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);
         }
     }
 }