more ideas ...
it seems like all you really need is a wireless microphone
, without all the overhead of digital conversions for transmission. The egg listens, the hub records. In other words, you could do this old school
using old-style radios - a pair to transmit and receive the audio directly
This opens the door to many possibilities. Adafruit has several radio options available. Look also at "transceivers" which do both transmit and receive in one device. Even that might be more machinery than you need ! This could be done very simply.
It would be smart to befriend a HAM radio person. Radio amateur clubs and groups are everywhere. (Start here: http://www.arrl.org
) You might be surprised to find some HAMs nearby, even if you live in a remote part of Alaska. Rural and remote locations have more need for communication - HAMs often fill that gap.
You can do the radio approach without a license, but a HAM could assist with technical details. (And I bet they'd be enthusiastic about your idea!)
On this track, here's some things to consider and research:
Wireless microphones are commonly used in sound production on stage or in a studio, or for public speaking, etc. Off-the-shelf versions would probably cost too much ... unless you can find some from Chinese vendors or on Ebay (but buyer beware).
However, you could DYI them inexpensively.
And egg would need only a microphone, battery, and transmitter. The battery would be the largest and, perhaps, most expensive object. A simple, small AM transmitter can be made from just a few components, costing only a few dollars. There are also cheap mics of various kinds ... I found one for <$6 online. It might also be possible to use a piezoelectric microphone, which might be more sensitive - you'd have to experiment. A piezo-mic would have to be glued to the inside of the egg wall. The wall itself then becomes the microphone's diaphragm. (Using an electret mic, also a good option, you'd probably still need to hot-melt glue or epoxy it to the egg wall for proper pick up.)
I'd put the battery on the bottom and mic on top, so the weight of the battery keeps the egg properly oriented. The transmitter, which could be as small as a US Quarter, could go in the middle. It would not need an external antenna if the nests are relatively close - ideally all in line of sight. The antennas of these little transmitters are just a small coil of wire. It could fit in the egg. Range out in the open is easily a few hundred feet. If there are rocks in the way, or the distances are further, you might need several smaller hubs closer in. (This approach is so inexpensive that the cost of the hub boxes and batteries would likely be the bigger factors.)
Each transmitter could be set to its own frequency by merely turning a "trim pot." Before sealing up in the egg, double check it with a listening receiver, tuned to the selected frequency.
The hardest part of this approach is the data-logging hub. You could "multiplex" all the various eggs into one high-speed data logger. But it might be easier, more straight forward, just to have the same number of individual small receivers as egg transmitters - each with their own SD card, putting all the receivers together in one hub box. The receivers and cards would be powered from one common source. The hub would need a bigger battery, and perhaps, ideally have a solar panel to recharge the battery. ( I have no idea how much sun light you'd get up there during the incubation period. Solar panels need a good amount of sun for some hours to convert the light to electricity effectively.) BTW, the SD cards would hold the audio in a directly playable format, e.g. a .wav or .ogg file. I'm uncertain if there are small devices that could take the audio (as audio) from the receiver then record straight (audio) to an SD card. However, there are many options that will convert the audio (Analog to Digital) into .wav or .ogg files. These are cheap too and would merely need some space and power in the hub box(es).
So the path is:Mic->transmitter ---> >--- receiver -> [optionally] A/D conversion -> SD card
for each egg.
The other thing that would have to be determined empirically, experimentally is transmitter power consumption versus battery life. Transmitters tend to be power hungry, but line-of-sight can reduce the requirements. Also these old-school, direct audio transmitters would use less power than the previously considered approach, which needed the added step of A/D conversion in the egg, which, in turn, uses more processing power juice. You'd have to set up a couple of these and just let them transmit and see. Fifteen days in one go might be a lot ... off the top of my head, it seems borderline. Worse case, you'd have to have the battery separately stashed close to the nest with a small power cable snuck in.
You can estimate these consumption specs, if you can figure out how much power the transmitter uses. That's one of the things a HAM can help with.
How close to the rookery is the nearest inhabited area?