The Wilson Journal of Ornithology 124 ( 2):277 285 . 2012 
NESTING ECOLOGY OF THE BLACK-CAPPED VIREO IN 
SOUTHWEST TEXAS 
KATHRYN N. SMITH. 125 JAMES W. CAIN III. 1 4 
MICHAEL L. MORRISON. 2 AND R. NEAL WILKINS' 
ABSTRACT.—There is little information about nesting ecology of the federally endangered Black-capped Vireo ( Vireo 
atricapilla) in the southern and western region of its breeding range, which is characterized by xenc thomscrub and patchy 
low-growing vegetation. We mapped territories and monitored 119 Black-capped Vireo nests across seven study sites in 
2009 and 2010 in Val Verde County. Texas in the Devil’s River region on the western edge ol the Edwards Plateau. We 
• Served69 nests with cameras to identity nest predators. Clutch si/e was significantly smaller in 2009 (3.4 ± 0.82) than m 
2010(3.8 r 0.43). Both nest depredation and parasitism by Brown-headed Cowbiids (Mololhrus nn>r) were >10 r higher 
hi 20<» than in 2010. There was a large diversity of nest predators identified including Brown-headed Cowbird (/i - 4). 
snakes In = 4). and Greater Roadrunner (Geocoeew ctilijomianus) (» = 3). Species identified that have not been 
previously observed as Black-capped Vireo nest predators were bobcat l Lynx rufus ). common raccoon IP racy on lotor). 
Greater Roadrunner. and the greater arid-land katydid (Neohmrettiu spinosa\. Productivity of Black-capped Vireos in the 
Devil’s River area appeared to be heavily influenced by weather, particularly precipitation during the breeding season. 
Received IJ August 2011. Accepted 15 December 2011 
The Black-cappetl Vireo (Vitro utncapiltu ) is a 
federally endangered migratory songbird (Raulaff 
1987) with a current known breeding range 
extending from central Oklahoma south through 
Texas to the Mexican slates of Nuevo Leon and 
southwestern Tamaulipas (Gtabcr 1961, Farquhar 
and Gonzalez 2005; Fig. I). The eastern limit in 
Texas follows the Balcones Escarpment (Cirabcr 
*961). and small numbers Black-capped Vireos 
have been observed as far west as Big Bend 
National Park (Grzybovvski 1995). Breeding hab- 
iiai is characterized by patchy distributions of low. 
scrubby growth mostly of deciduous woody shrubs 
and trees of irregular height (Graber 1961). Black- 
capped Vireos establish territories in areas with 
high vegetation density between 0 and 2 in in 
height (Grzybowski 1995), and build the majority 
°f 'heir cup nests in this zone (Graber 1961). 
Most of the intensive studies ol the Black- 
capped Vireo have occurred in a few locations in 
Department of Biological and Environmental Science. 
G\a% A&M University-Commerce. Commerce. I X 75429. 
USA. 
Current address: Department of Wildlife and Fisheries 
Sciences. Texas A&M University, College Station. TX 
7 ' *43. USA. 
InMituie of Renewable Natural Resources. Texas A&M 
University, College Station, TX 77843. USA. 
4 Current address: U.S. Geological Survey. New Mexico 
G"operative Fish and Wildlife Research Unit. Department 
of Fish. Wildlife, and Conservation F.cology. New Mexico 
State University, l.as Cruces. NM «8(X)3, USA. 
Corresponding author: e-mail: 
kathryns84@neo.tainu.edu 
the Edwards Plateau region of Texas and in 
Oklahoma tWilkins et al. 2006). To date, about 
75% of the known population in the breeding 
range is in four well-surveyed areas (Fig. I): Foil 
Hood Military Reservation and Kerr Wildlife 
Management Area (WMA) in Texas, and in two 
adjacent areas in Oklahoma (Wichita Mountains 
Wildlife Refuge and Fort Sill Military 1 Reserva¬ 
tion). These areas contain most of the known 
breeding population, but comprise \% of the total 
area in the Texas/Oklahoma range of the Black- 
capped Vireo (Wilkins et al. 2006). Kerr WMA is 
the furthest location south and west that has been 
intensively surveyed (Grzybowski et al. 1994. 
Dufault 2004. Pope 2011). 
Currently, little is known about the Black- 
capped Vireo’s ecology and threats in the more 
arid habitat of southwest Texas and central 
Mexico, a region characterized by xeric thorn- 
scrub, patchy low-growing vegetation, and 150— 
250 mm less rainfall per year than areas (USDC 
2010) where Black-capped Vireos have been well 
surveyed in the past (Fig. 1). Black-capped Vireos 
in Kinney and Edwards counties may be part of a 
metapopulation or series of isolated populations 
extending south and west in canyons traversing 
the upper bend of the Rio Grande River including 
canyons of the Devil’s River in Val Verde 
County, where the status of the Black-capped 
Vireo is not well known (Bryan and Stuart 1990, 
USDI 1991. Grzybowski 1995). Data collected in 
the Devil’s River area may also be applicable to 
the ecology of Black-capped Vireos in northern 
Mexico and could add to understanding the 
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