Ilex decidua possumhaw, can be a small tree, but usually more of a large shrub. We have them growing natively behind our home, and they can be VERY attractive in winter. Some are VERY bright red. After a major storm last winter, they were basically all eaten as well. There are selection for brighter red, and a couple of yellow selections as well. All very tolerant of site conditions. Recommended if they fit what your looking for otherwise.

Arktrees

Not sure if they'd be hardy in zone 6, but around here, late berry crops are available on Cotoneaster frigidus, C. ÃÂ watereri (Jan-April), and some of the hybrid hawthorns, notably Crataegus 'Grignonensis' (March-April).

Cotoneaster frigidus with a Redwing
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And with a Fieldfare
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Resin

I like the "whatcha looking at" pic!

Sorry, I don't have any good suggestions on trees beyond Malus...but I do get swarms of finches when I leave coneflowers up or they don't get crushed by snow.

Agreed on the cotoneaster and some hawthorn should hold; whether they are edible before spring is another matter. Pyracantha seem to get eaten right away and don't persist. Careful of the Ilex as some may be invasive in your area. Don't expect a bounteous crop - these fruits have evolved such that many don't persist this late, as environmental conditions for reproduction are not favorable.

Dan

Wonderful photos Resin.

You could look into (some birds forage harder on some trees than others)

Sorbus alnifolia - Robins will devour/Cedar Waxwings
Tetradium (Evodia) daniellii - just a guess but might be liked by birds.
Ilex verticillata is always recommended.

Dax

The Ilex I suggested is native to much of the eastern US including St. Louis, Missouri area. So no issue with this one for the OP.

Arktrees

Not sure about your zone, but here in North Carolina a large shrub called pyracantha provides late winter berries for birds. The berries are there all winter and ripe but it seems that the birds won't touch them until the bradford pears and hollies have been exhausted. Here is a link to a picture of what they look like:

Here is a link that might be useful:

Common hackberry; Celtis occidentalis L.

juniperus virginiana in my area. must be a popular food source since i find seedlings of them all over my property and the largest trees hold some of the blue berries until spring.
probably some of the viburnums, too (large shrubs/small trees).

Forgot about Viburnum. There's another option. Don't forget smaller shrubs as well - groundcover cotoneaster, pyracantha...

Dan

Some good ideas! I actually planted some small viburnums last year at the edge of the tree line where terribly aggressive and invasive honeysuckle previously had been.

The Ilex family has had my eye for awhile and I totally disregarded juniperius prematurely.

Nice bird pictures btw Resin.

I have a weeping crabapple, "molten lava" that the birds are only now descending upon. They ate the other crabapples last month, but for some reason this particular one they always leave for last, must not taste as good. Swarming with birds now, though.

Resin - did you get a lot of redwings this year? I have a tiny urban backyard (British meaning of 'yard') and there were about 15 redwings in it eating the rotting medlars on the ground. Usually nothing bothers with them.

Not only berries provide food in late winter. My best bird tree is a weeping birch which all the titmice (analogous to chickadees, I believe) and sometimes goldcrests frequent. They go over each twig very thoroughly and find something there - maybe aphid eggs or other invertebrates. Very entertaining, as much of the time they are hanging upside down.

"did you get a lot of redwings this year?"

Not many yet this winter; lots last winter (the two pics above were from January 2010). In April 2009, the same tree had up to 40 [Bohemian] Waxwings for 2 weeks. This winter's berry crop hasn't been touched much yet.

"My best bird tree is a weeping birch ..."

Also look out for Goldfinches, Siskins and Redpolls feeding on birch seed catkins.

Resin

Yaupon holly is the only other one I am familiar with not already mentioned.
Still have berries on possumhaw, Eastern Red Cedar, Ashe Juniper, and hackberry.

I have thickets of wild crabs out in the back of my lot, and they make an assortment of sizes and colors of berries. Some of them get eaten during the fall. Others linger for months. The ones that don't get eaten right away tend to be the big fat crabapples - perhaps the bigger ones need to be go through bletting - where the fruit softens and shrivels over the winter (hopefully I'm describing that right).

2010 was a poor year for fruiting on the Crabapples - as well as many of the birds sources of food - probably the drought. Some of the bigger fruits were being eaten during the fall.

Anyway, took this pic last February 17th - 2009 was a great year for the Crabs, and there were still lots of fruits on this tree -
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Mostly mentioned already....but here goes.
crabapple
Washington Hawthorne
Celtis
American Holly
Korean Mountain Ash......very prolific berry producer but most are gone by Jan.
Viburnums
Rosa rugosa , multiflora
Eastern Red Cedar
Ilex verticillata
Firethorn

Lots of small fruits on Bradford pears everywhere in my neighborhood.

The Bradford pears always have an abundance of fruits, however, here the supply seems to be exhausted by the end of December.

I have several different types of holly on my property - yaupon holly, American holly, gallberry holly, big leaf gallberry holly and some possumhaw hollies that need a male, apparently for them to hold the berries they make in spring and then drop quickly. All the others still have their berries.
If I were you, I'd just look around and see which types of hollies grow in your area and plant them. Non-native hollies are popular, too - the cedar waxwings come late, and have a feast on the various Asian hollies.
In my area, they eat the viburnum berries quickly, so they're not an option here.
Sherry