Do larger headphones drain an iPod's batteries faster?

Yes, headphones that are louder or have a larger speaker draw more power than the regular iPod headphones do

@jonno are you sure? I thought the ipod limited the output power. For example I must hook up powered speakers to push sound in room speakers.

The total power output is capped at a certain maximum level, but that’s probably not a big factor, since you don’t use headphones at max power. That said, a larger speaker driver will sound quieter than a small speaker driver at a given volume setting, so you’re likely to choose a slightly higher setting to drive the larger speaker. That would use power more quickly, though probably not much more.

smaller earphones, and especially ones with less efficient drivers have high Impedance ratings; the higher the impedance the lower the current (ohm’s law), so check the impedance rating on your earphones; generally 16 Ohms is the standard rating, but lower output earphones (i.e. Those with lower sound output have higher impedance ratings like 32 Ohms.

Not taking voltage into account the general rule of thumb in audio electronics is the lower the impedance the higher the current draw (and higher the power consumption). Many studio grade headphones with the larger drivers are rated at 8 Ohms, and thusly draw a larger current, but as chaosrob mentioned there is a max power output (measured in milliwatts or mW) that is an expression based on power consumption (voltage times current).

Wiki Ohm’s Law for a more in-depth explanation of electrical circuits and power consumption.

Your Bose headphones will be draining the battery more quickly, as the device is allowed to draw as much power as required to operate (within a limit, at which point the iPod would shut off). To be honest, there is unlikely to be a noticeable decrease — probably twenty minutes at the most.