According to the guidebook, "Guía del Zoo de la Casa de campo de Madrid", the majority of the concrete structures date from 1972 when the madrid zoo was inaugurated at the casa del campo park.Before it was a menagerie at the parque del retiro. The structures were designed by Engineer Antonio Lleo de la Vina and Architect - sculptor Jose maria Subirachs, though other persons also contributed. It is now rather evident that they were not trying to reproduce natural habitats, but rather contribute to "arquitectura española".
I visited the old Zoo at Parque del Retiro near to 40 years ago . Unfortunately I can remember virtually nothing about it and did not have a camera then . I do recall it being a very hot day and being very ill soon afterwards - probably ate a dodgy peach .