Photo's of birds

[crissyanon]

I have a Nikon D3100 and was using the 55-200 mm AF-S lens to take some pics of Peacocks but was not sure of the best setting to do the job. I heard Aperture Priority setting would be good not not sure if I would need to change other setting. I took the pics in the evening and plan on taking more in the evening to try differnt setting. Any advise would be great!
Another question I have is how can I get the entire bird. When I get close up I start to loose some of the peacock...Is this a lens issue? Is it best to take pics of the bird with some sort of background (tree's, branches)?