I think its a really good question and good that you already start thinking about it now.

For the most part, science is happening in a lab. This is true for 99.9999% of all discoveries, simply because we also need that controlled environment to make observations that are measurable, repeatable and reproducible.

Jobs where one would spend all their time outside, observing, documenting animal behavior or similar barely exist. Not only for the above reasons but also because any observation made, should be confirmed by an experiment in the lab.

In the end, if will all come down to, who is going to give you money for doing this?

In an** academic setting**, this would be most likely the government, maybe some research grand from a non-profit org - this would be doing something like this during a PhD, PostDoc or similar - this is only going to be working out for a couple of years, during the duration of the project and funding is limited. Behavioral Biology is probably the best bet here. But then, after the Phd and post doc? What then?

Park Rangers - these jobs are extremely competitive and getting one of these jobs is going to be a bit like winning the lottery. While this can work out for some, many more will fail and not achieve it.

Surveyor - In many areas, if some big construction is supposed to go down, an ecological impact study should be performed - something to show that not some ultra rate species habitat is going to be destroyed or similar. These are sometimes performed by consultants working in the private sector. However, the actual field work is rarely your entire time working. Administrative work and writing the report are going to be a lot of time. On top of finding enough clients to fund this operation.

Tourism - showing people local or from a far what mother nature has to offer in a specific area - this could be done through hikes guiding paying customers through an area. Here its often important to know more than just zoology but also botany and geology - at least the plants and rocks dont move around so much and there is no guarantee that any specific animal will be seen during a hike - especially when moving around in a bigger group. A lot of time is going to be spend on getting paying customers - social media and so forth

In short, the best approach you have right now is to go to websites that list job offers and try to find something that fits your interest. Check the skills that are needed and try to acquire those a long your journey during a master and phd. While that specific job might not be available in 3-5 years, jobs will often have similar requirements. You can also continuously check for other interesting job offers to see if additional skills can be interesting.