Mating Feathers, Loretober Day Eleven!

A mating feather is a magically infused, and typically beautiful and shiny, plume that male harpies gift to a potential mate, similar in symbolism to a wedding ring. Acceptance of the feather means agreeing to a life-long commitment, with each harpy promising to never court again for the rest of their life. This promise is meant to stand strong even if their mate dies. Though some harpies do seek out physical and even romantic relationships after being widowed, harpy society at large sees it as an insult to one’s mate to create another romantic life bond after their mate's passing.

Only male harpies can make mating feathers. It’s a magical process that females are incapable of biologically, where a harpy focuses on a particular part of their body for days/weeks at a time, infusing a newly growing feather with some of the magia they consume everyday. When accepted, the feather is magically fused to the giftee’s body, and is extremely difficult to remove without intense pain. If a harpy creates a mating feather and is rejected, they will return the feather to their plumage and reabsorb the magia within it. If their feather is accepted and attached to their new mate, then they will never be able to create another mating feather for the rest of their life. The same would happen to a harpy who misplaced their mating feather, (reabsorbtion is necessary to make another) so harpies tend not to pluck them until the moment of proposal.

Mating feather effects

Mating feathers are symbolic of life-long commitment, but they also serve a physical purpose, the magia within the feather enriching the health and fertility of the one it is attached to. This can extend their lifespan, make them stronger, and promote healthy + plentiful eggs (between straight harpies.) Though it will not allow two male harpies to biologically reproduce with one another, intersex harpies do exist that blur these lines.

Feather placement and meaning

Ultimately the more prominent/easy to see the mating feather is on a harpy, the more they are boldly proclaiming to others that they are taken. 
If the mating feather has been placed somewhere immediately visible like their chest or head, that could mean that the harpy is either head over heels in love with their mate or that they really wants others to know at first glance that they're is taken and unavailable. Choosing these areas is a great way to in general be left alone by others, especially strangers. 
Although a harpy may love their new mate deeply, they might want to be more social with others and decide to place the mating feather in a less conspicuous area like an arm, in the outer wing feathers, or on their tail. 
If the feather is in an even more subtle place like one's back or amongst one's inner wing feathers, then that could mean a myriad of things. It could mean the harpy wants a more private love life, that mating was more of an arrangement than a love match, or (especially if she/he has multiple male mates), it could mean that their mate isn't as close to her as he could be, etc. There are no exact answers, only assumptions. The only one who truly knows why they placed the feather there is the harpy themself.