One or two ducks are around the lakes towards Gibbet Hill at the far end of the campus but they don't go across the path. There are some over by Lakeside too, but they're only territorial in mating season and again you'd rarely see them. There's also loads of ways to get around, including a shuttle bus, so you could avoid them completely if you wanted.
As above, so long as you stay clear of Lakeside and the lakes behind Bluebell, Arthur Vick and Jack Martin, you will be absolutely fine . There's the odd one or two straying into library road or over by the maths department, but they move it quickly if they don;t want to be crushed by thousands of stampeding students