The wildlife park in France specifically holds two elderly crocodiles, that are too slow to go after the birds. I would say that larger birds would actually be the risk here, as they would be a larger and slower target.
Seeing other examples (like crocodile river in Blijdorp and the butterfly temple in wildlands) I think smaller birds would be better, since they would be quicker than the cross. Such as starlings and especially weavers.
On the other hand, Ferme aux crocodiles (also in France) holds ibises and hornbills with their crocs, that regularly fly down to the ground to walk between the crocs, so I think it might be a bit of a toss-up. Depending both on individual crocodiles and birds