From Youtube:

I filmed this from my office window. I had seen a huge flock of birds moving across the sky to the west, in the distance. By the time my camcorder had powered up, they were gone, but I picked up something else moving across the sky. This is looking out towards Baldonnel (Casement) aerodrome just west of Dublin, and Im thinking it may be an aircraft silhouette at an unusual angle. The fade at the end would suggest a shadow being blocked by a cloud.