Loyd Csizmadia
Bluebird Route Coordinator, Williams Lake Field Naturalists
In March or April, while driving along Highway 20, Dog Creek Road, Mission Road, or any road with bird houses on the fence-lines, you may have noticed masked individuals scooping nests out of the boxes.
Not to worry. Every spring, volunteers from the Williams Lake Field Naturalists clean and maintain mountain bluebird routes throughout the Cariboo-Chilcotin.
Many experts believe that the annual removal of old nests reduces the presence of lice, mites, blowflies and other parasites or pathogens that can harm or even kill the chicks.
Nest removal also reduces predation. Both mountain bluebirds and tree swallows will build new nests on top of old, and eventually, predators will be able to reach the chicks through the entrance hole if the old nests are not removed.
The masks worn by the volunteers are meant to protect them from hantavirus, which is often carried by the rodents that overwinter in some of the nest boxes.
For many naturalists, cleaning and repairing boxes is an excuse to head outdoors after the snow melts. Some volunteers, however, also collect data from the old nests.
Each bird house opened in 2024 will tell a story about the year before. For example, the route at the old LORAN-C site has 31 boxes. In March of this year, four were either empty or damaged; but 27 had sheltered 35 successful broods in 2023. Thirty-five, you say? Eight boxes were used twice: three contained two Bluebird nests, and five contained a tree swallow nest on top of a bluebird nest.
Another 19 boxes were used only once, 13 by tree swallows and six by mountain bluebirds. How do I know all of this when there aren’t any birds present? After removing each nest, I study it.
A mountain bluebird nest is all about woven grass.
The wall will be coarse grass and the cup, which is carefully shaped to the brooding mother’s body, will be fine grass. Sometimes other materials are added, such as cow hair or the odd feather, but generally speaking, the mountain bluebirds rely on grass.
A mountain bluebird nest has probably been 100 per cent successful if it is flattened to some degree and empty of all eggs and young. Mountain bluebird nests are usually very clean as well. In my experience, the parents regularly remove fecal packets from their nest as the brood matures.
Tree swallows, on the other hand, build the walls out of coarse grass and the cup out of feathers. With feathers for insulation, the brooding mother does not appear to spend much time shaping it to her body. That being said, a tree swallow has no qualms about utilizing an abandoned bluebird’s nest, custom-sized cup and all. Therefore, the best indicator that a tree swallow was present is an abundance of feathers. And if her nest has produced a successful brood, it will contain no unhatched eggs, no dead, and lots of flattened, poop-encrusted feathers.
Unlike mountain bluebirds, most baby tree swallows don’t seem to mind a little soil in their bed.
This year, the story told by the nests at LORAN-C is a positive one. Mortality was very low, meaning that almost every egg hatched a chick and only a couple of individuals died.
Given that mountain bluebirds lay about five eggs per nest and tree swallows seven, I estimate that this route fledged 85 Bluebirds and 126 Swallows. A most encouraging result!
In closing, I want to thank all the folks who volunteer to ready their routes for the returning birds. When the program began around 1978, the Williams Lake Field Naturalists installed nearly 500 nest boxes, hoping to convince agriculturalists to stop spraying insecticides. Today, there are over a 1,000 nest boxes in our area alone, and every year they fledge thousands of hungry birds. I believe that we are doing good work.
Amateur birder Loyd Csizmadia currently coordinates the Mountain Bluebird Program on behalf of the Williams Lake Field Naturalists. To become a member of the Williams Lake Field Naturalists, pick up an application at the Scout Island Nature Center, or contact Sue Hemphill at shemphill@xplornet.com. Applications are also available on the web site: https://williamslakefieldnaturalists.ca/
