Exercise extreme caution when approaching any dragon, especially a wyvern. When aroused they will often rise up and warn you off with a 'Threat display' that can put years on you!
This sample animation, an addition to the Wyvern 2 Motions, shows a Wyvern performing it's Threat Display. It might do this prior to attacking, or simply to ward off any perceived threat to it's cave and/or nest. Either way, it's an intimidating behavior!