Through my fieldwork in the summer of 2008 and the subsequent work by local staff, the following conclusions can be made:
The batteries (Alkaline D cell) can last around six months given a moderate amount of photos taken each day (around 10-20) and moderate level of resolution (1.1 MB per photo).
The infrared digital camera, or Cabela's Moultrie Spy 4.0-Megapixel Digital Camera with Infrared Flash (http://www.cabelas.com/), can work in very poor weathers (e.g., storms, high moisture).
An infrared flash can minimize theft or damage from people, and avoid game-spooking effects of a standard white flash.
Slight movements of twigs and branches caused by wind do not cause the cameras work, which assures me that the SD cards inside camera will not be occupied by garbage photos. However, birds or insects that quick fly over in front of the camera can cause a camera take empty photos.
Because there is a time-delay between detecting the target by the infrared sensor and taking a photo (about 1 second), it is better to mount the camera at a certain angle or place that maximizes the range of capturing humans or monkeys. The effective range is nearly 100º with a radius of 45 feet.
Better to choose 2GB or 4 GB (I chose 1 GB due to the funding and availability limitations) SD cards to minimize the frequency of downloading data or the risk of losing some data when the card is full. If the resolution of photos is set to low (I set to moderate resolution about 1 MB per photo), much more photos can be stored in one card.
A tree that has a good balance between camouflage and visibility (e.g., over 15 m in height) should be chosen to mount a camera. We put two cameras along one toruist trail for over one week, no theft or vadalism happened.
When it is dark (even at daytime), the cameras will take black and white photos. When it is bright, color photos will be taken.
To monitor monkeys on a certain tree, it is better to mount a camera on another tree nearby and let the camera facing the target area.