.. I copy this on the enet 2 or 3 years ago when I got mine... sorry I don't remember where it was... :
"Oncidium ornithorhynchum is a compact species which throws
short length spikes of pinkish 1" blooms with a delightful scent.
The plant is technically a cool grower, being grown mostly by
hobbyists in intermediate conditions. These conditions cause
pronounced markings on the leaves that are not harmful. This
condition is the reason the plant carries a "5" on our growability
scale. In practice, the plant is easy growing and will bloom readily.
To combat the problems with heat, we grow this species in a fine
fir bark mix, keeping damp, to facilitate cooling via evaporation.
The hobbyist can further help the cause by potting it in a clay pot.
Temps can range from the 50's all the way up to 90. This plant is
also an excellent candidate for water culture, blooming 2-3 times
per year for us."
... so I think it may be the same for most of his hybrids ... for culture conditions..
Phil's Orchid Site - Genus review - ONCIDIUM SECTION ROSTRATA ... Oncd ornyth on the same page... (hope this allowed...)