The availability or influence of water is a very important wetland feature to birds. Also the physical or biological factors include water depth and temperature, presence or absence of vegetation, patchiness or openness of vegetation, type of vegetation, foods, water chemistry, type of soils, and geographic or topographic location. Any variations in any of these wetland features will cause subtle, but distinct, differences in bird use.
Wetlands provide food for birds in the form of plants, vertebrates, and invertebrates. Some feeders forage for food in the wetland soils, some find food in the water, and some feed on the vertebrates and invertebrates that live on submersed and emergent plants.
Vegetarian birds eat the fruits, tubers, and leaves of wetland plants. Water temperatures influence food production. Invertebrate production in the water column may ultimately depend on water temperature and the ability of a wetland to produce algae. Cold water might not be a welcoming environment for small animals and plants that some wetland birds eat. However, water that is too warm also might not produce foods that some birds prefer.
