Zoos and wildlife parks are great places to get up close with wildlife but the fences and glass keeping us and the animals safe can cause a few problems for photographers.
Fences often rise above eye level and the tops aren't in easy reach (for good reason) so you can't hold your camera up above it to take your shots. As a result, we have to often take photos with the cage in front of us but this doesn't mean the fence has to appear and as a result spoil the shot.
Sometimes it's easy to capture fence-free shots as the gaps in the mesh are just big enough for a lens to be poked through, however when it's not, you'll have to use a few other tricks to capture your wildlife shot.
One way is to get as close to the fence as possible and select a wider aperture. Then, line-up your lens so it's over a gap or if they're too small, try and wait so the face of the animal you're photographing is in a gap. Once the animal has put some distance between them and the fence, take your shot.The fence will, hopefully, be thrown our of focus, thanks to the reduced depth-of-field, so you won't even notice it while your subject will be sharp. You may find that Auto Focus tries to focus on the fence rather than your subject so switch to manual focus to ensure your subject is sharp.
If you are using a lens that doesn't have a particularly wide aperture then don't worry; you'll still be able to capture a mesh-free shot with a longer focal range. If you can't shoot through or throw the fence out of focus you can often clone it out later using an image editing program.