Instructions
Make the spreaders less comfortable for the bird. Drape a net with large round buoys over the spreader. The net will keep the buoys down, and the buoys will discourage birds from landing since they will slide off the round buoys.
Make the spreaders a little more scary for the birds. Tie a long strip of very light cloth every 3 or 4 inches. This cloth will naturally move with even the slightest breeze and keep the spreaders from looking like a calm comfortable place to perch.
Keep the deck of your boat busy. Birds are naturally fearful of people. While some seagulls have overcome this fear, keeping the deck full of movement will keep most birds off the spreaders of your boat.
Keep your spreaders tied up close to the center of the boat. Use the rig set up for your spreaders and keep them close to the center of the boat. This will make them look less appealing to birds since they will appear to be part of the larger components of your sails.
Install a sonic antenna. These special antennae will transmit an annoying sound to the bird and keep them away from the spreaders.