University are potential foraging habitats that need further confirmation in the future using tracking technology to determine the daytime and nighttime activity areas.

Waterfowl prefer aquatic environments and have the lowest density in aquaculture ponds with low water coverage or that have dried up. In addition, according to observations in the study area, waterfowl often rested on land at the intersection of the water and the embankment. The reason for the lower density of waterfowl in ponds with full water coverage (>90%, Fig. 4b) may be due to the lack of suitable terrestrial resting spaces.

Black-crowned Night Heron

Many factors influence the selection of aquaculture ponds by piscivorous birds. Burr et al. (2020) found that the larger the area of the pond and the more fish in it, the higher the chance of fish-eating water birds appearing in the catfish ponds of the Mississippi Delta. In addition, factors such as the species of fish in the pond, whether there is an outbreak of disease, and whether there are non-cultured fish species will also affect the probability of the appearance of various piscivorous birds to varying degrees.

Some studies showed that herons prefer larger ponds (Sebastián‐González and Green 2014, Hsu et al. 2019, Burr et al. 2020). However, the density of Black-crowned Night Herons was highest in smaller fish/shrimp ponds at night, and lowest in the largest clam pond in our study. It is speculated that the difference in food resources is the main factor affecting the density of Black-crowned Night Herons. To achieve economic yields, the stocking density of fish and shrimp in the fish/shrimp ponds should be the highest among all types of ponds. Hard clam ponds mainly cultivate shellfish, and although they also mix milkfish and Sparidae spp. as working fish, they are not the main target of harvesting, and the stocking density is lower. The density of fish and shrimp in abandoned ponds is lower as there is no feed input, and the fish and shrimp grow in a semi-natural environment. Therefore, the highest density of Black-crowned Night Herons in fish/shrimp ponds may be due to the most abundant food resources. In addition, high-density aquaculture can easily cause fish to become sick or hypoxic, which attracts night herons to gather. Taylor et al. (2010) found that almost half of all night herons observed were concentrated in a small number of aquaculture ponds with disease outbreaks and that night herons consumed about twice as many fish in ponds with disease outbreaks compared to healthy ponds.

Black-crowned Night Herons exhibit gregarious behavior throughout all seasons, forming communal roosts even in non-breeding sessions (Endo et al. 2006, Hothem et al. 2020). C.K. Huang (2013) found that the Black-crowned Night Herons preferred to roost in mangroves, woodlots, and other open terrestrial areas, avoiding aquaculture ponds and artificial habitats during the daytime. This study also showed that the density of Black-crowned Night Herons during the day was significantly reduced in aquaculture ponds. Fishermen usually have more frequent activities in aquaculture ponds during the day, so night herons may move to other suitable habitats to avoid human interference. The night herons in the aquaculture ponds during the day also prefer abandoned ponds as their main roosting place, with lush vegetation and less disturbance.

Black-crowned Night Herons mainly forage at night but also forage during the day. Maccarone and Hamilton (2014) found that during the breeding season, the daytime foraging of night herons increased, which is important for meeting the energy requirements of breeding. The breeding season of Black-crowned Night Herons in Taiwan is from February to August. Chang (1997) found that the number of Black-crowned Night Herons foraging during the day in the Fa-Tse Creek increased significantly during the breeding season. However, in this study, daytime-foraging Black-crowned Night Herons did not increase during the breeding season (Fig. 2c). It is speculated that even if there is an increased demand for daytime foraging, Black-crowned Night Herons will avoid aquaculture ponds and move to adjacent wetlands with less disturbance.

Implications for conservation

Fish/shrimp ponds, often sun-dried, reduce water coverage and attract waterbirds. To increase waterbird utilization, it is effective to increase sun-drying frequency or extend low water levels. Shorebirds have nocturnal foraging behavior, suggesting insufficient energy intake during the day. The sun-drying process of the pond, by mitigating human interference, contributes to daytime foraging for shorebirds. Future research should address boosting benthic biomass in artificial wetlands. Abandoned ponds offer secluded, vegetation-rich habitats with low human disturbance, providing significant conservation value for waterfowl. However, long-term abandonment may render these ponds unsuitable. Therefore, it is crucial to preserve, maintain, and create suitable waterfowl habitats within aquaculture landscapes, such as in Cigu, to promote biodiversity and ecosystem function. This action is especially vital as natural wetlands decline and are replaced by aquaculture areas. Black-crowned Night Herons prefer fish and shrimp ponds for nocturnal foraging, indicating their highest density in these areas. During the day, they primarily roost in abandoned ponds within the aquaculture landscape. Accurately assessing the impact of night herons on fisheries is challenging, as they prey on economically valuable but weakened species, alongside non-cultivated fish and shrimp. Future studies using netting operations can better evaluate actual fishery losses by comparing catches in the presence or absence of piscivorous birds. In summary, encouraging waterbird utilization through sun-drying methods, mitigating human interference, and preserving suitable waterfowl habitats within aquaculture landscapes are critical for biodiversity and ecosystem functioning. Additionally, comprehensive studies on the impact of piscivorous birds, like Black-crowned Night Herons, on fisheries are essential for effective management and conservation in aquaculture areas.

Conclusions

We investigated the density of shorebirds, waterfowl, and Black-crowned Night Herons in different types of aquaculture ponds in the Cigu District of Tainan from October 2021 to November 2022. Our study analyzed how the density of these waterbirds was influenced by the time of day and water coverage percentage in different types of ponds, including fish/shrimp, hard clam, and abandoned ponds. Our findings suggest that different waterbirds have varying preferences for aquaculture pond types, and the time of day and water coverage percentage can significantly influence waterbird density and foraging behavior.

Shorebirds are active throughout the day, with no significant difference in density or foraging behavior between day and night. However, their density is influenced by the type of aquaculture pond and the extent of water coverage. Fish/shrimp ponds exhibit the highest shorebird densities among different pond types, while ponds with less than 90% water coverage have significantly higher shorebird densities. Waterfowl density in abandoned ponds is consistently higher than in other pond types, irrespective of the time of day. Moreover, most Black-crowned Night Herons prefer to roost outside the sampled ponds during the day and enter the aquaculture ponds specifically at night.

Our study highlights the importance of considering the unique characteristics of aquaculture ponds when developing conservation and management strategies for waterbirds. Encouraging waterbird utilization through sun-drying methods, mitigating human interference in shorebird foraging, and preserving suitable waterfowl habitats within aquaculture landscapes are critical for biodiversity and ecosystem functioning. Future management strategies should be tailored to specific waterbird species, such as targeting abandoned ponds for waterfowl conservation efforts, while fish/shrimp ponds can be managed to support shorebird populations.

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