How to fix error BCE0089:?

I'm making a zombie apocalypse game and I got the error message when I was trying to make a zombie spawner: Assets/Scripts/'Spawner'.js(16,10): BCE0089: Type 'Spawner' already has a definition 'Start()'. The exact line of code is:

function Start()

All of the code is:

 #pragma strict
 
 function Start () {
 
 }
 
 function Update () {
 
 } // The object to be spawned
 var SpawnObject : GameObject;
 
 // in seconds
 var SpawnStartDelay : float = 0;
 var SpawnRate: float = 5.0;
 
 function Start()
 {
     InvokeRepeating("Spawn", SpawnStartDelay, SpawnRate);
 }
 
 // Spawn the SpawnObject
 function Spawn()
 {
     Instantiate(SpawnObject, transform.position, transform.rotation);
 }

(I copied the code from here:http://www.instructables.com/id/Intro-to-Unity/step11/Spawning-Zombies/) Sorry if the answer is really simple i'm kinda new to unity. Thanks in advance:)