You can use Stack Mode with a Smart Object to show all of the changes to the wings at the same time. Here's how:
Create your stack (you've already created the stack, but for others who have the same question, you can
Go to File > Scripts > Load Files into Stack
Select the image files to include
Select Attempt to Automatically Align Source Images
Select Create Smart Object after Loading Layers)
Because your layers are in a group and not a Smart Object, select the group, and convert it to a Smart Object (either right-click to the right of the layer group name and select Convert to Smart Object or go to Layer > Smart Objects > Convert to Smart Object).
With the Smart Object layer selected, go to Layer > Smart Objects > Stack Mode > Maximum to show all the wings at the same time.
If you hadn't already removed the birds, you could have used a similar approach for that where instead of using the Maximum Stack Mode, you would change it to Minimum.
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