21030
Until recently , the only way to gather information of numbers and distribution of terrestrial mammals ( and many other vertebrates ) was through observational - based approaches such as visual records , the presence of tracks or spoor or even identification from bushmeat or hunters ' trophies pinned to the walls in local villages .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None