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<a href="../200904/14278.html">next message in arch Not sure what Paul found so objectionable about this story, which was perhaps a low grade report (little value-added material) but was actually excerpting analyses and quotations from several researchers and the RSPBirds in UK, not so much giving the reporter's own opinion (or that of `the media`). I didn't read it as suggesting that birds fly up seeking a particular temperature value, but that the southern border of the habitat to which they are specifically adapted is moving further north quite rapidly because of local warming, presumably itself a result of global climate change. If for example a particular bird species is evolutionarily-programmed to migrate north for a certain average time or distance, &/or is programmed to recognize exposed tundra before it lands and tries to claim territory, it may wind up exhausted in boreal forest instead of tundra within a few decades, if the northwards trends in vegetation cover observed already continue. Food sources there might be sub-optimal. The argument that small warblers seem to have made it through earlier more extreme climate changes just fine may be correct*, but misses the point: other species of small warblers may not have survived and become extinct, because the changes were too extreme for those particular species to adapt to. We do not now have these extinct species recorded or left to testify (few or no fossils). I don't believe that people who study it think that there is a `motive for migration` whether food or not. The proximate cause of migration would be a newly modified internal hormonal state (probably triggered by daylength changes) that elicits an anciently evolved behaviour to migrate, in the brain. The ultimate cause -- why such migratory behaviour evolved in the past -- is generally argued to be the lower density of predators and lessened competition for territory and perhaps food in the north; food (insects etc) obviously needs to be abundant, but is present in the summer both the winter grounds and temporarily in the northern habitat -- the difference is the competition. Certainly no one argues these days that such behaviours are purely instinctive and unmodifiable, but equally some species may be less adaptable to habitat change than others and less able to survive climate shifts. *or it may not be -- they may instead have survived further south and then gradually re-colonized the emptied northern zones as these warmed up. Quoting Suzanne Townsend <suzanne.townsend@gmail.com>: > I knew if I posted it here, if it were off the wall someone would comment. > Thank you Paul! Hope you post your comments at the source. > --ST > > On Wed, Apr 15, 2009 at 8:01 PM, Paul S. Boyer <psboyer@eastlink.ca> wrote: > >> This is a good example of GW hysteria by the mainstream media, in this case >> by the highly unreliable Reuters. The article is pure speculation. It also >> ignores the fact that the Earth was warmer just 7,000 years ago, and colder >> during the Little Ice Age, and warblers seem to have made it through those >> changes just fine. >> The principle problem for birds migrating between Europe and Africa, like >> those described in the article, is loss of habitat (particularly in Africa). >> It is also generally true that the bigger the bird, the more likely it is >> to be pestered by humans: chased, shot, eaten, &c. >> >> The conversion of temperature into an equivalent surface distance needed >> for migration assumes that temperature is the main control of bird >> migration, which almost everyone who has studied the subject knows is just >> not true. Food is the main motive for migration, and the food needs vary >> according to species. Birds will put up with a wide range of temperatures, >> if the food is available. That is the reason so many feeder-species have >> moved north, and now stay longer in the winter: if the food is adequate, >> they will stay. It is one of the amazing things we observe: tiny little >> creatures, out in the cold, with nothing but a thin layer of puffed-out >> feathers to separate them from freezing ? and yet they can handle this, if >> they have enough food. They certainly can tolerate temperature extremes >> much better than unprotected humans. >> >> Canada Geese have largely given up migration entirely, because they find it >> easier to graze on man-made lawns than to make an arduous migration flight. >> This certainly does not indicate that the seasons have ceased to occur. >> >> I have not been able to find a single convincing case of a migration >> problem which would be caused by a change in a fraction of a degree. >> Indeed, the severity of winters from year to years varies by much more than >> that. >> >> There is much we do not understand about bird migration. There is also >> much we have to discover about changes in bird population. Our lack of >> complete knowledge is no reason for us uncritically to believe every >> tendentious news story which comes along. >> >> >> On 15 Apr 2009, at 2:03 PM, Suzanne Townsend wrote: >> >> >> http://www.reuters.com/article/environmentNews/idUSTRE53D7G220090415?feedType=RSS&feedName=environmentNews >>
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