Trouble with my Trail cams

I need some advice.  Dad and I have 3 trail cameras that are spread throughout our hunting grounds.  In the past, we have seen photos like this:

But now, we are getting photos of the trees.  We have tweaked the timing so they are set for 15 seconds between photos.  We have them where the deer are (as evidence by the tracks) but no photos of deer.  We have them in the same spots we did at some point last year when we got the above photos. So…

What are we doing wrong???