Hunting Sika in winter IS quite challenging Hunty. They basically bed down, and you're fortunate to see them in the open.
Heading right over and in to Thunderbolt is a bit of mission, likely not worth the risk/reward in winter. I would recommend you just head over Urchin, then work your way across the bush saddle between Urchin and Umakarikari (there's a 'track' now), glassing and SLOWLY and QUIETLY hunting the bush edges and inside the bush edges as you go. If you don't see anything, nip in 'behind' Umakarikari itself and, like the other Member said, slowly hunt the north-facing slopes and bush edges/inside edges there.
This is a most enjoyable day-trip or overnighter route, even if you don't see anything.
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