Avalos • REPRODUCTION OF SWALLOW-TAILED COTINGA 
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2-5 6-9 10-13 14-17 18-22 23-27 
Nestling age (days) 
FIG. 3. Provisioning rate (mean ± SD) by parents in 
relation to age category of nestlings. 
0.9773 i 0.0065 (n = 20, total nestling exposure 
days = 378). The probability of success during 
the incubation period was 36% (mean incubation 
period = 18 days) and 53% for the nestling period 
(mean nestling period = 27.5 days). The proba¬ 
bility of daily survival during the nestling period 
was higher than during incubation period (X 2 = 
16.18, df = 1, P < 0.001). 
The probability of survival of a nest from 
incubation to fledging was 20%. Predation was 
the main cause of nest failure (72%). Eggs 
disappeared from 18 nests (75% of failures) and 
parents deserted six nests (25%) during the 
incubation period. Eight (72%), of 11 nests that 
failed during the nestling period, failed when 
nestlings were 18-20 days of age due to 
disappearance or the entire nest being destroyed. 
Three nests contained dead nestlings (28%) after 
heavy rain at night. I also found dead nestlings of 
-7 days of age on terrestrial bromeliads and rocks, 
apparently in failed attempts to fly from the nest. 1 
did not observed predation directly, but I observed 
Parental sentinel behaviors, including standing up 
'n the nest, inclining the head and body, 
v ocalizing alarm calls (especially females) in 
Presence of tayras (Eira barbara). Squirrel 
Cuckoos (Piaya cayana), and while escaping 
from snakes. 
DISCUSSION 
The first nest of the Bolivian Swallow-tailed 
Cotinga that I discovered was in early November 
and contained older nestlings; the last nests were 
found in late February and early March 2006 and 
contained young nestlings. Bromfield et al. (2004) 
reported nests with eggs in late September in the 
Pata area (Apolo). These reports suggest the 
breeding season for the Bolivian Swallow-tailed 
Cotinga is from September to March, between the 
end of the dry season and the end of the wet 
season in the study area. This time of breeding 
might be related to food abundance (Stutchbury 
and Morton 2001). The length of the nesting 
period is consistent with records for medium-size 
cotingas (Snow 2004), and its variation in length 
among nests might be a result of external 
conditions including: climate, and proximity of 
cattle, local people, and predators that affect 
fledging of nestlings (Skutch 1945). 
The clutch size for the Brazilian population 
(Phibalura f flavirostris) is 2-3 eggs (Snow 
2004). I recorded a clutch of two eggs for the 
Bolivian population in my study area, similar to 
fruiteaters in the Andes (Snow 2004). The eggs 
were incubated continuously and parents ex¬ 
changed nest care every hour as in some other 
monogamous species (Monaghan and Nager 
1997). However, incubation by both parents is 
unique among cotingas. even by those with 
biparental care (Snow 2004). Incubation periods 
of males were longer than those of females; 
probably because females needed more time to 
increase body mass after laying eggs. 
Both parents spent equal amounts of time 
caring for the young during the nestling period, 
concordant with some tropical species with 
biparental care (Wheelwright 1983, Dyrcz 2000, 
Dobbs et al. 2001). Parental care decreased as 
nestlings grew, as is the case in multiple avian 
taxa (Gill 1995), including cotingas (Amaya- 
Espinel 1997, Quispe and Flores 2002. Karubian 
et al. 2003, Muir et al. 2008). Small nestlings at 
the beginning of the study were continuously 
brooded by the parents because they did not have 
feathers and were presumably incapable of 
thermoregulation (Gill 1995). Brooding decreased 
and parents increased the time they perched near 
the nest once feathers began to grow and nestlings 
were older. 
Both parents perched in trees surrounding the 
nesting tree, which presumably facilitated preda¬ 
tor observation (e.g., Breitwisch 1986, Hall and 
Karubian 1996, White et al. 2006). This was 
important because nestlings flapped and moved 
which may have drawn the attention of predators. 
Parents also seemed to avoid possible dangers 
when they: (1) waited in canopy trees carrying 
