When learning how to shoot outdoor wildlife getting the hang of how to use your camera’s histogram is a must. This will go a long way to getting your exposure correct for the shot.
Many factors are involved when achieving proper exposure in your photos. This video will give you the tools to Evaluative Metering, know your Highlight Alerts and Histograms to help you achieve this.
A histogram with bars pushed up to the extreme side of each range can be an issue, unless you are looking to under or overexpose for a deliberate purpose. If your histogram has bars pushed up to the left, that means underexposed; bars pushed to the right means overexposure.
Use spot metering for objects and situations where you need a very accurate measurement of one particular subject, like portraiture or wildlife photography, or for backlit photography where there is a lot of light coming out from behind a subject.
Applying adjustments to a raw image in a software package like Lightroom or Photoshop is a non-destructive method of editing your photos to get a better exposure. That works but getting the photo with the proper exposure strait from the camera is the best way to start.