Smith et al • NESTING OF THE BLACK-CAPPED VIREO 
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TABLE 1. Nest observations of Black-capped Vireos in Val Verde, Kerr. 1 ravis. and Coryell counties, Texas during 
2009 and 2010 (MLM, unpubl. data). ND = no data. 
2009 
2010 
Val Verde 
Kerr 
Travis 
Coryell 
Val Verde 
Kerr 
Travis 
Coryell 
Find incubation observed 
14 Apr 
29 Apr 
ND 
9 May 
7 Apr 
23 Apr 
15 Apr 
ND 
Latest date of active nest 
14 Jul 
19 Jul 
ND 
13 Jul 
14 Jul 
24 Jul 
11 Jul 
ND 
Date of first parasitism 
21 Apr 
30 Apr 
ND 
9 May 
3 May 
ND 
23 Apr 
ND 
Clutch size 
3.4 ± 0.82 
3.7 ± 0.45 
ND 
3.4 ± 0.68 
3.8 ± 0.43 
3.8 ± 0.44 
3.8 ± 0.48 
ND 
March to 32.2 C in July. The mean temperature 
in 2010 ranged from 16.2 C in March to 29.4 C 
in June (USDC 2010). 
Mean (± SE) clutch size was smaller in 2009 
(3.4 ± 0.82) than in 2010 (3.8 ± 0.43; t,, 7 = 
-3.278. P = 0.0014). The proportion of Black- 
capped Vireo eggs that hatched did not statisti¬ 
cally differ in 2009 (0.84 ± 0.24) from 2010 
10.88 ± 0.21; l 62 = -0.697. P = 0.4881). 
The proportion of nests parasitized was lower in 
-010 (26%) than 2009 (37%). The proportion of 
nests depredated was also lower in 2010 (39.5%) 
than 2009 (51,3%). These differences between 
years were not statistically different for parasitism 
(r' = 13324. P = 0.2484. df = I) or depredation 
(r = 1.4250. P = 0.2326, df - I). The first 
record of Brown-headed Cowbird parasitism in 
2009 occurred on 21 April. Nest parasitism was 
not recorded in 2010 until 3 May and regular 
parasitism of nests did not occur until the end of 
May (Table I). We did not observe Bronzed 
Cowbird (Mololhrus aeneus) parasitism in either 
year. 
Mayfield estimates of daily survival rate (.v * 
'■'El for incubation and nestling periods combined 
Were 0,947 ± 0.007 (95% Cl - 0.931 -0.959) and 
*-*•968 ± 0.007 (95% Cl = 0.950-0.980) in 2009 
and 2010. respectively. Higher nest success obser- 
'cd in 2010 was primarily due to success of nests 
' n the llrst half of the breeding season (Fig. 2). 
( Tne monitored pair in 2009 attempted a second 
brood that subsequently failed. Black-capped Vir- 
e ° s at six monitored territories attempted second 
broods in 2010. and two Hedged young, bringing 
*bc total fledged in those territories to six and 
seve n young. An additional second brood attempt 
occurred in a nest that had not been previously 
Monitored (i.e.. male observed feeding fledgling 
w bile also building new nest), which was later 
Parasiti/ed and abandoned. 
Nest depredation was the leading cause of nest 
failure in 2009 and 2010 followed by parasitism 
(Fig. 3). Other causes of nest failure were 
abandonment, nest tailing because of apparent 
poor construction, eggs not hatching, and destruc¬ 
tion by flooding. No nest abandonments were 
caused by cameras. Both occasions of the nest 
falling and eggs not hatching occurred in 2009: 
nest failure because of Hooding occurred in 2010. 
We recorded video at 43 nests in 2009 and 26 
nests in 2010. Cameras recorded 20 depredation 
events and we were able to identify 10 predator 
species (Table 2). Seven (35%) of 20 depreda¬ 
tions recorded were in the incubation stage of 
the nest cycle and 13 (65%) were in the nestling 
stage: all events resulted in nest failure. Eight 
depredations occurred at night and 12 occurred 
during daylight hours. Most snake depredations 
occurred at night, all avian depredations occurred 
during the day, and mammal depredations oc¬ 
curred in riparian ureas and were mainly crepus¬ 
cular except for ringtail {Bassariscas astutus) 
depredation that occurred at night, Species 
depredating Black-capped Vireo nests most often 
were Brown-headed Cowbirdx (>i = 4) and snakes 
(n = 4); however. Brown-headed Cowbirds were 
only recorded depredating nests in 2009. We 
identified three snakes to species level: two 
Baird's rat snakes (Elaphe bairdi) and one 
Trans-Pecos rat snake ( Bogertohis subocularis). 
Avian predators accounted for 40% (n = 8) of 
nest depredation events observed on video. Insects 
(ants and greater arid-land katydid [Neobarrettia 
spinosa ]) accounted for 15% (>/ = 3) of 
depredation events recorded and all occurred 
during the nestling stage. Mammals were identi¬ 
fied as the nest predator in 25% of the events (n = 
5) and all occurred in riparian areas. 
DISCUSSION 
Black-capped Vireo nesting ecology in south¬ 
west Texas is similar in many ways to other areas 
of their range. Average dutch size (3-4) is the 
same as recorded in Oklahoma (Grzybovvski 
