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Re: [CALBIRDS] Tropical Kingbirds - Reverse Migration

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  • Eric Goodill
    First, this is a fascinating discussion, and I thank all who have contributed their thoughts. Mr. Garrett, one thing I didn t see mentioned in your post is the
    Message 1 of 12 , Oct 24, 2006
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      First, this is a fascinating discussion, and I thank all who have
      contributed their thoughts.

      Mr. Garrett, one thing I didn't see mentioned in your post is the
      percentage of TRKIs that make this reverse migration. You say

      In fact, most of the Tropical Kingbirds (and other
      "reverse migrants" from the northern Neotropics)
      are hatch-year birds.

      What percentage of the hatch-year bird population makes the reverse
      migration? If it's just a small percentage, then the 180-degree
      navigation mistake seems more likely to me. If it's a significant
      portion or even a majority, then the "mistake" idea seems less likely.
      Do you (or anybody else) have any data on this?

      Good birding,
      Eric Goodill
      Menlo Park, Calif.

      Kimball Garrett wrote:
      > Tom et al.,
      >
      > I am reluctant to wade into this, but fearing that the birding
      > "audience" out there is going to come away from this thread with a very
      > twisted understanding of bird migration, I had to throw in my 2 cents
      > worth. One of the true migration biologists on Calbirds can certainly
      > add a more coherent and correct version of what I am about to say, but
      > perhaps their time is better spent doing biology...
      >
      > Bird migration is a highly evolved phenomenon that essentially takes
      > advantage of seasonal differences in resource availability in different
      > regions. Most migration patterns are completely or almost completely
      > innate - birds are programmed to go where they go when they go there.
      > (The very interesting phenomenon of less hard-wired "facultative"
      > migration is a different matter). An individual bird does not sit there
      > and think "Hey, I'll go to California instead of southern Mexico (or
      > wherever) because I have a feeling things are better there." In fact,
      > most of the Tropical Kingbirds (and other "reverse migrants" from the
      > northern Neotropics) are hatch-year birds. They have no clue where
      > California is and what is there once they get there. They're hard-wired
      > to go southward (more or less) after the breeding season, and some
      > individuals simply go the wrong way. [Once one successfully winters in
      > California, that's a different matter - birds are also programmed to
      > repeat migration routes that are successful.]
      >
      > Our Tropical Kingbirds, etc., have merely gone the "wrong" direction.
      > [By the way, I very much doubt they come from "Southeast Arizona" -
      > there probably aren't more than a couple of dozen nesting pairs of TKs
      > in Arizona, as opposed to hundreds of thousands farther south in Sonora,
      > Sinaloa, etc.]. This "reverse migration" isn't limited to Neotropical
      > birds - just ask the folks in the Canadian Maritimes, n./nw. Alaska,
      > etc. about North American birds that go north in fall by mistake.
      >
      > In short, Tom's suggestion that Tropical Kingbirds (etc.) reach
      > California in fall from the south because they have made a strategic
      > ecological "decision" to do so flies in the face of all we know about
      > bird migration. Believe me, the resources (=insects) these kingbirds
      > need to get through the winter are much more available in central and
      > southern Mexico, etc., than they are here in California. It's possible
      > that all of our plantings and the abundance of certain insects (like
      > introduced honeybees) make it more likely now than a century or more ago
      > that TKs will survive the winter in California, but it seems highly
      > unlikely that a northward migration strategy has evolved in that time
      > frame. [I acknowledge that very interesting work in Europe and
      > elsewhere has shown that novel migration strategies can evolve rapidly,
      > but no such work has been done on the phenomenon of northern Neotropical
      > birds going north in fall.]. Even if our wintering TKs return to Mexico
      > to breed and their offspring show a genetically-based tendency to go
      > north like their parent, this is still a far cry from the "Dude, I think
      > I'll try California" theory Tom espoused.
      >
      > Thanks to Steve Hampton for pointing out the work of Dave DeSante that
      > demonstrates (at least in some cases) that misorientation is more likely
      > to be 180 degree off than other vectors. So perhaps TKs do go north
      > more often than they inappropriately go west (not a good strategy if
      > you've hatched on the west coast of Mexico) or east. But it's still
      > misorientation, not a pre-planned vacation.
      >
      > Kimball


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    • Feather Forestwalker
      This topic made me think of one species in particular, that is now wintering all over northern California; the Anna s Hummingbird. When I first moved up here
      Message 2 of 12 , Oct 24, 2006
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        This topic made me think of one species in particular, that is now wintering all over northern California; the Anna's Hummingbird.

        When I first moved up here in 1986, I never saw them at my feeders in winter. I had feeders up from Spring through Winter that year and by the winter of 1988, I was seeing them more frequently.

        Someone told me (I also read it somewhere) that Anna's are not migrating as much due mostly to planting's and people feeding them and some suggested that by feeding them through the winter we were inadvertently causing their demise as a species. Well, they are as abundant as ever.

        I don't feed birds anymore, but I have seen Anna's Hummingbirds, in winter, sip the juices of overripe apples in orchards. . .

        My point, I guess, is that species can, will, and do, adapt to changes within their environments, sometimes faster than we think they "should."

        Feather on the Mendocino coast

        [Non-text portions of this message have been removed]
      • B & C Yutzy
        As Scott Terrill pointed out - some species have a greater propensity to become vagrants than others and Tropical Kingbirds seem to clearly be one. After all,
        Message 3 of 12 , Oct 25, 2006
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          As Scott Terrill pointed out - some species have a greater propensity to
          become vagrants than others and Tropical Kingbirds seem to clearly be
          one. After all, there are years and years of records of this phenomenon
          in California now.

          It also seems clear to me that a flycatcher of any kind would not be
          heading North into California in the winter for any food source - if
          there was any intelligence or volition involved (and there isn't)!

          Bob Yutzy
          Shasta, California

          Nate Dias wrote:
          > Kimball Garrett wrote:
          >
          > "
          > In short, Tom's suggestion that Tropical Kingbirds (etc.) reach
          > California in fall from the south because they have made a strategic
          > ecological "decision" to do so flies in the face of all we know about
          > bird migration. Believe me, the resources (=insects) these kingbirds
          > need to get through the winter are much more available in central and
          > southern Mexico, etc., than they are here in California.
          > "
          >
          > -- I am afraid I have trouble with this statement, having had
          > experience in recent years with so many Cave Swallows' recent
          > "ecological decision" to head north and winter along the U.S. East
          > Coast (when so many more insects are available south of the border).
          > This is a well-documented phenomenon with hundreds, probably thousands
          > of individuals involved annually.
          >
          > I also do not believe the propensity of Tropical Kingbirds to winter
          > in coastal CA is 100% due to (180 degree) misoriented internal
          > compasses. If this were the case, why aren't multiple Thick-billed
          > Kingbirds found wintering each year in coastal CA? Or Fork-tailed
          > Flycatchers? Or ...
          >
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