Dive Dry with Dr. Bill

#317: Sea Gulls... Rats of the Sea

I had just purchased a cinnamon roll at the donut shop and was walking out to the dive shop on the pier when it happened. Donnie from the dive shop yelled at me, then immediately I heard (and felt) a "whoosh" over my right shoulder, then another one from the left and a third from overhead. Fortunately I instantly realized I was being mobbed by the rats of the sea, seagulls, who wanted my roll. I held it close to my chest and fended off the attack, feeling I was suddenly dropped into a Hitchcock movie. Now I've had seagulls grab bagels right out of my hand, and sneak French (not freedom) fries off my plate on Antonio's deck. But this was a well orchestrated sneak attack showing social cooperation!

Now all of Mother Nature has a purpose. I'm sure that in the Great Plan even mosquitoes, bedbugs and fleas are here for a reason beneficial to the ecosystem as a whole. Right? However, what I do know is that seagulls did not evolve to snatch bagels and cinnamon rolls out of my hands or French fries off your plate! The early members of this group evolved well before human beings appeared... and with them trash dumps, deep fat fryers and pastries. Much as you may be tempted to strangle them, it is said the souls of drowned sailors and fishermen become seagulls so they should not be killed. Hmmm. I wonder about the souls of divers?

Ecologically, seagulls are important members of the food webs. They are notorious scavengers that will take almost anything not nailed down. They also feed on live food including fish, crabs and other crustaceans, molluscs, insects, the eggs of other birds and occasionally small rodents (their "relatives"). However they are usually surface feeders at sea. While diving I once watched a seagull attempt to take jack mackerel several feet below the surface. It was unsuccessful at penetrating more than about six inches due to the bird's heavy build. Fortunately I have better luck. As diving birds, they are certainly no match for the cormorant which goes to depths beyond 150 feet in search of food. Of course I am!

Some exhibit "kleptoparasitism," the taking of prey from another species which did all the hard work. I guess the bagel and cinnamon roll put me in that category! This habit is one reason gulls are often strongly associated with human populations on coastal areas. Coastal development has created municipal dumps, open air restaurants and boat docks that provide easy pickings for these crafty birds. It is said that the gull population in the South Bay has gone from less than 1,000 breeding birds in 1982 to over 33,000 in 2006.

Because they are ground nesters, their eggs and chicks often fall prey to various vertebrate predators. I once watched a blue shark attempt to take a seagull out in the open ocean. It was not very proficient at this, allowing the gull to fly away after several unsuccessful attempts. However, tiger sharks and other more aggressive species may take them at the surface. I believe California sea lions will also do this, as I have seen them attempt it. I much prefer chicken or turkey myself.

Gulls exhibit some interesting behavior related to nesting and rearing of the chicks. One of them came to light in the early 1970's when I started teaching a course on animal behavior at the old Toyon school. Many of you have probably noticed that some species have a red or other color spot towards the end of their bills. Our course readings revealed that the spot serves as a target for the young chicks to peck at when the adult returns to the nest with food. This ensures a higher probability they will get fed... and survive. Some species of gulls are known to live nearly 50 years. I'm sure nutritionists will someday do a study to compare the health and longevity of those that feed on natural foods and those that frequent dumps and love pastries.

It's hard to believe, but seagulls are considered fairly intelligent by biologists. The are often very social, nesting in large colonies. From the great clamor that arises in them, it is obvious that they frequently talk to one another. I'm sure they aren't just doing it to hear their voice... definitely NOT American Idol material. They have evolved complex methods for communicating with other members of the colony, and act cooperatively to mob potential predators that enter the area. Some species have even demonstrated the ability to use simple tools. Of course I have yet to see one operate a router or a chain saw. The two to three speckled eggs hatch into chicks that have a warm coat of down.

A scientific study right here in the Channel Islands showed that occasionally two western gull females would pair up and guard a nest site. These nests had much higher than normal numbers of eggs, and were called supernormal clutches. Eggs are laid more frequently in these nests, indicating both females contribute their share. It appears that no males are allowed within their territory, so these have been referred to in the literature as homosexual pairings. Without a male, all the eggs are infertile. With the passage of Proposition 8, these poor birds can't even get a marriage license despite the fact they may remain together for several years.

In my various positions as a biologist, I've always had a birder on staff. Relying on their knowledge, I've never really learned to distinguish many bird species. If I did, I doubt seagulls would be a focus of my efforts. For that reason I tend to lump all 55 species into one category... rats, er gulls. Don't expect me to elaborate much on the differences between the various species. It was good to learn that even ornithologists who specialize in this group have made mistakes, and that their taxonomy is currently being revised based on genetic and other new information. I'll wait until they have it all worked out before I learn the different species.

© 2008 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

The rats of the sea and... whew, it missed me!

This document maintained by Dr. Bill Bushing.
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