Hearing it, and listening for a while, are enough. Seconds later, a second baby joins it. Then the two engage in a chase that includes leaping over one another. They look too small for such agility but there it is. We know we'll see certain things.
Phoebes always nest under the same bridge.
Kingbirds always hunt insects from the overhanging branches. Orioles always sing from the tallest trees. But there are surprises, too. My wife and I come to rivers like this in spring to see what changes have taken place over the winter. There will be changes year to year.