Dear Bird Folks,
Last week, while walking the beach, I fed a one year old Herring Gull some leftover bits of French bread. The bird ate quite a few morsels, stared at me for a minute, then waded out into the water and delicately took four sips of water. It was saltwater! Can gulls digest saltwater?
– Rhody, Harwich, MA
Come on Rhody,
Where are your manners? No wonder the gull “stared at you for a minute.” Even gulls know that when you are serving French bread you should also serve wine. And not just any wine. I think etiquette suggests a nice Burgundy should be served with bread, especially stale bread. I sure hope the people next-door in Chatham don’t hear about your faux pa. You could be banned from ever crossing their border again. Wait. Did you say the gull was a year old? Now it makes sense. Even in bird-years one year old is way too young for wine. You are off the hook this time, Rhody.
Birds gain water from a variety of sources. Much of what they need comes from their diet. That’s one of the reasons why we rarely find eagles drinking out of our birdbaths. Eagles, like all birds of prey, obtain most of the moisture they need from the fat, juicy creatures that they catch. Swallows and flycatchers obtain water from ingested insects. And to a lesser degree sparrows and finches derive moisture from the seeds that they pick up off the ground. With all that in mind there is no doubt that gulls are able to score plenty of moisture from their diet of fresh clams and raw fish. However, dry French bread is another story. With no wine in the offering, your gull was forced to find the next closest thing to wash down its food. Certainly drinking sea water would not be a good idea for us to do, but fortunately for the gull, it is able to handle sea water much better than it can handle French bread.
In humans it’s the kidney’s job to make sure we have the right balance of salt in our bodies. If we eat too much salt our kidneys flush it out of our systems. That’s why we get thirsty after eating salted popcorn at the movies. (That’s also why theater owners charge $7.95 for a small bottle of water.) If we humans were to drink saltwater we would become thirsty just like we do when eating popcorn. It takes a cup and half of fresh water to flush out a cup of saltwater. So the more saltwater we drink the more freshwater is purged from our bodies. If we drink too much saltwater we will die of thirst. That’s a bad thing.
Since gulls and other seabirds don’t have an extra $7.95 to buy a bottle of freshwater, they have evolved their own built-in desalination plant. A salt gland, located just above the bill, filters out much of the salt before it gets to the kidneys.
The next time you see a flock of gulls at the beach or in a parking lot, searching for a homeless French fry, take a good look at the tips of their bills. You may find one with a drop of liquid dripping from its bill. The drop is actually excreted salt solution. As the salt gland filters the salt it secretes a solution. The solution runs out of the nostrils, down the length of the bill and forms a drip at the tip. The bird then simply shakes it off. I used to know a guy who thought the reason why gulls sometimes had drips on the end of their bills was because they had “colds.” What bonehead he was. Don’t you think? Okay, fine, the guy was me. But I don’t think that way anymore, so let it go.
Many pelagic birds (seabirds that rarely come to land) can’t be bothered with this slow postnasal drip method of removing their salt. Instead they have developed a tube-like structure on the top of their bill. When it’s time to rid themselves of excess salt they simply “sneeze” the salt out of the tube. The sneezing process is not only an efficient way to remove salt, but it also grosses out all the other birds eating in the area.
Even our old pal the Mallard can handle its salt. A Mallard that lives inland has a rather small salt gland. But if the same bird takes a trip to the coast its salt gland enlarges to accommodate the increased salt intake. The bird’s gland will grow even larger if it buys itself a bag of movie theater popcorn.
It’s nice that you are worried about the Herring Gull’s salt intake, Rhody, but they have had that salt thing worked out for years. Also, I hope you know I was kidding about offering the gull a glass of Burgundy. That would be silly. Everyone knows gulls only drink Chardonnay.