|Subject:||More birds out there than previously thought|
|From:||Michael Todd <>|
|Date:||Sat, 25 Jun 2005 20:41:21 +1000|
Hello all,I also found David's paper interesting. However, many of Andrew's points are well made.
External appearance is certainly a major means of diagnosis of species in birds- obviously because birds are often so colourfully and distinctly plumaged. Mammals, particularly small ones, are usually variations of brown and grey with often great amounts of variation between individuals. In mammals, external appearance is often a poor means of separating species with a fair amount of overlap as opposed to the often clear differences in birds, ie an eyebrow being black or white! (as opposed to usually greyish-brown in contrast to usually brownish-grey!). I suspect that if external appearance could be used more often with other classes of animal it would be.
Nevertheless, I think that David's opinion that possibly good species are getting overlooked is worth considering. The level of variation between populations of birds is rarely adequately measured. Those who record bird calls (such as the Wildlife Audio Sound Recording Group) are acutely aware of how much variation occurs within separated populations of common species. This is putting aside the issue of whether or not the calls are audible to us or not. Could any of these different calling populations be hidden separate species? Well possibly...
Works such as the monumental Directory of Australian Birds (Vol 1) have attempted to describe the variation at a finer level using ultrataxa. This was mostly based on external appearance (skins) and internal morphology (bones) but used other info if it was available. Many Australian birds haven't had their genetic variation determined between what we now call species let alone between different populations. Analysis of behavioural differences between populations hasn't been done.
I guess what I'm trying to say is that we know very little about most of our birds and I don't know that it is so much a bias away from methods other than external appearance. It's more that we don't have much of the other info- you use what you have don't you?
Cheers MickMichael Todd Wildlifing Images & Sounds of Nature
Latest Additions: The Awaba Forest www.wildlifing.comToronto, NSW, Australia 04101 23715
Andrew Taylor wrote:
On Fri, Jun 24, 2005 at 08:14:47PM +1000, Ricki Coughlan wrote:Sorry for appearing to make a sweeping generalisation. Variances from 1- 5khz may occur in some species whilst among Barn Owls it can be up to 20khz - which is way out of the range for humans.I don't want to be tiresome but this is a topic I know well and this isn't true. Barn Owls have the best high frequency hearing of any bird tested but their high frequency limit is 12khz. See Dooling's chapter on auditory perception in Volume 1 of Acoustic Communication in Birds or look at the audiograms in the appendix of http://www.nrel.gov/docs/fy02osti/30844.pdf Presbycusis is taking its toll but judging by the audio generator on my workbench my ears still get close to the 20khz limit usually nomimated for humans. We can hear high frequency sounds better than any known bird.in the case of Oscine Passerines, which hear higher frequencies better than us but not lower frequencies.Again this isn't true. Look at the audiograms in the above ref. The oscine passerines' hearing sensitivity peaks are at 1.5-4khz. Around these peaks their sensitivity approaches and in some cases exceeds human sensitivity but at higher frequencies their sensitivity is muchpoorer than humans.I don't believe that there is any data to support your claim that variances in syringeal morphology don't produce changes to bird song which is impossible for humans to detect.True - its just speculation based on naive physics. But Watson's argument that syringeal morphology would be useful in separating crypto-species is also purely speculation.especially given that there are birds out there producing vocalisations which we cannot completely hear.Its possible their are crypto-species with calls with diagnostic temporal features that can not be distinguished by humans but without examples this is pure speculation.The point that David was making is that avian species diagnosis is made on a very restricted basis, compared to other classes and this isbiased toward field diagnosability.This isn't true. Look at Figure 1 of Watson's paper. Reptile descriptions have a more restricted basis than birds, frogs and birds are similar, only mammals have species definitions which are clearly more broadly based than birds, at least using these categories. Bird descriptions may rely more heavily on characters observable in the field but the causes and consequences are the issue. Andrew -------------------------------------------- Birding-Aus is now on the Web at www.birding-aus.org -------------------------------------------- To unsubscribe from this mailing list, send the message 'unsubscribe birding-aus' (no quotes, no Subject line) to
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