Cowbirds have evolved as migrating birds, following the bison across the plains, eating insects that are around the bison. Survival meant they had to lay their eggs in other birds' nests. The other birds raise them.

Google searches will give you more answers. Nature is interesting.

That was a great google search....

Unfortunately I can't find a robin's nest with cowbird & robin chicks...hopefully one of you have witnessed such a thing and have a picture.

This gives you all the info you could want to know if you read the whole article.

https://nestwatch.org/learn/general-bird-nest-info/brown-headed-cowbirds/

Sometimes the cowbird will push out an egg or eat it before laying hers. The host bird will raise it along with her own chicks, however, the cowbird demands much of the food and attention.

I'm sure Konrad knows all about cowbirds, but is just trying to see if anyone here has actually seen a cowbird egg in a Robin's nest. I've seen a few other birds feeding a young cowbird, but never a robin. I wonder if they pick nests where their egg size is most similar to the eggs in there already? Maybe that helps with the host bird accepting it (by not being able to tell that it's a different color.........only that it's a similar size??)

Exactly...you can see how small that cowbird egg is compare to Robin but size of bird is pretty similar...well, I would guess Robin a little larger, so growing up together would be more likely then say if cowbird would be in the chipping sparrow nest.

It would be so unique to see cowbird with robin chicks growing up lol..but maybe like suggested...the host bird sometimes finds out and tossing out....in this case, for a smart Robin it would look too weird and perhaps never gets incubated.

Just searched again and yes.....smart Robin!!

Interesting! Maybe when the cowbird egg is laid among more similarly-sized/colored eggs, the host bird isn't always able to differentiate them......then the cowbird baby grows bigger than the others, but by then is accepted? Maybe some host birds are more aware of egg differences? Are some host birds just more accepting?? It's all very interesting!

Cowbirds parents have been documented to retaliate if their eggs are rejected by the hosts and hosts have learned to pinch their nose and put up with it, right? This would reduce the need for the cowbirds to resemble their hosts, wouldn't it?

EDIT: Read more closely. RIP

Hey Konrad.....I just read Susan's link and it says that sometimes if the cowbird's egg is thrown out of the host nest, the cowbird gets retribution by destroying the entire host nest. I wonder if that's what happened to your nest? Or do you think it was another predator?

Yes..I was reading this also, think this nest was destroyed by something else because it was kind of shredded, some parts hanging and some fell down.

A whole year later but I just wanted to add something that may be interesting. Thanks to susanzone5 for that great article, by the way. So glad we all learn from each other. I have a Brown-headed Cowbird couple and one very aggressive Robin (yes, Robin) coming to one of my tube feeders, which I am going to change today. I'm thinking these 2 birds are always together at this feeder. This particular feeder has a seed mix and the Cowbirds seem to be eating the millet first and then the BOSS. Before I can change this one feeder to safflower-only, I am going out right now and replace it with a tube without its saucer, and another saucerless tube, in an attempt to move the Cowbirds to any of my other feeders in another location.

I really just wanted you to know that I think the Cowbird and Robin are travelling together because they always arrive at this feeder together.

Thank you for sharing your knowledge.

Many times I've witnessed a single cowbird chick in a nest of another species of bird's making; a singleton because it's pushed the chicks for which the nest was built from the nest where they've died or fallen prey to any of a host of other creatures - grackles, crows, blue jays, hawks, squirrels, cats, ....... many more.

Al