In 65% of cases "startle by" is used
We were both startled by this absence of modeling.
Staring at herself, Eira was startled by the empty, clueless-looking eyes she had.
Especially the one about Mark; I was so startled by it that I got him to repeat it to make sure I had not misunderstood him.
I was startled by the passionate objections of some contributors, when I said I felt that Yorkshire was the most English of all.
One is that a young Tamil (demali) shepherd woman who was carrying a pale of milk from Ambagaha Arawa village to Kiri Kandula village was startled by a nefarious king.
In 16% of cases "startle at" is used
Startled at the disturbance the bear gave chase.
He was startled at the sight of the rod bending so much and started pulling it up.
In 6% of cases "startle in" is used
I imagined myself to be quite alone; but I was startled in the midst of the darkness by a deep sigh.
In 6% of cases "startle out" is used
Startled out of his sleep, Chaton the Cat rushed out of the room and bolted down the stairs as though a thousand demons were at his heels.