The birds may have made a split second decision to adjust their flight path, making it seem as if they have an impressive understanding of physics, but who's to say that wasn't a lucky guess? Sure, their ability to make a split second decision and adjust their flight path was remarkable, but it's not uncommon for birds to instinctively do that. What was remarkable was the fact that the two birds were still flying together, at the same time, and that they both stopped flapping their wings almost simultaneously - this is where the real understanding of physics comes in.
It's clear that these two birds had a mutual understanding of gravity, as demonstrated by the way they continued their descent into what would have been an unfortunate crash had they not resumed flapping their wings. UrRong to think they had "engine failure" - these birds weren't malfunctioning and they weren't confused. At the last moment, they knew just when and how to get back on track before their altitude got too low to make it under the overpass.
These birds proved that even though we don’t all understand physics in the same way, nature can do it better: that's why it's important to pay attention to the little things in life. Their unplanned and instinctive maneuver proves that sometimes, when it comes to gravity, you don't need an engine or a fancy degree - you just need an eye on the sky.