Question:
There are thousands of species of animals and bird life. How did you manage to fit them all into the Ark?
Answer:
Good point. Actually, your numbers are a bit low—scientists in your times have already identified more than a million species of insects alone! And we also have to take into consideration the enormous amount of food and supplies that I had to fit into the Ark.
The biblical commentator Ibn Ezra posits that the Ark was huge. The measurements provided in the Torah (300x50x30) are in cubits, the length of the arm from the elbow until the end of the middle finger. Just as people in my generation lived unnaturally long lives – I lived 950 years! – so, too, they (and their arms) were physically much larger than yours are in the 21st century.
Nachmanides, another medieval biblical commentator strongly disagrees. He says that if humans were unnaturally large in my times, so were the animals, and they therefore required more space, too. He therefore concludes that the entire Ark experience was supernatural. There is no logical way to explain how an ark could provide haven for so many animals for such an extended period of time. It was simply a miracle.
But this leads us to another question: If the ark was a miracle, why bother building such a large one? Why couldn't I have made do with a canoe?!
Nachmanides provides two answers:
1) G‑d prefers to perform miracles in somewhat of a natural manner. He regularly uses his "system of nature" in conjunction with a supernatural event. In fact, even the splitting of the sea was accomplished through a "strong easterly wind"!
2) I was told to build a large ark in order to attract attention and to cause people to enquire as to my reason for building a huge boat—and not even near a sea! I patiently explained my reason for building the Ark, and man had the opportunity to repent. Unfortunately, mankind did not heed the warning, and persevered in their wicked ways.