Death gives birth to life...

Once you have your layers in place and you would like to start blending, this is the method I use: I begin by creating a layer mask for top layer. I select the layer mask and begin by making sure the foreground color is black and then I will use the gradient tool > black to transparent. I tweaked the opacity as needed on the gradient and finally touched it up with a soft lower opacity eraser.

For this entry I had to mask many animals... the easiest way to do this is with the pen tool zoomed in really far, but I didn't have to be a perfectionist about the tiniest things since I knew the images would be shrunk down with the transform tool significantly. A 1 pixel feather was applied to soften the animal edges.

When bringing the two giraffe necks together I did not use the blending method I talked about in step 1. This time I lined up the two different giraffe necks side by side as shown above so that the spots were somewhat lines up with each other.. but so that the one on the left was slightly raised. Then taking the clone stamp tool I diagonally worked the two together. Small pixel touches were made with the smudge tool.

Continue along with the same methods for the swan. I will now be taking a portion of the giraffes neck by placing the swan's neck on the giraffe layer. I then will select the swan layer by clicking on the layer and hitting ctrl on the keyboard. Finally you will switch back to the giraffe layer and do a 'copy layer selection' to make a new layer the same size as the swan's neck. Then I just keep doing the blending that I talked about in step 1.

More blending and adding more animals.