Time of day, water coverage, and pond type impact waterbird abundance in aquaculture ponds in Taiwan

Abstract

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. Past studies have examined how different assemblages of waterbirds use different types of aquaculture ponds, particularly based on water depth or water coverage. However, most studies have only been conducted during the daytime. As some waterdbird species are known to also exhibit nocturnal foraging behavior, it is important to also examine their nocturnal use of aquaculture ponds. 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 types of 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 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 was significantly higher during daylight 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, fish/shrimp ponds exhibit the highest density of 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.

Keywords

• waterbirds
• aquaculture pond type
• night
• black-crowned night heron