I played with this a bit during lockdown. I can’t call myself a long time camera trap expert but I can at least say my cost analyses are recent. I used two methods: A trailcam, and a Pluto trigger hooked up to an old DSLR with an inexpensive kit lens on it. The trailcam is a longer term solution and has infrared flash built in, and the old DSLR is just to leave out for a few hours in good weather and see if you catch anything cool before the battery runs out. I picked Pluto trigger because I can hook up other sensors to it, so I can do stuff like use multiple motion sensors to reduce false readings, or use a flex sensor to tell if a mammal brushes past a twig, or a water level sensor to detect when someone disturbs the water in a pond.
If you aren’t utilizing existing equipment, in USD I would expect to pay $75 on the very low end and $500 on the very high end, average would be $100-$200. Add the maintenance cost of batteries if you go the trailcam route.
Your big question here is “how are you going to power it?” Do you want to hook up to household power (look at home security cameras if so), run for a month or two on non-rechargeable batteries (look at trailcams and expect to pay a lot for batteries), or a day or so on a charge (the DSLR option, or you may be able to repurpose an old smartphone)?
If you get a trailcam, definitely look for infrared flash. This allows night photography without any disruptive visible light flashes, so you’ll see many more shy mammals. It’s a common feature on trailcams and hard to get otherwise.
If there’s a window where you can place a camera looking over the yard then you might have more options because you wouldn’t need weatherproofing.
Think about placement. If you put a wide angle lens overlooking your whole yard from a high angle you will catch more medium to large mammals, but you won’t be able to identify smaller mammals and birds. Also, smaller mammals at a distance may not set off your motion sensor. If you put the camera lower and closer to a specific area of interest, you can get close up pictures of smaller creatures but you will miss things happening in other areas of the yard.
Be aware that wind in vegetation will trigger a motion sensor, sometimes excessively. It is the single biggest problem with my camera traps - I live in southern CA in a very windy area. Wind triggering can happen due to several different causes:
- Vegetation moves in the motion sensor’s field of view
- Shadows on the ground move in the motion sensor’s field of view
- A shadow falls over the motion sensor itself
- Whatever the camera is fixed to gets moved or jostled, causing the camera itself to move
- On a very hot day, a gust of wind can cause sudden changes in the air temperature, which can actually trigger a PIR (passive infrared) sensor all by itself even though there is no visible change.
Can’t recommend a trailcam that connects to the household wifi and sends pictures, because I didn’t manage to find one! It may be easier with a home security system. I have no outdoor electrical outlets so that wasn’t an option for me.