My male Senegal has been carting bits of grass around!!!

One problem, he seems to be building on top of a nest box - and having seen the barbary dove nests at work, I have a sneaking suspicion the eggs will just roll straight off. Is there something I can do to stop this? They didn't like it at all when I put up some modified ice-cream containers as nest sites.
Which brings me to a funny anecdote. I could see from the kitchen window he was having difficulty with a long bit of grass, so I grabbed my binoculars and went to the sunroom to watch him.
It turns out, he was having difficulty picking it up because......
He was standing on it.
He didn't seem to realize this, and continued tugging for a good five minutes before (with what I fancy was a slightly surprised look) realized he was standing on it, moved to one side, and flew up with it.
Yep, not the brightest of animals!!!