Photo by David Kinneer. A juvenile (male) bluebird picks off some ripe pokeweed berries. My husband tried to get me to pull up these "weeds," but I showed him David's photos in my defense.
What bluebirds eat depends in part on what is available. On average over the seasons (based on analysis of stomach contents in the days when bluebird populations were higher and permits weren't needed to dissect them), 68% of a bluebirds' diet is made up
of insects: grasshoppers, crickets, beetles,
and caterpillars (usually spied from a perch and then caught on the ground.) (Beal 1915). They also eat ants, wasps and bees, flies, Myriapods, angleworms (Oligochaetest), snails, sow bugs (Isopodan), and black olive scales (Homoptera), moths, weevils and termites. (BNA). Bluebirds
love mealworms. Occasionally they catch insects in flight, especially when its warmer and flying insects are abundant.
The proportion of insects in the food bluebirds collect during nesting season is probably significantly higher than 68%. That is because their growing young need lots of protein.
The rest is mostly small fruit -
e.g., flowering dogwood, holly, mulberry, wild
grape, Virginia creeper, pokeweed, and Viburnum, gleaned from plants or foraged on the ground. (Although
they will eat the fruit of multiflora rose
and Japanese honeysuckle, these are invasive
species, and should be eradicated.)
Bluebirds rarely eat birdseed
(they will occasionally take shelled sunflower, safflower and peanut chips/nut meats). Seeds in fruit they consume will pass through their system undigested. If bluebirds are seen at a bird feeder, they may be seeking out insects/larvae in the seed, or dried fruits or nut meats mixed with seed.
Occasionally they may eat vertebrates: shrews, small snakes, salamanders, tree frogs and lizards. (BNA).
They may eat larger prey (e.g., vertebrates) or insects with hard exoskeletons against the ground or a perch before eating it.
Mountain Bluebirds tend to "hover-forage" more than Western or Eastern.
Migratory Bird Treaty Act - This law did not go into effect until 1918. It prohibits collection of native birds without a permit.
Guinan, Judith A., Patricia A. Gowaty and Elsie K. Eltzroth. 2008. 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:10.2173/bna.510
For those who want to reduce the use of pesticides, starting a bluebird trail in agricultural areas like vineyards can be a great addition to an Integrated Pest Management Plan (which minimizes the use of chemicals and relies more on natural alternatives.)
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