I have lost a few, but I had more of a problem when I live in in the "burbs", but not sure why... Just went outside and checked on them and it looks like I have 4 or 5 with ducklings, another 4 or 5 with chicks, and lord only knows how many are still sitting on nests.
It is because urban and suburban environs have exponentially more predators than rural areas per square mile.
That's what drives me nuts when people say they don't have predators because they don't live in the country.
When we lived on an 8000 square foot lot in Los Altos, CA we would often have families of 8 raccoon come and "play" in the sprinklers. Had one grab my favorite hen and take her up a tree... Of course I followed, but it didn't end well for me.