Friday, October 17, 2014

Rocky Mountain Juniper

Robins eating juniper berries (c) John Ashley
American Robins gobbling up Rocky Mountain Juniper berries last week
Bugs begin to disappear when temperatures fall. Most of Montana's songbirds also vanish, high-tailing it south before they're left without enough six- and eight-legged morsels to eat (insects and spiders). But some songbirds linger into fall and even stay through winter by changing their diets.

Enter winter's wild fruits.

Junipers are one of our most valuable wildlife trees in winter because they provide food and thermal cover. Of the 11 U.S. juniper species that reach tree size, our Rocky Mountain Juniper (Juniperus scopulorum) has the most far-flung distribution, which generally follows its namesake mountain range. And there's a flock of good reasons for that - a flock of winter bird species.

Hungry birds love Rocky Mountain Juniper berries, especially during the fall and winter. Eastern Bluebirds, Evening Grosbeaks, Townsend's Solitaires, Sharp-tailed Grouse, jays (Mexican, Pinyon, Scrub, Stellar's and Blue) and wild turkeys all eat the berries, tossing them down whole. An American Robin (above) can gobble up 200 juniper berries a day. And Bohemian Waxwings have been documented passing 900 juniper seeds in 5 hours - what I want to know is, who got to count them?

Each juniper berry contains 1-3 seeds, and passing through the digestive tract so quickly has little impact on germination. The fleshy berries really aren't berries at all, but "indehiscent strobili," or 3-8 pointy scales that fuse into a cone after fertilization. Male and female flowers occur on separate trees, which is why some some trees are barren while others are loaded with fruit.

Rocky Mountain Juniper berries remain on female trees through the winter, unless eaten by birds, and some berries hang on for 2-3 years. Berries are produced every year, but heavy crops only occur every 2-5 years. Females don't start bearing fruit until they're 10-20 years old, and the primary producers are 50-200 years old. "Grandmother" trees often live for another 100 years or more. Some Rocky Mountain Junipers in New Mexico have been aged at 2,000+ years, and one massive tree in Utah is estimated to be 3,000 years old.

That's a lot of hungry winters, hundreds of songbird generations, and an unimaginable number of Rocky Mountain Juniper seeds dispersed on the wing.