ERROR:Assets/Scripts/BirdMovment.cs(10,13): error CS0246: The type or namespace name `NavMeshAgent' could not be found.

Hello,

I'm lost.

After writing:

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class BirdMovment : MonoBehaviour {

[SerializeField]
private Transform target;

private NavMeshAgent birdAgent;
private Animator birdAnimator;

// Use this for initialization
void Start () {
    birdAgent = GetComponent<NavMeshAgent>();
    birdAnimator = GetComponent<Animator>();

}

// Update is called once per frame
void Update () {
    // Set the birds destination
    birdAgent.SetDestination(target.position);

    // Measure the magnitude of the nave mesh agents velocity
    float speed = birdAgent.velocity.magnitude;

    // Pass the velocity to the animator componenet
    birdAnimator.SetFloat ("speed", speed);
}

}

I get the error:

Assets/Scripts/BirdMovment.cs(10,13): error CS0246: The type or namespace name NavMeshAgent' could not be found. Are you missingUnityEngine.AI' using directive?

I noticed a pop up for a brief moment when returning to Unity to run the scene, and chose not to add the UnityEngine.AI. But I've looked around on google and I don`t know how to add that back into Unity. Or is that something that can be added? Or is the NavMeshAgent the issue?

Any help is much appreciated!