#aquila's definitely flown into glass windows before

[sonlightning]

at the exact moment santiago was born a sacred eagle ( one of zeus’ symbols of power ) was also born, and the two of their lives were entwined! the eagle made a few appearances whenever santiago was younger and looked after him when he and his mom ( and eventually felice ) were on the move, but he doesn’t really “meet” the eagle until he arrives at camp half-blood for the first time when he’s around 12 or 13. 

the eagle looks generally normal except that its eyes are a glowing gold and it has a row of gilded feathers around the cap of its head. santi names the eagle “aquila” after the constellation of the same name and eventually learns because their life forces are tied, he’s able to have limited communication with the eagle -- sometimes he knows generally what aquila is thinking, and if he concentrates santiago can even see what aquila is currently looking at.

however, because their life forces are entwined whenever santiago dies aquila will also die. while the inverse is not true, but santiago will be able to feel the aquila’s death if it were ever struck down or killed, and it would feel very much like losing a part of himself.