Sentence:  Even if <WSD>juveniles</WSD> acquire sex-specific adult-like foraging skills before reaching adult size, their smaller body size may put them at a foraging disadvantage. ... The size effect on foraging is reduced in species that use small or easily manipulated substrates. For instance, in Costa Rican squirrel monkeys, <WSD>juveniles</WSD> apparently mastered techniques for insect foraging only a few months after weaning, when they were still much smaller than adultsnb.... 
Meaning of the word marked with <WSD> tags:  A sexually immature animal.