Weights of yolk body and hatchling in relation to the egg weight in the Treecreeper Certhia familiaris
Keywords:egg morphology, egg size, hatchling size
The weights of fresh eggs, yolk bodies, and hatchlings were measured during the period 1998—2000 in a Treecreeper Certhia familiaris population in a deciduous forest in south-western Sweden. The weight of the hard-boiled yolk body was positively and significantly correlated with the fresh egg weight among and within clutches. The same significant inter- and intra-clutch relations were also found between eggs and young nestlings (average age 12 hours) or fresh hatchlings, both with regression coefficients of a magnitude surpassing those of other investigated passerine species. The proportion of yolk weight tended to decrease with increasing egg weight, whereas the proportional weight of the hatchlings increased, showing a significant linear regression upon egg weight. The pronounced weight increase of hatchlings from heavier eggs strongly suggests a possible adaptive significance of the likewise pronounced intra-clutch egg weight hierarchy in the Treecreeper population studied.
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