Soley et al. • HATCH ORDER OF EASTERN BLUEBIRDS 
777 
extreme food shortages (Kitaysky et al. 2001a). 
Thus, late-hatched Eastern Bluebirds were not 
likely experiencing extreme food shortage as 
glucocorticoid concentrations do not suggest a 
lush level of stress. Hatching later in the brood 
may not be extremely stressful for Eastern 
Bluebirds. Our data should be interpreted with 
caution because corticosterone levels and associ¬ 
ated responses by nestlings can vary across 
development (Schwabl 1999. Sockman and 
Schwab] 2001), and we did not measure circulat¬ 
ing corticosterone and begging on the same day. 
Early-hatched chicks were larger than late- 
hatched nestlings, but hatch order did not 
influence plumage coloration. Past research sug¬ 
gests UV-blue structural coloration is a condition- 
dependent trait in nestling Eastern Bluebirds that 
can be negatively influenced by natal stress 
induced by experimental increases in brood size 
iSiefferman and Hill 2007). We found nestlings 
reared in larger broods weighed less and were 
duller compared to those reared in smaller broods, 
suggesting some effect of natal environment on 
nestling coloration. It may be that conditions 
created by hatching asynchrony are not sufficient¬ 
ly costly to negatively affect plumage develop¬ 
ment of late-hatched bluebird nestlings. 
Our study provides a good estimation of the 
effects of hatching position on nestling condition, 
Late-hatched nestlings weighed less and had 
shorter wings than their siblings, and hatching 
asynchrony may jeopardize the first-year survival 
°t late-hatched nestlings. We found few costs 
associated with late hatching. Indicators of 
extreme stress were not evident in late-hatchcd 
nestlings and, as a result, plumage ornamentation 
Was not negatively influenced. Hatching asyn¬ 
chrony did not appeal' to he costly within this 
Population, perhaps because Eastern Bluebirds do 
not show extreme variance in hatching asynchro¬ 
ny and brood reduction is rare, ll is also possible 
'tat parents are able to compensate for potential 
detrimental effects on morphology and stress 
evfi k of late-hatched nestlings. 
ACKNOWLEDGMENTS 
Wc 'hank Amanda Bcssler, Laura Beard, and Russell 
C'£°n for field assistance and members of the Lynn 
■tafferman and Michael Gangloff laboratories for helpful 
“rnmenis on the manuscript. We are grateful to Robert 
Montgomerie for use of his spectral processing program, 
•bis research was conducted according to animal use 
fcunits from Auburn University and Indiana University. 
This work was supported by grants from the National 
Institutes of Health (Project # R01 AI049724) and the 
Centers for Disease Control and Prevention (Project # R01 
C1000226) to GEH and a National Institutes of Health- 
funded Common Themes in Reproductive Diversity 
training grant (N1CHHD-T32-HD-49339-0) to LS. 
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