I don't see any leaks or signs of oil, but I have to add oil to my car about once a month to bring it to the full level. So the car must be burning the oil right? What causes this? I'm pretty good with the basics but have never experienced this before.

Well depending on how many miles you have, and the condition of your motor, you could be burning it. You might have bad valve guides or other worn components the allow oil into the cumbustion chamber especially when your first start her up.

Check for signs of oil in the cooling system as well.

But, don't rule out a small leak. Valve cover gaskets will often leak only at higher RPM when the oil is pumped to top of engine. It will often burn off as you drive so you won't see spots on the ground.

Look for any work that might have been done on your engine that has an oil seal that may not have been replaced properly (or not at all).

Joe from Scottsdale is correct, was los'in small amt oil between changes on my 84 w/70k , after tightning the valve covers several months ago, oil loss has stopped.