The loss of coastal wetlands represents a grave threat to waterbirds, prompting the use of artificial wetlands, such as aquaculture ponds, as a means of conservation. Aquaculture ponds are common in coastal areas and provide production value and ecological function as waterbird habitats. However, certain piscivorous birds may cause economic losses to the aquaculture industry. Different types of ponds provide habitat for various bird assemblages, and waterbirds exhibit nocturnal feeding behavior and utilize habitats distinct from those used during the day. Most waterbird surveys were conducted during the daytime, limiting our understanding of their nocturnal habitat utilization. This study conducted diurnal and nocturnal surveys on shorebirds, waterfowl, and Black-crowned Night Heron (Nycticorax nycticorax) ten times in three aquaculture ponds situated in the Cigu District of Tainan, namely fish/shrimp, hard clam, and abandoned ponds between October 2021 and November 2022. The results showed no significant difference in shorebird density between day and night. However, shorebird density in fish/shrimp ponds was the highest and significantly higher than in abandoned ponds. Conversely, waterfowl density exhibits a significant increase in abandoned ponds compared to the other two pond types, irrespective of diurnal or nocturnal conditions. Furthermore, waterfowl density in abandoned ponds is significantly higher during daylight hours compared to the nocturnal period. In the daytime, the density of night herons was significantly higher in abandoned ponds than in the other two ponds. Nevertheless, during nighttime hours, fish/shrimp ponds exhibit the highest density of Black-crowned Night Herons, significantly surpassing that found in hard clam ponds. Notably, water coverage also influences the density of both shorebirds and waterfowl. The foraging frequency of waterfowl and night herons was greater during nocturnal hours, while shorebirds did not exhibit significant variations between day and night. Consequently, this study underscores the significance of considering both diurnal and nocturnal habitats in formulating strategies for waterbird conservation.

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. 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). Waterbirds were classified into at least three groups: shorebirds, waterfowl, and night-herons.