Ecology of Wild Animals is one of several known essays/reports written by the main protagonist, Hachiman Hikigaya. It is also known as "How Animals Live In The Wild", and was given as homework in biology class. It is seen in Season 1, Episode 2 of the series. In the Light Novel there is no report, Hachiman merely reflects on his failure with other social groups.
It revolves around Hachiman's ideologies regarding social circles, he surmises that forming packs only benefit the strongest in the group. Hachiman chooses to be a bear, a solitary animal, where even the lowest would not be sacrificed, as well as because he finds the idea of hibernation during winter wonderful.
Hachiman implies that with social groups there is a choice. One can either be a carnivore or herbivore. Carnivores form social hierarchies and those who aren't on top are burdened with failure until they die. On the other hand, herbivores must abandon their comrades to avoid predators which leads to guilt.
In either case, forming a group only benefits the strongest individuals. To an average or below person there is no benefit. Hachiman chooses to be a bear, which is a solitary animal, to avoid any social groups and any awkward dependencies. A solitary animal doesn't feel anxiety from solitude. Accordingly, Hachiman wouldn't have to experience the emotional disadvantages of his lonesome lifestyle. 
- It was used as a monologue introduction in the second episode of the anime.
Kanji & Translation
|テーマ「野生動物の生態」||tēma 'yasei doubutsu no seitai'|
|動物は基本群れるものである||doubutsu wa kihon mureru mono de aru |
|肉食獣にはヒエラルキーがあり、ボスになれなければ死ぬまで||nikushoku juu ni wa HIERARCHY ga ari, bosu ni narenakereba shinu made|
|ストレスを抱え続ける。||STRESS wo kakae tsudzukeru.|
|草食動物も天敵の襲撃で仲間を犠牲にして生き続ける||soushoku dōbutsu mo tenteki no shuugeki de nakama o gisei ni shite iki tsudzukeru |
|ことにジレンマを感じているはずだ。||koto ni DILEMMA wo kanjite iru hazu da. |
|このように群れとは個にとってなんら益をもたらさないのだ。||kono you ni mure to wa ko ni totte nanra eki o motarasanai noda. |
|ならば、私は決して群れることのない熊の道を選ぶ。||naraba, watashi wa kesshite mureru koto no nai kuma no michi o erabu. |
|熊とは一頭で生きていく事に何の不安も感じない孤高の||kuma to wa ittou de ikiteiku koto ni nani no fuan mo kanjinai kokou no |
|しかも、冬眠ができる。なんと素晴らしいことか。||shikamo, toumin ga dekiru. nanto subarashii koto ka. |
|次に生まれかわるなら||tsugi ni umare kawaru nara |
|私は絶対||watashi wa zettai|
|熊になりたい。||kuma ni naritai.|
Title: Ecology of Wild Animals
Animals naturally form packs.
Carnivores form social hierarchies in their packs,
those that fail to become alphas harbor the burden of failure until they die.
I'm sure herbivores feel guilt as they sacrifice their comrades to evade their predators and live on.
In this world, forming packs yields no benefit for the individual.
Thus I choose the way of the solitary bear, which does not form packs.
The bear finds no anxiety in living alone. He is proud. He is a lone wolf.
Furthermore, they hibernate in the winter.
How wonderful that must be.
There is no doubt in my mind.
In my next life,
I want to be a bear.
- The bear Hachiman drew at the bottom right corner of the essay establishes that he has drawing skills to a certain extent.
- nekotohigetoさん for kanji input.
- googleさん for (unreliable) transliteration.
- CrunchyRollさん for English translation.