National Bird Day
The world is filled with a plethora of different species of birds. From cardinals to doves, from parakeets to parrots. Different people have different relationships with the various species of birds. As such, one could easily imagine that there could actually be numerous National Bird Days in the world, serving different purposes and perhaps varying by region.
What this day refers to, however, is known as National Bird Day, observed primarily in the United States. This is a bit different from occasions such as International Migratory National Bird Day, World Migratory National Bird Day, National Bird Day (UK), and several other National Bird Days which do not follow the same etymology as "turkey day".
It is also worth noting that each of these is named for those avian friends, not the late Senator Robert Byrd!
The 'National' term might be a bit deceptive here, since it's not actually a national holiday in the United States. For a day to technically be a national holiday, an Act of Congress is required, and there is no evidence that has ever happened. That being said, this delightful day is still popularly known as National Bird Day, regardless of whatever Congress might think of that.