Best way to mark/tag ducklings?

[Sunny Side Up]

My ducklings came from the hatchery with leg bands to indicate their sex. I got 8 girls & 2 boys, and plan to keep 4 girls/1 boy and sell the other half asap. (I had to order all 10 for a minimum order) The hatchery advises removing the bands within a week so they don't constrict their growing legs.

I need to keep track of the 2 boys, so I don't mistakenly sell or keep both. What's the safest & most reliable way to mark them? Permanent marker? Zip ties? Nail polish?

Please advise. Thank you.

 

[warcard]

Zip Ties, just keep an eye on them so you can change them before they get too tight.