Walsh et al. • HYBRIDIZATION IN NELSON'S AND SALTMARSH SPARROWS 
317 
species that diverged < 1-2 million years ago and, 
1 ‘ierefore, have not yet evolved reproductive 
dialing harriers or hybrid inviability (Mallet 
2005 ). The occurrence of hybridization has been 
correlated with many ecological factors including 
purapatiy. scarcity, and low male parental care 
Randier 2006). Hybridization and introgression 
.an lead to harmful effects including hybrid 
'Winns, outbreeding depression, and reduced 
fitness, and can be especially problematic when 
k species is less abundant than the other 
'Rhymer and Simberloff 1996. Allendorf et al. 
2'dl). Hybridization with an invading eonspecific 
has been responsible, at least in part, for the 
extinction of several threatened species (Rhymer 
jedSimberloff 1996. Allendorf et al. 2(X) 1. Buggs 
-’ffil. Thus, it is important to monitor and 
consider the impacts of hybridization in Nelson's 
llli ! Saltmarsh sparrows in light of these poten- 
la ". v ne guiive consequences. Both species are a 
conservation priority in the northeastern 
’ wd States (USDI 2008), and the Saltmarsh 
Sparrow' is considered globally vulnerable to 
extinction (IUCN Red List criteria: Birdlife 
iiternational 2004). This concern is based on the 
^'marsh Sparrow’s limited range and its obli- 
: We dependence on a narrow strip of hcuvily- 
•ragmented coastal marsh habitat that is vulner- 
4 c 10 anthropogenic degradation and sea level 
pCjerdrum et al. 2005, Greenberg et al. 2006). 
x pansion ot the overlap zone and the potential 
nr mcreas *d hybridization, therefore, may pres- 
^“greater threat to the long-term persistence of 
’’ x ^“brnarsh Sparrow. 
Our objectives were to: (1) develop a diagnostic 
based on the DNA barcoding region to 
JfUfy Saltmarsh Sparrows of hybrid origin, 
u i “ l evaluate the extent of introgression 
g h°ut the overlap zone. 
METHODS 
,-( rea an j Sample Collectioru —We used 
010 six 12-m mist nets with size 36 mm mesh 
a ^ u lt sparrows. Blood samples (30— 
5 I o * ' VCrc drawn from the cutaneous ulnar vein 
Jj 1 * a non -heparinized capillary tube. We 
ecled one or two tail feathers instead of blood 
In 8 , Cw individuals. Individuals were identified 
p, c * le ld as either Nelson’s or Saltmarsh 
foj Ws ^ plumage characteristics and morpho- 
r ; | e Ca meas urements (Shriver et al. 2005). We 
all birds within 10-20 min of capture. 
*** samples were stored on Whatman filter 
cards at room temperature for later genetic 
analysis. All individuals were sampled during 
the breeding season (Jun-Aug) and only breeding 
adults were used in the analyses (confirmed by the 
presence of a brood patch/cloacal protuberance). 
We obtained blood or feather samples from 
known individuals from outside of the overlap 
zone (/i = 8 Nelson's Sparrows from Penobscot 
River, Maine: 44 36.58' N. 68 50.58' W and n 
8 Saltmarsh Sparrows from Shirley and 
Oceanside. New York; 40 47.50 N, 72 53.06 
W and 40 37.27' N. 73 37.38' W) to develop a 
genetic assay for species identification. Individu¬ 
als were also sampled within the overlap zone, for 
which species identification was based on mor¬ 
phological features (O. P. Lane. pers. obs.; n = 4 
Saltmarsh Sparrows and it = 3 Nelson s Sparrows 
from Wells and Scarborough, Maine: 43 16.96' N, 
70 34.97'Wand 43 33.90' N. 70 : 21.71 W). We 
obtained field measurements of culmen length 
(mm), bill width (mm), and depth (mm) using 
digital calipers, and mass (to the nearest 0.1 g) using 
a digital scale for allopalric Nelson's and Saltmarsh 
sparrows (« = 34 Nelson's Sparrows from 
Penobscot River, Maine and n = 29 Saltmarsh 
Sparrows from Shirley, New York). One individual 
made all bill measurements and weights, and 
performed all species identifications in the held. 
We applied our genetic lest to 426 samples 
collected from putative Saltmarsh Sparrows 
during ongoing toxicological (Lane and Evers 
->007 Lane et al. 2008) and population genetics 
(Walsh 2009) research. Our purpose was to 
identify sparrows of hybrid origin by a mismatch 
between morphology and mtDNA. We focused on 
introgression of Nelson's mtDNA into Saltmarsh 
Sparrows, as our samples were collected only 
from individuals identified morphologically as 
Saltmarsh Sparrow. Samples were collected from 
nine marshes along the northeastern U.S. from 
->006 to 2008 (Fig. 1). Study mashes were in 
Wells. Maine (Rachel Carson NWR: 43 163)6 
m 7 o 3497 ' W); Scarborough, Maine (Scarboi- 
ouah State Wildlife Management Area: 43 33 90' 
N 70 21.71' W): Hampton. New Hampshire (42 
S5 66 ' N 70 48.65' W); Rye. New Hampshire 
->() ->4' N. 70 43.27' W); Stratham, New 
Hampshire (43 20.44' N. 70 55.48' W,: New- 
burvport. Massachusetts (Parker River NWR 42 
46.45' N, 70 48.51' W); Narragansett. Rhode 
Island (John H. Chafee NWR: 41 27.41' N. 71 
-> 6 . 88 ' W): Shirley, New York (Wertheim NWR: 
40 : 47.50' N. 72 53.06' W): and Oceanside, New 
