Sentence:  The range is from 14 to 25 inches ; the former figure <WSD>is</WSD> based on a somewhat unusual birth of four by a Central American female ( see chapter on Laying , Brooding , Hatching , and Birth ) , the latter on a `` normal '' newly born individual . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)