I bought a 08 s40 with 5580 miles on it a little over a week ago and have put 180 miles on it since, most of them city miles.  The oil level was about 1/3 the way up the window when I picked it up and today it was barely at the bottom of the window.  Do I need to be looking for a leak or is this an expected amount of oil loss for this bike?

This is my first motorcycle so I'm learning how engines work and spending a lot of time reading this forum. I'm in Rhode Island and have been riding it in 45-60 degree weather.  

I've searched the forums and not found an answer so if the thread exists please point me in that direction.

The oil level should not change that much after 180 miles of city riding. Make sure the bike is on level ground and straight up and down when you check it. It doesn't take much of a lean to change the level in the site glass. It also makes a little difference if the oil is warmed up or not. It will expand a little bit. If you check it after riding, let it set a couple of minutes for the oil to drain down.

KennyG is right. If you don't know when the last time it was changed or what kind of oil was used, go and change it with Rotella. Write the mileage and date down in a notebook and keep accurate records.

And welcome to the forum  

Kris01 wrote on 10/30/15 at 12:05:35:

Oil level by the owner manual should be measured while held vertical.
But can be measured "on the kickstand" if you can see it and have previously measured it vertical and haven't changed any affecting equipment (tires, shocks, kickstand)

I measure mine with the kick stand on a brick.  This gets it to a vertical enough level.  The brick is probably an inch shorter then needed to get vertical.

Thanks everyone!  This forum is a gold mine of information.  I looked up how to build a stand/lift and how to change the oil. Since I don't know when the last oil change was so I'll do one and put Rotella in it.

Good advice by all
above all, get rid of contaminated oil and get the good stuff (Rotella) in there, god knows what the PO used, and chances are it was not up to par

I might point out that you want to check the oil after the bike has been off and allowed to settle for awhile.  If you check your oil after the bike has been sitting in the garage all night and then check it again after you've just gone for a ride you won't get an accurate read.