Honolulu Star-Advertiser © Susan Scott
December 7, 2007
In my Nov. 23 column, I wrote that one of the reasons gulls don’t live in Hawaii is they don’t have salt glands to excrete excess salt, and therefore, the birds can’t live in our marine environment.
That’s wrong. So wrong I asked my ornithologist friend (who had alerted me, kindly, to my error) how the statement came to be published in two of my favorite Hawaii bird books.
“It’s such a common misconception that the notion has taken on a life of its own,” she said.
So while I should have been throttling this avian myth, I was busy giving it CPR.
After doing some research, I discovered that researchers have known since at least 1958 that gulls have functional salt glands. A journal article from that year describes the salt glands of the herring gull.
And gulls’ salt glands work just fine. In a 1983 study, researchers force-fed a black-backed gull 10 percent its body weight in seawater, 3 percent salt. This would be the equivalent of a human drinking about 2 gallons of seawater, which would quickly kill us.
Our kidneys can’t get rid of that much salt. The gull’s salt glands, however, excreted all the excess salt in three hours.
And these amazing avian glands can do better when challenged, keeping up with even 5 percent salt solutions.
Salt glands are found in all seabirds and are widespread in birds with potentially salty diets, such as gulls, ducks and geese. When researchers gave mallards only seawater to drink, the birds’ salt glands immediately removed the excess salt from their bodies. When the ducks continued to drink salt water, their glands, over time, increased in size.
Salt glands sit in skull depressions, one above each eye, and extract salt from the capillaries running off the birds’ eye arteries. Each gland has a main duct that leads to the nasal cavity. The salt concentrate goes from the duct to the nostril and then runs down grooves in the bill.
In most birds, the salty liquid drips out on its own. Storm petrels, though, forcibly sneeze out their salty nasal fluid.
Salt glands use a lot of calories in their work, and therefore, unlike kidneys, the glands rest until they’re needed.
Researchers theorize that some gulls avoid salty water and food, given a choice, to conserve energy, especially when raising chicks. The youngsters then use their calories toward growing rather than desalinization.
OK, so if gulls’ bodies can handle seawater and salty food, why don’t they live in Hawaii?
I wrote in my Nov. 23 column that gulls are scavengers of shallow waters, and since we have no coastal shelf, Hawaii doesn’t have the kind of shoreline food gulls prefer. My bird expert says that’s an accepted theory, so for that reason, and perhaps others known only to the birds, Hawaii doesn’t work for gulls.
I felt bad about my error, and said so to my friend, but she saw it as an opportunity. “It’s a good way,” she said, “to show why in science it’s important to go to primary sources for information.”
By that she meant it’s better to read research papers and then draw one’s own conclusions on the subject.
The mistake also reminds me that even though I enjoy a particular publication, I shouldn’t believe everything I read in it. And neither should you.