magpies

[Muskett]

Hedges: several types of hedge. For small song birds then the denser they are the better. Stops larger predators getting in. To get the density of growth requires trimming often, the more often the better. Field hedges are a bit more open, and barely thick, dense, enough. Really bad to let these open up by not cutting in Autumn. Cut after the bird breeding season. When a hedge is left to "blow", open up, then predators can travel along them fast, patrolling, and take at their will.
Basically the best song bird hedges are those well groomed, nice warm and tight.

For larger song birds they need a bit of both. Here dense shrubs, and trees work better. Open enough to get in, but have some density to hide away.

Song birds will try different places until successful. If they lose a brood then they try another location. In a good summer they might try three times, and bring two broods to flight. A disaster is non survive. As most live two to three years only in the wild then every brood counts. Numbers will crash alarmingly on bad years. For every bad year it may take two to three to get numbers back up.
Remember predators will eat as many as they can, good or bad years, they don't care. If numbers are low then the predators may bring the numbers down to critical levels, and why managing predator numbers is so important.

So anything you can do to help song birds would be great. Managing Magpie numbers is positively helpful. Culling some isn't going to endanger them as there are loads, and there are plenty of places with no controls on their numbers at all. Road kill keeps them well fed all year around.
With changing agricultural practices then it is song birds that need the help. Do have bird tables, and control any rats. Also watch out for Sparrow Hawks that will use the bird tables as a take away. A bird table near a hedge is better than one in the middle of a lawn.