Effects of urbanization and nest box design on reproduction vary by species in three cavity-nesting passerines in the Okanagan Valley

Artificial nest boxes provide an important resource for secondary cavity-nesting passerines, whose populations may be limited by the availability of nesting sites. However, previous studies have demonstrated that the design and placement of boxes may affect the reproductive success of the birds that use them. In this study, we asked whether the habitat surrounding a nest box or the type of box influenced reproduction in three cavity-nesting passerines. We studied western bluebirds (Sialia mexicana Swainson, 1832), mountain bluebirds (S. currucoides Bechstein, 1798), and tree swallows (Tachycineta bicolor Vieillot, 1808) breeding in artificial nest boxes at sites across 70 km of the Okanagan Valley of British Columbia, Canada. Sites varied in their degree of urbanization, from relatively undisturbed ranchland, to cultivated vineyards, to frequently disturbed ‘suburban’ habitat, and boxes varied in type of entrance (slot or hole). Western bluebirds nested earlier in vineyards, and tree swallows produced significantly fewer fledglings in suburban habitat. In addition, tree swallows nested earlier and produced more fledglings in slot boxes. Our results suggest that conservation actions for cavity-nesting passerines may depend on the target species, which in turn should dictate the appropriate box type and habitat when erecting or replacing nest boxes.

Guardian of the Garden

This chapter describes what the author saw while watching the birdhouse outside her bedroom window. She enjoyed watching the domesticity of western bluebirds. The author then contrasts the beauty of the bluebird and the menace of the coachwhip. An ancient battle fraught with symbolism was being fought in the author's high desert garden. In Navajo culture, a bluebird is an allegory of creativity and creation, but a snake communicates with the supernatural. In Christian religions, the snake is blamed for the mess we've inherited, all because of a woman's desire for more. The author maintains a healthy respect for snakes and finds them fascinating, beautiful, and maligned. On the other hand, the author is an active advocate for bluebirds.

Long-term phenology of two North American secondary cavity-nesters in response to changing climate conditions

Wildlife populations can respond to changes in climate conditions by either adapting or moving to areas with preferred climate regimes. We studied nesting responses of two bird species, western bluebird (Sialia mexicana) and ash-throated flycatcher (Myiarchus cinerascens), to changing climate conditions (i.e., rising temperatures and increased drought stress) over 21 years in northern New Mexico. We used data from 1649 nests to assess whether the two species responded to changing climate conditions through phenological shifts in breeding time or shifts in nesting elevation. We also examined changes in reproductive output (i.e., clutch size). Our data show that western bluebirds significantly increased nesting elevation over a 19-year period by approximately 5 m per year. Mean spring temperature was the best predictor of western bluebird nesting elevation. Higher nesting elevations were not correlated with hatch dates or clutch sizes in western bluebirds, suggesting that nesting at higher elevations does not affect breeding time or reproductive output. We did not observe significant changes in nesting elevation or breeding dates in ash-throated flycatchers. Nesting higher in elevation may allow western bluebirds to cope with the increased temperatures and droughts. However, this climate niche conservatism may pose a risk for the conservation of the species if climate change and habitat loss continue to occur. The lack of significant changes detected in nesting elevation, breeding dates, and reproductive output in ash-throated flycatchers suggests a higher tolerance for changing environmental conditions in this species. This is consistent with the population increases reported for flycatchers in areas experiencing dramatic climate changes.