do these sentences express the same meaning? (seem, as if, appear to, look like, seem like, sound like)
The quick answer is "yes".
Although whenever you have alternative choices they may have nuanced differences. "Sound like" brings to mind spoken words or thoughts. "Looks like" indicates visible appearances. Yet, even these may end up being used interchangeably.
I feel like I were a bird
The tenses should match up, so it would sound better as "I felt like I was a bird" or "I feel like I am a bird".
I feel as if I were a bird
That may be alright. Other variations could be "I felt as if I were a bird" or "I feel as if I am a bird". From a US English perspective all of these "I feel as if" variations have a poetic or archaic quality. "I felt like" or "I feel like" are more common.
Further discussion of the Subjunctive Mood:
"as if/as though" usually takes the subjunctive mood for hypothetical/imaginary situations. The subjunctive is often used with the word "if". Therefore "I feel as if I were a bird" is correct.
Next, "I feel like I am a bird" has the standard indicative, not the subjunctive. Why? A few reasons come to mind.
- "like" already indicates an imaginary situation, so it does not need to be re-emphasized with a different verb tense.
- It's not hypothetical to look or feel "like" something. You're not saying that you "are" a bird, only "like" one. So it becomes factual, rather than hypothetical.
- BTW - casual (not formal or proper) conversation sometimes drops the subjunctive mood.
- "if", "as if", "as though" are not present.