Which is the better choice for controlling pests in our gardens and vineyards: man-made pesticides with their environmental cost or nature's pest squad in all of its beauty?
Consider songbirds. They eat a wide variety of insects, including aphids and snails. They feed on the ground, in mid-air and from vegetation. Especially during their breeding season, songbirds need a high-protein diet. The nutrition they derive from insects is essential for the growth of nestlings and even for the breeding adults. Could there be an easier, more natural way to control garden pests?
To attract these birds to your garden or vineyard, build some birdhouses. Before you begin, take a look at “Songbird, Bat and Owl Boxes” (University of California Publication 21636). The information is aimed at vineyard managers, but it's useful for homeowners as well.
“Songbird boxes should keep birds safe from predators, protect them from weather extremes, and be placed in a manner that is attractive to native species but not to non-native birds,” the publication says. For recommended box styles and building plans, consult conservation groups, specialty stores, woodworkers or the local grape growers' association.
In natural tree cavities, the songbird nesting success rate is 50 to 70 percent. However, boxes mounted on eight-foot T-posts and protected with a PVC sleeve under each box average a 99 percent success rate.
Barn owls were common before agriculture replaced grasslands. By installing nest boxes, you can help increase their numbers to near the level found in their native habitat. Barn owls have exceptional low-light vision, and their hearing is so acute that they can locate prey by sound alone. Adult barn owls kill and eat the equivalent of a large rat, a gopher or a dozen mice every night. How's that for an effective rodent trap?
Barn owls will readily nest in boxes larger than about two square feet. You can build the boxes from materials such as barrels and beehive boxes. Follow the guidelines in the University of California publication or buy a box from a specialty store.
My husband and I built an owl house for the Master Gardener Demonstration Garden at Connolly Ranch in Napa. We will wait until December to install it, since the owls show interest in newly erected boxes around January and lay eggs between February and April.
Owl boxes should be installed 12 to 20 feet above the ground. Add flashing to prevent predators. You can tell that owls have occupied the boxes if you find undigested matter from their prey. Listen for screeching and clicking sounds at night—another sign that owls have taken up residence.
Sadly, young barn owls have a high rate of mortality. Sixty percent die within the first year, and only two percent survive to 10 years. In captivity, they live more than 15 years. Cars and great-horned owls kill both flying and roosting barn owls. Even more reason to build and install owl houses.
There are 25 species of bats in California. These creatures mainly eat insects, including mosquitos, scorpions and centipedes. Bat houses or roost boxes will attract them.
Bat colonies range from a dozen to thousands, with several species sharing the same roost. They are the only mammal capable of flying. Most bat species will feed on crop pests, making them extremely beneficial to farmers. They rely on echolocation and sight to navigate and hunt for food.
Bats live 10 to 15 years and only have one offspring per year. The pallid bat is California's largest bat. Its large ears are so sensitive they can hear insects several feet away. They feed on the ground and catch their prey in the air. Bats can consume their body weight in insects in one night, and they seldom eat beneficial insects.
Due to the loss of natural roosting sites, bats have declined substantially in both species and number. Bat houses can replace the lost roost sites if sited and mounted properly. To keep bats out of reach of predators, mount houses at least 10 feet off the ground and the same distance away from objects that might block the entrance.
Standard bat houses are usually made of plywood and can accommodate about 300 residents. An open bottom serves as both entrance and exit. Do not paint or stain the inside of a bat house. Bat mothers with young prefer houses that receive morning sun and afternoon shade, or no sun.
It can take up to four years for bat houses to be occupied and up to 10 years to build a colony of several hundred.
For many years, humans have been destroying the habitat of these beneficial creatures. Consider taking the time to install houses for some of nature's pest squad so we can help restore our environment one garden or one vineyard at a time.
Workshop: Napa County Master Gardeners will hold a workshop on “Rose Care” on Saturday, June 4, from 10 a.m. to noon, at University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Join the discussion about spring and early summer rose care, issues and solutions. Learn about integrated pest management for common pests and diseases and how to keep your roses healthy during our current drought. On-line registration (credit card only); Mail-in/Walk-in registration (cash or check only).
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.