Hi,
I have two sugar gliders and they just had two babies, and one of them looks a lot bigger and fatter than the other, almost double the size, and we are very worried, we are trying to give him milk separately on a bottle, but he won't drink much! Is that normal? Is there anything we can do to help him?
Thank you in advance

As long as mom and dad are caring for both joeys and the smaller one is nursing - I would not supplement. Supplementing will only cause him to nurse less which reduces the milk supply.

It is also possible that the smaller joey is actually younger than the fatter one. Gliders have a unique reproductive system with 2 uterus so the joeys may have been born at different times.

Do you have any history on the parents - lineage to guarantee they are not related? There is also a possibility that this joey is not thriving due to health problems that are not easily seen.

If the parents do reject the joey you will want to be prepared to hand raise him. This web page has information that will help.

http://www.suzsugargliders.com/helpforrejectedjoeys.htm

If you notice the little one is nursing less/less often than his sibling, supplementing the bigger joey may help the smaller be able to nurse a little more.

But I agree, that it is possible they are different ages and that is why you could be seeing a size difference.