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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 2. June 2012 
TABLE 1. Lilac-crowned Parrot productivity and sex ratios from 2001 to 2009. 
Breeding season Number of clutches Nestlings examined 
Nestling survival 
(lledglings/hatchlings l Proportion of males 
2001 
2002 
2003 
2004 
2006 
2007 
2009 
Overall 
11 
0.583 
0.55 
17 
0.778 
0.59 
9 
0.313 
0.56 
10 
0.909 
0.40 
4 
0.50 
0.50 
8 
0.50 
0.50 
7 
0.813 
0.29 
66 
0.619 
0.50 
all years combined to test the date of hatching 
hypothesis (Dijkstra et al. 1990. Genovart et al. 
2003), which predicts manipulation of brood sex 
ratio early in the season to allow more parental 
investment and ensure survival of the most fit 
young. (3) We examined the distribution of males 
and females with hatching order within a clutch to 
test the sequence of hatching hypothesis (Dijkstra 
et al. 1990, Genovart et al. 2003). which predicts a 
sex bias with order of hatching within clutches. 
METHODS 
The study population inhabits the tropical dry 
forest o! the Chamela-Cuixmala Biosphere Re¬ 
serve along the Pacific Slope of Jalisco. Mexico. 
Rainfall is highly seasonal with 80% occurring in 
the rainy season from June to October (Bullock 
1986). Lilac-crowned Parrots nest during the 
dry season from February to May (Renton and 
Salinas-Melgoza 1999). and fluctuations in rain¬ 
fall influence subsequent availability of food 
resources (Renton 2001. 2002). We used the 
amount of rainfall from June to February, the 
period prior to egg laying, as a proxy for 
environmental quality. We monitored 32 nesting 
attempts between 2001 and 2009, and collected 
f °- 6 
E °« 
I “ 
a 02 
e 
0.1 
200 400 600 800 1000 
Rainfall Jun-Feb (mm) 
FIG. 1. Linear regression of ihe proportion of m 
L lac-crowned Parrot offspring produced in the populat 
,ainfa " ” « 
blood samples from 66 nestlings; no samples were 
collected in 2005 or 2008. About 20 pL of blood 
was collected when nestlings were >1 month of 
age. Blood was stored in lysis buffer at -20 C 
until analysis. Purified DNA was extracted using a 
Qiagen DNEasy kit. The primer multiplex of Han 
et al. (2009) (PO-P2-P8) was used for polymerase 
chain reaction (PCR) amplification (conditions 
available upon request). PCR products were 
examined on a 2% agarose gel to score sex by 
product size. 
We calculated sex ratios for the entire data set and 
by year. A Chi-square goodness of fit test was 
applied to identify any deviation from a 0.5 
proportion of males in the entire population of 
nestlings. We used linear regression on the yearly 
proportion of males with the amount of rainfall poor 
to egg-laying to evaluate whether sex ratio wa- 
related to environmental quality. The breeding 
season was divided, for analysis of hatch date, into 
three hatch periods of equal length between the 
earliest (26 Feb) and latest (1 Apr) recorded hatch 
date over the 7 years, and young were assigned to a 
period by hatch date. We used Chi-square contin¬ 
gency table analysis to examine whether offspring 
gender was associated with (I) hatching period, and 
(2 ) hatching order within a clutch (first, second or 
third-hatched). We used nominal logistic regression 
to examine the effects of rainfall prior to egg-laying 
hatch date, and hatch order on gender of nestlings 
1 ABLE 2. Frequency of male and female Lilac-crowned 
Parrot offspring by hatching order. 
Hatching order 
Males 
Females 
First hatched 
15 
14 
Second hatched 
15 
13 
Third hatched 
3 
6 
