Time has no divisions to mark its passage; there is never a thunder-storm or blare of trumpets to announce the beginning of a new month or year. Even when a new century begins it is only we mortals who ring bells and fire off pistols. ~Thomas Mann

I'll agree with Mr. Mann on an empirical basis; we humans are infact (fact as far as I know, which is about as far as the end of my nose,) the only species here on this planet, Earth, who mark the passage of time with a calender and mark time in years.
On the pragmatic side that is true, but as a writer of fiction, poetry and as a man, I like to look at the hypothetical, speculative or even the dreamy side of things:
Yesterday was the first day of the year 2008. In celebration, mother Nature (speculative to believe in such an entity), blanketed our neck of the woods with a fresh coat of white. In fact giving us a clean page to mark. We could choose to stay inside and leave it unmarked and pristine, waiting for nature to do what it will to change the scene, turn the page if you will, or we could choose to make a mark of our choosing on the new page; the new page of life.

Or, we can make our mark, a foot print, to speak figuratively as well as literally. The fact is that for us here in my home town have been offered an example which we can choose to apply to our lives; Today starts a new day, a new year. The slate is cleared and our past deeds covered over, left in the past where they belong. We can make the same marks we did last year or we can chose a new tact, behave differently and make a different mark .

That Mr. Mann is the difference: the other species do not enjoy those choices and therefore have no need to mark time.