A recent incident of a plane with a dent in its nose raised a lot of interest on Twitter after basketball player Steve Adams and other players posted photos of the dent, saying they were 30,000 feet up. While 30,000 feet is not an unprecedented altitude for a bird, it is very unusual. However more professional reports say the plane was descending, and do not give an altitude.
The flight history was recorded:
And in fact the plane never got over 27,000 feet, and was at 24,000 or below for a good portion.
It's not clear where the bird strike occurred, but a good candidate is the sudden deviation from the flight plan and the increase in the rate of descent seen here. That would indicate a possible strike at around 19,000 feet. However it's possible that it was later. It's not clear from the above report.
High altitude birdstrikes are rare, but there's a lot of planes flying, so they still happen every so often.
There's no particular reason for a bird to hit one forward-facing part of a plane more than any other, and yet we quite commonly see these big dents in the nose. The reason is quite simple: the rest of the plane is both much stronger, and largely at an angle from the forward direction. So a bird strike is much less likely to damage the plane in other areas.
The nose cone of a plane is weak because it houses the forward looking radar. The nose cone needs to be transparent to radar, so it can't be made of metal. Manufacturers are starting to use carbon fiber in some cases, however most radar-transparent nose cones are still made of fiberglass.
So it's not that the nose gets hit any more, it's just that it's much more likely to sustain damage. Other areas can still be damaged, particularly from impact with a larger bird. Here's an aircraft windscreen after being hit by two wild turkeys shortly after takeoff.
And there are many other examples of bird strikes on other parts of the plane:
But nosecone damage does predominate, due to the structural weakness.
Why is there sometimes no blood? The simplest answer is that the plane flew through some rain while landing. But it's also possible that combination of speed and angle simply resulted in the bird not being in contact long enough for blood to get past the skin and feathers. A significant portion of the known bird strikes don't have any blood or feathers, like this one in Seattle:
That one was not quite as big as it looked. Most close-up images of a birdstrike will exaggerate the size of the dent, simply due to perspective. Look at it from a distance:
While the dents are mostly caused by birds, they can also be caused by particularly strong hail.
Image Source: http://www.dailymail.co.uk/news/article-3177369/American-Airlines-new-Dreamliner-jet-pummeled-hail-forced-return-Beijing-terrified-passengers-plane-dropped-hundreds-feet.html
These images of a hail damaged plane illustrates how the damage gets focussed at the center of the nose. Obviously the hail would have hit everywhere on the front of the plane, but the center of the nose was the only place that was both weak enough and at the right angle for damage to show.