Vanessa movements and Peck's skipper

[Woody Woods]

A borrowed thought about what migration is and what it is not: Dingle (1996)
spends the first two chapters of his excellent book (his second on the
subject) categorizing forms of movement and defining migration; distilling it
down to a sentence is not easy, but he does (with modifications) quote J.S.
Kennedy as having provided the most complete definition: "Migratory behavior
is persistent and straightened-out movement effected by the animal's own
locomotory exertions of by its active embarkation on a vehicle. It depends on
some temporary inhibition of station-keeping responses, but promotes their
eventual disinhibition and recurrence." 

Elsewhere, Dingle says "The most distinctive characteristics of migratory
behavior are the UNDISTRACTABILITY (caps mine) of the individual displaying it
(if an animal) and the special physiological mechanisms in both animals and
plants assuring that it takes place." In other words, the bypassing of
opportunities to feed or to mate is a defining element in Dingle's and others'
view. 

A good clean definition, but here's an example of the grey areas encountered
in practice. I worked for a couple of seasons with Bill Haber and Rob
Stevenson in northern Costa Rica while they were studying butterfly migration.
Bill had established that seasonal migration was much more widespread among
butterflies in the region than had been previously thought (Haber 1993), and
there are now years of documentation. However, females of most migrating
species remained reproductively active, and oviposited where hostplants were
available along the migratory pathway. Bill found that Costa Rican Monarchs
(Danaus plexippus megalippe) migrate altitudinally, from west to east, and
remain reproductively active.  On their travels, they never really "closed the
suitcase". I can't help but wonder whether Dingle would consider this
migration or whether he would call it seasonal movement. 

Woody

Patrick Foley wrote:
> 
> Bill and Dale,
> 
> I do not think there is a consensus about the exact meaning of the movement
> words. Two reviews that address some of the terms are R. R. Baker 1978, The
> Evolutionary Ecology of Animal Migration, and
> Hugh Dingle 1996. Migration. The biology of life on the move. The latter
> book is much more available than the former, but Baker is a butterfly guy.
> 
> <snip>
> 
> Baker tends to minimize the differences between migration (as Dingle defines
> it) and normal animal movements (which Dingle calls 'ranging'). The problem
> may be that there are many intermediate cases where evolution has not
> settled down to a clear nexus of adaptations. Dingle argues that migration
> involves behavioral and physiological peculiarities not typical of animals
> in their home range. For example Vanessa cardui doesn't seem to stop for
> much during migration even to feed. Once she slows down the female behaves
> in the "normal" way feeding and ovipositing etc.
> 
> There is plenty of room for exhausting argument in these definitions, but I
> suggest a look at the Dingle book to get a fairly pragmatic overview.
> 
> Patrick Foley
> patfoley at csus.edu
> 
> 
-- 
*********************************************************
William A. Woods Jr.
Department of Biology
University of Massachusetts Boston
100 Morrissey Blvd                      Lab: 617-287-6642
Boston, MA 02125                        Fax: 617-287-6650
*********************************************************

 
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