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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 2. June 2011 
nestling observation was 16 July 2007 with no 
checks performed during the interim. We esti¬ 
mated from size and appearance that the trembler 
nestlings hatched on 15 July 2007, based on our 
experience observing >100 nesting attempts by 
the closely related White-breasted Thrasher. Thus, 
the incubation period of this nest was —14 days. 
The last day we observed nestlings was 25 July, 
and the nest was empty on 30 July 2007. The 
nestling stage was a minimum of 11 days if the 
nestlings hatched on the date we estimated. 
However, we saw no evidence of fledging (i.e.. 
we did not hear fledglings calling from outside the 
nest nor observe any adult trembler behavior 
suggesting that fledglings were in the immediate 
vicinity of the nest). The trembler nest was 
possibly depredated, given the high rate of failure 
for the open-cup and similarly placed White¬ 
breasted Thrasher nests in the same habitat 
(Mortensen 2009). 
We observed two Gray Trembler fledglings at 
different locations within the study site on 27 and 
28 June 2007. If we assume a nesting cycle of 
~25 days (likely an underestimate due to 
uncertainty about clutch initiation date, hatching 
date, and date of failure/fledging), the known 
Gray Trembler breeding season extends, at least, 
from the beginning of June until the end of July. 
Nest Description.—The Gray Trembler had a 
bulky, open-cup. not domed, nest (Fig. I A. B). The 
cup of the nest consisted mostly of dead leaves and. 
to a lesser extent, thin twigs, and lacked the cleanly 
woven cup-structure of rootlets and other plant 
fibers typical of some other members of the catbird 
and Caribbean thrasher clade (RLC. pers. obs.). 
The outer portion of the nest consisted of larger 
twigs with dead leaves between the twigs sur¬ 
rounding the cup. The nest was in the forking 
branches just below the lop of the crown in a -4.5- 
m tall Myivia deflexa (Myrtaceae) tree. 
Eggs, Hatching Success, and Brood Reduction. _ 
The Gray Trembler nest contained three light 
greenish-blue eggs (Fig. IB), nearly identical in 
appearance to eggs of other members of the catbird 
and Caribbean thrasher clade. especially to those of 
the White-breasted Thrasher (JBL. pers. obs.). All 
three eggs hatched. One of the three nestlings 
disappeared from the nest between 23 and 25 July 
2007, but the parents continued to feed the 
remaining two nestlings. 
We used two still-frames from one of our 
videos and morphometric data from the literature 
to estimate sizes of the three eggs. Storer (1989) 
reported a mean beak from nostril length of 
31.38 mm for female St. Lucian Gray Trembler. 
We used this value and ImageJ (Abramoff et al. 
2004) to estimate the length of a small stick in the 
nest visible in a still-frame with a Gray Trembler, 
which we assumed to be female, incubating 
(Fig. 1 A). We used this reference to estimate the 
length and width of the three eggs in another still 
frame. Estimated dimensions (length X width) of 
the three eggs were 19.37 X 16.73 mm. 21.32 > 
16.63 mm, and 19.91 x 15.61 mm. yielding mean 
(± SD) length of 20.20 ±1.01 mm and width of 
16.32 ± 0.62 mm. However, these estimates have 
limited accuracy because of the assumptions 
inherent in our methodology. 
Parental Behavior .—Parents fed the nestlings a 
combination of arthropods, small vertebrates, and 
fruit. Specifically identified food items included 
centipedes (Scolopendra spp.) and dwarf geckos 
(Sphaeroductylus spp.). We did not band any 
adult tremblers near the active nest, and wc 
observed no more than two adults concurrently in 
the vicinity of the nest. One trembler, on more 
than one occasion, flew at and pecked the video 
camera. However, even with the camera posi 
lioned < l m from the nest, at least one adult 
continued to incubate during the egg stage and 
provision chicks during the nestling stage. 
DISCUSSION 
Our observations of St. Lucian Gray Trembler 
nesting biology question the accuracy of historical 
nest descriptions, while highlighting the necessity 
of rigor in field studies of avian reproduction. We 
propose two reasons for the discrepancy between 
our observations and previously published Gray 
Trembler nest descriptions: (1) initial descriptions 
of a Gray Trembler’s nest were inaccurate and 
open-cup nests are typical for the species, on - 1 
the disparity between accounts reflects natural 
variation in the species, as recently obsened in 
another Caribbean mimid. the Black Catbird 
(Mehmoptila glabrirostris), which can nest la,' 
in open, cavity-like depressions in dead or Inina 
trees, (b) between peeling bark and tree tninks. 
and (c) in typical, mimid open-cup nests in 
branches (JBL. unpubl. data). Some variation in 
nest structure exists among and within species in 
the Mimidae, including Sage and Brown thrash¬ 
ers. species that occasionally nest on the ground 
(Cody 2005), and Pearly-eyed Thrasher, which 
often nests in secondary cavities (Arendt 2006). 
However, construction of a domed nest for Gray 
