sebastian, from what i have heard, anhinga trail has nothing but mosquitos right now!! and very hot!! hopefully some locals will chime in and help you out. i understand there is a bird rehab center just south of key largo that holds lots of pelicans. may be worth checking out.
I didn't see your question here at BPN until just now..so I'll paste in the reply that I gave to you over at NSN in case it helps others here as well.
Sebastian, you are not going to find a lot of wildlife at Anhinga Trail this time of year. It's amazing how the wildlife spreads out during the wet season (right now). Just out of curiosity I went by on Saturday. I didn't see a single heron, anhinga, cormorant, etc. In fact the only birds that I saw were a few crows in the parking lot. I did see a couple alligators, but they are also spread out right now and not as easy to spot. The mosquitoes were present but bearable at Anhinga Trail. Farther down the park road they were everywhere and really tough to ignore. If you venture into the park I highly recommend long pants, long-sleeves, gloves, and head net.
I know that you will find ways to enjoy your visit, but it will be tougher right now than during the dry season (approximately Nov-May). I suggest you visit Green Cay and Wakodahatchee north of Ft. Lauderdale...as well as Loxahatchee National Wildlife Refuge. Those spots are all fairly productive right now. The Florida Keys can also be quite nice. No matter where you go you can expect hot and humid weather, and big afternoon thunderstorm most afternoons. Good luck!!