What is the size holes in the metal screening? My first though is that birds are able to poke their head or beak through and pluck them out. Another thought is slugs or maybe pill bugs.

Rodney

My bet would be on slugs or snails.

They'd be out of reach of birds. I haven't seen any evidence is snails of slugs. Pill bugs are a definite possibility since they are present in my compost. I didn't know they would go after the sprouts.

Is this window screening? If it is something like 1/4" hardware cloth a small slug could easily fit through it. Also you wouldn't see slugs unless you went out at night with a flashlight. They could have been in your compost as well and hide out under compost during the day. A few pellets of Sluggo sprinkled on top of the soil would take care of them.

The first and third time was poultry fencing, and 2nd was 1/4" hardware cloth. It keeps the squirrels from digging. When I've had snails in the garden in the past, they were visible, don't know about slugs. I think the pill bug theory still has the most merit.