SHORT COMMUNICATIONS 
627 
DISCUSSION 
The median hour of egg deposition for the 
Pearly-eyed Thrasher population studied was 0723 
hi*. which is similar to the median hour of laying 
(0700 hrs) calculated for the Gray Catbird 
(.Dumetella carolinensis) (Scott 1993). Official 
sunrise in Puerto Rico varies 73 min (0547 to 
0700 hrs; median = 0613 hrs) throughout the year 
(U. S. Department of Commerce 2011). The 
Pearly-eyed Thrasher has an extended laying 
period, laying most of its eggs by 1129 hrs. or 
-5 hrs and 7 min after local sunrise, and can delay 
deposition until at least 1429 hrs. This pattern is 
similar to its close relative, the European Starling 
iSrumus vulgaris ), which also has close phyloge¬ 
netic affinities with the Gray Catbird (Mcijer 
I992:fig. 2: Ericson and Johansson 2003: fig. 1). 
Other members of the superfamily Muscicapoidea, 
e.g.. thrushes and flycatchers, are also known to lay 
in the afternoon (Brackbill 1958. Weatherhead et 
al. 1991). Oppenheimer et al. (1996) reported that 
much of die variation in laying limes reflects 
phylogeny, which is reflected in the pattern 
recorded for the Pearly-cyed Thrasher. 
The initial egg mass at laying for most birds is an 
important factor affecting hatchling mass (Deem¬ 
ing and Birchard 2007). The first two eggs in the 
hying sequence of the Pearly-cyed Thrasher are 
heavier and are laid earlier in the day than the last 
une or two eggs completing the clutch (Arcndl 
-Mb). Initial eggs of a clutch laid early in the day 
contribute to a greater age gap between older and 
younger siblings, giving older siblings develop¬ 
mental and survival advantages over younger nest 
males during periods when food and other 
resources may be critically limited (Esler 1999. 
Maddox and Weatherhead 2008). First- and 
second-hatched Pearly-eyecl Thrasher fledglings 
hud a higher probability of being recruited into the 
breeding population and dispersed earlier and 
•anher than younger siblings (Arendt 2006). First- 
J| id second-hatched thrasher fledglings, heavily 
Parasitized by philomid (Philomis spp.) botfly 
larvae (Diptera: Muscidue), lived significantly 
,0 nger and survived better than younger siblings 
"'■to comparable larval numbers (Arentll 1985. 
-900). Unparasitized third- and fourth-hatched 
siblings would often fledge at similar body masses 
und appendicular measurements as those of older 
Ablings but, during food shortages, many would 
la g in development, eventually becoming runts. 
They would be trampled to death by older siblings. 
or simply disappear from nests. I observed females 
on several occasions carrying runt nestlings and 
discarding them 20-30 m from their nest boxes 
(Arendt 2006). Delayed laying in the LEF 
population of the Pearly-cyed Thrasher of the final 
eggs of a clutch may be an adaptive strategy 
triggering brood reduction to ensure survival of 
older, more robust siblings during periods of 
physiological and environmental stress, c.g., food 
shortages (Knight 1987, Murray 1994. Maddox and 
Weatherhead 2008). 
ACKNOWLEDGMENTS 
I appreciate the assistance of my wife Angela I. Arendt. 
parrot project volunteers, and my staff: G. Caban Ruiz, 
Carlos Cianchini Oscar Diaz. Roberto Diaz and M. R. Ford. 
This research was done in cooperation with the University 
of Puerto Rico. 
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