>> On Oct 28, 2009, at 4:30 PM Kevin Purcell wrote:

> > The discovery of a south bound breeding site seperate from the
> > northern breeding site in Neotropical migrants by Rohwer et al. is a
> > remarkable find. However, it should be noted that this phenomena has
> > been hypothesized for many years in Sedge Wrens in eastern North
> > America with much evidence to support it.
>
> Not quite the same phenomena as they start the paper with this
> paragraph to make some distinctions:
>
> > Itinerant breeding, wherein the same individuals breed in different
> > regions in a single season, is established or suspected for just a
> > few species of New and Old World birds (1). Some itinerant breeders
> > exploit unpredictable food supplies, so their breeding areas may not
> > be in the same place from year to year, as in the red-billed quelea
> > (Quelea quelea) (2, 3). However, 2 other species, European quail
> > (Coturnix coturnix) and dotterel (Charadrius morinellus), apparently
> > breed first in southern regions, then move north with the
> > progression of spring to breed again (ref. 4 and Whitfield in ref.
> > 5). We suggest that the term migratory double breeding might
> > appropriately distinguish species with dual breeding ranges that are
> > consistent from year to year. Unlike more nomadic itinerant
> > breeders, migratory double breeders move between early and later
> > breeding sites that are used reliably from year to year.

This study only has three years of data so it might be a little early to conclude
that the birds on their study site are reliable breeders. I don't know if the study
years included a drought year but I wonder what the double breeders would do
in those years.

> The Sedge Wren, I think, falls into the itinerant breeders category
> with low site fidelity -- it's an opportunist breeder breeding (as the
> paper you cited points out).

I think the Sedge Wren falls somewhere in between the species addressed
in the paper and what the author's classify as nomadic itinerant breeders.
Sedge Wrens can be found regularly breeding in late summer in their southern
breeding range (at least in eastern KS where I have the most experience with
the species). In addition, it is true that Sedge Wrens appear to be opportunistic
breeders often appearing in larger numbers during "wet summers" to occupy and
breed in wet prairies. However, I would have to argue that Sedge Wrens should
be classified as "migratory double breeders" for the following reasons:

1.) Sedge Wrens appear to reliably breed in two separate locations each year
with one northerly site and then on their southward migration at one southerly
site.
- Evidence for this is supported by strong correlation between the
northerly departure dates and southerly arrival dates
- "Location" is a loose term wholly defined by scale. I would argue that
Sedge Wren breed regularly in the same location at an eco-regional
scale e.g. the Flint Hills tallgrass prairies.

2.) Sedge Wrens are also known nocturnal migrants as many Great Plains radio
towers have inadvertently documented through strike kills.

3.) Sedge Wrens also appear to be double breeding on the southbound track
of migration first breeding in the northern prairies in early summer and then
in the southern prairies in late summer or early fall.

> I think this adds another layer to a previous list discussion of the
> proper nomenclature for describing the (apparent) movement of birds
> after breeding: post-breeding dispersal versus post-breeding movement
> versus migration. If this is true then a whole interesting new
> terminology needs to be invented (post-breeding1-pre-breeding2
> dispersal) or perhaps we just start to drop the more simplistic ideas
> we have :-)

I completely agree with Kevin here. What an exciting find! I think the
most exciting things about discoveries such as these is how they make us
rethink what we believed we knew.

I am excited to know whether or not reproductive success is higher or
lower in the Mexican breeding grounds than in the northern? Makes me
want to drop butterflies and herbicides and jump into the thorn forests
of Latin America!

Cheers,

Tyler


Tyler L. Hicks


Ph.D. Student
Washington State University Vancouver

E-mail: tyler_hicks at wsu.edu
Web Page: http://thingswithwings.org

"We were certainly uncertain. At least, I'm pretty sure I am." - Modest Mouse
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