SHORT COMMUNICATIONS 
625 
TABLE I. Number of nest visits (n = 1,089) for the egg of the day. The proportion of nests containing a new egg 
changed from <50 to >50% by 0829 hrs (bold). 
Ho 
Egg of the day 
Present 
Nesr visits 
Yes 
No 
Proportion 
Percent 
0530-0629 
3 
0 
3 
0/3 
0 
0630-0729 
27 
12 
15 
12/27 
44 a 
0730-0829 
85 
63 
20 
63/83 
76 a 
0830-0929 
132 
110 
24 
110/134 
82 
0930-1029 
181 
163 
18 
163/181 
90 
1030-1129 
228 
222 
6 
222/228 
97 
1130-1229 
160 
156 
4 
156/160 
98 
1230-1329 
85 
82 
3 
82/85 
96 
1330-1429 
56 
54 
2 
54/56 
96 
1430-1529 
34 
34 
0 
34/34 
100 
‘ Two lime periods between 
which the increase i 
n the proportion of EOD' 
s (egg of the day) 
was significant (:-test for rates and proportions using Yates 
conation). 
1 18 iy' N, 65 45' W). Average annual rainfall and 
temperatures range, respectively, from 200 cm and 
-5 C in the foothills to >500 cm and 19‘ Con peaks 
reaching 1,075 m asl (Garcia-Martino et al. 1996). 
The forest is comprised of four major vegetation 
associations that are altUudinally stratified and 
placed into separate life zones (Wadsworth 1951. 
Ewel and Whitmore 1973 ). 
Egg-laying was monitored from December 1978 
to July 2000 (study design and protocols are 
described in Arendt 2006). I used a standard 
method to estimate the hour of egg laying (Scott 
'993). which entails recording the hour each nest is 
visjted during days females are laying eggs and 
noting whether the *egg of the day' (EOD) is 
present. Scott (1993) also proposed a method for 
calculating the median time for the 24-hr laying 
interval; this is the time when the proportion of 
nests containing a new egg changes from <50 to 
> 50%. Few nest visits in the present study 
occurred during crepuscular and early diurnal 
hours (0530-0630); some early-laid eggs may have 
gone undocumented, especially first eggs. I 
calculated the median time for egg deposition as 
ihere were >100 observations between 0530 and 
9829 hrs AST. the period within which the 
Proportion of nests containing a new egg changed 
from <50 to >50%. I used a c-test for rates and 
Proportions (using Yates correction) to examine the 
too hourly ranges between which the increase in 
l he proportion of EODs was significant (a = 0.05). 
RESULTS 
One egg was laid each day until the clutch was 
complete (n = 1,089 observations during 1979— 
2000). Most eggs were laid in the morning (0630- 
1129 hrs; median lay hour = 0723). Forty-four 
percent were laid by 0729 hrs and 76% were laid 
by 0829 hrs. However, the latter eggs (2nd. 3rd. 
4th eggs in 2-, 3-. and 4-egg clutches) are laid 
later in the day. and all EODs were not found in 
the nest until 1529 hrs (Table 1). 
The first two eggs of a clutch were generally laid 
by mid morning (0630-0929 hrs), whereas the last 
egg (usually the third, and much less frequently a 
fourth) was often laid later in the day (until 1429 hrs) 
and was responsible for expansion of the hourly 
laying period (Fig. I). Almost 90% of the eggs 
initialing a clutch were laid by 0729 hrs, and most 
were present by 0829 hrs (median = 0642 hrs). 
Second-laid eggs were not always laid in the early 
morning hours as were initial eggs of a clutch 
because second-laid eggs in 151 nests completed the 
clutch and some were laid as late as 1529 hrs. Only 
about half of second-laid eggs were present hy 0729 
hrs (median = 0713), whereas most (88%) were not 
present until 0929 hrs. .All second-laid eggs were 
present well after mid-day (1529 hrs at the latest) 
(Fig. I). Most third-laid eggs were laid between 
0729 and 0829 hrs (median = 0826) when 39% 
were present, and 74% were present by 1029 hrs. All 
third-laid eggs were present by 1529 hrs. None of 
the 22 fourth-laid eggs was present until between 
0830 and 0929 hrs (median = 0957) when 25% 
were recorded. All fourth-laid eggs were present by 
1029 hrs (Fig. 1). There was no significant trend for 
day of the week initiatory eggs were laid, although 
there was a continuous increase each day from 
Sunday to Friday, with prominent increases from 
Sunday to Monday and Thursday to Friday (Fig. 2). 
