Which is the best camera for taking wildlife photography?

I'm sure you've looked at the various models of DSLR on the market and probably got a little overwhelmed and confused as to why all the different models.  The simple answer is that each model is specifically designed for specific types of photography.

For example, a high-resolution camera like a Pentax 645Z or the Fujifilm GFX-100 are designed for not only those who need to make large prints, but specifically for fashion, portrait, landscape, architecture, commercial and fine-art photographers.  You can technically use these camera for, say, wildlife if you so desired.  But when comparing them to a camera specifically designed for wildlife like the Nikon D5/D6, Canon 1DX or 7D Mark i/ii, you will see why you rather uses these models even though they have lower image quality than the medium-format cameras from Pentax and Fujifilm.

These four models have vastly faster and more accurate focusing systems than what you'd get out of the $10,000 GFX-100.  Tech like eye detection and now Canon is developing tech to determine the species of animal being photographed! 

Other tech such as an internal buffer that is capable of writing data to the SD card faster than the data coming thus enabling the photographer to shoot for as long as the action lasts.  Other cameras from Canon and Nikon can't do this, which is why the models mentioned are the best sports models.  The Nikon D5/D6 and the Canon 1Dx are professional models, while the 7D is a high-end consumer grade body which are far less expensive.  But when comparing the cost to performance of these models, it only makes sense to buy the $5,000 D5/D6 or 1DX if you're making money with it, or you have the disposable income and talent to justify spending that much.  The 7D Mark i/ii are pretty darn close in performance making them highly popular for those who do not rely on their photography to put food on their table and pay their mortgage.

Since you asked what the best was without any budget or other qualifiers, the answer is either the Nikon D5/D6 or the Canon 1Dx.  Both are so close to each other that it boils down to personal preference and how they feel in your hand or what lenses that they offer that best suit your needs and/or personal style. Nikon has their super-telephoto zoom and Canon has theirs.  Which one you like or can afford may dictate which brand you go with.  It's all rather subjective at this level.

But if you're just starting out, go with a used Canon 7D Mark I (about $400 on eBay) and use that to learn with over the next few years.  Once you gain the experience, you'll know when it's time to upgrade to a different body.  Or if your budget will allow it, go with the 7D Mark II which sells for about $1,800 body only.  Personally, I suggest that you go with a used, $400 7D Mark I and put the $1,400 you didn't spend on a new 7D Mark II towards the expensive lenses that you'll need.

One which you did not leave at home because it was too inconvenient to carry with you! Pros use expensive cameras with 35mm sensors and heavy fast lenses, with 1.4 or 2x teleconverters. Nikon, Canon or Sony in no particular order. Enthusiasts can benefit from using DSLRs with crop sensors because the lenses can be much less bulky to reach 400mm focal length. Much depends on the type of wildlife. See info in the link: