Can the microphone in your design be replaced

A: Yes, any mic will work. Mics can be optimized for specific goals. The Knowles mic element we recommend for avian night flight call recording has a freqency response that is optimized for picking up the flight calls of most night-migrating songbirds in North America. It has a 12 dB per octave rolloff below 2kHz. This is very useful for limiting wind thumping, jet, and auto noise resulting in a cleaner signal for the 100 or so night-migrating birds that have flight calls above 2 kHz. Almost all commercially available mics such as the one you mention have much better low frequency response. But those won't be as functional for recording night migrating songbirds for most rooftop microphone location. They would work just fine if the mic is located in a sheltered, wind-free location or on nights with light winds. But imagine a 20 mph wind directly buffeting a microphone. Even in the flowerpot protective structure, wind noise would be a significant issue.

A higher end mic with flatter frequency response will provide a more accurate sound recording if you want to record birds in the woods and listen back for enjoyment but, as mentioned, it is not as functional for general avian night flight call recording. If you want to do both, a higher end commercially available mic is certainly one way to go, though the Knowles mic element can be used effectively for recording birdsong in the woods. A benefit of buying a commercially available mic is that is will have more sophisticated electronics that will better at limiting electronic interference. The mic design offered here is about the simplest electronic design possible and was offered to encourage beginners to get involved.

You will also have to consider how you will mount other mics to gain the amplification benefits of the PZM. If you want to amplify the low frequencies equally with the highs, you will need a larger boundary (the breadth of which equal to the length of the lowest freq you want to amplify).