I work in a nature center. We have PZM-30D mics hooked to an amp and speakers to bring the bird sounds from our feeders outside into the classroom/viewing area. They seem to pick up all the local truck noise from the highway but hardly any of the bird calls. The mics were installed by the designer who built the building. They are in 8-inch square boxes set into the stone walls.
Olewine Nature Center
Reply: Here's a suggestion. Basically you will need to put the mics closer to the birds and make the mics waterproof.
Remove the PZM mic holder from the plate by removing the screws on the bottom of the plate. Purchase another mic cable (say, from Radio Shack) and plug it into the mic to extend the cable length. The mic cable should have a female XLR connector on one end and a male XLR connector on the other end.
Cover the mic and its connector with a thin sandwich bag or Saran Wrap to make it waterproof, and wrap the open end of the bag with electrical tape to seal it to the mic cable. Mount the mic near the bird feeders.