Western Bluebirds
(Scroll down below the photographs for the Exploring the Web of Life column).
Photo by Ron LeValley
Western Bluebird at nest hole. Photo by Jon Klein
EXPLORING THE WEB OF LIFE
with Kate Marianchild
January, 2008 Species of the Month: WESTERN BLUEBIRD
Species of the Month: Western Bluebird
WESTERN BLUEBIRDS bring flashes of color to tree branches, fence posts, telephone wires, and grassy fields. They like open woodlands, edges of forests, hedgerows, native grasslands, and grazed fields.
• Bluebirds don’t kiss under mistletoe (see last column), but it provides essential winter warmth and food. In winter, if you see a tree with lots of mistletoe, you’ll probably find the “owners” nearby–a family of bluebirds.
• Bluebirds spend the fall and winter in family groups of 7 or so. They bathe, forage, and sleep together. Whole families sometimes squeeze into one nest box or clump of mistletoe in cold weather.
• A family group consist of the parents, 1-2 sons from the summer’s brood, and one or more daughters of another family. Frequently the sons and newcomer females end up getting hitched–their version of arranged marriage!
• The young adult birds in the family are “helpers” who often stay through the next spring and help raise the nestlings. The helping sons stick around partly to help themselves to the family fortune–mistletoe berries! 1,2
• Bluebird couples stay together so long they’ve been thought to be monogamous. But actually both males and females get a little on the side. Someone other than the resident dad–often the guy next door–fathers one fifth of the babies.3
• The guys with the brightest and most iridescent feathers are the best at preening feather bacteria.4 They’re extra-popular with the girls and make the best providers. And those blue feathers? They’re really brown. The blue is a trick of light! 5
• In addition to Mistletoe, bluebirds also dine on berries of Elderberry, Juniper, Poison Oak, Toyon, and others. In summer they stop eating berries and dart around catching insects–mainly grasshoppers–and also caterpillars, beetles, ants, bees, and wasps.6 Even though bluebirds are related to robins, eating earthworms makes them sick. 7
• Adult birds get eaten by hawks, owls, House Sparrows, and domestic and feral cats. They have to defend their nestlings from European Starlings, House Sparrows, gopher snakes, king snakes, weasels, and squirrels.8
• One of the jobs of the adults is to remove baby poop from the nest. The babies’ poop comes out in little white sacks that the adults carry away from the nest in their beaks. 9
• Bluebirds usually nest in cavities in dead trees and snags, or in nest boxes provided by humans. Those boxes, which are available online, are an enormous help to them. If you put some up, proper maintenance is critical (see www.sialis.org/myths).
• Forest fires help bluebirds by providing dead trees in which woodpeckers and nuthatches can excavate cavities. (Bluebirds can’t peck their own holes). Fires also keep fir trees from crowding out meadow habitat. 10,11
• Bluebirds like grass tall enough to harbor insects and provide cover but short enough that they can see the insects and also see predators. Non-native grasses often grow too high, so bluebirds benefit from grazing, mowing, weeding, and planting of native grasses. 12
• Western Bluebird populations have declined drastically, mainly due to theft of their nest cavities by House Sparrows and European Starlings. Pesticides, fire suppression, and loss of open space (due to expansion of residential and industrial areas), have also contributed.13 In northwestern California, however, they’re doing pretty well. Let’s keep it that way!
• If you get up early, listen for Western Bluebirds in the dawn chorus during breeding season. They are often the second species, after Tree Swallows, to chime in, starting longer and longer before daylight as the nights get shorter. 14 They have a special song they sing only at dawn. 15
Exploring the Web of Life© is a monthly column written by Kate Marianchild of Ukiah, CA, with lots of help from her friends. www.ukiahdailyjournal.com/insideudj for more info on BB’s, and citations. Click on Exploring the Web of Life.
Sources:
1 Kraajveld, Ken and Dickinson, Janis L, “Family-based winter territoriality in western bluebirds, Sialia mexicana: the structure and dynamics of winter groups,” Hastings Natural History Reservation and Museum of Vertebrate Zoology, University of California at Berkeley
2Britt, Robert Roy, “Meet the Bluebirds: Wealth, Nepotism and Ungrateful Offspring,” LiveScience Managing Editor www.livescience.com/animals/051025_bird_wealth
3 Among birds, only 10% of socially monogamous species (species that form long-term pair bonds) are also genetically monogamous. – BBC News Online, SciTech section, “Infidelity is Natural,” 9/25/1998, http//news.bbc.co.uk/2/hi/science/nature/1799883a
4 Shawkey, Pillai, Hill, Siefferman, and Roberts, “Bacteria as an agent for change in structural plumage color, correlational and experimental evidence,” American Naturalist, University of Chicago Press, January, 2007; and http://mainebirds.blogspot.com/2007/06/comfort-behavior-in-birds-as-spring.html
5 Sieferman, Lynn and Hill, Geoffrey E, “Structural and melanin coloration indicate parental effort and reproductive success in male eastern bluebirds” Behavioral Ecology Vol. 14 No. 6: 855-861, © 2003 International Society for Behavioral Ecology
6 www.fs.fed.us/database/feis/animals/bird/sime/all
7Sialis (website): www.sialis.org/myths
8 www.fs.fed.us/database/feis/animals/bird/sime/all
9 Guinan, Judith A., Patricia A. Gowaty, and Elsie K. Eltzroth. 2000. Western Bluebird (Sialia mexicana), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/510
doi:bna.510
10 Guinan et al, op. cit.
11www.birdweb.org
12 www.laspilitas.com/bluebird
13www.sialis.org/myth.
14 Guinan, Gowaty, and Eltzroth, op. cit.
15 Personal communication with Bob Keiffer of Hopland Research and Extension Center, Hopland, CA.