As I understand, most birds don’t have good sense of smell. And bird feeders aren’t usually built to provide a specific visual cue for the birds. So how do the birds find them?
In most bird feeders I’m aware of the seeds or other food is visible. There is often spilled seed on the ground as well. Birds are moving through the environment constantly looking for food; they will soon see food provided in a feeder. Once a few birds find it, others may be attracted by calls or activity. Also, birds are good at learning to recognize potential food sources. Once they become familiar with the shape of a conventional feeder, they are likely to investigate new ones that are put up within their home range.
Finding food is their job. They are good at it.
They follow the squirrels.
The same way they find all the other food they eat. Why would you think putting it in a big pile would make it harder to find?
When I was shopping for my hummingbird feeder, I kept asking the guy at the store,“will they find this one?-will they be attracted to this?” I thought that because some of them look very unnatural, the birds would never realize it was food. The guy assured me hummingbirds are very curious, “I guarantee they will find it” he said. The feeder I bought is one of the pie shaped ones, with three little ‘flowers’ on top. Hanging from the chain it looks completely inorganic. It’s mostly clear plastic and glass, but within days it was a ‘buzz’ of hummingbird activity.
Birds have amazing vision.
Anecdotally, I’ve heard that hawks would be able to make out newspaper print from a mile away: if they could read of course.
My birds seem to tell each other when I put new food out. Also, the make a lot of noisy racket when I put fresh water in the bird bath. I do both of these about once a day.
Because it doesn’t look like a big pile of bird food, at least not to me. And on most bird feeders, the food is only accessible through small openings.
Perverted bird lover?
Simple test, raise birds in cages, fed on stuff that does not resemble a pike of seeds, and don’t ever let them see birds or other animals feeding on a pile of seed or at a bird feeder. Then make a pile of seed that looks like a cat. See how if the bird will figure out that it is seed, and how long it takes.
ETA: well it’s simple if you have a lot of time to waste and don’t mind raising some birds in cages.
Among raptors, newspapers have been losing ground to electronic media for quite some time now. Your modern hawk is much more likely to be checking out a distant iPad
Google Maps on their Androids
Actually most of them use twitter instead. The birds I see are constantly tweeting.
The food they get in the wild doesn’t look like a big pile bird food either. It’s most likely under some leaves, or in grass, or nestled next to a rock.
The birds in my yard are happy to dig up seeds I bury… little SOBs.
Ah, I knew there was a good joke lurking in there somewhere. Well done.
Ferlinghetti:
What could she say to the fantastic foolybear
and what could she say to brother
and what could she say
to the cat with future feet
and what could she say to mother
after that time that she lay lush
among the lolly flowers
on that hot riverbank
where ferns fell away in the broken air
of the breath of her lover
and birds went mad
and threw themselves from trees
to taste still hot upon the ground
the spilled sperm seed.
Humming birds are attracted to red.
Colibri do you get hungry when you see red? 
The ones who don’t recognize the feeder are a food source die. You only see the smart ones.
In summary, to answer the OP, birds are smarter than you think.
Don’t forget memory. Bird life expectancy is low, but a reasonable number of birds live from year to year. The survivors remember that those things near houses contain food. That’s why they keep coming to check, even when the feeders are empty.
Also, birds can learn from each other. In the past, milk was delivered to homes in glass bottles with foil caps. Blue tits in Europe learned that they could peck a hole in the foil and drink the milk. It became so common to find a pecked bottle that many people had to buy bottle covers to prevent it. This was learned behaviour passed on through many generations of short-lived birds, over many countries.
The description “bird brain” is a misnomer, as many birds are actually quite smart. Some years ago, I watched a documentary, in which wild blue tits learned to perform increasingly difficult tricks to extract peanuts. At one point, they had to pull out six match-sticks to make peanuts fall. No problem, matchsticks flying everywhere.
My sister-in-law kept finding her bird feeder on the ground, with its contents spilled. She assumed it was being blown down by the wind. One day, she watched a crow lifting the feeder off the branch on which it was hung, and dropping it on the ground. That required the ability to analyse the situation (food in container I can’t access), and to conceive a process which would result in access.
Have you ever watched crows by a busy road? They know that these speeding things stay on the roadway, and will not attack them. They will come within a very narrow distance of the speeding wheels, with confidence, and rarely miscalculate.