There are two main eagle calendar markers which later became „mythologised“. One is double headed eagle, like this Hittite one from Alaca Höyük…

This symbol was derived from annual vulture mating „synchronised flying“ ritual, where two birds fly next to or on top of each other…Which from the ground looks like this…
In Eastern Anatolia, Northern Mesopotamia and Central Asia this coincides with the arrival of rainy season…Which is why in these areas this calendar marker was associated with rain and rain gods…Hence this eagle dude from Bactria, c: 2500-1500BC separating summer and autumn (winged lion) and winter (boar). I talked about this in my post „Double headed eagle“
This guy also has two vulture heads pointing to two opposite directions…The way a couple of vultures looks like during their mating synchronised flying from the ground…In November, when rain clouds arrive. Which is why he is fluffy, like a cloud. Bezoar cloud is there too as Bezoar goats mate at the same time too. Bactrian.