The passage provides three pieces of evidence to prove that humpback whales navigate by relying on the stars. The professor, however, believes that although this theory might sound interesting, none of the provided evidence are compelling enough to prove that humpback whales find their ways based on stars. The professor's arguments to further discuss her reasons for this opinion are as follows.
First, the passage states that since humpback whales are intelligent animals and have a complex brain, they can use stars to find their ways during migration. The professor, on the other hand, opposes this statement. According to her, there is no evidence to prove that there is a connection between cognitive abilities of an animal and navigation by stars. In fact, many other animals such as ducks which have an average degree of intelligence navigate by stars. Therefore, the fact that humpback whales have high intellectual abilities does not prove that they use stars for navigation since no relationship has been established between these two things yet.
Second, the author notes that since humpback whales swim in a straight line, they orient themselves by an external object and since, despite birds, they can not use landmarks, they probably use stars for this aim. In contrast, the professor refutes this argument and suggest that this external orientation might be established in another way, for instance by using earth's magnetic field. Since the presence of a chemical substance in birds, named Bio-magnetite, has been proved as a tool to benefit from earth's magnetic field for navigation and evidence proves that this substance exists in the humpback's brain, it is likely that these animals use the same strategy to find their ways for navigation. Thus, the presence of Bio-magnetite might be a sign of using earth's magnetic field for navigation rather than finding their way by using stars.
Finally, the article states that an unusual behavior of humpback whales names "spy-hopping" might be an indication of using stars for navigation. In fact, since whales in this situation keep their heads out of the water, many people might conclude that they are actually looking at stars. Nevertheless, the professor repudiates this statement as well. She alludes that this specific behavior has been observed in other sea animals which do not migration such as sharks. Besides that, humpbacks do this behavior in the daytime when there is no star in the sky. Therefore, the reason of such behavior might be something other than using stars for navigation, for example, spotting potential preys for hunting. Thus, "spy-hopping" could not be considered as an evidence to prove humpbacks navigate by stars.