Camera traps in the tropics: no detection of wildlife visits

Hello everyone,

I'm Patrícia and I'm currently working as a reseach assistant in Príncipe island. One of my tasks here is to use artificial nests to understand how introduced mammals (i.e. Mona monkeys, african civets, rats, feral cats, etc) might be impacting a critically endangered endemic bird species. We are placing camera traps facing the nests to record visitors and predation events, however, the camera traps are not working properly. They take photos of us during instalation and when we go back to get them but not of anything in between (and we know something should be recorded because eggs disappear, nests are found on the ground, etc). 

Does anyone have an idea of why this can be happening? I thought it might've been due to camera or nest position (i.e. exposure to sun so the difference in temperature might not be enough to trigger the camera) but cameras and nests are in shaded/not under direct sunlight areas. I also put the sensor on high.

We are using the Bushnell trophy cam HD model 119776

Thank you!