
Given the following passage

"Short-distance passerine migrants have two evolutionary origins. Those that have long-distance migrants in the same family, such as the common chiffchaff Phylloscopus collybita, are species of southern hemisphere origins that have progressively shortened their return migration to stay in the northern hemisphere.",

answer the following question. Note that the answer is present within the text.

Question: Where do the migrations occur 

northern hemisphere
