In Warframe, you will need Medjay Predasite Tags to rank with the Entrati Syndicate. To get them, you'll need to engage in animal conservation on the Cambion Drift on Deimos.
What do you need
You are going to need very specific items to have a chance of catching a Medjay Predasite. First, you'll need a Tranq Rifle which you can purchase from Son in the Necralisk if you don't already have one. It will cost you 500 standing. You will also need to purchase a Predasite Echo Lure from Son for 1000 Standing, and finally you will need a Predasite Pheromone Gland. These single-use items cost 150 standing points and will increase the rarity of the Predasite that appears when you follow them.
How to capture a Medjay Predasite
Head over to the Cambion Drift and pull out your Tranq rifle. Switch to the Predasite Echo decoy so that only these sites appear on the map, then go to one of them. Once there, find the animal's poop and interact with it, then follow the trail. The predasite trails are pretty easy to follow, just don't get into the toxic crap.
When you get to the nest, use the Predasite Pheremone Gland before using the Echo Lure. This will increase the chances of a Medjay Predasite spawning. Use the Echo Decoy, then repeat the Predasite call and return to the Tranq Rifle. When the animal shows up, strike twice with the Tranq rifle. If you are lucky, a Medjay will appear, otherwise you will have to rinse and repeat until you have one.
Remember, Warframes with invisibility make it easier to capture animals, as the animal won't know you're there.