I don’t know how reliable it is, but I’ve heard if you take the dead egg away too soon mom will lay another unfertilized one to replace it. For what its worth (not much) I’d advise leaving the egg there and keep an eye on mom’s behavior. Once she decides for sure the egg is dead (ignores it?) she’ll go back to her normal routine and you can chuck the egg.
I looked for and found a pigeon board. In one of the forums I found the following thread that is of interest. It’s about an unhatched egg in a nest.
Thanks. We’re leaving the egg in place for now. Hard to tell if they’re ignoring it or not. They’re still covering it, but that may just be incidental to their covering the squab.
Thanks for that thread! That could have been me writing! I’m pretty sure the egg is not going to hatch by now, but I’ll leave it four more days – until George is 10 days old – just to be sure. (I have visions of it finally hatching minutes after I’ve placed it in the garbage outside. :()
I just posted in that thread. Thanks, Baker! 
New pidgee photos!
Monday, April 20
Here we have Big Pidgee taking a snooze while guarding Little Pidgee like he always does when she’s preparing to lay her eggs. She laid the first egg of the latest batch the next day.
Wednesday, April 22
Here is Big Pidgee with the egg the day after it was laid. And Little Pidgee with it later here.
Thursday, April 23
The second egg was laid this day, and here they both are. Sadly, only one hatched.
Sunday, May 10
George hatched this day, and here he is with Mama. (The sun gets a little bright this time of the year in the morning.) You can see him better here. and later that morning, Big Pidgee arrived for the Switch and met his new son for the first time.
Wednesday, May 13
George is 3 days old here with Father.
Friday, May 15
George, aged 5 days. By now, we’re pretty sure the other egg’s not going to hatch. That’s a feather stuck to it in the photo, not a crack. Of all the squabs I’ve handled – the first few batches I never touched, fearing the parents would reject them if we did; we now know Big and Little Pidgee don’t really care if we’ve touched them – George is so far the most okay with it. Reactions from others when we’ve petted them have ranged from “Oh no! This is it! My time is up!” to “Oh, crap. Okay, go ahead and do it if you must.” But George is seemingly completely at ease. Pecks at my finger a little to see if it’s something he can eat and looks around. He’s in my hand here and here. Then I stepped inside briefly, and the wife took this shot; it’s fuzzy, but we wanted photographic evidence of the first pigeon actually to make it inside our home.
Sunday, May 17
And that brings us up to today. (Sort of; it’s after midnight here and technically Monday now.) George is 1 week old now. Here he is with Big Pidgee. And in the afternoon, after we did our weekly balcony cleaning. And with Little Pidgee after the Switch in the late afternoon. In these last two shots, you can see the beginnings of feathers, or at least feather shafts. That’s the whitish streaks now appearing.
Poor Big Pidgee was a bit put out today. I moved the flower box over to the other side of the balcony so we could clean around the box’s usual area. If he’s still watching after eggs or young squabs, he’ll stay around in the afternoon; once the squabs are older, the parents will often leave them alone in the afternoon for long stretches. It looked like he was going to stay in the box with George, so we put down a little Dettol disinfectant on the floor and were going to wait five minutes before washing it away like we usually do, as per the instructions. But Big Pidgee decided he wanted to know what we were doing with his prized living area, so he hopped out of the box to come see. He and Little Pidgee are often extremely concerned about what we might be doing there. I did not want him to get into the disinfectant, so I had to shoo him back. He did NOT like that. He grunted at me, and I swear it looked like he was scowling. I had to shoo him a couple of times. Gently, but he was not a happy camper. We washed the Dettol down quickly and moved him back over. But I got my hand too close, and he gave me a wing slap.
We’ve decided to remove the unhatched egg on Wednesday, just to make absolutely sure it’s not going to miraculously hatch somehow. George will be 10 days old, and that will be more than a week after the last day of what we we figured was the window for the egg to hatch (assuming this one was the second egg laid; if it’s the first one laid, then the window will have ended even longer ago). I keep having visions of what would have been little Gracie popping out shortly after I’ve disposed of the egg.
Oh, and all of the photos of George can be seen on one page here. Again, click on any photo to enlarge it.
Monday morning here, and Little Pidgee left George alone to go find some breakfast earlier this morning. 8 days old now. I can see little gray feathers starting to appear from the feather shafts. He’s now entering the phase where he’ll try to stand and “click” at me when he sees me in the window. But when I went outside to give him a little pet, he didn’t snap at me when he tried to rear up. He did peck around my fingers, looking for something to eat maybe, but again he was fine with being handled. We’re wondering if lack of a sibling is altering his behavior pattern.
Did you take the other egg out yet? I think I would at this point. I’d probably take it inside and open it up and have a look.
Tuesday morning, George is 9 days old, and we went ahead and removed the egg when Little Pidgee was out for breakfast. We noticed yesterday that both of the parents were starting to ignore it. Covering up the squab while leaving the egg exposed. Sitting over on the rail, leaving the egg exposed. We didn’t open it, though; but it felt very light, like it was hollow. Not that these eggs weigh a lot anyway.
George tries to raise up now when he sees and when alone, but unlike the previous squabs, he doesn’t try to snap at us. Petted him a bit this morning, and he’s fine with it.
Some decidedly gray feathers appearing now.
But I’m glad little George seems to be OK.
We’re assuming it was an unfetilized egg. I could have used a flashlight to “candle” it and try to see inside, but I sort of didn’t want to know.
George is 10 days old now (Wednesday morning). Alone again while Little Pidgee went to breakfast, so I picked him up. I’m getting the distinct impression that he likes me. He seems not to be the least bit afraid or put out. Stares around him; nibbles on my finger in apparent hopes that it’s some sort of beak he can plug into and be fed. On the other hand, the wife said that late yesterday afternoon while I was away, George did rear up and snap at Little Pidgee when she came back from somewhere and that Mama had to soothe him a bit. Is this because of a lack of a sibling? Could he think he’s … human?
Thursday morning and George is 11 days old. His instincts may be kicking in, as he does not seem quite so easy at seeing me coming now. Lots more feathers coming out now.
Pics?
New pics coming soon. Friday morning, and George is 12 days old. There are enough feathers out that he’s feeling soft now. He’s at that stage where he looks like a little feather ball with a squab’s head sticking out.
Definitely not so easy anymore when he sees me coming but seems fascinated with what’s going on inside our home, which he can see into easily.
Sunday morning, and George is two weeks old. He spent his first night completely alone last night. Little Pidgee did not stay here. Happens about this time. she was here to feed him this morning, though.
And the parents were romping in the designated sex area of the balcony again yesterday, so more eggs are probably on the way. I just hope Big Pidgee can fertilize both eggs this time. I managed to take a shot of him mounted on top of Little Pidgee. Will post that and other new photos soon, probably after I take some more after today’s balcony cleaning.
When I pick George up now, he loosens up after a few minutes, I guess once he figures he’s not going to die. But he’s never as aggressive as some of the previous squabs – even though he’ll rear up and “click” his beak a little, he does not snap at me – so we’re wondering if this is actually Gracie instead of George. But he or she is stuck with the name George now.
Oh, and yesterday at age 13 days, George made it over to the other side of the flower box for the first time. Another week, and he’ll probably be hopping out of the box.
Sam, I would just like to say that this thread was the inspiration for me to share the exploits of my house finches. Thanks for the pigeon updates!
We need a birdie forum.
New photos. Including some hot pidgee sex! 
Monday, May 18
Here George is 8 days old. You can just see the other egg. A cute one here. And with Little Pidgee.
Tuesday, May 19
George at 9 days. Then a little closer. And taking a snooze. This is the day I removed the other egg.
Wednesday, May 20
With Mother at 10 days. He’s bulking up good now. And one alone.
Thursday, May 21
At 11 days
Friday, May 22
With Big Pidgee at 12 days.
Saturday, May 23
And now we get to what you’re all waiting for: Pidgee sex! But first, here is George at 13 days. Notice he’s spread out a bit. Being an only child, he has more room in the nest and been able to spread himself out more than the other squabd were able to.
And now for the adult material. Big and Little Pidgee sharing a kiss during foreplay in their designated sex area. (The little triangles reflected in the window are from what’s called an axe pillow we have on the floor.) And firmly mounted on her. Just after I took this shot, he flapped his wings, signalling “The Moment,” but I was unable to get that like I did that one time. Funny, too, but immediately afterward he flew what looked like a victory lap, going way out into the distance and then back, landing on the balcony above us. Big and Little Pidgee are rather shameless; George was watching the whole time, apparently wondering what they were doing and why they weren’t feeding him.
Sunday, May 24
George at 2 weeks. Then me holding him up, still fitting into my hand, barely. We’d moved the flower box over for the balcony cleaning that day. And here that side is clean again. (But it did not stay that way for long!)
Monday, May 25
Looking a little droopy-eyed here at 15 days. You can see how his wing pattern is developing.
Tuesday, May 26
Checking out the other side of the flower box at 16 days. (This was not the first time he ventured over there, though.) Another nap here. That second photo was taken only 23 seconds after the first one; he’s a sleepy little guy. He seems to sleep more than the other squabs. Again, the absence of a sibling jostling him seems to allow for more rest. Also in that second one are budding signs of the same facial “mask” features of his father, Big Pidgee. And one more.
And again, you can see all of George’s photos on one page here. Click on any one of them to enlarge it.
Sunday morning, and George is three weeks old. We did the balcony cleaning on Saturday this time, because we have to be out and about today. He hopped out of the box for the first time on his own, but I’m not sure it counts, because I think he was just got caught up in the excitement. But he’s not ventured out again despite walking back and forth to each end of the flower box and looking curiously at the balcony floor. When he did hop out yesterday, he went and hid behind the “living room,” one of the big tree pots. Other squabs have done that, too; we get the impression they think if they can’t see us, then we can’t see them.
Big and Little Pidgee still stop by to feed him, but they’ve stopped spending a lot of time here. And we’ve noticed fewer pigeons on the mansion grounds next door. We’re wondering if there’s some sort of seasonal thing with pigeons that make them go elsewhere. Not actual migration, as Big and Little Pidgee have been here a full year, and our seasons are not the same as in the West anyway, but something causing them to change location.