Bird diversity and the design of wetland ponds

Posted on December 18, 2015

Although aquatic restoration projects can play an important conservation role by offsetting the loss of wetlands to development, project planners need to be mindful of the influence that wetland design features such as pond size and water depth have on biodiversity. In a study focusing on waterbirds, researchers repeatedly surveyed 96 artificial ponds in Do˜nana National Park, south-west Spain, over a three-year period. Do˜nana is one of the most important wetland sites in Europe. Ponds were 0.18, 0.74 or 2.95 ha in area and 30 or 60 cm deep, with the same elliptical shape. In total, 38 species of waterbird were recorded. For birds of all sizes and types (waders, shorebirds, ducks, gulls, terns), pond size was the best predictor of abundance, with more birds occurring in the largest ponds, but depth, isolation and spatial location were also important for some groups. Small birds were most abundant in the shallow ponds. Isolated ponds surrounded by terrestrial vegetation suitable for nesting were used by large birds and ducks significantly more often than other ponds. Waders and ducks were more abundant in ponds near other wetlands and agricultural areas, while shorebirds were more common in ponds that were closer to natural marshes. Previous researchers have found that bird densities (i.e., the numbers of birds per unit area of water) tend to decline with increasing pond size, presumably because in larger ponds the ratio of shoreline to pond area is relatively low. However, in the recent study, densities of waders and gulls were higher in the larger ponds, and this difference was explained by the fact that the ponds had even bottoms, rather than being deeper in the middle like the natural ponds monitored in previous studies. The authors recommend that, to maximise bird diversity, it’s better to create a set of small ponds than a single large one. Ponds should vary in area but be at least 1-3 ha in size, and pond depths be varied, even within the 0-60 cm range. And some ponds be relatively isolated.

Reference: Sebastian-Gonzalez, E. & Green, A.J. 2014. Habitat use by waterbirds in relation to pond size, water depth, and isolation: lessons from a restoration in southern Spain. Restoration Ecology 22 (3), 311–318.