_DIR_ is also not available in older versions of PHP and then there is a nasty bug in the loaded file (line 183) causing the whole WordPress to crach.
Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM in /mnt/XXXXX/htdocs/blog/wp-content/plugins/sightings/theme-files/shortcode-sightings-map.php on line 183
Have to ask my hosting service how to upgrade the PHP
