You probably won’t like this answer, but my recommendation is to go with the squirrel and the heron only. The others really aren’t that good from a viewing perspective.
I realize it may have taken considerable skill, patience, hard work, and technical knowledge to make these shots, but that’s irrelevant to your audience. You need to let go of the emotion that these pictures were difficult to get and that you’re naturally proud of them. It’s rough, but the people judging these pictures don’t know nor care about any of that. Get over it.
It seems you need these pictures to appeal to ordinary people based on the images alone. It might be quite different if you were showing your work in a nature study class, and they’d all make great observations here on iNaturalist.
Critique from best to worst:
The squirrel is good because it feels like we’re there with the squirrel while it’s eating that seed. It’s not just sitting there. We feel engaged.
The heron works because it’s something hard to see for ordinary people. That background is blurred, so not getting in the way of the theme. It may be “just sitting there”, but it’s majestic and draws you in to take a closer look.
The butterfly is just a butterfly sitting there in the middle of a mostly empty picture. It’s not majestic like the heron. If this is a special species the picture might have some appeal to those that know about it, but it’s just a “marginally pretty butterfly” to everyone else, including me. It’s not a bad picture, but I wouldn’t ever hang it on the wall either.
The dragonfly picture is difficult to look at. First, there’s the artificial surface it’s on. The edge of that cutting right across the middle of the picture really detracts. It’s hard to see the wings on one side as a result.
The otters are cute, but surrounded by way too much distracting stuff. Again, I understand it might not have been easy to get this shot, and you may be justifiably proud of capturing the otters at all, but it’s not a good picture just as a picture.
The robin is surrounded by even more distracting stuff. It’s not even a good picture of a robin. Honestly, delete it and move on.
Now for another issue: Framing. Others have brought this up too.
There is too much unused space left of the squirrel. Some unused space there is good because the animal is looking in that direction. But, you have too much. Here is a suggestion working only with what you showed us:
That changed the aspect ratio, so I don’t know if it’s allowed or not. It will be tough to make this a good picture if 4:3 is required and there isn’t more in the original that you didn’t show us.
The heron has too much blank space all around. Basically, it’s too small a bird in too big a picture. Some space is good, especially to the right where the heron is looking.
I also made the whites white and the blacks black in both the cropped pictures. Using the whole available dynamic range is usually good. It makes the pictures “pop” more without losing information. Note how your heron looks fine on its own, but a little “dingy” after you’ve looked at my version.
A long time ago an old photographer said something profound to me that really changed how I think about presenting my pictures. He said there is just one rule for being a good photographer: Only show good pictures.
Think about that for a while. Nobody knows nor cares how many pictures you take. If you take 1,000 pictures with only 1 great one and show only that picture, you’re a good photographer. If you show 10 merely decent pictures, you’re a “meh” photographer and nobody will take notice.
Present only the squirrel and heron, and those will be what you’re judged by. The others will hurt, not help.