How are unwitnessed behaviours (such as an adult bird building a nest the chick never saw the construction of) passed onto the next generation?
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Nest building is a species-specific innate behavior, birds don’t learn how to build a nest, they’re born with an instinctual drive that lies in their genetics. It’s also why different species make different types of nests which be radically different in construction.
For a contrast, brown bears are NOT born knowing how to fish, they have to both learn from their mother by watching her, and also they develop their own unique style. Each bear fishes in slightly different ways, some like to wait under the water, others prefer to wait at the top of a fall for a fish to practically leap into their mouths, others wait behind the boil of the fall to pick up fish that failed the jump, some use jaws first and others use paws.
A lot of animal behaviors are instinctual. For example beavers have an instinct to build dams if they hear the sound of fast flowing water. It works out for them, but they’ll also start to build a dam if there is a loudspeaker playing water sounds. It’s an example of relatively simple fundamental behaviors building up to a big complex thing.
Other behaviors are learned. Either by the bird remaining with their parents and helping out the next years hatching before flying off on their own, or by watching adult birds do it and then practicing (weaver birds building nests is not an inborn instinct. Males will watch, try, fail and retry until they build a nest that a female accepts).
I don’t think this question has been answered yet. Yeah, it’s “instinct” but how exactly does that work? My go to example is spider webs. Those are deliberately built in a specific way with no instruction from the elders.
This is a very good question. There are a whole pile of answers to this thread that basically say “instinct.” But that doesn’t really mean anything. What do we mean when we say instinct? Is it some sort of neurological pathway that forms during embryogenesis? Or maybe it’s something that develops at different lifestages. Can it be hormone mediated? If so, can we manipulate instinct? Perhaps it is actually a learned behavior based on based on a mother’s stereotyped dance that we have not yet developed the ability to observe. There could be any number of answers to this question. Is instinct the same thing from one species to another? Is the instict for nest building, bird migration, butterfly migration, etc all explained by the same mechanism?
You’ve asked one of the big questions of natural history/ethology/neurology/developmental biology…
Top-voted comment over-simplifies the case. In all vertebrates, at least, it’s fair to say that some behaviors are entirely instinctual but most are a mix of instinctual and learned. Birds comprise a whole order of vertebrates and a very wide range of behaviors and genetics. Highly social species such as parrots have young that accompany the parents for several years. IDK if they help build the nest of subsequent generations [but they do help rear the young](https://phys.org/news/2012-07-family-key-social-birds.html), and it’s very likely that they learn some things by watching. I’m not an ornithologist, but I’d love to hear from one about this.
No helpful answers so far. Only “instinct” and “random mutations that are passed on”. That doesn’t answer the OPs question of *how*instinct works. How does a spider know to build a hexagonal web? A robot spider would have that programmed in its code—you could Control-F and look up the number “6”. How does a bundle of proteins know the concept of “6”? How does ACGT in a beaver know what a running river sounds like? I think that’s the actual question
These are what are called innate behaviors, animals know them from the time of birth roughly speaking. Another great example is the fact that calves can stand and walk within hours of being born.
We have no idea how these behaviors are encoded genetically or neurologically and this is an active area of research.
It’s hard to imagine how a complex behaviour like nest building can be instinctual. Think of it as less of a piece of code or some blueprints that have been embedded in the brain from birth, and think of it as an automatic reaction to a particular stimuli. Just like how a human brain typically reacts with fear to the stimulus of seeing a spider. It’s an uncontrollable reaction that is hardwired into our brains.
Similarly, when a bird sees a twig and it’s brain receives that particular stimulus, combined with the innate desire to breed and raise young that all animals have, the way it automatically reacts is with an impulse to organise that stick into the shape of a nest.
It can’t control that impulse. A better example of a human equivalent would be how babies like to bite everything, because that is an action response instead of just an emotional response to a stimulus. Babies love to bite things, because it’s a human instinct to explore different things so we can learn what is edible. Plus it feels good to activate the reward centre associated with biting in the brain.
It’s the same for birds. They see a stick and their subconscious reaction is to want to pick it up, and then a separate reward centre in their brain tells them to organise it in the shape of a nest. Just like how we can’t really explain why some buildings look good and some look ugly, like, they’re both concrete cubes with window holes, but some look appealing and some look ugly. We don’t know why, they just do, because our brains respond that way. In the same way, a bird can’t explain why it finds the shape of a good nest so satisfying and appealing, it just does, so it’s driven to arrange all the sticks it bites into the shape of a nest.
Also I know nothing about birds and this is entirely my intuitive idea of what must happen inside a birds brain, based on their actions.
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