How does the mother bird know which baby bird to feed next?

August 16, 2013 7:41 AM

Little daughter and I were watching a birds' nest this morning where four little sparrows were getting fed by their mom (or maybe dad?) Each time the mother bird came back, all four sparrows would screech and open their mouths wide and the mother would give one of them some food. My question is: how does the mother ensure that each chick gets enough food? I can think of at least two theories: 1. The adult bird has enough working memory to know who got the last bit of food, or even who's gone the longest without food; or 2. Hungrier chicks screech louder and the adult bird gives food to the loudest screecher. Do we know which of these is right, or whether the real answer is something else entirely?
posted by escabeche to Science & Nature (7 answers total)

It's usually a combo of loudest-screecher plus pushiest chick. The strongest one, the one that can shove his nestmates aside from Mama, gets the food; plus the one that just got a gulletful of food might be temporarily-silenced while he's swallowing.
posted by easily confused at 7:45 AM on August 16, 2013

I heard that the blood from the gape is diverted to the stomach to assist with the digestion process. The parent bird looks for the chick with the reddest mouth. I have no idea if this is the case or not.
posted by Solomon at 7:50 AM on August 16, 2013

It's also pretty common with birds that one chick takes an early food avantage and grows stronger while another grows weaker. Eventually the weaker chick starves, dies, and is pushed out of the nest. This may or many not be the case with sparrows, I don't really know.
posted by kavasa at 7:52 AM on August 16, 2013 [3 favorites]

1. The adult bird has enough working memory to know who got the last bit of food, or even who's gone the longest without food

In some birds, chicks have individualized mouth markings (as well as an overall species pattern which helps them to reject nest parasites such as cuckoos); finches are spoken of most often in the search results I looked at, but I couldn't find anything definitive about sparrows.

My sister and I hand raised a nest of hawks when we were kids, and I found the din they raised during feeding so overpowering and continuous I couldn't possibly have sourced parts of it to individual chicks.
posted by jamjam at 8:48 AM on August 16, 2013

Have you heard of the cowbird? It's a "brood parasite". The female cowbird lays its egg in some other bird's nest (a different species). The cowbird egg hatches faster than the others, and the cowbird chick is particularly aggressive at trying to get fed. As a result it grows faster than its broodmates and often it shoves them out of the nest. It's not uncommon for the cowbird chick to be the only one to survive.

Part of why this works is that the parent birds do not keep score about who they've fed.

By the way, Cuckoos do the same thing.
posted by Chocolate Pickle at 8:49 AM on August 16, 2013

Best answer: I worked through college in something called "The Bird Lab" or The Montana Cooperative Wildlife Research Center. It was our job to watch tapes of bird nests and transcribe all the behavior for study. The fact is each type of bird acts differently, has different markings, and different numbers of babies. Each nest is also different.

Generally a baby's job is to open their mouth wide for mom (or dad, depending on the species) to put food into their mouth. Their mouths are bright yellow often (seen here) and serve as a target. Keep in mind that birds can also see UV colors outside of the human spectrum as well. (From Life of Birds, if you are curios - on Netfix.)

The fact is, sometimes they don't get enough food. That means that a baby isn't doing it's job in showing the parent that it needs food, or another sibling is bigger and stronger. It may be sick, or it may depend on the bird. Some birds have multiple eggs but only one baby - the strongest who gets the most food - will survive each brood. (Again, Life of Birds). It also comes down to survival of the fittest.

As mentioned above - cowbirds take advantage of this. The largest and strongest bird will get the most food. Cowbirds kick out other eggs and lay their own, leaving the other species of bird to take care of it.

Babies often die for whatever reason, but I have seen many who didn't get fed as often during our research tapes. If a baby does die, the parent will take it out of the nest. Many of the smaller birds are what I would describe as dumb-smart. Their actions are very interesting, but often caused by instinct, which makes it seem very intelligent, but they are "dumb" sometimes too. Sometimes after their nest is destroyed, they don't get the hint for a while and keep coming back with food. The same with feeding the Cowbird that isn't their own, it's based on instinct.

Full feeding behaviors might be able to be found online if you can identify the specific type of bird.
posted by Crystalinne at 11:51 AM on August 16, 2013 [4 favorites]

Your question takes me two places right away clutch size and bird digestive anatomy. A variety of factors determine how many eggs a bird lays and whether the young are precocial or in the case of your question, altricial. When studying bird digestive anatomy, notice when the parents feed the chicks, that food comes to rest in the crop on the front of the chick's body, where the neck meets the body. In altricial birds, the last place on the body the chick will fill in with feathers is over the crop. Perhaps this allow the feeding parent to take visual notice of which chick still needs more to eat. Sometimes the food itself, in the crop, is visible through the skin covering the crop rather than just appearing as a bulge. The crop will only hold so much, so even if one chick is overfed, the chicks will regurgitate and share amongst themselves if food is plentiful.
posted by txtwinkletoes at 9:41 AM on August 17, 2013