FOOD HABITS: Eats insects, spiders, earthworms, other invertebrates, and some plant material. Forages through ground litter, under vegetation, and beneath logs,
Learnt is the correct past tense for learn. Although many people now use learned. I think its a case of when you went to school, the correct english usage is learnt, americans say learned and this has been absorbed in to our language use.
Why is the author using time and learning as x and y axis? A steep learning curve is used in the context of a pre-existing domain of knowledge and refers to the amount one needs to learn in order to be operating effectively within that domain of knowledge.