Av = "Aperture value" mode -- meaning you set the aperture (f-stop) and the camera will set the shutter speed (and possibly the ISO if you have it in auto-ISO mode).
Tv = "Time value" mode. You set the shutter speed (time) and the camera will set the aperture (and possibly the ISO).
P = "Program" mode. The camera sets both aperture and shutter speed... but it does this based on an algorithm described by the "program line" in which the camera prioritizes things based on the available light. In very dark situations it will set the aperture to wide-open and for any increase in light, the first thing it will do in response to increase the shutter speed. It's trying to get the shutter speed up to a point where you can safely shoot "hand held" based on the focal length of the lens. Once it attains that safe shutter speed... it'll start balancing between stopping down the shutter and also speeding up the shutter in roughly equal parts... until it gets to the point where the lens aperture is at it's highest f-stop... and then it'll just continue to use faster shutter speeds. But in "program" mode, while the camera will intiially meter and suggest it's setting... you can override it with something called "program shift" by turning the main dial on the front of the camera near the shutter button.
M = "Manual" mode. The camera doesn't set anything in this mode... it still meters the shot and will suggest to you if it thinks your settings will result in either a correct exposure, under-exposure, or over-exposure... but it's up to you to adjust settings.
For your Robin...
If the lighting is consisten... in other words if these birds are coming to a specific spot to get the worm, then you can use manual exposure. But using one of the automatic or semi-automatic modes will allow the camera to adjust to any changes in lighting much faster than you could do in manual mode.
The clue to me is that you asked about "when using a remote" which implies the camera may be on a tripod and the camera is pointing at a fixed location and the birds are coming to you... you aren't chasing the birds.
Depending on fast the birds are moving, you migth even want to use Tv mode. For example if you were shooting hummingbirds and wanted to freeze the wings then you might use that mode so that you can guarantee your shutter speed will be used.
I spend most of my time shooting in Av mode because I want to control the apeture for purposes of controlling the depth-of-field for the shot (the range of distances at which subjects will appear to be reasonably well-focused) and this lets me create deliberate backround blur. But my subjects typically don't require any minimum shutter speed so I'm free to let the shutter speed be as fast or as slow as needed. If I were shooting sports or any type of "action" photography (including wildlife) my priorities would likely shift to putting more importance on the shutter speed.
You didn't mention lens and distance to the subject... so there's not really enough info to suggest specific exposure settings. I would likely try to create a blurred background and to do that, I'd use Av mode with an appropriate aperture to create a depth of field good enough to completely focus the bird, but shallow enough nicely blur the background.
Tim Campbell
5D III, 5D IV, 60Da
