Fumo has an obsession with infants. There’s a reoccurring theme of juvenile males at Taronga having a fascination for infants - Monte, Sule, Fumo etc. It appears to be common behaviour in juveniles who don’t have a younger sibling and receive little maternal attention - with these three males all fitting this criteria.
Fumo has latched onto Shiba for a while due to his fascination with Safiri (he previously hounded Ceres and Cebele). Shiba is very patient with Fumo. When he throws tantrums and hits her, she simply attempts to restrain him versus Ceres who would hit him back - leading to Kuma to intervene.
Spitter is not just Taronga’s oldest chimpanzee, but the eldest in the region. At 61.5 years of age, she’d rank highly on the world scale too.
That would make sense as he also hounded Naomi for a second, which led to her running inside.
Shiba was very patient and she elected not to intervene with any of the drama. Right before I left she and Safiri went over to the termite mound and Fumo joined them. They were eating together and one of the older males (I believe Samaki) came over and barred his teeth at Fumo before settling in next to his mother. It was quite a sight!