Premium
Correcting eggshell indices of raptor eggs for hole size and eccentricity
Author(s) -
NYGÅRD TORGEIR
Publication year - 1999
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.1999.tb04266.x
Subject(s) - eccentricity (behavior) , eggshell , shell (structure) , index (typography) , statistics , mathematics , biology , materials science , ecology , computer science , composite material , world wide web , political science , law
Eggshell thickness is often expressed by means of an index based on the length, breadth and weight of the shell. The effect of the blow‐hole and egg eccentricity on Ratcliffe's shell thickness index was investigated in a sample of 585 eggs from six raptor species. Corrections for the size of the hole and egg eccentricity are proposed, as is a combined formula to correct both sources of error at the same time. It is shown that by using these formulae, considerable improvements in estimates of shell thinning are obtained. These may be especially useful when sample sizes are small, which is often the case when working with species that have been reduced in numbers.