There is no best aspect ratio for wildlife photography only the best aspect ratio for a particular photograph or stage of your workflow.
Similar Articles you may like to read –
Is full frame better for wildlife photography?
Best Bird Photography Lens For Long Distance Photos. What To Look For?
How many megapixels are good for wildlife photography?
Best Aspect Ratio While Shooting
While shooting the best aspect ratio is the standard one for your camera which is the same as your camera’s sensor. In the DSLR field, this is 3:2 or the width is one and a half times the height.
Many DSLRs and mirrorless cameras offer the ability to capture photographs at other aspect ratios but you are only losing pixels if you do because the alternate ratio has to be cropped out of the 3:2 array available. You might as well do that cropping in post processing and have the ability to change your mind on what crop to use or to use more than one.
The ideal situation is when you are able to decide in the field how you are going to use the shot and you get the time to frame exactly what you want allowing you to “crop as you shoot”.
If you come to need another crop ratio in post processing it’s always useful to have space around the subject of the photo. It is therefore wise to not fill the image too fully when you shoot to leave flexibility at the final crop. Since this will waste pixels if you don’t use the space it’s probably best to take two or 3 shots with different degrees of excess space for possible cropping and one where there is no excess space. I guess this could be called crop bracketing.
Best Aspect Ratio in Cropping
This really depends on the image and the composition you find the most suitable for the image and the story/feeling you are aiming to transfer. There are really no rules – not even that a standing-up giraffe should be in a vertical crop and a snake in a horizontal crop.
This composition changes a giraffe snapshot into a feeling for the vastness and harshness of the environment the giraffe inhabits. Breaking the rule of filling the frame but following the rule of thirds and making sure there is space in front of the giraffe.
Generally, it’s good not to crop wild animals too tightly, they need some space in front of their face.
There is a feeling amongst some photographers, a bit like those who will only use one or two fonts, that lots of variation in aspect ratio is distracting and should be avoided as much as possible. I am not sure it’s that important but give it some thought when you are compositing or cropping. Besides anything else, it’s harder to lay out images on a webpage or in a book if all aspect ratios are different.
Cropping can also improve your photography by correcting some of the errors that are likely to occur occasionally.
More articles you may like to read –
The Best Camera Settings for Wildlife Photography
Wildlife photography camera setting for long distance objects
How do you shoot wildlife in low light?
Distracting elements, especially in the foreground. Finding an aspect ratio that allows the elements to be cropped out is often easier than trying to clone them out.
Bodyparts cut off by the shot are often disturbing. Changing the cropping to a different position can often make the “amputation” less distracting.
Lack of space in front of a subject, can be corrected by changing from landscape to portrait and leaving little space behind the subject
Fitting the display system. For instance to fit the image to the requirements of social media or a particular frame.
Horizons that look crooked can be corrected during cropping. We of course always get the horizon horizontal while shooting!
Flawed shots can sometimes be saved by cropping really tight onto a part of the animal rather than trying to correct the full shot
Emphasize the foreground or background by using the rule of thirds to ensure that the 2/3rds is the better part of the photograph.