I have just set up a birdbox cam this year and there are Blue Tits taking up residence right now; I've attached an almost-live picture to this post (NB: it looks out of focus, but it is in fact about 1AM here and the bird is sleeping/resting with its head tucked away and its feathers fluffed right up.
Anyway, my choice of construction was to use a cheap USB webcam -the cheapness somewhat offset by the expense of other components - USB natively has a maximum cable length of 5m, so I bought a pair of extender units from Lindy.co.uk (
Link to product page ) - one has a USB A plug, the other a USB a socket - the pair of devices are connected together by RJ45 connectors on up to 50m of Cat5 cabling (i.e. a network cable).
I unscrewed the front lens of the camera and popped out the small square plastic IR filter that was sitting in there, then I stripped the external casing off it (it was all on one smallish PCB). I bought a weatherproof project box from Maplin and cut a hole in it, then covered this with a transparent piece of acrylic sheet, cemented with silicone. I cut the USB cable off the camera and shortened it to about 5cm, soldering it back on and heatshrinking the joints. I stripped two low-power IR LEDs out of a couple of old remote control units I got in some box of surplus junk and soldered these together in series with an appropriate resistor to drive them off 5v (I actually backed them off a bit from full output, because I don't want them to fail early); this was connected directly to the +5v and 0v lines of the USB connection at the camera PCB (Probably shouldn't have done that, but what the heck).
I filed the front lenses of the led packages to make them disperse a little more evenly and inserted them facing out of holes drilled in the project box /camera housing, again, sealed with silicone.
The camera PCB was mounted inside the case by custom standoffs made from little bits of plastic pipe and a couple of screws.
I attached a cable gland to the project box and threaded one end of my cat5 cable through it, then added the RJ45 termination (wouldn't thread through the gland with the plug on it), then I plugged the short camera cable into the 'remote' USB transciever, plugged the network cable into this and packed it all inside the project case, which was sealed tight - it had a rubber gasket, but I also gave this, and the cable gland, a good dollop of vaseline for a proper seal. I also popped a sachet of silica gel inside the housing to absorb any errant moisture.
I built a custom birdbox with a false ceiling made of plywood, on top of which the camera assembluy sits, then the roof. It's fixed about 15 feet off the ground to an oak tree in my garden, in the same spot when the old non-camera box previously resided.
Anyway; the cat5 cable was then run down the tree trunk, along a fence, up and through the house wall and across to the computer indoors; terminated with another RJ45 connector and plugged into the 'local' USB transciever, which in turn is plugged into the computer.
The USB transcievers are transparent to the computer, so it just detected the camera and asked for the driver; the rest was pretty easy.
The IR illumination cannot be turned off independently of the camera, as it's powered directly from the USB cable, but that doesn't really matter; in the daytime, a bit of stray light does creep in and colours are discernible, otherwise, it's all monochrome under IR. Pretty much any cheap webcam can be converted to IR sensitive just by popping out the IR filter.