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As a result of abundant prey resources on Guam and the absence of natural predators apart from feral pigs and mangrove monitors , brown tree snake populations reached unprecedented numbers .
 location: Guam
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 location: Guam