sys.platform does not start with 'bsd' on any of the BSDs implementing
kqueue.

Use an explicit enumeration of those that do (at least in recent
releases).
diff --git a/src/watchdog/utils/platform.py b/src/watchdog/utils/platform.py
index cc46192..fc4527d 100644
--- a/src/watchdog/utils/platform.py
+++ b/src/watchdog/utils/platform.py
@@ -33,7 +33,7 @@
         return PLATFORM_DARWIN
     elif sys.platform.startswith('linux'):
         return PLATFORM_LINUX
-    elif sys.platform.startswith('bsd'):
+	elif sys.platform.startswith(('dragonfly', 'freebsd', 'netbsd', 'openbsd', )):
         return PLATFORM_BSD
     else:
         return PLATFORM_UNKNOWN