英语阅读有个句子看不懂,

英语阅读有个句子看不懂,
To South Americans,robins are birds that fly north every spring.To North Americans,the robins simply vacation in the south each winter.Furthermore,they fly to very specific places in South America and will often come back to the same trees in North American yards the following spring.The question is not why they would leave the cold of winter so much as how they find their way around.The question perplexed people for years,until,in the 1950s,a German scientist named Gustave Kramer provided some answers and,in the process,raised new questions.
我不懂得是The question is not why they would leave the cold of winter so much as how they find their way around.这句话,尤其是 so much as