Nesting season is a busy time for birds.  A bird must find a mate, build a nest, lay eggs, incubate, then care for the young.  At least if they're lucky enough to get that far.  But remember that to be "successful" from an evolutionary perspective, all a bird needs to do is replace itself before it dies.  So even if the nest fails (the eggs or young don't survive), the bird has a chance to try again, sometimes several times in a season.  This year I noticed three American Robin nests that I was able to observe at close range.  One nested on the tire of a vehicle. The vehicle was not driven to protect the nest.  Although it was sheltered from the rain, just about the time the eggs should have hatched, a predator got the nest.  It was found knocked off the tire one morning.  While I don't know for sure what the culprit was, it could have been a raccoon or opossum.  Another nest was on top of a light fixture on a building.  One morning there were broken eggs on the ground beneath the nest--they had been knocked out of the nest but not eaten.  Since there were many House Sparrows nesting in the area and one immediately began nesting on top of the robin nest, I'm pretty confident that the invasive House Sparrows destroyed the eggs.  Another nest was right outside my bedroom window.  We had watched the robin incubating 3 eggs, then saw the young nestlings begin to grow.  The adults often sat on the rim of the nest, and the female spent the nights there.  One night just after I fell asleep at 10:00 I was awakened by a robin alarm call just a few feet from my head.  I looked out the window, but couldn't see anything in the dark.  A few minutes later I heard squealing that lasted a couple minutes (which seemed like an eternity), then eventually stopped.  The next morning the nest was tipped sideways and was empty.  I'm not sure what kind of predator it was, but it was a silent nocturnal mammal capable of climbing into a shrub.  While each of these nest failures was sad for me to witness, I had to remind myself that these are American Robins, one of the most adaptive of North American species.  They are found in almost any kind of environment.  Their association with humans may be to their advantage in many situations, but it this case it didn't serve them well.  In each of these cases the birds shifted to another area and re-nested in a location unknown to me, so I won't see how they fare.