I have to agree with Rich's comments, and the crop is much the same as I would have approached it. Regarding the Robin, ground shots rarely work, again, as Rich said. In addition, showing the food/bribe doesn't work either so there is a lot wrong with that. If possible, place the food somewhere near a branch that the bird will land on before coming in for the food, watch them for a time to see the pattern of approach and you will see what I mean. If there isn't a suitable branch/perch, you can place one there yourself, its a bit of observation and planning that's needed.
Your exif:
Exposure0.008 sec (1/125)
Aperturef/8.0
Focal Length500 mm
ISO Speed500
Exposure Bias
0 EV
At 500mm hand held you should aim for a speed at least equalling the focal length, i.e. 1/500 at 500mm. With a crop camera you need to increase the shutter speed by the crop factor. By using a tripod you can reduce this figure of course, to be honest, I have never tried a 500mm on a monopod (as you have here) but I feel it would have to be quite sturdy and strong to cope with a 500mm. Having said that, they are used a lot at sports events so I'll leave that for someone with experience of monopods to comment, but generally you need more movement for birds, especially if you are going after them in fight, and so I can only advise that a tripod with a gimbal type head is preferable. Birds make very quick movements even when sitting apparently still, you do need a fast shutter speed to stop these movements, rarely do I come below 1/500 on small birds, maybe a bit slower on larger birds when conditions and poor light doesn't allow fast speeds. Always focus on the eye to get the best out of an image.
You could have reduced your aperture and increased the shutter speed, or even increased the ISO by a stop or two and increased the shutter speed even more. Not being a Nikon user I am not conversant with your camera or lens model so cant be more specific about how fast the lens is or how your camera handles high ISO's.
I hope this helps.