static int minSpacing(Venue nest, Venue other, Species species) {
    final Species OS = (other instanceof Nest) ?
      ((Nest) other).species : null ;
    int spacing = (species.browser() && OS != null && OS.browser()) ?
      BROWSER_SEPARATION : PREDATOR_SEPARATION ;
    if (species == OS) spacing += SPECIES_SEPARATION ;
    return spacing ;
  }