determinands
An estimate of egg shell thickness where Egg Shell Index is equal to the mass of the egg shell (mg) divided by the product of the length and breadth (mm) of the eg shell, as described by Ratcliffe, D. A. (1970). Changes attributable to pesticides in egg breakage frequency and eggshell thickness in some British birds. J. Appl. Ecol. 7: 67-115.
egg shell index