They are not quince.
I have an old, old orchard where in is a pear tree that long ago had suckers sprout from the root stock that were never removed because there was no one around to care for the trees. The named variety is ancient and dying off and is virtually surrounded by these suckers, now full sized trees 10 to 12" in diameter themselves. Your photos look exactly like the fruit from my pear tree root stock trees...hard, green and useless. Even the deer do not eat them unless it is such a bad year that there is little else for them to forage. The leaves are a match as well.

Thanks. That's remarkable. Now, after doing a little research, I've learned that quince trees were often used as root stock for pears. That's unusual, as most fruit trees use a different variety of the same fruit for root stock. But not pears. I believe it isn't done as much these days because pears are very finicky about the kind of quince they want to get attached to. Could it be that this is a variety of quince that isn't much good for quince fruit, but was once intended just as root stock? Kind of hard to understand what it's doing there. Maybe someone once had a grafted pear there, and the pear branches disappeared.

Leaves are wrong for a Quince, quintessentially pear leaves.

OK, I went out and picked one. Bit into it. (They're only about two inches long.) Zero flavor. I mean zero. No sugar, not even any astringency. Like biting into soft wood. I vaguely remember that apples and pears, when very immature, have taste of apple or pear (though with a grainy feel and a lot of astringence). Not these. So ... ?

Hmm. OK, so it's a pear horticulturally, but not one that produces fruit that is good to eat. Somewhat like the Callery/Cleveland/Bradford ornamental pear, although it isn't one of those, it would seem. Those don't look like real pears, as they're round. These sort of do. It would be interesting to know exactly what it is. Have to wonder if it was planted as an ornamental or, as you say, from wild bird droppings. To the extent that the fruit is edible by the birds, I suspect they'll do a good job of distributing the seeds.

You could ask over on the Fruit and Orchards Forum for a closer idea of the id. Even these hard pears can make a good jelly or wine.

Yes, I'll ask there. Thank you. As to jelly and wine, these fruit don't, as far as I can tell, have any sugar, astringence, or flavor. So all they'd do for jelly is bulk it up. Of course, same problem with wine. With no sugar, there is nothing to ferment.

Definitely a pear, like other orchard fruits these aren't any good until sized up and ripe. Some European pears have to be ripened in cold storage before they are palatable.

Fruit for preserves does not have to be sweet. You can make jelly or wine from many sour fruit which are unpalatable raw: rowan berries, chaenomeles fruit, rosehips, hawthorn fruit, crab apples, rhubarb, sloes, unripe gooseberries, wild pears, even cranberries which are vile raw imo. Jelly is much easier than jam because you don't have to peel or cut up the fruit. Therefore it is well suited to hard or small fruits. The sugar is added in the making and cooking changes the flavour considerably.

Some people would enjoy the experiment but if you aren't into preserving it's not going be something that would interest you probably.

I understand they don't have be sweet to make jelly or jam or wine. You can always add sugar. But the things you list have *flavor*. These maybe-pears don't. You add sugar to these and they'll taste like ... sugar. Maybe they eventually will have some taste? (Raw cranberries are wonderful, BTW, but that's my own taste.)

OK - I misunderstood when you said 'these fruit don't, as far as I can tell, have any sugar'. I assumed you thought that unless they were sweet you couldn't make jelly from them.

Possibly I have never had a good raw cranberry. The ones we get are chilled and tasteless until turned into cranberry sauce. Probably picked unripe like most fruit that is exported. Ocean Spray is the commonest brand on sale here.

Yep, I'm saying that these (albeit immature) fruit taste like soft wood. No flavor. No sugar. No astringence. Nothing. That's why I'm reluctant to think they are an edible variety of pears. As noted above, there are plenty of fairly inedible varieties (Bradford, Callery, etc.) but these aren't those.

I believe that is a Bradford pear.

I have to believe it isn't a Bradford. These fruit are very pear-shaped. Bradfords are spherical. See link below. Also, I understand that at least Bradfords are tart. These fruit of mine are flavorless, though admittedly the ones I'm tasting are very immature.

Here is a link that might be useful: {{gwi:193092}}

Definitely a pear and definitely an orchard pear. If an unnamed seedling fruits may not be up to the level of the best named cultivars, but with fruits that big it is still an orchard pear.

First.....there are 2 different species out there commonly called Quince. Cydonia and Chaenomeles (AKA Flowering Quince). Cydonia are related to Apples AND pears.

See the images of Cydonia oblonga at the following link

Vera

Here is a link that might be useful: Cydonia oblonga

Unripe pears are not tasty and have little real flavor. Especially if it is a junk tree that doesn't have quality fruit to start with.

If you have a pear and quince (Cydonia) side-by-side, the differences are quite obvious. You may wish to check out how my quince looks - close ups of it in flower, its leaves, and its fruit. See the link and I think you'll see what I mean.

FataMorgana

Here is a link that might be useful: Quince article

Thank you. That's good information. Now, I've tasted immature pears before, and I remember the flavor to be distinctly (if vaguely) pear-like, but it's possible that these are some inferior variety.

Now, that being said, and many people concluding they must be pears, I have to say that the immature fruit in your quince picture sure looks a lot like mine, and the leaves are similar too. Except my fruits have no fuzz.

I don't recall what the flowers on this tree look like. Recall that the tree is overrun with Bougainvilla, which makes any fruit blossoms pretty inconspicuous in the early spring.

I wanted to get back to everyone, as I think I have the answer. As some here guessed. It's NO. I brought the question (as recommended here) to the Fruit and Orchards forum where there was considerable back-and-forth about it. But a few answers there led me to this.

It's a seedling pear. A seedling pear is a pear that has grown up from a pear seed (as in, one a bird has dropped). Interestingly, seedling pears (and apples too) are rarely type-true. A good eating pear won't likely make a seed that produces a tree bearing good-eating pears. Stone fruits are a little different, as the pit (peaches, plums) often do produce type-true pits. The way you get a good-eating pear tree is by taking a rootstock and grafting stems from a good-eating pear tree. That's what you buy, when you buy an apple or pear tree marketed as producing edible fruit.

One poster there lives near a creek, in an area with many orchards. He/she has lots of seedling apple trees near the creek, and NONE produce good-eating fruit. I understand that some such fruit are like mine. No flavor whatsoever. Seems that "Johnny Appleseed" went around seeding apple trees specifically for apple cider. Because he knew those trees wouldn't produce good-eating fruit (and he knew they might even produce trees that produced wholly worthless fruit).

Now, if birds are going to drop seeds, makes some sense that the seeds that sprout will do well if they are near a creek, as my tree is. So riparian habitat is a good place to find such seedling trees.