356 Relations within the Species 



Among many species the instinct to return to a certain area is exceed- 

 ingly strong, as will be realized, for example, by anyone observing fish 

 migrating up a river. According to an early colonial report in New 

 England: "Alewifes continue to move up the stream, yea though ye 

 beat at them with clubs." Perhaps some of these migrations may be 

 thought of as movements out from and back to a home territory and 

 hence an extension of the homing reaction. Return migrations as 

 adaptations to (1) climatic conditions, (2) feeding needs, or (3) 

 breeding activity, have been discussed in previous chapters. 



In some of these migrations members of the population come back 

 to the same general area or even to the same locality. Birds return 

 to the same region after journeys of several hundred or several thou- 

 sand miles and after absences of 9 months or more. Frequently a 

 pair of banded birds uses the identical nest site for two or more sum- 

 mers in succession although the birds have journeyed to the tropics 

 during the intervening winters. The greater shearwater roams widely 

 over the North and South Atlantic Oceans during most of the year, 

 but its only known breeding place is on the Island of Tristan da Cunha 

 about 2000 miles south of the equator (Murphy, 1936). In some 

 similarly mysterious way slender-billed shearwaters ("mutton birds") 

 from all over the Pacific Ocean locate two tiny islands between Aus- 

 tralia and Tasmania and all descend on the islands on the same day 

 in a huge flock to begin the breeding season (Griscom, 1945). 

 Alaskan fur seals breed only on the Pribilof Islands in the Bering 

 Straits, and they manage to locate in some unknown way these tiny 

 bits of rock in the vast ocean after swimming for a 1000 miles or more 

 from regions off the coast of California where they spend the winter. 



In some of these breeding migrations the reaction to the home ter- 

 ritory may persist over the winter and stimulate the animal to return 

 to the breeding area at the next season. It is difficult to believe, how- 

 ever, that after several years in inland streams adult eels retain any 

 homing reaction to the area in the Sargasso Sea where they were 

 hatched— yet they do return there. The same might be said of the 

 Pacific salmon that ascend the rivers to spawn after spending 4 to 7 

 years in the ocean, but something does stimulate the salmon to under- 

 take the migration and something orients the fish to the very tributary 

 in which they developed as larvae (Hasler, 1954). Perhaps migra- 

 tions taking place after long intervals and also those correlated with 

 climatic changes and feeding activities are unrelated to homing or only 

 secondarily related to it. In these instances, external or internal fac- 

 tors may stimulate the animal to migrate at a certain time, and condi- 

 tions along the way may orient the animal back to the region of its 



