The breeding ecology of the Western Scrub-Jay (Aphelocoma californica) in the midwestern United States is relatively unknown compared with Aphelocoma species in other geographic regions. We examined Western Scrub-Jay breeding biology in Colorado between 1970 and 1992. Incubation was initiated in early April and lasted 16 days, while the nestling stage lasted approximately 17-18 days. Clutch size averaged 4.0 eggs per nest, reproductive success was 25%, and productivity averaged 0.66 fledglings per nest. The low reproductive success and productivity measures may be due to high predator densities in the surrounding suburban landscape. Western Scrub-Jays preferred nesting in eastern red cedar (Juniperus virginianus) with nests placed on southern exposures. Western Scrub-Jays bred monogamously and were more similar in their breeding biology to the Island Scrub-Jay (Aphelocoma insularis) than to the Florida Scrub-Jay (Aphelocoma coerulescens).
Vierling, Kerri and Winternitz, Barbara L.
"Western Scrub-Jay breeding biology in central Colorado,"
Western North American Naturalist: Vol. 63
, Article 12.
Available at: https://scholarsarchive.byu.edu/wnan/vol63/iss4/12