Why are my Iris germanica spikes breaking off before flowering?

Hello. I have some lovely established iris germanica plants in the front of a south east facing chalky border. They’ve been perfectly happy, and this year I’ve been ‘on it’ with slug and snail control. Lots of buds and I was feeling pretty pleased with myself, but over the last week I’ve lost 4 spike tips. They’ve just snapped. I blamed the pigeons at first but they don’t go own to the sunnier end. No sign of slug damage. No wind to speak of. The plants are over 5 years old and split them every few years. Fed with BFB.
Thanks in advance!

 

Coincidentally I've had the same with a few of mine out of about 30.
Not happened before in the 15yrs I've had them, just this year for the first time. About 30" from the ground one top snapped off and a few buds snapped off on a couple of others.
The only cause I could think of was pigeons too

 

Yes exactly like mine @Pete8. Blooming pigeons!