My favorite is Bearded Tit by Rory McGrath. Also, The Dune by Bruce Beckham and Pelican Blood by Cris Freddi (a bit harsh). Anne Cleeves, who wrote the Vera Stanhope mysteries and the Shetland novels (both now TV series), was married to an ornithologist and served as a cook at Fair Isle while her husband was working there. Her early work includes a series of birding mysteries - the George and Molly Parker books. There are eight in all including one involving a pelagic trip (what could go wrong?) and one at High Island. I concur with Beverly on the excellent Steve Burrows books, a series of six birder mysteries so far, set in Norfolk with Inspector Jejeune.