This mission requires you to destroy buzzards while knocking, and collecting, trinkets from the Cargo Buzzards (you don't need to destroy, these, simply damage them.
You actually have a lot of space to use in this mission. As easy as it is to just stand in the open, taking on all aggressors, you can – if you're struggling – use the shacks littered around as defence from buzzard fire raining down and reply when they're not looking. The only issue with this is that you are being timed, so you need to ensure that you're making the most of your attacks.
Another point, just in case you forget, is to watch the radar. If you're struggling to spot the buzzards swivelling to look for the red dots will help you when thinking about what direction in which to fire.