diff --git a/gerbil-manager-web/e2e/bestand.spec.ts b/gerbil-manager-web/e2e/bestand.spec.ts
new file mode 100644
index 0000000..acdf559
--- /dev/null
+++ b/gerbil-manager-web/e2e/bestand.spec.ts
@@ -0,0 +1,29 @@
+/** BESTAND-FILTER: die Tiere-Liste zeigt standardmäßig nur den eigenen Bestand. */
+import { de, expect, gotoSection, skipUnlessMock, test } from './fixtures'
+
+const t = de.pages.gerbils
+
+test('Tiere-Liste blendet externe Ahnen standardmäßig aus', async ({ page }) => {
+  skipUnlessMock()
+  await gotoSection(page, de.nav.gerbils)
+  await expect(page.getByRole('heading', { name: t.title, exact: true })).toBeVisible()
+
+  // Bestand ist sichtbar …
+  await expect(page.locator('.gerbil-row', { hasText: 'Krümel' })).toBeVisible()
+  // … aber die externe Ahne „Max“ (isResident=false) nicht.
+  await expect(page.locator('.gerbil-row', { hasText: 'Max' })).toHaveCount(0)
+})
+
+test('Toggle „Externe Ahnen einblenden“ zeigt externe Tiere mit Extern-Markierung', async ({ page }) => {
+  skipUnlessMock()
+  await gotoSection(page, de.nav.gerbils)
+  await expect(page.locator('.gerbil-row', { hasText: 'Krümel' })).toBeVisible()
+
+  await page.getByRole('checkbox', { name: t.filters.showExternal }).check()
+
+  const maxRow = page.locator('.gerbil-row', { hasText: 'Max' })
+  await expect(maxRow).toBeVisible()
+  await expect(maxRow.getByText(t.externalBadge, { exact: true })).toBeVisible()
+  // Der Bestand bleibt weiterhin sichtbar.
+  await expect(page.locator('.gerbil-row', { hasText: 'Krümel' })).toBeVisible()
+})
diff --git a/gerbil-manager-web/e2e/mock-data.ts b/gerbil-manager-web/e2e/mock-data.ts
index 129874e..f481ba1 100644
--- a/gerbil-manager-web/e2e/mock-data.ts
+++ b/gerbil-manager-web/e2e/mock-data.ts
@@ -88,6 +88,8 @@ function gerbil(
     nameSearch: name.toLowerCase().replace(/[\s._-]/g, ''),
     genotype,
     notes: null,
+    // BESTAND-FILTER: default = eigener Bestand; einzelne externe Ahnen unten gesetzt.
+    isResident: true,
   }
 }
 
@@ -110,8 +112,9 @@ export function seedDb(): MockDb {
     gerbil('greta', 'Greta', 'female', '2019-05-23', null, 'cv-schwarz'),
     gerbil('frieda', 'Frieda', 'female', '2020-01-18', null, 'cv-gold'),
     gerbil('emil', 'Emil', 'male', '2017-03-03', 'w-emil', 'cv-agouti'),
-    gerbil('hilde', 'Hilde', 'female', '2017-11-11', null, 'cv-schwarz'),
-    gerbil('max', 'Max', 'male', '2015-08-08', null, 'cv-agouti'),
+    // BESTAND-FILTER: externe Ahnen (Gründertiere fremder Zuchten, nur für den Stammbaum).
+    { ...gerbil('hilde', 'Hilde', 'female', '2017-11-11', null, 'cv-schwarz'), isResident: false, originBreeder: 'Zoohandlung Meier' },
+    { ...gerbil('max', 'Max', 'male', '2015-08-08', null, 'cv-agouti'), isResident: false, originBreeder: 'Zoohandlung Meier' },
     // Statistik: Verstorbene + Abgegebene für Verluste/Bestandskurve
     { ...gerbil('willi', 'Willi', 'male', '2019-09-09', null, 'cv-schwarz'), status: 'Deceased', dateOfDeath: '2022-04-04' },
     { ...gerbil('rosa', 'Rosa', 'female', '2020-02-02', null, 'cv-gold'), status: 'Deceased', dateOfDeath: '2023-08-15' },
diff --git a/gerbil-manager-web/src/api/types.ts b/gerbil-manager-web/src/api/types.ts
index bcd7f6f..40024b2 100644
--- a/gerbil-manager-web/src/api/types.ts
+++ b/gerbil-manager-web/src/api/types.ts
@@ -47,6 +47,13 @@ export interface Gerbil {
    */
   characterTraits?: string[] | null
   characterNote?: string | null
+  /**
+   * Residency (Bestand): true = part of the own clan (Kleine Chaoten), false =
+   * external/pedigree-only ancestor imported for the Stammbaum. Gridify-filterable
+   * (`isResident==true`); the Tiere list defaults to resident-only. Absent = treat
+   * as resident (backend default true).
+   */
+  isResident?: boolean
 }
 
 /** Payload for POST /gerbils. */
@@ -68,6 +75,7 @@ export interface CreateGerbil {
   notes?: string | null
   characterTraits?: string[] | null
   characterNote?: string | null
+  isResident?: boolean
 }
 
 /** Payload for PUT /gerbils/{id} (all optional / partial update). */
diff --git a/gerbil-manager-web/src/index.css b/gerbil-manager-web/src/index.css
index f382e0c..2dbc2d4 100644
--- a/gerbil-manager-web/src/index.css
+++ b/gerbil-manager-web/src/index.css
@@ -330,6 +330,24 @@ textarea {
   color: #3a6ea5;
 }
 
+/* BESTAND-FILTER: subtle marker for external (non-Bestand) animals. Inline next
+   to the name, so it should not be pushed to the grid edge like the status badge. */
+.badge--external {
+  justify-self: start;
+  margin-left: 0.4rem;
+  vertical-align: middle;
+  background: #f0f0f0;
+  color: #777;
+  border: 1px dashed #bbb;
+}
+
+/* Checkbox-style filter (label text + box on one row), vs. the stacked .field. */
+.field--check {
+  flex-direction: row;
+  align-items: center;
+  gap: 0.4rem;
+}
+
 @media (min-width: 768px) {
   .gerbil-card {
     grid-template-columns: 2fr 1fr 1.5fr 1fr auto;
@@ -741,4 +759,4 @@ textarea {
   border-radius: 50%;
   object-fit: cover;
   border: 2px solid var(--color-border);
-}
+}
diff --git a/gerbil-manager-web/src/pages/GerbilDetailPage.tsx b/gerbil-manager-web/src/pages/GerbilDetailPage.tsx
index c5b2b82..b8208e7 100644
--- a/gerbil-manager-web/src/pages/GerbilDetailPage.tsx
+++ b/gerbil-manager-web/src/pages/GerbilDetailPage.tsx
@@ -104,6 +104,11 @@ export default function GerbilDetailPage() {
           <GerbilProfilePhoto gerbilId={g.id} />
           <h2>{g.name}</h2>
           <span className={`badge badge--${g.status.toLowerCase()}`}>{statusLabel(g.status)}</span>
+          {g.isResident === false && (
+            <span className="badge badge--external" title={de.pages.gerbils.externalTitle}>
+              {de.pages.gerbils.externalBadge}
+            </span>
+          )}
         </div>
         <div className="head-actions">
           <Link to={`/rennmaeuse/${g.id}/bearbeiten`} className="btn btn--primary">
diff --git a/gerbil-manager-web/src/pages/GerbilsPage.tsx b/gerbil-manager-web/src/pages/GerbilsPage.tsx
index 5044ea2..9d90657 100644
--- a/gerbil-manager-web/src/pages/GerbilsPage.tsx
+++ b/gerbil-manager-web/src/pages/GerbilsPage.tsx
@@ -32,6 +32,8 @@ export default function GerbilsPage() {
   const [gender, setGender] = useState<Gender | ''>('')
   const [colorVarietyId, setColorVarietyId] = useState('')
   const [originBreeder, setOriginBreeder] = useState('')
+  // BESTAND-FILTER: default to the own clan (Bestand); opt in to external ancestors.
+  const [showExternal, setShowExternal] = useState(false)
   const [sort, setSort] = useState<SortKey>('nameAsc')
   const [page, setPage] = useState(1)
 
@@ -50,6 +52,9 @@ export default function GerbilsPage() {
     gender && condition({ field: 'gender', op: '==', value: gender }),
     colorVarietyId && condition({ field: 'colorVarietyId', op: '==', value: colorVarietyId }),
     originBreeder && condition({ field: 'originBreeder', op: '==', value: originBreeder }),
+    // Default view = own clan (Bestand). Unless "externe Ahnen einblenden" is on,
+    // restrict to resident animals (server-side, so paging/counts stay correct).
+    !showExternal && condition({ field: 'isResident', op: '==', value: true }),
   )
   const orderBy = SORT_ORDER_BY[sort]
   const query: GridifyQuery = { filter: filter || undefined, orderBy, page, pageSize: PAGE_SIZE }
@@ -62,6 +67,7 @@ export default function GerbilsPage() {
     setGender('')
     setColorVarietyId('')
     setOriginBreeder('')
+    setShowExternal(false)
     setPage(1)
     setSort('nameAsc')
   }
@@ -186,6 +192,14 @@ export default function GerbilsPage() {
             <option value="birthAsc">{t.sort.birthAsc}</option>
           </select>
         </label>
+        <label className="field field--check" title={t.filters.showExternalHint}>
+          <span>{t.filters.showExternal}</span>
+          <input
+            type="checkbox"
+            checked={showExternal}
+            onChange={(e) => onFilterChange(setShowExternal)(e.target.checked)}
+          />
+        </label>
         <button type="button" className="btn" onClick={resetFilters}>
           {t.filters.reset}
         </button>
@@ -234,7 +248,14 @@ export default function GerbilsPage() {
                 aria-label={g.name}
               />
               <Link to={`/rennmaeuse/${g.id}`} className="gerbil-card">
-                <span className="gerbil-card__name">{g.name}</span>
+                <span className="gerbil-card__name">
+                  {g.name}
+                  {g.isResident === false && (
+                    <span className="badge badge--external" title={t.externalTitle}>
+                      {t.externalBadge}
+                    </span>
+                  )}
+                </span>
                 <span className={`badge badge--${g.status.toLowerCase()}`}>
                   {statusLabel(g.status)}
                 </span>
diff --git a/gerbil-manager-web/src/strings/de.ts b/gerbil-manager-web/src/strings/de.ts
index fd74bf3..d2d3fbe 100644
--- a/gerbil-manager-web/src/strings/de.ts
+++ b/gerbil-manager-web/src/strings/de.ts
@@ -49,6 +49,9 @@ export const de = {
       empty: 'Keine Rennmäuse gefunden.',
       countLabel: 'Tiere',
       searchPlaceholder: 'Name suchen …',
+      // BESTAND-FILTER: Kennzeichnung externer (nicht zum eigenen Bestand gehörender) Tiere
+      externalBadge: 'Extern',
+      externalTitle: 'Externes Tier — gehört nicht zum eigenen Bestand, nur für den Stammbaum erfasst.',
       // Filter-Beschriftungen
       filters: {
         title: 'Filter',
@@ -58,6 +61,9 @@ export const de = {
         all: 'Alle',
         reset: 'Filter zurücksetzen',
         sortBy: 'Sortieren nach',
+        // BESTAND-FILTER: eigener Bestand (Clan) vs. externe Ahnen (nur Stammbaum)
+        showExternal: 'Externe Ahnen einblenden',
+        showExternalHint: 'Tiere aus fremden Zuchten, die nur für den Stammbaum erfasst sind.',
       },
       // Sortier-Optionen
       sort: {