For Peter (and others) with high-frequency hearing loss, the newest technology is a device that folds high frequencies into the range where most of us (with high-frequency loss) can hear. The device is described at http://www.naturesound.com/songfinder/songfinder.html and there are samples of what various birds sound like with/without the device. I have Resound aids that help by amplifiying up to about 6000 or so but this device does not depend on amplification to overcome loss of acuity at high frequencies. I have not personally tried this but is sure sounds (pun not originally intended) interesting.

Best,

Joe McDaniel
Monrovia