From the passage it can be inferred that the call pulse rate of male northern elephant seals in the southern rookeries was faster because:

• A. a large number of male northern elephant seals migrated from the southern rookeries to Año Nuevo Island in the early 1970s
• B. a large number of male northern elephant seals from Año Nuevo Island might have migrated to the southern rookeries to recolonise them.
• C. the male northern elephant seals of Isla Guadalupe with faster call pulse rates might have been the original settlers of the southern rookeries.
• D. the calls of male northern elephant seals in the southern rookeries have more sophisticated structures, containing doublets and triplets.