Propose an evolutionary hypothesis to explain the observation that some bird populations do not migrate if people supply food for them in feeders.

Video transcript

Hi everyone. Let's look at our next question. It says migration refers to the pattern of behavior among animals in which they travel from one location to another for several reasons Salmon start their lives in rivers and migrate to the sea to feed and grow. Why did they migrate back to rivers after a few years? So when salmon migrate back to the river, um their purpose in going back is to spawn in the same area where they were hatched. And the benefit of that maybe that the salmon only live for a short time after spawning. Um they don't have much time. So the time that would be needed to search for a suitable nesting area might be too much. We don't know exactly but um that is the purpose when they come back to their nesting site navigating back that is presumably a safe nesting site for them to spawn themselves. So they migrate to the ocean um after when they get to a suitable size to take advantage of the more abundant food in the ocean but then come back at the end of their lives to spawn in the river. So we look at our answer choices. We see Choice A is for reproductive reasons and that would be the answer there. So let's just look through our other answer choices. Choice B says for protection against predators. Um Again, it's just the um need to spawn that brings them back to the river. So not Choice B. Choice C. Says for better conditions. Um Well you could say they're searching for better conditions for laying their eggs but that's not as specific as reproductive reasons. So not as good an answer as choice A. And Choice D. Says for more abundant food. Well that's why they migrate to the oceans for a time for more abundant food, but not why they migrate back to the rivers. So not our answer here. So again, why did the salmon migrate back to the rivers? Choice A. For reproductive reasons. See you in the next video.