We've been hearing White-breasted Nuthatches singing their, "wer-wer-wer-wer" song. Not the most musical or exciting sound, but it accomplishes their purpose, to define a nesting territory (of about 25-45 acres) and attract a mate.
Years ago when we first started our publisheing career, we wrote 3 volumes of Stokes Guide to Bird Behavior, which documented the lives and behavior of 25 species in each volume. We would research all that was published, then spend many hours in the field following and watching all the behavior of each species. We saw White-breasted Nuthatches do some fascinating behavior, including sweeping the entrance around their nest hole with crushed insects or bits of fur. It has been suggested that this leaves a scent that deters squirrels and other mammal predators from the nest.
Nuthatches store bits of food under bark. We once saw a nuthatch come to near its nest hole and store food under the bark. A second nuthatch who was on the same tree, saw it coming, went and hid on the backside of the tree, and when it was gone, went around to the front of the tree and stole the bit of food!
Birds are always doing fascinating behavior, which you can see, if you take the time to look.