Does Udyr's effect trigger when his buff is spent by another card's effect (like Wildclaw Shaman)?

Ruling: No. Udyr's effect is an activated ability with the template "cost: effect" where spending his buff is the cost. You must directly activate his effect and spend the buff on him as a cost to get one of his four effects.

Nuances:

• Effects that trigger whenever you spend a buff are phrased as "when you spend a buff" - Udyr does not have this wording
• You cannot spend the same buff as the cost for multiple effects (e.g., spending Udyr's buff for both his effect and another card's effect like Monastery of Hirana)
• Conquering a battlefield with a buffed Udyr does not automatically trigger his effect