Okay here’s what you do:
Choose Luma matte for the bird layer.
Create a new solid (LAYER > NEW > SOLID) and give it a color other than black or white.
Place the solid at the bottom of the layer stack.
Duplicate the Pier Struts layer and put it at the top of the stack.
Set the Pier Struts blend mode to multiply.
You’ll need to crush the blacks on your pier struts layer also because you can still see the bird layer through the poles if you don’t.
You could also forget the track matte step altogether and just put the pier layer above the bird layer and set it’s blend mode to Multiply. You’ll still need to crush the blacks though.
John Dickinson
Motionworks
https://www.motionworks.com.au