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The Wilson Journal of Ornithology 123(3):624-628, 2011 
Hourly Laying Patterns of the Pearly-eyed Thrasher {Mcirgcirops fuscatus) in 
Puerto Rico 
Wayne J. Arendt * 1 
ABSTRACT.—Temporal aspects of egg deposition 
are important factors governing avian reproductive 
success. I report hourly egg-laying patterns of the 
Pearly-eved Thrasher (Margarops fuscatus) in the 
Luquillo Experimental Forest in northeastern Puerto 
Rico during 1979-2000. Initiatory eggs were laid by 
early morning (median - 0642 hrs. AST) and almost 
half of the eggs were laid by 0723 hrs. Many 
penultimate and eggs completing a clutch, however, 
were laid later in the morning and some not until mid 
afternoon 1 1429 hrs). thus extending egg deposition to 
8 hrs. Delayed laying of the last eggs in a dutch may be 
an adaptive strategy triggering brood reduction to 
ensure survival of older and more robust siblings during 
periods of physiological stress and food shortages. 
Received 20 March 2007. Accepted 21 February 20! 1. 
There is substantial variation in the precise hour 
of egg laying in birds (Scott 1991, McMasteret al. 
2004), but most birds generally lay their eggs in the 
morning. Many north-temperate passerines lay one 
egg per day, often within 2-3 hrs shortly before or 
after local sunrise until the clutch is complete 
(Skutch 1952. Brackbil! 1958, Nolan 1978. Scott 
1993, Hattom 1996, McMaster el al. 2004). 
Temporal aspects of egg deposition affect all 
aspects of avian reproduction, e.g., egg size. 
• ! U „ SDA - ForcsI Service. International Institute of Trop- 
i F n r8 ^’ Sabana Research Station, HC 2 Box 6205. 
t|U ' °' R 00773. USA; e-mail: waynearendt@gmail.com 
hatching patterns and synchrony, size, fitness, and 
viability of nestlings (Williams 1994 , Maddox and 
Weatherhead 2008). Egg size, usually expressed in 
volumetric or longitudinal measures (Barta and 
Szekely 1997). is often correlated to hatchling sue. 
fitness, and subsequent nestling development 
(Slugsvold et al. J984, Deeming and Birchard 
2007). However. Ricklefs (1984) cautioned u>ui- 
egg size or muss as a measure of egg quality 
actual composition, e.g., the amount and quality ■•'t 
yolk, is usually independent of linear or volumes - 
measures. Even variation in embryonic meiaK'^ 
rates influences time of hatching and hatchling 
size, and maturation and fitness (Badzinskt et al 
2002 ). Maddox and Weatherhead (2008)suggest 
that other maternal factors, e.g.. asynchronou' 
hatching, override many of the previously es¬ 
poused endogenous and environmental factors 
Knowledge of timing of laying appear to IJ " 
have been reported for the Pearly-eyed Thrashci 
(Margarops fuscatus). The objective of this paper 
is to report the chronology and pattern of eg_- 
deposition for a montane population in Puerto 
Rico and relate it to the asynchronous hatching' 
observed in this population. 
METHODS 
The study area was within the 11,330-haLuquili*'’ 
Experimental Forest (LEF) in eastern Puerto Rico 
