Mulberry sparrows decline (text and photos at
http://www.ccbbirds.org/2014/06/17/mulberry-sparrows-decline/ ;)
By Bryan Watts
The population of coastal plain swamp sparrows (Melospiza georgiana nigrescens)
breeding within Mulberry Point along the Rappahannock River in Virginia has
experienced a dramatic decline over the past ten years. A survey conducted by
the Center for Conservation Biology on June 7th detected only 5 singing males,
in stark contrast to an identical survey conducted in 2005 that resulted in the
detection of 41 singing males. Discovery of the site in 2005 extended the known
breeding range 90 kilometers to the south.
The coastal plain swamp sparrow is restricted to the mid-Atlantic coast. The
form is distinctive in having a larger bill, grayer plumage, and more black in
the crown and nape compared to other swamp sparrows. A recent assessment of
the population within Maryland, Delaware, and New Jersey resulted in a
conservative estimate of 28,000 pairs and established a center of abundance
around Delaware Bay and the Tuckahoe and Mullica rivers in coastal New Jersey.
The survey also suggested a decline in both abundance and distribution along
the western shore and lower eastern shore of the Chesapeake Bay.
Within the Coastal Plain, swamp sparrows occur in marshes within a fairly
narrow salinity band from tidal fresh to approximately one part per thousand.
Pairs utilize habitats with a mix of marsh vegetation and shrubs that typically
form along the marsh-upland interface. Within the Mulberry Point site, habitat
components include olney threesquare (Scirpus olneyi), salt meadow hay
(Spartina patens), marsh hibiscus (Hibiscus moscheutos), and cattail (Typha
augustifolia).
The cause of the population decline is unclear. The preferred ecotone habitat
has been visibly reduced over the decade with invasive common reed (Phragmites
australis) occupying more of the adjacent uplands and the wetter portions of
the marsh containing pickerelweed (Pontederia cordata) expanding. These two
patterns have effectively squeezed the preferred breeding habitat within the
site. It is also well known that occupation of sites by the form may be
episodic. Populations seem to come and go over relatively short periods of
time.
The Coastal Plain Swamp Sparrow is morphologically distinct, geographically
isolated, and specialized in a narrowly-defined habitat type. All of these
characteristics are common to other sparrow forms that were extirpated or have
been of high conservation concern in recent decades, such as the Dusky
Seaside-sparrow (Ammodramus nigrescens), Cape Sable Seaside-sparrow (A.
mirabilis), and Ipswich Sparrow (Passerculus sandwichensis princeps). Given
the uncertain status of this form in the southern portion of its range, a broad
investigation of occurrence within appropriate habitat seems warranted.
______________________________
Michael Wilson
Center for Conservation Biology
College of William and Mary & Virginia Commonwealth University
P.O. Box 8795
Williamsburg, VA 23187-8795
phone: 757-221-1649
fax: 757-221-1650
email: mdwils@xxxxxx
web: www.ccbbirds.org
