Some rational discussion; fantastic!
I put my two bob's worth in on cannon netting earlier. After thinking
about it for a while, I estimate that bird mortalities in those early days
were occasionally as high as 10%, but normally 1-5%. This is based on
hazy recollection, but it's still very high. This is certainly not a new
debate, but it's one I haven't heard much about for a while.
I've been trapping and mist-netting forest and cave bats now for about 15
years. Until recently, there was so little physiological, ecological and
conservation data available on forest microbats in particular, that some
mortality might have been justifiable "for the greater good". It's not
possible to "watch" them in the manner of birdwatching for obvious
reasons. I'm happy to report however, that after trapping and handling
perhaps 4,000+ bats, I can only recall 3 deaths (less than 0.1%)! One bat
flew into a trap support at top speed and died, one perished from exposure
(I think), and the third was killed by another bat. From chatting to
other batfolk, that is fairly typical. The amount of data collected on
bats during this time period, about analagous with the reign of
cannon-netting in Australia, is at least as great if not greater than that
gained on waders - but at such a minute cost in bat lives compared to
As Sean pointed out earlier on, it's a subjective process to set the level
of acceptable mortality for a study technique. Some methods are clearly
more hazardous to the study subjects (and to the students if Russell's
story is any indication) than others.