Vanessa movements and Peck's skipper

Patrick Foley patfoley at
Sat Jun 2 17:37:32 EDT 2001

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.

Baker defines (p 21) migration as " the act of moving from one spatial unit
to another."

This may seem so general (Dingle is more restricitve) that it requires more
definitions, and Baker makes them and I quote

Exploratory migration: a migration beyond the premigration limits of the
familiar area during which the ability to return to that familiar area is
retained, though not necessarily exploited.

Removal migration: a migration away from a spatial unit (U), usually ending
in some other comparable spatial unit, which is not followed by a return to
U, or at least not until the passage of a sufficiently long, but arbitrarily
determined, interval of time.

Return migration: migration to a spatial unit that has been visited

Regular migration: migration that occurs at a more or less fixed peiodicity.

Irregular migration: migration that occurs at irregular intervals.

Many authors use the term 'irruption' to describe irregular migrations,
particularly when large numbers of animals are involved.

This ends the Baker quotes.

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

bill and Dale wrote:

> Hi Everyone,
>        This is my first post to this group so please be gentle with me.
> I have a couple of questions that I'd like to pose to the group and as
> I'm both an amateur and somewhat of a beginner (one of those expatriated
> birders) I'm not even sure that these questions are appro[priate for
> this forum but here goes:
> 1. The large movement of Vanessa sps.(V. atalanta, V.cardui), Admiral
> and Lady, that we are experiencing here in the northeastern U.S., is
> this properly termed an irruption, emigration or migration? Are these
> terms interchangable or is one or  another term more accurately
> descriptive of what's happening?
> 2. Polites peckius vs.Polites coras ? Since I use "field guides" rather
> than monographs to ID butterflies I'm confused about the classification
> of Peck's skipper in the Glassberg book vs. the classification of
> Yellowpatch skipper in Pyle's Audubon guide. I'm not interested so much
> in the competing English vernacular names as I am in the competing
> Latinized binomials. Specifically are the two different specific
> circumscriptions taxonomic issues or nomenclatural issues?
>                                                             Thanks,
> Bill Yule
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