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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 124. No. 3. September 2012 
TABLE 2. Growth parameters for Yellow-olive Flatbill 
fledglings based on the logistic equation: A = mean final 
value. / = inflexion point or stabilizing age at 50% of final 
value, and % Adult = percentage of A in relation to mean 
adult size. 
A 
/ (days) 
% Adult 
Body mass (g) 
17.1 
8 
107 
Wing (mm) 
47.1 
12 
Tail (mm) 
26.7 
14 
Tarsus (mm) 
19.0 
5 
Nostril (mm) 
4.8 
5 
supports the relevance of annual precipitation 
peaks in inducing nesting activity (Cody 1985, 
Hau el al. 2008). Precipitation may affect insect 
abundance (Tanaka and Tanaka 1982), and food 
abundance has been shown to affect breeding 
cycles in other tropical regions (Young 1994. Best 
et al. 1996, Woodworth 1997: reviewed by 
Stutchbury and Morton 2001). 
The nests of the Yellow-olive Flatbill resemble 
those of other species in the genus Tolniomni ; 
from Suriname with the exceptions that eggs were 
smaller, lighter in color, and usually lacked the 
spotted pattern described for congeners (Ha- 
was irregular in rhythm delay (terminology 
reviewed in Wang and Beissinger 2011) and 
hatching was asynchronous, Clutch size was 
unusually large and survival rates were relatively 
low for tyranninds or tropical passerines in 
general (e.g.. Aguilar et al, 1999. 2000; Robinson 
et al. 2000: Aguilar 2001; reviewed by Yom-Tov 
et al. 1994). Our observed clutch sizes agree with 
previous descriptions for the species in Brazil 
(Sick 1997) and in southwestern Ecuador (H. F. 
Greeney. pers. comm.), although other breeding 
accounts for the species indicate clutch sizes are 
usually only 2-3 eggs (reviewed by Jetz et al. 
2008). A higher initial investment could represent 
an opportunity lor increased reproductive success 
in favorable seasons (Forbes 1991, Stienen and 
Brenninkmeijer 2006). It is important to focus 
further studies on sampling the temporal variation 
in resource availability and abiotic conditions, 
including precipitation and effects on survival 
rates. 
The hypothesis that breeding cycles are asea- 
sonal in the tropics has been recently refuted, as 
more climatic and reproductive data became 
available (Hau et al. 2008). The common 
association between breeding and annual precip¬ 
itation cycles may apply to tropical birds in 
strongly seasonal environments, such as our study 
population of Yellow-olive Flatbills. The marked 
breeding seasonality of the Yellow-olive Flatbill 
is similar to that observed for all tyrannids studied 
in the sanie reserve system (Aguilar et al. 
1999, 2000; Aguilar and Marini 2007). and is in 
agreement with findings for other passerines in 
southeast Brazil (Cavalcanti and Pimentel 
988, Mann, 1992, Belton 1994. Picltorim et al. 
QOO 2 aSCOnCdos ami Lombardi 1996. Sick 
997, Marini and Duraes 2001). The association 
between nesting and precipitation observed 
were more similar to those described for ihis 
species Irom Colombia (Hilly and Brown 1986). 
Eggs were laid at irregular intervals (i.e.. more 
than 24 hrs apartj in the majority of nests in = 
47), and were incubated for longer periods than in 
regular egg-laying tyrannids, including Leptopo- 
Ron omaurncephalus (Simon 1997. Aguilar and 
Marini 2007). Pyrrhomyias citmwmmeus ( Collins 
and Ryan 1995), Lathrotriccus euleri (Aguilar 
el al. 1999), and Mionectes rufiventris (Aguilar 
et al. 2000). 
Hatching success (i.e., the probability of an egg 
to produce a nestling) was higher than for several 
passerine species reported in Ricklefs (1969). and 
lor tyrannids studied by Aguilar ct al. (1999. 
2000). Aguilar (2001). and Aguilar and Marini 
(2007 1 in the same study areas. Eggs may fail if 
hatch due to infertility (Davis 1958 ) or embryonic 
death (Clemmons and Buchholz 1997. Yerkes 1998). 
Other causes of egg loss may include infections, 
nutritional deficit, and water loss (Jamieson el al. 
1999). Causes of egg failure were not systemati¬ 
cally investigated in our study, although some 
unhatched eggs did not have embryos, possibly a 
sign of inbreeding due to low dispersal in thes 
fragmented landscape. Other indicators of distur¬ 
bance caused by restricted gene flow in the area are 
mutant phenotypes from other species (Anciaes 
et al. 2005) and higher developmental instability in 
forest fragments in the same region of the study 
area (Anciaes and Marini 2000). 
The present data suggests the high investment 
in egg production is not related to low hatching 
success in the species, but may reflect an 
opportunity to increase fitness under favorable 
abiotic (e.g.. rain) and biotic (e.g., food) condi¬ 
tions. Limits to the number of eggs laid seem to be 
more affected by the capacity of parents to raise a 
brood than energetic requirements to lay more 
