Letters from the January 22, 2005, issue of Science News

Timely comments

The researchers featured in “Summer births linked to schizophrenia” (SN: 11/6/04, p. 301) suggest that a higher incidence of schizophrenia may be due to summer-related infections “or other seasonal factors.” June and July births would have been in early gestation during late fall and winter, when there is increased incidence of depression among adults. Might it be reasonable to suggest that “other seasonal factors” might include some hormonal influences on the developing fetus?

Gene Addor
Steele, Ala.

Fetuses are most vulnerable in the second or third month of gestation. So, it seems much more likely that causative infections occurred the previous winter.

Sharon Rudahl
Los Angeles, Calif.

What birds do

There is another answer to how the toxin gets on the bird’s feathers besides the birds eating the beetles (“Poison Source: Toxic birds may get chemical from beetle,” SN: 11/6/04, p. 292). Many birds use insects to preen their feathers.

Ralph Gundersen
St. Cloud, Minn.

“Because we do find significant toxin levels in internal organs . . . we believe that [the birds] are ingesting at least some of the beetles,” says Jack Dumbacher of the California Academy of Sciences.—S. Milius

On the road again

“Heavy traffic may trigger heart attacks” (SN: 11/13/04, p. 316) seems to confuse triggers with long-term contributing factors. Traffic might just cause small peaks in stress that trigger only heart attacks that would have otherwise happened days later. To recommend staying out of traffic, research would need to show that people regularly in traffic are more likely to have heart attacks or have them significantly earlier than people who don’t spend time in traffic.

Paul Ramsey
Tucson, Ariz.

Carbon monoxide may be the primary reason for heart attacks after being in traffic. As carbon monoxide replaces oxygen in the blood, it may push people with constricted blood flow to the heart into a heart attack.

Jim Beregi
Port Orford, Ore.