Smith et al. • NESTING OF THE BI.ACK-CARPED VIREO 
283 
TABLE 2. Nest predators identified using nest cameras 
depredating randomly-selected Black-capped Vireo nests in 
the Devil's River area. Texas in 2009 and 2010. 
Predator 
2009 
2010 
Totals 
Brown-beaded Cowbird ( Molothrus 
titer ) 
4 
0 
4 
Snakes 
2 
2 
4 
Greater Roadrunner (Geococcyx 
califomianiu) 
2 
1 
3 
Ants 
2 
0 
2 
Gra;> fox ( Urocyon cinereoargenteus) 
2 
0 
2 
Bohcat (Lynx mfits) 
0 
1 
1 
Greater arid-land katydid 
(Neobarrettia spinosa) 
0 
1 
1 
Common raccoon ( Procyon lotor) 
0 
1 
1 
Ringtail (Bassarisais amutus ) 
1 
0 
1 
Western Scrub-Jay ( Aphelocoma 
lolifomica) 
1 
0 
1 
Totals 
14 
6 
20 
1995) and other studies in central Texas during 
2009 and 2010 (Table 1). Nest building and 
incubation began 1-2 weeks earlier in the Devil's 
River area than in other areas being monitored 
during the same years in Texas, but final nesting 
attempts ceased at approximately the same time as 
areas being monitored in central Texas (Table I). 
Thus, the breeding season is longer for Black- 
upped Vireos in the Devil's River region. This 
vxtra time at the beginning of the breeding season 
is likely giving Black-capped Vireos in south¬ 
western Texas and northern Mexico more oppor¬ 
tunity to produce young. Black-capped Vireos in 
region also had an advantage over vireos 
breeding in central Texas where parasitism 
pressure and initial incubation began simulta¬ 
neously in 2009 and 2010. because parasitism 
h . v cowbirds was delayed 1-2 weeks after the 
commencement of incubation (Table 1). 
Productivity of Black-capped Vireos in the 
0eul\ River area appeared to be heavily influ¬ 
enced by weather, particularly precipitation during 
'he breeding season. Other studies of avian pfoduc- 
bviiy have indicated increased rainfall during the 
breeding season directly affects avian populations 
1 1 'emi-arid regions (Bolger et al. 2005. Djerdali et 
a l Several studies indicated tood supply 
the main cause of increased nest success when 
Precipitation increased (Nutt et al. 2002. Ulera and 
Ouiz 2006). However, Coe and Rotenberry (2003) 
s ho\ved that supplying water i<> Black-throated 
Sparrows (Amphispiza bilineata) increased clutch 
s >ze independent of food availability. The increase 
in mean clutch size we observed in 2010 may have 
been caused by one or both of these factors, both 
relating to precipitation. Long-term studies are 
needed to fully understand the relationship between 
climate patterns and population dynamics of 
Black-capped Vireos in southwest Texas. 
Nest parasitism and nest predation were >10% 
higher in 2009 than 2010. although not statistically 
different, but were likely biologically significant. 
Weather and precipitation can affect animal move¬ 
ment and habitat selection (Vickcrv and Rivest 
1992). The multiple occurrences of flooding of 
Dolan Creek and other creeks and drainages within 
our study area in 2010 may have influenced the 
normal movement and activity of terrestrial nest 
predators, allowing higher nest success during the 
early part of the breeding season. Increased 
precipitation may have increased food supply tor a 
variety of other potential prey species of local 
predators within the study area. Increased food 
supply may have increased the survivorship and 
reproduction of alternant prey, consequently increas¬ 
ing prey availability for predators within the study 
area and decreasing predation pressure on nests of 
Black-capped Vireos. The influence of cowbirds, 
both as nest predators and parasites, was reduced in 
2010. It is unclear how or if higher precipitation or 
flooding affected Brown-headed Covvbird behavior 
and abundance in 2010. The increase in nest success 
due to decreased depredation and parasitism during 
years with high rainfall may have a role in 
maintaining vireo populations in semi-arid areas ol 
their breeding range. 
There is a diverse assemblage ot Black-capped 
Vireo nest predators in the Devil's River region 
and several had not been previously identified as 
potential nest predators (Stake and Cimprich 
2003, Conk ling 2010) including bobcat (Lynx 
niftis), common raccoon (Procyon lotor), Greater 
Roadrunner (Geococcyx califomianits), and the 
greater arid-land katydid (Smith el al. 2012). 
Avian predators (i.e.. Brown-headed Cowbird, 
Greater Roadrunner. and Western Scrub-Jay 
[Aphelocoma californica]) were most common, 
comprising 40% of all predation events recorded. 
Fire ants are a major threat to Black-capped Vireo 
nests in other areas of their breeding range (Stake 
and Cimprich 2003) but were not observed 
depredating nests in the Devil's River area, likely 
because fire ant occurrence is limited in the study 
area and did not overlap with a large portion of 
Black-capped Vireo breeding habitat (Campo- 
mizzi et al. 2009; KNS. pers. obs.). 
