Somebody on Goodreads made a comment about how this book demonstrates that there is nothing that humanity has created that has not already been developed by the animal kingdom. I would probably say that this is pushing it a bit too far because the animal kingdom has yet to develop the ability to fly in space, but that is probably about it (animals have never had a need for cars, and there are animals out there that can build sophisticated tunnel networks as well as roads).
I feel that this is more of a book where Ernie is being smart and getting his kicks out of bursting Bert's bubble, but I guess that he does have a point when he demonstrates that all of these inventions have been developed by animals previously (that is if you believe in Atheistic evolution), however it does not address the fact that the difference between the animals and the humans is that humanity has built all of these inventions for itself whereas the animals have only developed certain characteristics for their species. For instance, the armadillo does not have a light source and the billy goat cannot fly, whereas humanity can wear armour, turn on a light, and fly, all at the same time.
I guess the idea is that one should not get too ahead of themselves, or two arrogant about their accomplishments because the ability to render these things obsolete also exists. For instance, people do not wear armour anymore, probably because armour is too heavy (though we do have bullet proof jackets). We still can fly, but it is also interesting that Bert's plane crashes where as the bird does not. As for aircraft flying like birds, that tends to still exist only in the realm of science-fiction.