iOS line-drawing game Pigs in Trees has received 15 new levels and various gameplay tweaks in an update, bringing the total number of levels up to 60.

Tactile Entertainment's casual hit tasks you with defending a treehouse full of your pig buddies against an aggressive avian attack force as you shoot down wave after wave of birds from your fighter plane.

Enhancing the game’s simple line-drawing gameplay is a plentiful assortment of power-ups and the ability to call on your fellow swine for assistance when things get hectic.

Pigs in Trees is available as a Universal app for iPhone and iPad for 69p/99c.