 On the larger and more humid islands , the tortoises seasonally migrate between low elevations , which become grassy plains in the wet season , and <unk> areas of higher elevation ( up to 2 @,@ 000 ft ( 610 m ) ) in the dry season . The same routes have been used for many generations , creating well @-@ defined paths through the undergrowth known as " tortoise highways " . On these wetter islands , the domed tortoises are gregarious and often found in large herds , in contrast to the more solitary and territorial disposition of the saddleback tortoises . 
