What kind of skateboard should you get for optimal birding?

You want to get a basic "street board". That is the kind with an upward slope on both ends. Usually about 8" wide by 32" long. If you don't care about fancy artwork you can get a basic plain wood deck for about $20. Basic metal trucks are about $20 each. The most important detail is the wheels. The Ballona Creek path is made of pretty rough asphalt so you want to get soft wheels. Softer wheels will slow you down a bit but they give you a MUCH smoother and more comfortable ride when the ground is rough. Hardness is measured in "duro" and you want to stay in the upper 70's. My wheels are 78. Most skate shops will let you pick your component parts and they will build it for you right there for no extra charge.