With (chicken) chick, which are precocial birds, I know that they have the yolk inside them when they hatch, so they have something to 'eat' for the first little while.
recently I found a broken egg of a pigeon, which are altricial birds. out of curiousity, I opened it up, and found an almost developed chick, with the yolk beside it connected at the cloaca.
So I wondered, do all precocial birds have their yolk inside them, and all altricial birds their yolk outside?
I've hatched and raised chickens for years, I was always under the impression that the yolk was not inside them but attached to them and that as they feed from it it slowly went away, the same way you are describing the pigeon egg you opened.
>>2121370
This. I'm pretty sure chickens start eating shit the day they're born.
>I know that they have the yolk inside them
Wat
Unhatched birds use the yolk the same way that many mammals use a placenta. It gives the fetus nutrients that it needs until it is hatched.
Hope that helps
>>2121713
I'm not completely sure on the why, but it is in there. maybe in case the chick can't find food at first. I've only seen the yolk in one day old chicks, so I don't know how fast it's used up.
>>2121733
Chickens have their yolk inside them when they hatch. They absorb it into their bodies during the hatching process and then use that as a fuel source for the first few days (which is why newborn chicks can be shipped without food; they are still digesting their yolks!)
Pic is just to help show what I mean; chicks can hatch sometimes without having fully absorbed their yolk sacs. Depending on the severity of this they can still make it (The one in this picture did), but unabsorbed yolk sacs are very prone to infection. Both because it's hanging out of the body and also because the umbilical opening hasn't closed properly, so theres easy entry into the body for bacteria.
For OP: I did a bit of raeding and it looks like precocial and altricial birds are the same re: yolk absorption. Both absorb the yolk as they are hatching, which is probably why you saw the yolk outside the chicks body. If it hadn't started hatching, the yolk wouldn't have started absorbing yet.
>>2121351
Just a cool pic to show that altricial birds also absorb the yolk, no idea what species that chick is sorry!
>>2122022
thanks. interesting that the yolk is outside of the chick in the egg, i thought they just grew around the yolk
