diff --git a/engine/src/modules/ecology/ecology_db.gd b/engine/src/modules/ecology/ecology_db.gd
index c544d368..c537cddc 100644
--- a/engine/src/modules/ecology/ecology_db.gd
+++ b/engine/src/modules/ecology/ecology_db.gd
@@ -94,6 +94,7 @@ func add_species(data: Dictionary) -> int:
 		"maturity_age": data.get("maturity_age", 5),
 		"max_age": data.get("max_age", 50),
 		"quality_up_threshold": data.get("quality_up_threshold", 20),
+		"migration_pattern": data.get("migration_pattern", ""),
 	}
 
 	_species[id] = row
diff --git a/engine/src/modules/ecology/fauna.gd b/engine/src/modules/ecology/fauna.gd
index 38c45db7..ce22547a 100644
--- a/engine/src/modules/ecology/fauna.gd
+++ b/engine/src/modules/ecology/fauna.gd
@@ -9,6 +9,8 @@ const LV_SUBSTEPS: int = 3
 const PERTURBATION: float = 0.05
 const MIN_VIABLE_POPULATION: int = 2
 const QUALITY_MISMATCH_TIERS: int = 2
+## Seasonal migration occurs every N turns (approximate season length).
+const SEASONAL_MIGRATION_INTERVAL: int = 12
 const LOOT_DROP_CHANCE: Dictionary = {1: 0.0, 2: 0.0, 3: 0.25, 4: 0.60, 5: 1.0}
 const GRAZING_BY_SIZE: Dictionary = {
 	"tiny": 0.005, "small": 0.01, "medium": 0.02, "large": 0.04, "huge": 0.08,
@@ -24,7 +26,9 @@ func invalidate_region_cache() -> void:
 	_biome_regions.clear()
 
 
-func process_turn(game_map: Variant, ecology_db: Variant, seed: int) -> void:
+func process_turn(
+	game_map: Variant, ecology_db: Variant, seed: int, turn_number: int = 0
+) -> void:
 	rng.seed = seed
 	var lp: Variant = DataLoader.get_land_fauna_params()
 	var mp: Variant = DataLoader.get_marine_fauna_params()
@@ -37,6 +41,8 @@ func process_turn(game_map: Variant, ecology_db: Variant, seed: int) -> void:
 	_process_herbivore_grazing(game_map, ecology_db)
 	_enforce_carrying_capacity(ecology_db, mp)
 	_process_migration(game_map, ecology_db, mp)
+	if turn_number > 0 and turn_number % SEASONAL_MIGRATION_INTERVAL == 0:
+		_process_seasonal_migration(game_map, ecology_db)
 	_process_lair_habitat(game_map, ecology_db, lp)
 
 
@@ -333,7 +339,11 @@ func _find_target(
 			if not game_map.tiles.has(c):
 				continue
 			var ct: Variant = game_map.tiles[c]
-			if not ct.is_water() and ct.biome_id != ob:
+			# Amphibious species can cross land/water boundaries
+			var habitat: String = sp.get("habitat", "terrestrial")
+			if habitat == "amphibious":
+				pass  # amphibious can go anywhere (land or water)
+			elif not ct.is_water() and ct.biome_id != ob:
 				continue
 			if _is_whale(sp) and mp != null:
 				if not ct.is_water() or ct.depth_from_coast < mp.whale_min_depth or ct.depth_from_coast > mp.whale_max_depth or ct.quality < mp.whale_min_quality:
@@ -387,6 +397,58 @@ func _abandon_lair(pos: Vector2i, tile: Variant, ecology_db: Variant) -> void:
 	EventBus.lair_abandoned.emit(pos)
 
 
+# -- Seasonal migration (aerial herd/swarm move to warmer biome) --
+
+func _process_seasonal_migration(game_map: Variant, ecology_db: Variant) -> void:
+	## Seasonal migrants move toward warmer tiles within migration_range.
+	## Simulates flying herds/swarms following temperature gradients.
+	var migrated: Dictionary = {}  # creature_id -> true (prevent double-move)
+	for pos: Vector2i in game_map.tiles:
+		var creatures: Array = ecology_db.get_creatures_on_tile(pos.x, pos.y)
+		for c: Dictionary in creatures:
+			var cid: int = c.get("id", -1)
+			if migrated.has(cid):
+				continue
+			var sp: Dictionary = ecology_db.get_species(c.get("species_id", -1))
+			if sp.is_empty():
+				continue
+			if sp.get("migration_pattern", "") != "seasonal":
+				continue
+			var mrange: int = sp.get("migration_range", 3)
+			var target: Vector2i = _find_seasonal_target(pos, sp, game_map, ecology_db, mrange)
+			if target != Vector2i(-1, -1) and target != pos:
+				ecology_db.update_creature(cid, {
+					"tile_col": target.x, "tile_row": target.y,
+				})
+				migrated[cid] = true
+
+
+func _find_seasonal_target(
+	origin: Vector2i, sp: Dictionary, game_map: Variant,
+	ecology_db: Variant, search_range: int,
+) -> Vector2i:
+	## Find the warmest tile within range that has capacity for this species.
+	var otile: Variant = game_map.tiles.get(origin)
+	if otile == null:
+		return Vector2i(-1, -1)
+	var best: Vector2i = Vector2i(-1, -1)
+	var best_temp: float = otile.temperature
+	for r: int in range(1, search_range + 1):
+		for c: Vector2i in HexUtilsScript.hex_ring(origin, r):
+			if not game_map.tiles.has(c):
+				continue
+			var ct: Variant = game_map.tiles[c]
+			if ct.temperature <= best_temp:
+				continue
+			var count: int = ecology_db.get_creature_count_on_tile(c.x, c.y)
+			var cap: float = sp.get("carrying_capacity", 10.0)
+			if float(count) >= cap:
+				continue
+			best_temp = ct.temperature
+			best = c
+	return best
+
+
 # -- Biome region cache (flood-fill connected same-biome tiles) --
 
 func _rebuild_biome_regions(game_map: Variant) -> void:
diff --git a/engine/src/modules/ecology/water_body_finder.gd b/engine/src/modules/ecology/water_body_finder.gd
index ee3af766..bb28db22 100644
--- a/engine/src/modules/ecology/water_body_finder.gd
+++ b/engine/src/modules/ecology/water_body_finder.gd
@@ -75,15 +75,19 @@ static func identify_water_bodies(
 		# Store in ecology_db
 		ecology_db.add_water_body(body.id, body.type, body.size, body.tiles.size())
 
-		# Set water_body_id on each tile in this body
+		# Set water_body_id and water_body_type on each tile
 		for tile_pos: Vector2i in body.tiles:
 			var tile: Variant = game_map.tiles.get(tile_pos)
 			if tile != null:
 				tile.water_body_id = body.id
+				tile.water_body_type = body.type
 
 	# Compute depth_from_coast for all water tiles
 	_compute_depth_from_coast(game_map, water_bodies, ecology_db)
 
+	# Detect river mouths: ocean tiles at depth <= 1 adjacent to river tiles
+	_detect_river_mouths(game_map, water_bodies)
+
 	return water_bodies
 
 
@@ -152,3 +156,42 @@ static func _compute_depth_from_coast(
 
 		# Store in ecology_db
 		ecology_db.add_water_body_tile(body_id, pos.x, pos.y, depth)
+
+
+## Detect river mouths: ocean/sea tiles at depth <= 1 with adjacent river tiles.
+## Sets is_river_mouth = true on qualifying tiles.
+static func _detect_river_mouths(
+	game_map: Variant,
+	water_bodies: Array,
+) -> void:
+	# Build set of river tile positions
+	var river_positions: Dictionary = {}
+	for wb: Variant in water_bodies:
+		if wb.type == "river":
+			for pos: Vector2i in wb.tiles:
+				river_positions[pos] = true
+
+	# Also consider land tiles with river_edges as river-adjacent
+	for pos: Vector2i in game_map.tiles:
+		var tile: Variant = game_map.tiles[pos]
+		if not tile.river_edges.is_empty():
+			river_positions[pos] = true
+
+	if river_positions.is_empty():
+		return
+
+	# Check ocean tiles at depth <= 1 for river adjacency
+	for wb: Variant in water_bodies:
+		if wb.type != "ocean":
+			continue
+		for pos: Vector2i in wb.tiles:
+			var tile: Variant = game_map.tiles.get(pos)
+			if tile == null or tile.depth_from_coast > 1:
+				continue
+			var nbs: Array[Vector2i] = (
+				game_map.get_valid_neighbor_positions(pos)
+			)
+			for nb: Vector2i in nbs:
+				if nb in river_positions:
+					tile.is_river_mouth = true
+					break