help, one duckling is a midget

Hi
We hatched two indian runner duck eggs. One egg was at least 50% bigger than the other. This one hatched first, the second two days later. Big duck (Spongebob) has always been much bigger and more active than little duck (Squarepants). After two weeks little duck seems to be struggling, he only weighs 70g vs. 250g for big duck. He makes much less noise and is less enthusiastic about feeding. Today he appears very docile and not that keen on eating. Big duck is an eating machine, little duck appears to be struggling. We feed them chick crumb, grated cucumber, grated melon, catfood and small slugs.
What can we do to help little duck? He is happy grazing in the garden and loves slugs, but just appears very docile today and nothing like as active as the big one.

 

Thanks for the advice. Small duck getting is smaller. Big duck is best mates with him, no pecking or bullying, but yes, he does try and get all the food. We have been separating them when we feed them to try and make sure he gets his share. Little duck used to like the chick crumb and grated cucumber, now he only is interested in tiny slugs and brown crickets, he gets really excited about these, but not sure how much he actually eats after pecking them to bits. He has lost another 10 g so we are now syringe feeding him with chick crumb mash mixed with some maple syrup to try and get some energy into him. Its not looking good for him

 

thanks for all the replies, little duck is hanging on in there, but only just.
So, for the last 3 days he hasn't eaten anything by himself, We have been feeding him liquefied chick crumb with a bit of olive oil and maple syrup via a syringe. He appears to have a problem with his gizzard (ducks don't have crops?). When he gets fed his neck swells up quite a lot, then during the day it goes down. As if he has a blockage. So, yesterday morning he did a lot of snorting and shaking of his head, and a slimey slug was vomited up, along with lots of goo. Since then, he has started eating again on his own. Mashed cat food, liquefied crumb, some grated cucumber and water. He is appearing a bit more duck like, grooming and chirping to his mate. But, he still has a neck that swells up after he eats. So not fixed yet. His weight went down to 55g, and is now back to 74, it was 70 when I weighed him before he went down hill.

So maybe there is still something stuck? I'm very surprised he is still alive. We have put him in in a separate box to big duck who is now huge and was stepping on him. As far as I can see from the manufacturers the chick crumb is non medicated. It is this stuff
http://www.animalfeedstore.com/The-Organic-Feed-Company/Organic-Baby-Chick-Crumbs.aspx

Any advice on what can be wrong with his neck and how to fix it appreciated.

tom