Calcium Craving Blue Jays vs. Homeowners

Blue jays. Love them or hate them, you have to admit that these boisterous, brazen corvids are smarter than the average bird. And apparently some of these mischievous backyard visitors have discovered a unique way to satiate their cravings for calcium. They eat house paint. No, really.

Most of us are aware that songbirds require additional calcium during the breeding season for egg laying. They will readily accept crushed eggshells offered by humans during the spring and summer months. But blue jays seem to require more calcium, almost twice as much as other species. And they seem to seek it out all year long, even in the winter months.

A participant in the Cornell Lab of Ornithology's Project FeederWatch discovered blue jays chipping the paint off her house last winter. After contacting the experts at Audubon and Cornell she tried offering the blue jays oyster shells, sand, dirt and other trace minerals as substitutes for the house paint. The only thing that worked was eggshells. As long as she provided plenty of eggshells on a daily basis the birds left her house alone.

Intrigued by this paint-eating behavior in blue jays, Cornell asked other FeederWatchers if they had experienced this same phenomenon. Several had - three from New Hampshire, one from Wisconsin and one from Pennsylvania. When Massachusetts Audubon and the Audubon Society of New Hampshire became involved and posed the question to their membership the results were startling. In these two states there were hundreds of incidents of blue jays eating light-colored paint from people's houses and garages. (So far, no reports of this behavior have been recorded in Connecticut.)

Paint contains limestone, or calcium carbonate, which is used as an extender pigment. Like eggshells, it is a source of calcium. But why is it attractive to the jays only in the northeast and only during the winter months? One theory is that snow cover prevents the birds from consuming grit and soil, which can contain calcium and other minerals. And in the northeast we seem to have calcium-poor soils anyway. Add to that the impact of acid rain, which leaches calcium from soils, and you have the perfect mix of circumstances that would oblige the jays to look for alternatives.

If, by chance, you have blue jays in your yard with a hankering for house paint, Cornell wants to hear from you. Help their scientists document regional trends by contacting them at 607-254-2427 or feederwatch@cornell.edu.

If, by chance, you would like to provide your backyards birds with calcium, please remember to protect the birds from Salmonella by boiling the eggshells for 10 minutes or by baking them at 250 degrees F for 20 minutes. Crush the shells into small pieces. Then sit back and watch the show. I began offering eggshells in late October and immediately had a flock of five blue jays visit daily at about 7am to stuff their faces. A male cardinal took a few little pieces one day, and a titmouse came two days later, grabbed a piece of eggshell and promptly wedged it in the bark of a tulip tree nearby for later consumption. A white-breasted nuthatch flew off with a piece a few days later. While the other bird species clearly don't have the same appetite for the eggshells that the blue jays have, they are willing to supplement their diets, even in the winter. Indulge them.

Submitted by Cindi Kobak

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Last updated 18 September, 2004 .