Apparently this has already been done, but here's my attempt anyway. I can't reproduce the original book material as there's no open use license for it, so if you want to know the background of this weird beast, look it up in the references I've given above.
Expanded Race - Duck
Racial Traits and Abilities
Water Affinity - Ducks are naturally at home in and around water, which is where they spend most of their time. They have learned to move stealthily in and around such bodies of water, and as such gain a +2 bonus to such attribute checks. Sentient ducks, whilst at home in the water, are expert boatmen and gain a +4 bonus to any attribute checks involving boats and small watercraft, such as Intelligence checks for boating knowledge or Dexterity checks for handling boats. This bonus does not extend to handling ships. Ducks may also swim in any situations with a +12 bonus to their Strength attribute check. Diving below the surface is also possible; ducks may remain underwater for up to 2 plus 2 times their Constitution modifier in rounds without the need for a Constitution check, in addition to a +6 bonus to Constitution saving throws against drowning.
Ungainly - The webbed feet and hands of the duck, whilst useful for swimming, present some problems for athletic feats. A duck suffers a -4 penalty to attribute checks for climbing or scaling, and a -2 penalty for attribute checks for jumping or leaping. A -1 penalty is also applied when the duck makes a Dexterity saving throw where leaping out of the way of a trap, breath weapon or similar is required.
Fast Talk (Charisma) - Ducks are renowned for talking quickly and confusingly. Duck logic, it seems, is almost irrefutable - but it's all a ruse. Oftentimes the person at which a duck talks is simply baffled by what's being said, and goes along with it to avoid appearing foolish in front of such an odd creature. Once per round, a duck may use this ability to try to persuade or dissuade someone into doing something. If the target fails an Intelligence saving throw (CL 3), they will go along with reasonable instructions, unless this is clearly philosophically or morally unappealing to their nature.
Languages - Duck, Common, Dwarf, Elf, Gnome, Halfling, Sylvan.
Size - Small.
Movement - 20 feet.
Typical Classes - Assassin, Druid, Illusionist, Ranger, Rogue.
Attribute Modifiers - -1 Charisma, +1 Constitution, +1 Dexterity, -1 Strength.
Ranger Modifiers - +2 Conceal, +2 Move Silent, -4 Scale
Rogue and Assassin Modifiers - -4 Climb, +2 Hide, +2 Move Silent