Don't underestimate birds, they are often extremely quick learners.
Some things to keep in mind while enriching:
When enriching birds they may try to take flight and so become injured.
Can they carry the enrichment and 'drop' it on another animal?
Beaks—they do not have hands, so most birds use their beaks to investigate. Design your enrichment to suit the beak's shape and use. Raptors often tear, ibis like to push their beaks into mud and so on.
Legs—sometimes they can get stuck, when creating enrichment always keep in mind how legs and toes will interact with the device or materials.
Colour—most birds can see colour, some even like or are drawn to it. Use this to your advantage.
Taste—most birds have limited taste, but research your bird to find out.
Texture—birds can feel with their tongues, use this dynamic element, especially animals that chew.