diff --git a/app/src/main/java/com/danilafe/fencelessgrazing/CollarListActivity.kt b/app/src/main/java/com/danilafe/fencelessgrazing/CollarListActivity.kt
index 5ca61b4..ee217b4 100644
--- a/app/src/main/java/com/danilafe/fencelessgrazing/CollarListActivity.kt
+++ b/app/src/main/java/com/danilafe/fencelessgrazing/CollarListActivity.kt
@@ -2,19 +2,35 @@ package com.danilafe.fencelessgrazing
 
 import androidx.appcompat.app.AppCompatActivity
 import android.os.Bundle
+import android.widget.Toast
 import androidx.preference.PreferenceManager
 import androidx.recyclerview.widget.DividerItemDecoration
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.RecyclerView
+import com.android.volley.RequestQueue
+import com.android.volley.Response
+import com.android.volley.toolbox.Volley
+import com.danilafe.fencelessgrazing.model.CollarSummary
+import com.danilafe.fencelessgrazing.requests.CollarRequest
 import org.osmdroid.config.Configuration
 import org.osmdroid.tileprovider.tilesource.TileSourceFactory
+import org.osmdroid.util.GeoPoint
 import org.osmdroid.views.MapView
+import org.osmdroid.views.overlay.Marker
 
 class CollarListActivity : AppCompatActivity() {
 
-    private lateinit var token: String
+    // The list of collar summaries and its list adapter.
+    private val summaries : MutableList<CollarSummary> = mutableListOf()
     private lateinit var summaryAdapter: CollarSummaryAdapter
+
+    // The API token and request queue.
+    private lateinit var token: String
+    private lateinit var queue: RequestQueue
+
+    // The OpenStreetMap map.
     private lateinit var map: MapView
+    private val collarOverlays: MutableMap<Int, Marker> = mutableMapOf()
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
@@ -27,14 +43,15 @@ class CollarListActivity : AppCompatActivity() {
         val collarList: RecyclerView = findViewById(R.id.collarSummaryList)
         val layoutManager = LinearLayoutManager(collarList.context)
         token = intent.getStringExtra("token")!!
-        summaryAdapter = CollarSummaryAdapter(collarList.context, getString(R.string.apiUrl), token)
+        summaryAdapter = CollarSummaryAdapter(summaries)
         map = findViewById(R.id.map)
         map.setTileSource(TileSourceFactory.MAPNIK)
+        queue = Volley.newRequestQueue(this)
 
         collarList.adapter = summaryAdapter
         collarList.layoutManager = layoutManager
         collarList.addItemDecoration(DividerItemDecoration(collarList.context, layoutManager.orientation))
-        summaryAdapter.triggerRefresh()
+        triggerRefresh()
     }
 
     override fun onResume() {
@@ -47,4 +64,41 @@ class CollarListActivity : AppCompatActivity() {
         map.onPause()
     }
 
+    private fun triggerRefresh() {
+        val request = CollarRequest(getString(R.string.apiUrl), token,
+            Response.Listener {
+                summaries.clear()
+                summaries.addAll(it)
+                summaryAdapter.notifyDataSetChanged()
+                updateMapOverlay()
+            },
+            Response.ErrorListener {
+                Toast.makeText(this, "Failed to retrieve collar list!", Toast.LENGTH_SHORT).show()
+            }
+        )
+        queue.add(request)
+    }
+
+    private fun updateMapOverlay() {
+        val currentSet = mutableSetOf<Int>()
+        summaries.forEach {
+            // Create or update overlay
+            val overlay = collarOverlays[it.id] ?: Marker(map)
+            overlay.title = it.name
+            overlay.position = GeoPoint(it.pos.longitude.toDouble(), it.pos.latitude.toDouble())
+
+            // Store new / existing overlay.
+            if(!collarOverlays.containsKey(it.id)) map.overlays.add(overlay)
+            collarOverlays[it.id] = overlay
+            currentSet.add(it.id)
+        }
+
+        val previousSet = collarOverlays.keys
+        previousSet.forEach {
+            if(!currentSet.contains(it)) {
+                map.overlays.remove(collarOverlays[it])
+                collarOverlays.remove(it)
+            }
+        }
+    }
 }
diff --git a/app/src/main/java/com/danilafe/fencelessgrazing/CollarSummaryAdapter.kt b/app/src/main/java/com/danilafe/fencelessgrazing/CollarSummaryAdapter.kt
index b20caf1..9611a8f 100644
--- a/app/src/main/java/com/danilafe/fencelessgrazing/CollarSummaryAdapter.kt
+++ b/app/src/main/java/com/danilafe/fencelessgrazing/CollarSummaryAdapter.kt
@@ -12,9 +12,7 @@ import com.danilafe.fencelessgrazing.model.CollarSummary
 import com.danilafe.fencelessgrazing.requests.CollarRequest
 
 class CollarSummaryAdapter(
-    private val context: Context,
-    private val baseUrl: String,
-    private val token: String
+    private val items : List<CollarSummary>
 ) : ListAdapter<CollarSummary, CollarViewHolder>(DiffCallback()) {
 
     class DiffCallback : DiffUtil.ItemCallback<CollarSummary>() {
@@ -25,9 +23,6 @@ class CollarSummaryAdapter(
             = oldItem == newItem
     }
 
-    private val requestQueue = Volley.newRequestQueue(context)
-    private val items = mutableListOf<CollarSummary>()
-
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CollarViewHolder {
         val layout = LayoutInflater.from(parent.context).inflate(viewType, parent, false)
         return CollarViewHolder(layout)
@@ -43,18 +38,5 @@ class CollarSummaryAdapter(
 
     override fun getItemCount(): Int = items.size
 
-    fun triggerRefresh() {
-        val request = CollarRequest(baseUrl, token,
-            Response.Listener {
-                items.clear()
-                items.addAll(it)
-                notifyDataSetChanged()
-            },
-            Response.ErrorListener {
-                Toast.makeText(context, "Failed to retrieve collar list!", Toast.LENGTH_SHORT).show()
-            }
-        )
-        requestQueue.add(request)
-    }
 
 }
\ No newline at end of file