Yes, shutter speed, ISO and Aperture are all interconnected. The way to understand it is like this. Let's assume that a perfect exposure for that bird in that particular light at ISO 200, is going to be f/8 at 1/400s. So, all of a sudden, a cloud comes over and makes it darker, by one stop. You have three choices to still get a perfect exposure, by changing just one of the three settings. You can up the ISO by one stop, to ISO 400, or, the Aperture by one stop, to f/5.6, or, the shutter speed, by one stop, to 1/200s.
Each setting change is in one stop increments. That's the easy way to remember the relationship to all the settings. One click of the dial is one stop, whether it's Aperture, ISO or shutter speed. Spend a half hour out on a park bench one day and go ahead and get a perfect exposure. Make note of the settings, then change one by one stop, then change another by one stop to compensate. You will still end up with the same perfect exposure. Once that snaps into your memory, you'll never have another problem making sense of it all. 