Investigate at an electronic store. Nanny cams are very popular! The set-up can be very simple to very elaborate. You have to decide...do you want to record or do you want to observe. Your not "mad"! It is a great idea. The possibilities if what you could learn are endless.
Looking to do the same also.. My 2 Rollers always fly around my home 2/3 x's then diappear for 2-4 hours. They will return for alittle then again disappear. The other day they came home with a stray.. Like to see where they are picking up there friends from lol..
You'll have some technical problems though.
Range - wireless cameras do have 30~200 m transmission range. The bigger the range, the more power required. More power=more weight.
If you plan to use it only for recording without transmitting live, you could use one of these cell phones to record and/or even transmit images but there is and issue with quality and speed.