In this video this animals had to do a difficult thing that was falling 120 meters in the air to continue their life as birds, if they survived they followed their mom and dad and move on, so this relates to the natural selection theme because the birds that didn't have the skills or characteristics needed for that fall didn't survive and the ones who did have the abilities and strengths were the ones that survived. There are many more species like this that have to make a big sacrifice to keep the species better.
Video 7: Kangaroo
Since the baby Kangaroos are born it's their responsibility to train and learn how to fight for years so that they have the respect of the clan and have the chance to be the big champion, and win all the female Kangaroos in the clan, so that only that Kangaroo can have offspring and the species keeps on evolving on the best way possible. This is also an example of Natural selection because the best offspring with the best abilities can be the winner and the others would be the losers and won't get any female to reproduce.