Script error: OnCollisionEnter2D This message parameter has to be of type: Collision2D The message will be ignored.

 Vector3 velocity = Vector3.zero;
 public float flapSpeed = 50f;
 public float forwardSpeed = 1f; 

 bool didFlap = false;

 Animator animator;

 bool dead = false;

 // Use this for initialization
 void Start () {
     animator = transform.GetComponentInChildren< Animator >();
     
     if( animator == null )
     { Debug.LogError( "Unable to find Animator!" ); }
 
 }

 //Do Graphic & Input updates here
 void Update(){
     if(Input.GetKeyDown(KeyCode.Space) || Input.GetMouseButtonDown(0)) {
         didFlap = true;

     }
 }
 
 // Do physics engine updates here
 void FixedUpdate () {

     if (dead)
         return;

     gameObject.GetComponent<Rigidbody2D>().AddForce(Vector2.right * forwardSpeed);

     if(didFlap) {
         gameObject.GetComponent<Rigidbody2D>().AddForce(Vector2.up * flapSpeed);
         didFlap = false;
         animator.SetTrigger("DoFlap");

     }

     if(gameObject.GetComponent<Rigidbody2D>().velocity.y >0) {
         transform.rotation = Quaternion.Euler(0, 0, 0);
     }

     if(gameObject.GetComponent<Rigidbody2D>().velocity.y >0) {
         float angle = Mathf.Lerp(0, -25, -gameObject.GetComponent<Rigidbody2D>().velocity.y / 4f );
         transform.rotation = Quaternion.Euler(0, 0, angle);
     }

 }
 void OnCollisionEnter2D(Collider2D collision) {**ERROR**
     animator.SetTrigger("Death");**ERROR**
     dead = true;
 }

}