This Errand will unlock after you complete the Hunter’s Blind sidequest, speak to Talanah to start it. All you need to do is get a Stormbird and Thunderjaw trophy, easy right?
The best place to get the Stormbird trophy is beside the Greatrun Hunting Lodge as there’s a Merchant nearby that you can replenish any needed stocks at. There will be two Stormbirds stalking around the place that you can pick a fight with, but once you do, get ready for a serious battle. The Stormbirds have a lot of health, and not many weakpoints, as well as an array of attacks ranging from just annoying to utterly devastating. One of the most important things to remember in a fight with these things is to keep moving. Standing still for any length of time will have you taken out quickly. If you can, use Tearblast and Hardpoint arrows to knock parts off of it, especially the jets on its wings to stop the powerful diving attack and the Lightning Gun which is its main weapon. The individual parts have a lot of health though, so you’re going to have to consistently hit them with Tear weapons to get rid of them. Another tactic is to use a Ropecaster to hold it down whilst you hammer it.
Thunderjaw sites are scattered around the game map, and thankfully they are not as tricky to kill as Stormbirds, although don’t go in expecting an easy fight. The simplest method is to use Tearblast arrows to pull off the two disc launchers then use them to hammer it. This won’t outright kill a Thunderjaw normally, but it will severely damage it and also expose its heart. Once that’s exposed, a few good shots with Precision arrows and it should go down without too much trouble.
When you have both trophies, head back to Ahsis at the Lodge. He won’t be there, and neither will Talanah so you’ll need to speak to Ligan to complete the Errand. Doing so will also start the Red Maw Sidequest.