Depends on how the song is interpreted. The intention is probably “by the 𝑛ᵗʰ day of Christmas, my true love had given to me [list of 𝑛+(𝑛–1)+...1 items]” but the actual grammar means that by day 12, you'd have received 𝑛(13–𝑛) of the 𝑛ᵗʰ item, or

• 12 drummers drumming
• 22 pipers piping
• 30 lords-a leaping
• 36 ladies dancing
• 40 maids a-milking
• 42 swans a-swimming
• 42 geese a-laying
• 40 gold rings
• 36 calling birds
• 30 French hens
• 22 turtle doves
• 12 partriges in pear trees

Total is 184 birds. By day 7, only 69 birds, up 50 % from 46 by day 6. At least the number of received birds stays constant (23) on days 8-12. The geese technically-a-reproducing are not accounted for, as the eggs might not be fertilized and take several weeks to hatch.

Also explored in an awesome video by Vihart: YouTube/Piped/Vimeo

Lol, eight maids a milking... Slaves. He's sending you slaves darling.

Plus, you have to provide room in your house for a huge number of new lodgers. Drummers, pipers, lords, ladies, maids... and then you've got to find a place for all the birds.

Your "true love" is clearly taking advantage of you by unloading all of this onto you and calling it a gift.

It's 184 birds, 140 humans, 40 rings, and 12 trees. The rings are almost a normal present but when it's that many you're just Sauron.

Edit: fixed math

I think they're for eating

1. From days 8 to 12 your true love gives you milkmaids, dancing ladies, leaping lords, pipers and drummers. Human beings. As gifts. Which makes eating the birds feel a lot more okay.
2. This carol was written back when Christmas was a mere 12 days long. Now Christmas starts in mid-October. "On the ninety-ninth day of Christmas, my true love gave to me, ninety-nine wall beers..."

I wonder who's behind it. c/birdsarentreal

At least you can eat the geese. What the heck am I going to do with turtledoves and partridges?

Pertinent

If my true love flips me the bird, she might not be my true love after all.

This is quality shit.