Indian Runner Ducks are often referred to as "upright ducks" as they stand erect and walk in this position (see picture).  They were particularly liked as a breed of duck in the past as they could be herded to market as they can be walked along in a group either to market or better pasture/water.  The duck in the picture is obviously either an Indian Runner or has some Indian Runner in him (he is clearly a drake by the curled tail and markings). 

It is not always guaranteed that an Indian Runner will walk upright though just simply because it is of that breed, nature versus nurture comes into as well.  We once had a duckling who was raised by a standard duck and always walked quite hunched over as he didn't seem to know what to do - his body was designed for upright walking but he would mimic the actions of the other ducks nearby.

Caroline Solly, Rye, UK

Try shouting "Duck" in a loud voice and see if he puts his head down.

He looks to me like he's having a good stretch. He also looks like a normal mallard drake, though ducks are notorious for their promiscuity so it's not impossible that he's a hybrid of some sort - you'd expect him to differ more from his chums if he had dubious parentage though. You don't make it clear whether he always walked like this.

There are records of birds taking funny notions - almost like OCD in humans - but we'd probably need a bit more info to come to conclusions.

I have been visiting Caudwell MIll at Rowsley for 10 years and there have always been some very strange looking ducks there. The local population of mallards have obviously interbred with some exotic ducks and now you see a range of shapes and colours.

The odd-looking duck in the picture is either a domestic runner duck or a hybrid of a wild mallard and a runner duck. Runner ducks are bred to run rather than waddle and have a characteristic upright body stance similar to the pictured duck. This stance is not a behavior but a product of deliberate breeding. It is possible that this duck may be a hybrid because most purebred runner ducks are not this color.