American oystercatchers first breed at an age of 3-4 years.
When courting, the birds will walk together and make a single piping note. This progresses to leaning towards each other, extending and lowering the neck, and running alongside each other while calling. The pair may then burst into flight and fly in a tight formation around their territory.
The killdeer feeds primarily on insects (especially beetles and flies), in addition to millipedes, worms, snails, spiders, and some seeds. It opportunistically takes tree frogs and dead minnows. It forages almost exclusively in fields (no matter the tide), especially those with short vegetation and with cattle (which likely shorten the vegetation) and standing water.