Plankton (singular plankter) are a diverse group of organisms that live in the water column of large bodies of water and that cannot swim against a current. They provide a crucial source of food to many large aquatic organisms, such as fish and whales.lankton are primarily divided into broad functional (or trophic level) groups: 1  Phytoplankton (from Greek phyton, or plant), autotrophic, prokaryotic or eukaryotic algae that live near the water surface where there is sufficient light to support photosynthesis.
Tree swallows breed between May and September. They raise one brood per year. Tree swallows usually nest solitarily. However, they may nest near other tree swallows if nest cavities are close together. Tree swallows build their nests in late April or early May. Their nests are usually built in holes in dead or live trees or in hollow stumps. The female builds the nest using grasses, mosses, rootlets, and aquatic plants.
These droppings may end up on the ground under the nest or as a layer along the rim of nest, sometimes causing barn swallows to be labeled messy. Barn swallows are the most common swallow found in Iowa and are one of the most abundant species in the state. Although we don't have an estimate of their population, in a study of nesting birds in Iowa completed in 1990, barn swallows were found nesting in every county and were the sixth most widespread nesting bird reported in the state. Part of that apparent abundance is because of the ease with which their nests can be found and monitored. Also the fact that barn swallows are so often found closely associated with humans makes them a conspicuous part of the bird life in Iowa.