No, this is not a national holiday day. But they cleverly have arranged the ceremony to match with a local holiday day at Madrid.
They are trying to transmit "austerity"... in the same way THEY are applying austerity to the people at Spain.
The old king abdication and the new one proclamation is motivated by so many things. Note that the new king grandpa didn't reign over Spain, as not so time ago Spain was under a dictatorial regime. And previously, we had a Republic.
So, if I were the new king, I would try to be as correct & transparent as possible... just in case, who knows.
But I'm digressing. It's a too long history and it deserves some beers in a quiet place ;-)
Re the European Swallow stuff... it seems that there is people around the world that really cares about this question:
"Although a definitive answer would of course require further measurements, published species-wide averages of wing length and body mass, initial Strouhal estimates based on those averages and cross-species comparisons, the Lund wind tunnel study of birds flying at a range of speeds, and revised Strouhal numbers based on that study all lead me to estimate that the average cruising airspeed velocity of an unladen European Swallow is roughly 11 meters per second, or 24 miles an hour."