Some birds put cigarette butts to good use

A house sparrow, one of the species in the Mexico City study, flies into its nest inside an exhaust hole above a window in S.F. A house sparrow, one of the species in the Mexico City study, flies into its nest inside an exhaust hole above a window in S.F. Photo: Michael Macor, The Chronicle Photo: Michael Macor, The Chronicle Image 1 of / 3 Caption Close Some birds put cigarette butts to good use 1 / 3 Back to Gallery

Smoking may cause cancer in humans, but discarded cigarette butts appear to have health benefits for nesting birds, concluded a recent study of avian adaptations to urban environments.

The study, by a team of Mexican researchers, found that sparrow and finch nests that incorporated the discarded remnants of smoked cigarettes had fewer parasites than those with no butts.

The findings, published online in the Royal Society Journal, are an indication that urbanized fowl, including several species common to San Francisco, may be deliberately selecting cigarette toxins like nicotine and cellulose acetate to ward off mites and protect their young.

Mexico City study

The research team from Mexico's Universidad Autónoma de Tlaxcala collected mites and weighed the cellulose fiber from cigarette butts in 28 nests from urban house sparrows and 29 nests from house finches in Mexico City in 2011. The more smoked butts there were, the fewer ectoparasites there were in the nests, the study concluded.

Joseph Morlan, an ornithology instructor at City College of San Francisco and one of the foremost birders in Northern California, said house sparrows and finches are common in San Francisco. Other species in San Francisco and Northern California that are known to collect butts include the northern mockingbird, killdeer, tree swallow and the wrentit, he said.

Morlan said the results do not necessarily mean that cigarettes are good for birds.

"It merely showed that nests with cigarette butts have fewer parasites than control nests," said Morlan, the author of several books on local birds. "It did not show that the young have better survival rates long-term, nor did the study look at survival rates of the adults. Further study would be needed to establish that."

Discouraging parasites

It is, nevertheless, well established that harmful blood-sucking mites are common in nests and that mother birds often use aromatic plants to either drive away parasites or stimulate their nestlings' immune systems. Morlan said nicotine occurs naturally in a number of plants, including Nicotinia glauca, or tree tobacco, which grows wild in the San Francisco hills.

"However, the idea that birds may use nicotine or cellulose acetate in their nests to deliberately repel parasites is new," said Morlan, who remains skeptical. "My guess is that the use of cigarette filters is largely opportunistic and that any benefit to birds is probably accidental."

Picking a butt apart

Alan Hopkins, a dedicated birder and the co-compiler of the annual San Francisco Christmas bird count, said the winged creature he recently spotted poking at a cigarette near Hunters Point sure seemed to be deliberately selecting material.

"It was a house sparrow that tore it apart and took part of it away," Hopkins said. "It was going to use it for nesting material. Birds wouldn't pick up and carry something away like that unless it had a function."

Still, he said, "people shouldn't be throwing their cigarette butts out for birds to collect whether it is good for the nests or not. They end up in the ocean and aren't good for creatures or the ecosystem."