Here the immediate reference is to Man's deeds, the result of which is attacked to his neck. So that he cannot get rid of it, and will see it openly in the day of final Judgment.
In the other verse (NO.15) four important Islamic Principles have been put forward which are as follows:-
1- he who accepts guidance, is guided to his own benefit.
2- he who is strayed, he only strays against himself.
3- No carrier will carry the heavy load of sins of some one else.
4- god will not punish His servant until he explains to him and gives him a warning through his Messengers.
The Arabic, TAIR literally means, BIRD but it also connotes fate, bad omen, fortune, and also the results of Man's deeds.
To the Arabs, when a bird approached them from the left or from the right, his approach was or good or bad omen.
Even to-day when an owl sings on our roof, in the sight of some of my towns folk, the bird has a bad news! TRANSLATOR
This is when all such superstitious ideas are strictly rejected by Islam, enjoining that, man should always put his trust on God.
In fact; our fate, to a large extent, depends on our intention and endeavor; and our life is what our hands has made it. Our deeds that fly out of us like birds, are all recorded on a scroll, and fastened to our neck. In the Day of God's Judgment, the scroll will be opened for us to read it and judge for ourselves.
About omen and augury from the stand point of Islam. Enough detail has been given in commenting S7:131 volume 2 of this book.
The last of the above verses (NO.15) of which we extracted the said four Islamic principles, included the basis of ethics too: -
He who is guided he is only guided for the benefit of himself, and he who is strayed, he only strays against himself.
In other word: whatever of good or bad you do, you do it to yourself. So, the basis of ethics is the reflection of deeds and the reaction of all actions, that turn back to the doer.
This verse in another way condemns the doctrine of vicarious atonement:-
No carrier will carry the burden of the sins of another.