I don't understand the disorientation issue. During the day moths just sit.
What is the difference between a disoriented moth sitting and a completely
oriented moth sitting?
If you want to look up predators on moths I would look food preferences of
tits (Parus spp.; chickadees in the US). There are also a multitiude of
other scansorial feeders (creepers and woodpeckers) that would find moths
even if they were tucked away in the crevices of bark.
>From: Biochmborg@aol.com
>To: D.Tyler@mmu.ac.uk, evolution@calvin.edu
>Subject: Re: Peppered moths...again???
>Date: Thu, 9 Sep 1999 13:16:41 EDT
>
>In a message dated 9/9/99 7:48:33 AM Mountain Daylight Time,
>D.Tyler@mmu.ac.uk writes:
>
> > my comments:
> > 1. Kettlewell and Tinbergen's film was not "natural" predation.
> > My understanding is that the moths were disoriented - having been
> > released in the day time in a sluggish state. (If this unnatural
> > situation has been the trigger for an increasing perception that bird
> > predation is important, it would be wise for lepidopterists and
> > ornithologists to check that the mistake has not been repeated in
> > later "observations and experiments").
> >
>
>The claim of "disorientation" is special pleading; there is no evidence
>that
>the moths were disoriented. Instead this claim is based on an
>anthropomorphic reaction, specifically the "How would you feel if you were
>in
>the moth's place?" reaction. Even if that were a valid basis for
>comparison,
>it is not scientific evidence, just a subjective emotional response.
>
>The film itself may have been made under "unnatural" conditions, but it was
>meant to document and illustrate what Kettlewell and Tinbergen were seeing
>on
>a regular basis. As such, despite its "unnaturalness", other people found
>it
>convincing because it backed up Kettlewell's and Tinbergen's observations
>in
>a way that was indesputable. The reason is very simple: birds do not
>waste
>time going after unfamiliar objects in the hopes that it might be food;
>they
>concentrate instead on what they believe to be food. If birds did not eat
>moths, the mere presence of moths on tree trunks would not incite birds to
>eat them, because the birds would not recognize the moths as food. It was
>because birds love to eat moths that they attacked those that had settled
>on
>the tree trunks. The ornithologists and entomologists recognized this from
>the film, hence its "unnaturalness" was irrelevant to them. And this new
>perception was reinforced by their own experiments and observations which
>they made to test this new idea. Many such experiments and observations
>probably were "unnatural" as Dave would define it, but since the question
>being tested was, "Are birds a major predator of moths," and not, "Is bird
>predation of moths important for understanding the cause of industrial
>melanism", the "unnaturalness" of the experiments and the observations is
>irrelevant.
>
> >
> > 2. I am entirely comfortable with the thought that birds are the
> > major predators of many species of adult moth. Perhaps we ought to
> > be enquiring about the relative importance of other predators - such
> > as bats.
> >
>
>Bats are indeed major predators of moths (probably more so than birds, but
>not by much), but because they locate and capture prey using sound rather
>than sight, their "relative importance" with regard to industrial melanism
>would be very slight. The same is true for mammalian insectivores like
>shrews, except that they use smell instead of sight or sound. Reptiles and
>amphibians would probably follow close behind bats and birds as major moth
>predators, but there are no major tree-dwelling species in Great Britain,
>Europe or North America, so their "relative importance" is likely to be
>very
>slight as well. That leaves birds, which are the most aubundant moth
>predators after bats, and the easiest to study in a "natural" setting. So
>while bats probably eat more moths than birds do, they would eat both color
>phases indescriminantly; with the evidence we have, birds are the most
>likely
>predator to cause the industrial melanism affect.
>
> >
> > 3. We have almost no information about the peppered moth
> > predators in the natural state, nor which is the most important.
> >
>
>We have no *direct* evidence, but the indirect evidence by itself is
>sufficiently convincing to the experts that, until contradictory direct
>evidence is discovered, they will use what they have, plus informed
>speculation, to establish an explanation. Besides, assuming that the
>"important" predation with regard to industrial melanism is predation of
>resting moths rather than of active moths, the most important predators
>(based on general observational history) are likely to be those predators
>who
>go hunting for moths in their resting places. In Great Britain, Europe and
>North America, this is predominantly the small "creeper" birds that "crawl"
>around tree truncks and branches looking for insects, birds like titmouses,
>nuthatches, chickadees, wrens and certain species of warblers.
>
> >
> > 4. Majerus's view is that significant bird predation levels are
> > "highly probable" - but this is based on the consensus that bird
> > predation is important in many species. Majerus points to the lack
> > of data relating to the Peppered Moth.
> >
>
>But this lack of specific evidence in the case of the peppered moth is not
>enough to cause Majerus to doubt the overwhelming evidence establishing the
>general trend that birds are the most important predator as far as
>industrial
>melanism is concerned. That is what we need to keep in mind. The question
>is, what causes industrial melanism in moths? The evidence we have so far
>indicates that it is selective predation by visually-oriented predators.
>Of
>the three major groups of vertebrate predators of moths -- bats and other
>mammalian insectivores, birds and reptiles/amphibians -- only the latter
>two
>hunt predominatly by sight, so only the latter two are likely to cause
>industrial melanism. And since birds are far more numerous and far more
>active hunters than reptiles/amphibians, birds are the best candidates to
>be
>the predator that causes industrial melanism. As such, only if birds took
>a
>tiny fraction of all moths eaten by all predators would bird selective
>predation have no significant affect, and this is very much not the case;
>they rival bats as far as total intake is concerned.
>
> >
> > It MAY BE that the story about bird predation will turn out to be
> > true. But our present state of knowledge is inadequate for this to
> > be the textbook example of natural selection changing gene
> > frequencies in a population of organisms.
> >
>
>Only if we concentrate on the gaps in our knowledge. In point of fact, the
>evidence we do have paints a very strong picture in favor of selective
>predation by birds as the cause of industrial melanism.
>
>Kevin L. O'Brien
>
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