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ON THE HOUR OF LAYING AND HATCHING OF BLRDS‘ EGGS.
Author(s) -
Skutch Alexander F.
Publication year - 1952
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1111/j.1474-919x.1952.tb01787.x
Subject(s) - hatching , morning , zoology , nest (protein structural motif) , biology , troglodytes , ecology , geography , botany , biochemistry
Summary.1 Observations on the hour of the day when the eggs are laid are presented for about 40 species of Central American birds; observations on the hour of hatching for about 14 species. 2 In a single locality each species has its own time for laying. There are also well marked family trends, to which, however, exceptions are found. Tanagers, finches (with one decided exception), wood warblers, honeycreepers, wrens, and hummingbirds usually lay early, from before to soon after sunrise. Turdus grayi lays considerably later. American flycatchers lay consistently later than the tanagers, finches, etc., often waiting until the second half of the forenoon. Manacus aurantiacus and two species of Crotophaga lay around midday; the goatsucker Nyctidromus albicollis rather late in the afternoon. 3 Birds which lay about sunrise show less variation in the hour of laying than those which lay later in the day. 4 Among birds which lay sets of two, some deposit both at about the same hour, so that the interval between layings is about 24 hours ( e.g . tanagers and very small finches). Others lay the second egg later in the morning than the first, so that the interval is 25 or 26 hours ( e.g . the larger finches Arremonops and Saltator). Tioris olivacm which has sets of two or three, and Troglodytes musculus whose set is three or four, both lay their eggs at intervals of approximately 24 hours. 5 The hour of hatching, for a given species or in a single nest, is more variable than the hour of laying. 6 With flycatchers of the genus Myiozetetes , eggs hatch during the (late ?) night and forenoon, scarcely ever in the afternoon. Apparently there is a diurnal rhythm in the birdling's efforts to break through and escape from the shell. 7 With the tanager Ramphocelus passerinii , eggs hatch predominantly in the forenoon, not infrequently in the afternoon, rarely during the night. Here the predominance of hatching in the forenoon may be caused by constancy in the hour of laying and in the length of the incubation period when this is not retarded. 8 Among passerine birds, there seems to be a well marked tendency for eggs to hatch in the afternoon far less frequently than would be expected if the distribution of this event were random through the 24 hours of the day. But apparent exceptions are noted.