It's mainly space - Shepreth is a very small wildlife park. It started as a local wildlife hospital - people would bring in hedgehogs, badgers and foxes that were hurt by cars or that they came across. Then the owner realised they needed a sustainable source of income and so bought a tiger. This was back in the early-mid 1900s. I believe his family inherited the park and decided to expand the private animal collection to draw in more visitors. All of the big attraction animals were kept in very small enclosures...they still are. The big cat enclosures are far, far too small. But they were kept really for the purpose of funding the small wildlife hospital. The park still have a very good hedgehog hospital and a local wildlife 'ambulance'.
So, they have one line of very small aviaries in a corner of the park and they take the birds out regularly to fly and exercise them. All the animals have a bit of extra space behind the scenes, eg the red pandas will be circulated out so that two are on display while the other two rest in a private space away from visitors. Many of the larger animals they have, such as the maned wolves, were hand-reared and the keepers play with them after closing time

They do actually have more birds than are listed on their website - they've got (from memory) black and mute swans, many species of rare duck, some kind of crane and ibis, several species of owl and falcon. Possibly more than that but that's what I remember - I was last there a couple of times last summer.
I volunteered there for a bit many years ago and will never forget playing with the baby skunks after closing! They were like kittens, really sweet and playful and funny! The skunks they have have never sprayed because they're never scared - there's a nice thought for your Wednesday