Key to zips is to 'feel' the tooth strength.
If it feels mushy or soft as you tighten, it may not work well.
Stiffness of band can play a part too and actually back bend repeatedly to soften the stiffness for eaiser application.
I use the skinny ones, teeth are plenty strong and actually run a...
I was wondering about this too...was there part sticking out further that where it was trimmed too @Mosey2003 ?
I believe it happened, but it's probably very rare.
I guess the OP has had it happen too.
I have not had that prob with the leg band zipties I use, but I have had other zipties that are too easy to close and thus can kinda see how they might tighten on their own.
I've tried marking birds with blukote and despite the way it can stain feathers, and everything else, it didn't last long even on a light colored bird.
Anything you 'paint' on a bird they will try to preen off and thus ingest, so be careful.
I've seen folks use nail polish on toes and legs...
That is very odd!
Even when clipping end off close to lock,
the end was stuck out farther and loop was tight the next day??
Have never seen that happen, sounds like a faulty ziptie.
Then why not say that, instead of
SMH.
I use zipties too....no lost legs here either.
https://www.backyardchickens.com/articles/leg-banding-with-zipties.68075/