Temporal and interspecific dietary variation in wintering ducks in agricultural landscapes

Farmlands are becoming more important as waterfowl foraging habitats,
while natural wetlands are being lost globally. However, it is unclear how
waterfowl coexist in agricultural landscapes by resource partitioning. We
evaluated the diets of seven sympatric dabbling ducks foraging in rice
paddy and lotus fields around Lake Kasumigaura, the second largest lake in
Japan, during two wintering seasons (from November to February) by fecal
DNA metabarcoding using chloroplast trnL and mitochondrial CO1 region
sequences. We examined 420 fecal samples and found different patterns of
dietary diversity and composition among the duck species. The pattern also
differed between plant and invertebrate food. Dietary niche partitioning
was clear in plant food. Large-bodied ducks intensively use crop plants,
and other ducks might mediate competition by using terrestrial and aquatic
plants that are suitable for their foraging behaviors or microhabitats.
Dietary segregation among species was the most apparent in February, when
the abundance of foraging ducks was the largest. This study illustrated
the complex pattern of dietary niche partitioning of dabbling ducks in
agricultural landscapes, which might be difficult to evaluate by
conventional approaches. The availability of crop plants, as well as other
plant food resources in flooded areas and farmland dikes, may enable ducks
to coexist by spatial or behavioral resource partitioning.