I see birds like pigeons and seagulls, not the brightest sparks of a fairly dim fire, wandering around pecking at food on the ground.
How do they know which bits of stuff are food and which are just bits of stuff (like polystyrene, etc.)? Why do they ignore some actual food and eat other “portions” of the same foodstuff? Why does some food just sit on the ground, uneaten, until it goes off?
Keeharrr!!!
Birds do have tongues, ya know. They can taste food, and choose not to eat anything which they don’t care for, just like, well, you or me. Example: I have two cockatiels which have wildly varying tastes: one will eat just about anything that people eat (including chicken!), while the other couldn’t care less for most of it. Both enjoy various breakfast cereals, though.
However, birds do tend to have rather poorly-developed senses of taste when compared to mammals. But, they don’t typically keep food in their mouths for extended periods, so only taste their food briefly. It is thought that other cues, such as texture or “squishiness”, also figure into how a bird determines how palatable a given item might be. And, of course, particular “tastes” vary from species to species.
Sometimes birds don’t know what to eat. Some will eat plastic, spoiled food, poisonous insects, etc., and get sick and die. Some birds have instincts that draw them to certain foods, and others live though their experiences and quit eating nasty stuff, and manage to pass their hard-earned knowledge on to their chicks (not often though – they don’t call 'em “bird-brains” for nothing!)
Darwin’s Finch, your cockatiel is sick, sick, SICK! 
In certain cases, a bird knows what to eat because its beak will only allow it to ingest certain foods. The swordbill hummingbird whose body length is a mere three inches in length had a beak that is nearly double that. This little avian fencer specifically feeds upon the datura blossom’s nectar, located in the base of its thirteen centimeter long trumpet shaped bloom. Let’s just say that steak is off the menu for this needle beaked little devil.
Parrots, grosbeaks and many other species also have beak structures specifically adapted to cracking open only certain kinds of seeds and are not drawn to other food sources like fruit or nectar. Another example are raptors whose beaks are designed for tearing flesh. Sunflower seeds just aren’t going to interest these avian carnivores. The examples are as varied as the birds are themselves.
As to “knowing” what to eat, I’m sure a lot of this is related to the texture, flavor and appearance of what they are fed in the nest.
Oh, I just cannot resist. Where I live we have a MacDonald’s at the end of the street. I always see humans hovering around there, and I swear I have seen several enter the building, and then walk out devouring something wrapped in paper that they got in there. (Shudders). Is that instinctual? Any bird or animal knows what to eat, why don’t these ugly hairless apes?
Actually, this is something we talked about here before IIRC, corvids and parrots have been shown to have intellectual abilities surpassing many mammals.
they don’t call 'em “bird-brains” for nothing!
If you ever get a chance to see the TV program
“Bird Brains of Britain” tape it as well.
I saw it years ago and would like to do so again.
Not only was the show charming, the birds exhibited high degrees of intelligence.
Zenster, your post seems to address the topic “what will bird’s beaks allow them to eat”. How does a raptor know not to swoop down on an unsuspecting peach? I’m sure its beak would be quite adequate to tear the peach apart once it’d caught it.
You think peaches are easy to catch? 
Birds eat a lot of shit. Many eat small stones to aid their digestion. They can eat plenty of other shit which, as long as it is not poisonous to them, just passes through and exits the usual way.
I wonder what chicken tastes like to a chicken?
Meanwhile, I think that I meant to ask: How does a bird differentiate between a seed or breadcrumb and a piece of dirt or a broken button or a polystyrene ball?
Also, why do I sometimes see scads of breadcrumbs (chunks actually) lying in a park that is usually full of birds but which have not deigned to eat them?
Well, on the one hand, some birds may not even bother to differentiate between a breadcrumb and a piece of dirt (besides, as mentioned, some birds will purposely down some gravel and such for gizzard-use). On the other hand, if the bird is primarily a seed eater, part of its “is this edible?” algorithm may have to do with how resistant the item is to crushing. Seeds are hard, so they may be more likely to eat other hard things, mistaking them for seeds. Breadcrumbs, being soft and mushy, might be rejected as “not seed”, whereas for a duck or goose, soft and squishy is right up their alley.
“I’d rather starve than touch that!” Whether because they hate the food or just don’t know it’s food, some birds can and do starve to death rather than eat new foods. (And even if a bird nibbles at something, it doesn’t mean he understands it’s food; he might just think it’s a chew toy! Make SURE he’s swallowing it and knows it’s food!) In switching to new foods, always make sure the bird is eating enough food of some sort to stay healthy (and if you don’t know how much is enough, talk to your avian vet). A very small bird has a high metabolism and requires frequent meals, so while one night of hunger may be OK for a healthy bird, more than that can be dangerous. Bird Talk magazine, among other sources, has more information on how to convert birds to new foods.
I have a flock of pigeons I feed every morning. I feed them a pigeon mix of seeds. If I overfeed all of one particular seed will be left behind. The white peas go first, the corn second and the smaller seeds are eaten last.
The pigeons we feed out on our balcony are quite picky. The seed we give them has some green stuff that they won’t touch unless all the other colors are gone, and even then they have to be hungry still.
I think I read that bread crumbs are starvation rations for birds. Bread is basically junk food that we really ought not be feeding them in the first place, as it makes their gut work for almost no return.
I sometimes mix cereal or leftover bisquits in with the pigeon food. They won’t et it unless they are very hungry.
zombie or no
birds evolved finding a diet.
some die, nature is like that.
I suspect it depends on the species. I’ve seen Jays obviously teaching young ones where to look for bugs.
And many species are born into a flock - you go where they go and you eat what they eat.
And birds do indeed eat shit they really shouldn’t eat. When soda cans first evolved pop-tops, the pop-tops weren’t attached to the can after you popped them. Needless to say, humans had no evolved instinct regarding what to do with the loose pop-tops, and the landscape and beaches quickly became littered with them.
It quickly became a problem that birds sometimes ate them. Not to mention people getting their feet cut on them at the beach.
Some humans soon evolved the behavior of putting their loose pop-tots into the can. But this was not widespread enough, and apparently didn’t confer enough reproductive advantage to those humans with this mutation. It became necessary for men who instituted governments among themselves to pass laws requiring pop-tops to stay attached to the can, as we see to this day.
The pigeons I feed in a park want bread, only bread, and they go ga ga over it. I’ve seen others toss the moldiest, nastiest, hard as a rock bread and they will spend an hour picking it apart.
I tried feeding em seeds one time, nope. Some old jar of poppy seed, nope. Stale popcorn, nope. I have seen them ignore fried rice some slob left on a table, eat only the bread and ignore the chickpeas in a food.
An old woman told me they like bread and mushy bananas.