Yep, I did set up a hammock under my swallow nest.
Actually, I had to set up two this year. My normally anti-social swallows either changed their minds or it’s a different pair…but this year I have 2 nests. (previous years the pair I had would chase out all other swallows)
And this year the two pairs of swallows have dive bombed and crashed into the English sparrows so often that 90% of them left my barn! 
I use one of those cargo nets for an SUV lined with a piece of feed bag under one nest and under the other I just tacked up an old piece of bed sheet lined with a piece of feed bag. (feed bag to catch crap and then throw out) I just attach it from beam to beam under the nest. If you have a barn with a ceiling, you can loop an old sheet and tack it in a swag under a nest. Leaves room for parents to fly in and out.
The hammocks work great! Any baby birds that get knocked out/fall out only drop about 12-18" and are fine and can still be fed. And I don’t have a pile of bird crap on the floor/bedding/horse under the nest.
And I did rig up a fan in the rafters to blow on the nest(s) when the weather gets really hot. Under the roof the temps are a lot higher than lower down. When I see the parents sitting with wings pulled away from the bodies or the babies with beaks left open all the time, it’s too hot for them. So I switch on the fan up there. It’s kinda funny…the parents all settle right in front of it and spread their wings and enjoy the breeze, LOL!
I know it’s probably odd to do that, but I enjoy the heck out of my barn swallows. I love watching them and the decimation of the insect population (well, except for the overzealous one that left luna moth wings on my barn floor last month! That moth is bigger than the birds!) and I even enjoy getting crashed into when the babies are learning to fly. :winkgrin:
And this year with 2 families I’ve been sitting in the barn for ages to watch them. Nest 1 hatched out 5 (and like mentioned, swallow nests aren’t made for 5!) about 9 days before nest 2 hatched. All 5 made it fine until flight, now one is missing when they come back to the barn at night. When nest 1 hatched, the daddy swallow of nest 2 got overexcited about the peeping and kept trying to feed those babies. Parents of nest 1 weren’t amused, LOL! Now nest 1 has been flying about a week and nest 2 (hatched out 4) is about ready to fly. Parents are already trying to coax them off the nest. So far, they’re refusing. 
But now at night when nest 1 babies come in to roost, some try landing on nest 2. Nest 2 babies think they’re getting fed by a whole squadron and beg like heck, their parents have a fit and the older babies look confused as to why the nest is so crowded!
sigh So much fun to watch!