Duck egg - internal pip over 48 hours ago, external about 36...Intervene?

[ProudMom]

How much longer should I wait to assist with the hatching? There is plenty of movement and chirping. The egg rocks sometimes a little. There is only a little slit in the membrane where he externally pipped, but he's breathing. About a nickel size of shell came off and we are able to see the membrane. It is just starting to tan and it has sort of "deflated" inwardly. This is allowing us to see his/her breathing. We really want this little duck to make it. Can anyone advise? Please?

 

[ProudMom]

I cross posted this in the duck forum. I got only one response. That person said they wouldn't wait much longer to intervene, and I tend to agree. Any one else? Please, please, please share your wisdom...