A: Set the gain and trigger settings on your detectors dependent upon your goal; whether to sample for activity or just confident presence/absence. I don’t like to mess with lots of low quality signals if I just want to get the best files for knowing what’s around and for that purpose I use a gain/trigger combination of 80/200. That seems to work well, but will require a bit of experimentation for different habitats. The higher trigger setting should also make it less sensitive to triggering by noise. Check all the hardware in the mount around the mic and the pole and connections. If anything creaks or slaps it could generate signals that trigger the detector. To get more activity monitoring (but many more lower quality recordings), reduce the trigger setting from 200 to perhaps 120 or 80.
Of course your best solution would involve recording away from the insects or during a season when the insects don’t makes as much sound! This sounds impractical, but should be considered for longer term planning. This complication affects acoustic bat work in many parts of the world and we also suspect that it must also affect the bats, too.
As a compromise the best that you can do involves reducing the trigger sensitivity of the detector. Also, you will gain some improvement by locating the microphone as away from vegetation and the ground as you can to gain some distance from the insect sound sources and get it closer to the bats in the air that can trigger it. Example recording settings:
Gain: 70 or 80 (I typically use 80, but up to 120 when I want to get quieter signals)
Trigger level: 200 (I use 120 in quiet environments)
Trigger Sensitivity (found in the user profile menus): very low (I use medium in quiet environments)

Note: the somewhat mis-representationally named Sensitivity setting controls the duration of the sound that triggers the detector. By setting it to very low you avoid short duration sound sources (like rain drops) from triggering the detector, but “longer” ones like 2ms bat calls will still trigger the unit.

A: Wildlife Acoustics bat detectors allow sampling frequencies of 192kHz, 256kHz or 384kHz. Binary Acoustic Technologies detectors allow sampling frequencies of 250kHz, or 375kHz. And Pettersson detectors allow sampling frequencies of 300kHz, 500kHz, 750kHz or 768kHz.
What does this mean, functionally? Digital sampling takes snapshots of a signal at regular intervals, equivalent to the sampling frequency (e.g., at 500kHz sampling frequency, digitizing the signal occurs 500,000 times a second). But it can’t “see” what happens between those snapshots. According to digital sampling theory, detectors can only resolve real, i.e., non-aliased, sounds up to one half of its sampling rate. This limiting frequency is called the Nyquist frequency. So, for Wildlife Acoustics detectors, that means it can only sample bat calls up to 96kHz, 128kHz, or 192kHz; Binary Acoustics Technology detectors allow resolutions up to 125kHz or ~180kHz; and Pettersson detectors allow resolutions up to 150kHz, 250kHz, 375kHz or 384kHz.
Capturing fully formed bat pulses, with the full upper frequency portions is often essential for species ID, and especially for capturing harmonics. Plus, when sampling a too low a rate, aliasing can occur, creating artifactual harmonics. This can interfere with the original signal and confound analysis. For example, recording bats out west with Wildlife Acoustics detectors at a 192kHz sampling rate can create spurious identification results for Myvo as the aliased signals resulting from a low sampling rate can appear like upsweeps typical of Myvo, when in fact the recording may actually belong to one of 6 other 40kHz Myotis species. Therefore, to render accurate recordings, you should always use the highest sample rate possible, or choose a detector that allows for the highest sample rate.

A: There are several techniques. One of the best is to use a Zoom H2 connected to a Pettersson D240x for manual tracking and reference call collection that can be off-loaded call-by-call to a laptop int he field running SonoBat using the AutoRecorder Utility. To set up the hardware and software properly, follow the directions available at the following link:
http://www.sonobat.com/download/ZoomAutorecording.ppt
. . . and change the light setting to ON and after triggering a call, watch the seconds on the Zoom and when it counts up to 16 (or 33 for 3.4 sec) and click the StartStop button to end the playback and prevent recording the D240x button sound.
Other detector/netbook configurations using Binary Acoustics Technology equipment allow for realtime viewing of the bat call and manual tagging of using voice notes or text headers. The new Pettersson D500x FD allows for a realtime audio-output of the recorded signal. Switching user profiles to a 44.1kHz sample rate with a manual trigger allows for recording voice notes after each recording. The Pettersson D1000x is a higher quality, all-in-one recorder also with voice note capabilities. And, the new Wildlife Acoustics EchoMeter Touch with an iOS device and EchoMeter application provides similar realtime viewing and tagging capabilities.

A: Most researchers who record voucher calls keep moving the number up as we keep finding more and more variety and unexpected vocalizations. These days we would consider 30 calls per species to be too low by an order of magnitude. For some species we would want more than that, for other species we might feel fine with less. The number varies both by consistency of calls represented in the repertoire of the species, and its acoustic distinctiveness from other species.

Some citations to support this include:
Duffy, A.M., Lumsden, L.F., Caddle, C.R., Chick, R.R., Newell, G.R. 2000. The efficacy of Anabat ultrasonic detectors and harp traps for surveying microchiropterans in south-east Australia. Acta Chiropterologica 2(2):127-144.
Waters, D.A., and W.L. Gannon. 2002. Bat call libraries: management and pote ntial use, p. 150-157. In: Brigham, R.M., E.K.V. Kalko, G. Jones, S. Parsons, H.J.G.A. Limpens (Eds.) 2004. Bat Echolocation Research: Tools, Techniques, and Analysis. (Proceedings of the Bat Echolocation Symposium and Tutorial April 15-17, 2002) Bat Conservation International, Austin, TX. 167 pages.

A: If done properly it should not distort the signals. However, when you reach further through the air you will enhance the differential frequency attenuation effect of propagated ultrasound. That is, higher frequencies get more attenuated than lower frequencies. So I suspect you would detect bats at greater distances, but your rate of effective species ID may diminish from the selective loss of higher frequency content..