Animating an arc

I'm trying to animate a bird moving from one location to another in an arc.

I based my code off the answer to this question: http://answers.unity3d.com/questions/11184/moving-player-in-an-arc-from-startpoint-to-endpoin.html

The problem at the moment is that the animation isn't all that smooth - it starts really quickly and disappears from view but then takes a long time to fly down to the ground at the end. I thought it would just be linear but perhaps I'm not understanding something... Any ideas?

Thanks in advance, sorry if this is a pretty basic question.

 function moveBird() {
 
     var t : float;
 
     for (t = 0.0f; t < 1.0f; t += Time.deltaTime / animTime) {
         
         // calculate straight-line lerp position:
         var currentPos = Vector3.Lerp(startMarker.position, endMarker.position, t);
 
         // add a value to Y, using Sine to give a curved trajectory in the Y direction
         currentPos.y += trajectoryHeight * Mathf.Sin(Mathf.Clamp01(t) * Mathf.PI);
 
         // finally assign the computed position to our gameObject:
         transform.position = currentPos;
         
         yield;
 
     }    
 
 }