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  1. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    I think this is what I am talking about. Do a small percentage of birds migrate the wrong way in any case and at a completely random bearing, and then topography, climate etc shape our understanding of the pattern. As you say not many birds orientating north will survive in the arctic and there...
  2. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    This is quite complex to untangle. For a starters why are some American Sparrows much more frequent in the UK in spring rather than autumn. Presumably these are mainly spring migrants moving up to Newfoundland, then overshooting and travelling through Greenland and Iceland to reach the...
  3. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    Also forgot to mention that Vagrancy in Birds states for the Azores 'While tropical storm systems can bring large influxes of vagrants to the Azores, arrivals there show far less clear association with these fast-moving systems. Some of the largest 'falls' of American vagrants have occurred...
  4. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    Forgot to say that according to my guide to Southern Africa (which seems to include vagrants) there are no North American passerines mentioned. So you are not the only one with no American passerine experience from Southern Africa. I think that most american passerines reaching the UK, do not...
  5. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    I suppose that this is the point of my thread in the first place. A Siberian Thrush arrives in Shetland and is obviously not purely a weather driven arrival - there would be plenty of options for it to put down and ride out adverse conditions - there is something else going on. A bird arrives...
  6. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    Although 160 sounds a lot, in the UK 5 or so birds is a good autumn. When you think about trying to relocate 5 birds, I think the odds are quite low of rediscovery. We then need to think about longevity and mortality rates when thinking about the potential for spring birds. You will probably...
  7. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    I have carried on reading the book on Vagrancy in Birds and there is a section on natural dispersal, but this seems to be considered a secondary driver compared to navigational error or weather induced vagrancy. Interestingly, there is a section on colonizing new wintering sites, which...
  8. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    Yes you are right. I was really meaning the few birds that reached western Europe did not seem to return east, so perhaps were driven to continue west. The northern birds are quite long distant migrants, so it seem odd to think that the rest ran out of steam and perished soon after being...
  9. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    The Vagrancy in Birds book gives some examples of where migration points are presumed to be hard coded into a birds genetics. One of these examples is Marsh Warbler, where first-winter birds will use a set of staging posts in Africa during the autumn migration (they apparently do not just...
  10. J

    Do theories regarding the mechanisms for Vagrancy stand scrutiny, and what does vagrancy tell us about migration?

    I have been reading 'Vagrancy in Birds' and the sections on how birds navigate is very interesting and informative. I find however, the theories on compass errors, reverse migration, mirror-migration, and drift, as mechanisms for vagrancy not totally convincing. Of course I am not discarding...
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