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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 123. No. 2. June 2011 
TABLE 1. Eigenvalues, proportion of variance 
explained, and cumulative variance of principal 
components for Brown Pelicans nesting on Gaillard 
Island. Alabama. 
PCI 
PC II 
Eigenvalue 
3.439 
2.132 
Proportion of variance 
0.491 
0.305 
Cumulative variance 
0.491 
0.796 
the layer 1-2 m (low height DV), vegetation 
density of the layer 2-3.5 m (moderate height 
DV). vegetation density of the layer 3.5 m to the 
top of the vegetation (tall height DV), nest density 
(number of nests/m 2 ), and number of nests on the 
ground (as a percent of total nests). 
Pearson’s correlation was used to examine if 
year or position relative to (he berm had an effect 
on hatching or egg success. A principal compo¬ 
nent (PC) analysis was performed using the above 
variables; principal components were selected for 
and used in regression analyses with egg success 
and hatching success. Quadrats one and four could 
not be used in this analysis as no nesting occurred 
in either. Pearson's correlation was performed 
between each variable and each principal compo¬ 
nent to examine any relationships. A stepwise 
regression routine was performed to select a 
model that best fit the relationship between date 
of arrival and vegetation variables. 
RESULTS 
We observed 384 Brown Pelican nests and 852 
eggs over two breeding seasons on Gaillard 
Island. The largest clutch size observed was three, 
and this was a common clutch size. Brown 
Pelicans nested primarily on the ground and in 
marsh elder; however, two nests were in (he 
invasive Chinese tallow tree ( Triadica sebifera ). 
No nests were found at a height >2 m. Study year 
had no effect on egg (P = 0.144) or hatching 
success (P = 0.176). Principal component 1 (PCI) 
and principal component II (PC II) were chosen 
based on eigenvalues (Table I). 
Egg success ranged from 0.046 to 0.659 
(Table 2) with a mean of 0.507 and had a 
significant and negative relationship with PC I 
(P - 0.006. R- Adj. - 69.0%, (3 estimate = 
-0.086 PC I). Hatching success ranged from 0 to 
0.695 young hatched per laid egg (Table 2) with a 
mean of 0.539 and was significantly related to PC 
UP = 0.002) and PC II (P = 0.027) IR : Adj = 
79.5%. pestimate = -0.091 PCI, -0.068PCII). 
The relationship between hatching success and PC 
I was also negative. 
Date of arrival ranged from no arrival (no 
nesting in the quadrat) to Julian day 161 (9 Jun) 
and the mean day of arrival was Julian day 125 (4 
May) for those quadrats that had an arrival date 
(Table 2). The best regression routine selected 
two variables for the regression model: low'height 
DV and the interaction between the first two 
vegetation layers (ground height DV X low height 
DV). Arrival date was significantly related to low 
height DV (p = 0.004) and the interaction 
between the two vegetation layers (P = 0.015). 
DISCUSSION 
PC II was a function of the vegetation layers in 
which Brown Pelicans were nesting and PC 1 was 
a 1 unction of those factors that did not directly 
involve the nesting vegetation layers (Table 3). 
(NoG). and vegetadon cover (HS^) J'd.an date of arrival (JD). percentage of nests on the ground 
Brown Pelicans nesting on Gaillard Island. Alabama. ' MH ~ 2 ~ 3 ' 5 m - TH > 3-5 m) for each quadrat for 
ES 
N/A 
0.393 
0.452 
0.046 
N/A 
0.535 
0.562 
0.639 
0.659 
0.649 
0.626 
HS 
N/A 
0.500 
0.537 
0 
N/A 
0.677 
0.635 
0.576 
0.695 
0.588 
0.646 
JD 
N/A 
148 
145 
161 
N/A 
113 
113 
108 
117 
112 
112 
N/A 
0.500 
0.114 
0 
N/A 
0.979 
1.000 
0.834 
0.510 
0.620 
0.711 
GH 
0.80 
0.45 
0.70 
1.00 
0.90 
0.84 
0.90 
0.97 
0.87 
0.70 
0.95 
LH 
0.20 
0.40 
0.35 
0.98 
0.02 
0.57 
0.73 
0.70 
0.47 
0.40 
0.60 
MH 
0.12 
0.12 
0.15 
0.70 
0.00 
0.01 
0.02 
0.15 
0.35 
0.12 
0.11 
TH 
0.90 
0.00 
0.40 
0.22 
0.00 
0.00 
0.00 
0.02 
0.09 
0.30 
0.01 
