Choosing your equipment
From experience, do not invest most of your budget in the camera. It is better to choose an older model or mid-range camera for prioritise quality lenses.
A camera with an APS-C sensor can be a better choice than a full format in the case of wildlife photography because you get a longer focal length on the same telephoto lens (x1.5).
Also think about the species you want to capture. A 600mm will be useful mainly for small birds or to observe wild animals without scaring them. And then ask yourself what type of wildlife photos you want to take ? Do you simply want to show the animal up close or prefer a larger composition to show it in its environment ? In the later case, there is no point in choosing the most powerful zoom possible. Choosing higher quality optics with a larger aperture but a shorter focal length will bring you more interesting photos than just showing the animal in the center of the image up close.
Another essential point for me : the weight of your kit. Wildlife photography requires endurance, a lot of walking, etc… and if you also want more dexterity and flexibility in your movements, it will require freehand photos without the aid of a stand. This is where the weight of the camera becomes an essential factor.
Examples of kits :
Beginners
Nikon D3500 + Nikon 100-300mm : 775g (lightest configuration possible)
Canon 200d + Canon EF 100-300mm : 950g
Expert
Nikon D7500 + Tamron 100-400mm : 1,8kg (good for freehand photos to follow birds in flight and the lens becomes a 150-600mm because mounted on an APS-C body)
Pro
Nikon D850 + Sigma 200-600mm : 2,8kg (configuration that requires a tripod or monopod)
Nikon D6 + Nikkor 500m F/4 : 4,5kg
Also you should choose a camera with a fast and precise autofocus. The Nikon D500 has long been considered the best for this. But the new hybrids like the Nikon Z7II or Sony a7iv are now equipped with very good autofocus, which was far from the case on the first versions.
Also look if the body camera and the lens are “tropicalized”, i.e. resistant to humidity, dust, etc.
Digital cameras are subject to rapid discounts so it is often wiser to choose an older “pro” and tropicalized camera than a more expensive new model. Keep in mind that the more megapixels your camera’s sensor has, the more you’ll need to invest in high-quality lenses…
The stealth and the hide
Before approaching an animal you should know its behaviors, its hearing, visual and sensing abilities, along with its possible reactions to your presence…
The birds are generally more active at the beginning and end of the day, which is good because the light is more interesting at these times (golden hour, backlight, etc.). They will also be more easily observed after a period of rain, often feeding earthworms forced to the surface.
Your approach will also have to adapt according to the seasons of migration, reproduction, hibernation…
Mammals have a less developed view than birds but will be more sensitive to your smell and noises (especially for felines).
So learn to walk slowly and discreetly with clothes that blend into the landscape. And above all, be very patient!
To observe rare and exceptional moments, using a hide is ideal. It allows you to completely blend into the landscape without disturbing animal life. A simple camouflage net can be enough to improvise a hide or place you can use vegetation to conceal yourself. Your car can also be used for animals living near roads. For birds, nature reserves often offer observatories that serve as camouflage.
Also scout and use bait in strategic locations (checking local laws before baiting). Accustom the animal to always find food in the same place. Then place yourself according to light and wind (to avoid being detected by your smell).
For the composition, try to be as often as possible at eye level with the animal, play with the rule of thirds and take care of your background to make your subject stand out.
