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Re: Orenstein's pedestrian arguments.



At 02:03 PM 2/22/97 -0500, John Bois wrote:
>Surely this needs justification!  Is he really suggesting that flight is
>not important for flying birds?

I said this before, Mr Bois, but here we go again.  Yes, flight may indeed
not be important for certain flying birds AS PART OF THEIR DAILY ACTIVITY.
There are many flying birds that rarely fly, or only do so (a) on
migration, (b) for other lengthy transfers from place to place, (c) to
reach high roosts at night, or (d) as a last resort.  Flight is
energetically expensive and if terrestrial birds can avoid it while
escaping predators many will do so.  In fact given that many of their
predators may be aerial themselves (birds of prey) flight may be the worst
means of escape as it involves breaking cover.  Such birds will usually
either sit very tight and depend on camouflage, slip away through the
densest cover they can find or both.  There are MANY examples of this sort
of behaviour pattern; rails are just one, but I could mention (restricting
myself to terrestrial birds of forest or dense scrub) tinamous; many
quails, partridges and pheasants; buttonquails; mesites (endemic to
Madagascar, which does have  terrestrial mammalian predators in the form of
various civets such as the fairly large fossa); numerous ground pigeons;
the grass parrot of Australia (which despite its name lives in dense heath
scrub); ground cuckoos; ground rollers (Madagascar again); pittas; numerous
antbirds and antpittas; tapaculos; scrub-birds; lyrebirds.

>       In any case, since rails quickly evolve to a flightless state when
>flight is non-essential, it seems reasonable to suggest it has some value
>when they have not.  Of what possible value could flight be to a rail?

Many rails are migratory, and do undertake long-distance flights as their
very presence on so many oceanic islands indicates (they had to get there
somehow).  Their chief use for flight may be long-distance transfers
between habitat patches on the one hand, and (as I implied) a final defense
mechanism on the other.  I noted that many birds that usually escape
predators on foot may fly to reach high-level roosts at night; though most
rails roost on the ground some forest rails (even some flightless ones)
roost above ground in trees or dense bushes.

Later in his message Mr Bois refers to what I think may be the real
critical difference between small terrestrial bipeds and quadrupeds.  Birds
are far less likely to be burrowers than mammals, though some certainly do
construct nesting tunnels (Bank Swallows can dig a tunnel six feet long).
However, I know of no bird that can dig itself rapidly out of sight as some
mammals (eg some small armadillos) can do, nor do I know of one offhand
that maintains burrow systems as a means of escape from predators.  There
are, of course, no truly fossorial birds.  I suspect that this is a genuine
result of the adaptation of the forelimbs as wings - an avian mole is
pretty much an impossibility.  Perhaps the use of flight as a final escape
route by undergrowth birds reflects not a (mythical) inability to navigate
on two legs but the lack of access to the mammalian alternative - a quick
dive down a handy burrow.

>1. Accounts I have read of rails say that they fly when flushed from
>cover.  They only seem to do this as a last resort.  But, as a last
>resort, it is probably adaptive. 

See above.  Certainly some rails can be flushed - I know a story of a
Toronto birder years ago whose dog flushed a Yellow Rail that flew up,
struck him in the chest and fell into his coat pocket.  In fact some rails,
eg the African flufftails, are highly unlikely even to do this - their last
resort is often to sit as tightly as possible.  There is the famous story
about a group of birders in California who organized a drive through a
marsh in an attempt to flush a rarely-seen Black Rail, only to discover
that one of them had inadvertently killed the bird by stepping on it.  It
simply would not fly.

>Clearly, rail species that live where there are mammals and snakes _need_
>to be able to fly.

Agreed, but as noted above this may have more to do with the lack of
alternative last-resort defenses such as burrowing than with the inability
of a bird to run away.  After all mammals have to have other defenses
besides running, too.

>2. A flighted rail has a greater selection of nesting sites than a
>flightless bird.  Many birds are happy to spend their day to day existence
>in places they would not nest. 

True, though it is surprising that a number of warblers that forage in
trees nest on the ground.  In fact ground-nesting is widespread among
terrestrial birds - again suggesting that the best defense may be cryptic
colouration and the ability to sit tight.

To bring this back to dinosaurs (non-avian ones), crypticity of both colour
and behaviour seems to have been overlooked in considering a list of
dinosaur defenses (no, I do NOT want to get into Michael Crichton's
fantasies about Carnotaurus!).  It may well have been that many small
dinosaurs were good at this.  A possible model might be some of the smaller
African bustards or korhaans, which are fairly substantial birds with long
necks and, often, strikingly-coloured (eg black) underparts.  They can
literally vanish, even in fairly open country, by lying flat on the ground
with their necks extended, their brown, vermiculated upperparts blending in
to the earth and making them remarkably hard to see even when you know they
are there.

>Here is my preconceived notion: dinosaurs of the late cretaceous got
>bigger.  There was none smaller than a chicken.

That we know of, but OK.

  There must have been a
>reason for this.  I think this quote from John McLoughlin's _Synapsida_
>can enlighten: "Represented by the rodent-like multituberculates,
>marsupials, forest-bottom insectivores, and tree-dwelling primates, these
>furry creatures shared with a growing number of birds the art of being
>small and living in micro-habitats in which larger animals could have no
>interest." 

Yes, BUT - this may not have been driven by predator avoidance but by food
availability, and even if it was I suggest the possibility at least that it
might have been fossorial habits, rather than maneuverability, that gave
mammals the edge below a certain size (perhaps they were better climbers,
too; some of them may have been treetop animals, after all).  Note, of
course, that there were also small birds in the Mesozoic and that they,
too, may have excluded non-avian dinosaurs from some of the arboreal niches
at least.

As noted, flightlessness does not mean defenselessness even for small
forms.  A number of flightless or near-flightless birds can reach quite
high in trees by strong leaps (eg lyrebirds, which are very poor flyers and
may be incapable of flying upwards to any degree).  Small dinosaurs could
well have done this too.  Remember that it is not safe to generalize from
flightless birds evolving on islands in the absence of predators (and, as a
result, losing defensive behaviours and abilities that they might have
retained otherwise) to flightless small dinosaurs evolving in a
predator-rich community.  Even a kiwi can pack a hell of a kick, for example.

>       The "larger animals" here are of course dinosaurs.  But surely
>McLoughlin is being colloquial. 

And crocodiles, large monitor lizards, giant snakes, even surviving
labyrinthodont amphibians in a few spots (though these were probably
aquatic), plus, in the Triassic when mammals got started, larger synapsids
and large non-dinosaurian archosaurs.

 Rather than having no interest,
>dinosaurs lacked the _abilty_ to reenter this niche.  This was because
>other animals did it better.  To suggest that dinosaurs could not radiate
>into these niches out of choice denies such well established theories as
>character displacement, niche partitioning.  SMALL, NON_FLYING,
>EGG-LAYING, BIPEDAL animals were indeed excluded from those micro-niches
>of the late cretaceous.  THEY ARE ALSO EXCLUDED TODAY.  But really,
>Orenstein, these are not preconceived notions, they are facts.

The preconceived notion is WHY this happened.  You have suggested that it
is because of lack of maneuverability in dense undergrowth by bipeds.  I
have replied that (a) bipeds are perfectly able to get around efficiently
and at speed in such habitats and (b) there are probably better
explanations for this exclusion than the one you suppose.

Further, the absence of many such creatures today may reflect evolutionary
foreclosure through lineage extinction rather than simply competitive
exclusion.  There are no non-flying, egg-laying bipeds WITH FUNCTIONAL
FORELIMBS (ie functional for grasping, digging etc) in existence today, for
example, so no real analogue to a Compsognathus (say) exists.  It may be
that if such a lineage survived it would do just fine - we don't know.
There are certainly small bipedal mammals, of course - kangaroo-rats,
jerboas, springhares - though they are leapers rather than runners and so
adapted to open country (long leaps are surely of little use in dense
undergrowth).

>This is, of course true.  But mammals (dogs, for example) can catch lots
>of certain rails. 

And lots of mice, shrews and other mammals of similar habit.  The point is
that the mice survive in their presence as species, and so do the rails.

 >Relative to a biped of equal mass, a quadruped
>can dig better burrows (is it only the kiwi which digs burrows)

Highly important as I suggest.  Other burrowers include some petrels,
motmots, some swallows, some parrots (eg the Burrowing Parrot or Patagonian
Conure of southern South America), some kingfishers, a few woodpeckers and
probably others that I have forgotten.

>Relative to a
>biped of equal mass, a snake can pass through much narrower holes, can
>take advantage of holes in the ground, can lay its eggs in inaccessible
>places...

Also true relative to a quadruped of equal mass.

>I think this is the area we need to look.  Quoting from Betty Cunningham's
>post: "fern and briar and brush and gorse and other plant-like nouns that
>sound short make a far denser ground cover than mere grass can."  We can
>argue all day and night about rails' abilities.  Why could no dino-morph's
>make it here, in these micro-niches?  I'm not sure rails are a valuable
>analogue at all, in this instance.

See above but I often wonder if our assumption that no dinos did is an
artifact of the likelihood of such habitats to provide good sites for
fossilization.  This sort of difference may explain why fossil birds and
pterosaurs are so heavily weighted towards water forms - there may have
been (am I right on this, folks?) whole communities of forest creatures of
the period whose existence has entirely escaped us.  Are we to assume, for
instance, that Anurognathus was the ONLY pterosaur of its type, or the tip
of the iceberg?

>I meant: If bipedalism was no impediment to dinosaurs below the
>chicken-threshhold, why do you think they were excluded from these
>micro-niches?

See above.

>I don't have any argument with this.  I repeat, no argument.  But, where
>they coexist with mammals and snakes (are Guam rails flightless?)
>they must also be able to fly (in nearly all cases).

Guam rails are flightless, but this is not the best example as the Brown
Tree Snakes that got loose on Guam have devastated ALL the native land
birds, both flying and flightless - the Guam Flycatcher, for instance, a
perfectly good arboreal flyer, is now extinct.  See the book "And No Birds
Sing" by Mark Jaffe for the Guam story in detail.

Also, as I noted, there are flightless rails on Tasmania (the still-common
Tasmanian Native Hen) and New Guinea (the New Guinea Flightless Rail), both
places with terrestrial carnivorous mammals, so it is not quite true to say
that the two can never coexist.

>This is utter nonsense.  Cruel, utter nonsense.  I have never said rails
>were clumsy.  I have said their body plan has limitations--all body plans
>do.

I will NOT get into personalities here, but I could think of no other way
to interpret your comparison of a rail to a dog walking on its hind legs.
I believe that you certainly were implying that bipeds could not manoeuver
well in dense growth.  If you do not, in fact, hold that view, I am glad to
hear it.

>For our purposes this generic description of rails is imprecise.  For
>example, we need to know how low are the branches relative to those an
>insectivore can hide under, what sort of habitat are we talking about
>exactly.  Are they talking about a marsh environment (probably) or what?

Frankly, I doubt that the information exists - these are notoriously
difficult birds to study.  However, given the way the Handbook is put
together I suspect that if the authors had meant to restrict the statement
to marsh birds they would have done so.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net