Help on specific spawn position for a single prefab

Hi I am having real trouble trying to figure this out at the moment I have a script which allows me to be able to insert as many enemy prefabs in to the inspector and will allow me to spawn them within a local boundary, my problem is I have to brefabs one which is a butterfly and a bird, the butterfly is fine and that needs to be able to spawn anywhere in the local boundary but I need a way to be able to spawn the bird randomly but no lower than 5 in the y-axis, can anyone help, be much appreciated as im racking my brian round it, I know its probably some think simple that im over looking but any help would be great, THANKS.

using UnityEngine;
using System.Collections;

public class EnemySpawnerController : MonoBehaviour {

	private Collider collider;

	int hazardCount;
	public int hazardCountMax;
	public int hazardCountMin;

	int WaveWait;
	public int WaveWaitMin;
	public int WaveWaitMax;

	float WaitMax =10f;
	float WaitMin = 5f;

	public float spawnWait;

	public float SpawnValueX;
	public GameObject[] EnemyPrefabs;
	void Start () 
		collider = GetComponent<Collider> () as Collider;
		StartCoroutine (SpawnWaves ());
	// Update is called once per frame
	void Update () 

	private Vector3 MakeRandomSpawnPosition()
		Vector3 local = collider.transform.position;
		local.x = SpawnValueX - (collider.transform.localScale.x/2);
		local.y = Random.Range(local.y, local.y + collider.transform.localScale.y) - (collider.transform.localScale.y /2);
		local.z = 0f;//Random.Range(local.z, local.z + collider.transform.localScale.z) - (collider.transform.localScale.z /2);
		return local;

	IEnumerator SpawnWaves ()
		float currentWait = Random.Range (WaitMin, WaitMax);
		WaveWait = Random.Range (WaveWaitMin, WaveWaitMax);
		hazardCount = Random.Range (hazardCountMin, hazardCountMax);

		yield return new WaitForSeconds (currentWait);
		while (true)
			for (int i = 0; i < hazardCount; i++)
				GameObject gameObjectInstance = MakeRandomGameObject(MakeRandomSpawnPosition());
				//Instantiate (enemyPrefab, spawnPosition, spawnRotation);
				yield return new WaitForSeconds (spawnWait);
			yield return new WaitForSeconds (WaveWait);

	private GameObject MakeRandomGameObject(Vector3 position)
		GameObject enemyPrefab = EnemyPrefabs[Random.Range(0, EnemyPrefabs.Length)];

		Vector3 spawnPosition = MakeRandomSpawnPosition();	
		Quaternion spawnRotation = Quaternion.identity;
		GameObject gameObjectInstance = Instantiate(enemyPrefab, spawnPosition, Quaternion.identity) as GameObject;
		return gameObjectInstance;

	void OnTriggerExit (Collider other)
		if (other.gameObject.tag == "Enemy") 
			Destroy (other.gameObject);
		else if(other.gameObject.tag == "PickUp")
			Destroy (other.gameObject);

What you are looking for is a randomizer. Randomizers can help bring your game to life and help create unpredictablility which replicates that of A.I. decisions.

// Create a random position for the game object
// For now I'll just use the transform.position but you could create a new vector 3
Vector3 position = transform.position;

// Generate a random range for the position of your object on the X and Y axis (you could also use the Z axis), this  could will generate a random number between 1 and 5. If you want different ranges/bounds you can modify them and even include negative numbers
float x = Random.Range(0, 5f);
float y = Random.Range(0, 5f);

// Add the random values to the position
position.x = x;
position.y = y;

// Update the transform position
// It's best to use a new variable for C# because you cannot directly modify the transform position
transform.position = position;

Just be careful with randomizers. They can get slightly resource demanding. I would only use it in the “Start()” call when instantiating an object. But doing that should allow your objects to spawn randomly.

have a look at Mathf.Clamp function also