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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

Flotation 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. Length of incubation and duration of hatching period were also documented for each species. Although species 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 data only to within 3.8 d for Snowy Egrets, adn 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. For all three species, the number of days between hatching of A and B eggs was significantly less (median - 1 d) than between hatching of B and C eggs (median = 2 d).

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
Contributing office(s):
Patuxent Wildlife Research Center
Description:
145-154
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Field Ornithology
First page:
145
Last page:
154
Number of Pages:
10