The Bullock’s orioles have arrived at the arboretum. They are medium-distant migrants, most of them wintering in western Mexico. A few individuals may be resident in coastal southern California. On the range map, it looked like the Santa Barbara area down to San Diego.
They are starting to build their nests and often look for man-made materials such as rope fibers, baling twine, fishing lines, etc. I have seen nests next to rivers where at least fifty percent of the nest is constructed of these materials. During the setup for the wildflower festival, I saw them removing fibers from the ropes used to tie down the tent canopies. Two of the nests I have seen built this year have orange twine from the hay bales woven in.
The Peterson Field Guide to North American Bird Nests wonderfully describes the nests of orioles as: “Nests are pensile (hanging and attached only at the rim) or semipensile (with additional attachment at the sidewalls) and can be loosely separated into two categories: those that are classically pendulous and socklike, typically longer than wide with a narrow top, and those that are like a shallow, open gourd, the opening of which is often fairly wide and more broadly secured, in part due to the span of the fork or branches to which the rim is fastened. Nests of Bullock’s, Baltimore, and Altamira Orioles fall into the first category: Altamira nests are the longest of any species in N. America.”
The nests I see at the arboretum are constructed mostly of grasses and lichens with other bits of string, ribbons, twine, etc. utilized. The nests are lined with soft materials such as feathers or the cottony filament that disperses the seeds of cottonwoods and willows.
Happy birding! See you out there!
Resources
Bullock’s Oriole Range Map, All About Birds, Cornell Lab of Ornithology. https://www.allaboutbirds.org/guide/Bullocks_Oriole/maps-range. Accessed 21 May 2024.
McFarland, Casey, et al. Peterson Field Guide to North American Bird Nests. Houghton Mifflin Harcourt, 2021.