private void ChangePage(ViewModelBase page)
        {
            if (!Pages.Contains(page))
            {
                Pages.Add(page);
            }

            if (page is BirdManagerViewModel)
            {
                BirdManagerViewModel.ResetWorkspace();
            }

            CurrentPage = Pages
                .FirstOrDefault(vm => vm == page);
        }        
 public static void ResetWorkspace()
 {
     _currentWorkspace = null;
 }