I have read in the Mahabharata that at birth, Duryodhana’s nature was shown by some warnings and 'ashubh suchana' (bad omens) like the sound of crying donkeys. So my question is, how is nature able to know of upcoming dangers and show appropriate signs according to that upcoming danger.
It is not nature that knows everything. It is Krishna, and as the Paramatma He is everywhere as you can see here:
Bg. 9.4 मया ततमिदं सर्वं जगदव्यक्तमूर्तिना । मत्स्थानि सर्वभूतानि न चाहं तेष्ववस्थित: ॥ ४ ॥ mayā tatam idaṁ sarvaṁ jagad avyakta-mūrtinā mat-sthāni sarva-bhūtāni na cāhaṁ teṣv avasthitaḥ By Me, in My unmanifested form, this entire universe is pervaded. All beings are in Me, but I am not in them.
However, we cannot see Him with our material senses, but He can reveal Himself to us.
If everything reminds you of the Lord, you will have no reason to fear.
We still fear and have desires, attachments and anxieties, this is due to our karma and the fact we are in material bodies - but this is out of the scope of this question.
But check this out:
Are there no torn clothes lying on the common road? Do the trees, which exist for maintaining others, no longer give alms in charity? Do the rivers, being dried up, no longer supply water to the thirsty? Are the caves of the mountains now closed? Or above all, does the Almighty Lord not protect the fully surrendered souls? Why then do the learned sages go to flatter those who are intoxicated by hard-earned wealth?