A mi tambien me rachazaron unas cuantas.
No se realmente a que se debe, mientras la calidad sea buena, deberían aceptarlas, ya que la fotografía se trata de arte, lo cual permite crear imagenes desde la perspectiva del fotografo. Por cierto, muy lindas tus fotos.
Please do not piggy pack your refusals to a different post, but create your own thread, as this will help making clear to whom the response is addressed. I separated the post from the original thread.
Concerning your pictures: do not use artistic filters or convert to black and white. Such pictures limit the commercial appeal for stock and most often lead to a refusal.
As for your colour picture, I think that it is out of focus (looking from my iPad is always a little difficult) and you have sensor dust that needs to be edited out.
Your birds picture, besides that it is showing no details on the birds, but washed out grey tones on the tree, contains also these sensor dust marks. I even think that I saw the problem on your first image too.