In this thread, it was noted that birds don’t have much sense of smell. This sort of flies in the face of what I would expect, based on what I’ve seen in my backyard feeder. When I fill the feeder, particularly for the first time in the winter, it takes a very short time for birds to discover it and start flocking to it. Even though the feeder, a transparent tube with perches sticking on it, looks very little like anything you might find in nature. And birdseed is rarely if ever found in large tubular quantities in nature, so I wouldn’t expect a bird to be able to identify it by sight.
It seems much more reasonable that the birds detect the scent of the birdseed and then home in on it.
Am I wrong here? Can a bird really detect seeds visually at a distance? Is it possible that seeds have visual properties that humans are insensitive to, e.g. do they reflect strongly in some wavelength so that they are easily visible to birds?
A few birds have decent senses of smell and use it to find food - turkey vultures for example or some seabirds ( procelliformes - albatrosses, shearwaters and the like ) that can detect animal oils spread on surface waters.
But for most the sense of smell, while it is there, is very secondary ( or tertiary, or quaternary ). By contrast the vision of most birds is pretty impressive. A bird of prey 1/10 your size will have eyes larger than you. Ostriches have larger eyes than any other land animal. A little house finch with its tiny eyes will have vision at least as good as yours, probably better in most respects.
As to feeders, if it is a suburban area with a lot of them, maybe they just have a good search image :). Regardless they almost certainly did find them by sight.
Hmmm… I may have to run some controlled experiments with some photorealistic pictures of grain and some hidden grain. (Oh, further evidence for my smell hypothesis – I just remembered that I’ve seen large ravens pulling apart one of my (opaque) trash bags to get at the insides. But of course, they fall into the scavenger camp, so might be expected to have better olfactory senses.)
Well, ravens are very intelligent and also relatively long-lived. If a raven ever sees another raven or any other animal get food out of an opaque trash bag he’s going to remember it for the rest of his 15 to 30 year life.
By the way kiwis (the birds) are also known to have a good sense of smell.
As LL notes, this is almost certainly learned behavior not related to a sense of smell. Those ravens have figured out that tearing into a trash bag is often worth the time and energy it takes.
I had this happen to me in a Montana campground - ravens came by one day and tore open a trash bag containing charcoal. They lost out in that case, but I was later told they made a habit of opening trashbags in this campground, which often yielded food.
I remember learning that Kiwi are the only birds to have their nostrils at the end of their (rather long) beak. Their vision is poor - ‘the eyes are small and the optic lobes of the brain very reduced’, however they have a keen sense of smell and excellent hearing.
Coincidentally, I have a Staff Report coming up on why birds are so quick to find feeders. Basically, there are a lot of birds always searching around. Seedeating birds, of course, have long ago learned that human-made feeders are a source of food. And many individuals will have encountered feeders in the past, either locally or on their migratory travels. Once a few experienced individuals have located the feeders, individuals which have not previously seen feeders will be drawn in by the noise and commotion.
Regarding birds’ olfactory capabilities, the previous posters have pretty much covered the ground. It’s generally pretty poor, except for Turkey Vultures, some seabirds, and kiwis.
See here for my Staff Report on “Why do vultures circle dead stuff?” (back when I was a Guest Contributor.)