berries jubilee

Setting the scene
Early autumn. There is a stunning intensity to this time of year. So much plenty in anticipation of a long period of austerity. Unassuming weeds burst forth as lanky plumes of goldenrods and bushy clouds of asters. Monarchs, bees, and migrating hummingbirds – all soon to disappear – drink deeply from these last bountiful blossoms. And trees and shrubs that will quickly become naked, stripped by brisk fall breezes, now bear sagging loads of fruit. Wild grapes have produced a larger crop this year than any I can remember. Intertwined in many grape vines are Virginia Creepers (Parthenocissus quinquefolia), also full of plump, dusky blue berries. It won’t be much longer before the Gray Dogwood shrubs (Cornus racemosa) will have only delicate red panicles where creamy white fruit once clustered. All these fruits are eagerly eaten by birds helping them pile on the fat they need to continue their journeys south.

A popular native
In my yard, I observe typically retiring Swainson’s and Gray-cheeked Thrushes pop into view, here to feast on another avian favorite, Pokeweed (Phytolacca americana). These husky, red-stemmed perennials can grow to nine feet tall, bearing racemes of white flowers followed by juicy purple berries. American Robins are the first to find them, clumsily leaping from the ground or awkwardly inching along arching stems to reach the first ripening fruits. Red-eyed Vireos, descending from their usual treetop haunts, are more agile in their pokeweed berry-plucking, and I frequently see brown-eyed youngsters at my poke plants.  Warblers wrestle the berries, most too large for them to handle easily, but White-throated and White-crowned Sparrows enjoy the bounty.

That Pokeweed berries are eagerly consumed is evident by the crimson stains all over my hands and clothing after a September morning of banding birds. I see many a Gray Catbird like the one shown here, unable to disguise the fact it had a recent meal of pokeweed berries. In 1851, Thoreau in his journal wrote of the pokeweed, "Its boughs, gracefully drooping, offering repasts to the birds. ... Nature here is full of blood and heat and luxuriance. What a triumph it appears in Nature to have produced and perfected such a plant..."

An unpopular non-native
Birds also eat a variety of non-native species, especially buckthorn (Rhamnus sp.). The specific name of Common Buckthorn, R. cathartica is an indication that the fruit of this European native was once used as a powerful cathartic.  There is a misconception that if birds eat buckthorn berries, it will kill them.  This is absolutely untrue; I catch birds that have been eating buckthorn (pooping out seeds in my hands) that I recapture days later, still very much alive and often having gained mass.  Nor have I ever seen proof that buckthorns have an extreme cathartic effect in birds.  Birds process most fruit rapidly, both because it can be easier to digest than fats and proteins, and to reduce mass in the gut that could prevent the consumption of the necessary volume of food needed to put on mass.  In fact, many birds regurgitate fruit skins and seeds rather than wait for them to pass through their systems.

Plants produce secondary compounds to prevent herbivory.  The main compound in buckthorns is emodin, and predictably it is highest in the leaves.  It is present in the fruit, but decreases as the berry ripens.  It is in a plant's best interest to prevent insects and mammals from eating its leaves and seeds.  It is not beneficial for plants to kill the animals -- birds -- that are required to disperse their seeds.  It's not even especially helpful to a plant to produce chemicals that are exceptionally cathartic; for most species the goal is to disseminate seeds as far from the parent plant as possible. Plants that contain secondary compounds often provide a reward for their dispersers.  Buckthorns are no different.  Berries with higher levels of emodin have been found to have higher levels of carbohydrates that are valuable to birds.

Setting the table for migrant birds
Before we go any further, let me say that I'm not advocating buckthorn!  It degrades habitat in many ways: it is extremely invasive, alters water tables, and creates monocultures by outcompeting native species and acting synergystically with non-native earthworms.  It should not only not be encouraged, it should be eradicated.  That being said, if you wanted to provide fruiting plants for migratory birds, what should you plant?

One might guess birds choose fruits based on their nutritional content, pulp-to-seed ratio, or color.  Various studies have tried to quantify fruit preferences in birds, which, as it turns out, vary between species, years, and even individuals.  There are many additional factors in addition to those mentioned that determine fruit choice in birds, including size and concentration of the fruit crop (and therefore convenience) , and handling and processing costs of berry-handling.  Audubon Magazine provided this good primer on what to plant for migrant birds, including a regional guide to native plant species. Remember that, just like buckthorn, some native species of bird-dispersed fruits can be poisonous to animals, pets, and small children.  Pokeweed, for instance!

How you plant is also important.  Migratory birds often favor edge habitats, especially those that have complex structure: thickets and vines and areas with dense understory.  This provides protection from predators, and fruits concentrated in one area enable birds to maximize their foraging efficiency.

"Give me juicy autumnal fruit, ripe and red from the orchard, " Walt Whitman wrote.  He could have been speaking from the perspective of a migrating bird!

Comments

[afarensis]

Pokeweed - so that's what those plants are. I have one growing next to my wife's hydrangia bush. I had no idea what it was. I was going to cut it down but since bird's eat it's berries I guess I'll just move it somewhere other than near the front door so they can eat to their hearts content without being disturbed.

[Nuthatch]

You probably won't be able to move it. They have an enormous tap root, and even when small (<1 foot) they wilt like crazy when you move them around. Pokeweeds flourish for a few years, then often die. I just find some seedlings (they come up pretty late in the spring) and plant them where I want them.

[Sandy]

I'd be careful handling the pokeweed and berries, and wear gloves if possible. Although young "poke" shoots were historically a favorite spring food, recent research has uncovered a lot of mutagenic phytochemicals in the sap(some proving very useful medically). See www.ppdl.purdue.edu/ppdl/weeklypics/Weekly_Picture7-30-01-1.html or James Duke's "Handbook of Edible Weeds".

[Nuthatch]

I was going to get into the chemical properties of pokeweed, but the post was wandering away as it was. I've never had a reaction to it myself, nor has anybody I've known. I handle plenty of raw berries and plants (I prune my own regularly), but most of what gets all over me are, um, pre-processed by the birds. I'm also nearly immune to poison ivy, also a good thing!