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Determination of hatching date for eggs of black-crowned night-herons, snowy egrets and great egrets

Journal of Field Ornithology

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Abstract

Floatation of eggs in water and specific gravity of eggs of Black-crowned Night-Herons (Nycticorax nycticorax ), Snowy Egrets (Egretta thula ) and Great Egrets (Casmerodius albus ) were evaluated as methods to determine date of hatching. Although specific gravity was a better predictor of hatching date than egg flotation, both techniques were imprecise. The regression between specific gravity and the number of days before hatching differed among clutches, but not among eggs within clutches. Specific gravity of eggs predicted hatching date only to within 3.8 d for Snowy Egrets, and 4.7 d for Black-crowned Night-Herons and Great Egrets. The mean incubation period was 27.3 d for Great Egrets, 23.7 d for Snowy Egrets and 22.8 d for Black-crowned Night- Herons. For all three species, the A egg (first egg laid) had a longer incubation period than the B or C egg.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Determination of hatching date for eggs of black-crowned night-herons, snowy egrets and great egrets
Series title:
Journal of Field Ornithology
Volume
63
Issue:
2
Year Published:
1992
Language:
English
Publisher:
U.S. Fish and Wildlife Service
Contributing office(s):
Upper Midwest Environmental Sciences Center
Description:
pp. 145-154
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Field Ornithology
First page:
145
Last page:
154