The sea, is, as always, inconveniently choppy. On this particular February pelagic, my stomach is hurdling back-and-forth at a rate where my life depends on my death grip on the railing of the ship. Everyone else around me seems to be doing fine. I smile and clench the boat so hard that my knuckles turn white.
When the boat speeds up, so does the wind. Everyone is repelled off the front of the ship. Only I remain, insistent to subject my skin and eyes to the wrinkling sunlight. Ahead of me is pure water. Behind me trails a long intestine of seagulls. Western Gulls, with their dark slate backs and massive bills, and California Gulls, with their dainty long wings, as graceful as gulls can be. Heermann's Gulls are chocolate brown and sleek. The chum is thrown out again and again, in mechanical motions that belies the person in charge of the chumming. Popcorn lands deftly on the water. Half-a-dozen birds hurtle towards it, clashing wings and beaks. It reminds me of that cloud of dust and limbs that artists always use to depict a fight in the Sunday cartoons.
As the boat keeps moving out to sea, the chum trail sputters as gulls fly off to other pursuits. A few birds cling on, persistently, and others seem to be newcomers joining the fight for a kernel. I'm reminded of a study done on Northwestern Crows. The study found that crows would open mulloscs by flying up and dropping them on the rocks. The shorter the drop height, the more times the crow will have to fly up to drop the mullosc. So, to optimize energy usage, Northwestern Crows fly to an average height of 5.23 meters to crack open a mullosc. Any lower, and the energy expended for more frequent flights would outweigh that of a less frequent, higher flights, and vice versa. That something so simple as a crow's whelk-dropping pattern is optimized for maximum efficiency is unsurprising.
So chumming, then, becomes an equation too. There can’t be that much energy in a kernel of popcorn. Considering the fanatic fight for a single piece, as well as the energy required to keep up with the boat, it doesn’t seem very energetically efficient for every gull to fly behind the boat. If a gull is unable to overpower or outsmart other gulls to grab a popcorn, then it makes no economic sense for it to continue staying in the chum line. A gull must be able to win a popcorn kernel a certain percentage of the time for it to be efficient to stay. That means that there must be a very fast turnover rate in the chum line, and maybe a few consistent winners that pick up popcorn with skill. I wonder what the maximum distance a single bird has stayed in the chum line has been. As the boat heads out to sea, where shore-monging gulls are less inclined to be, I wonder, too, how far the boat would have to go before no gulls are left. Given the probable low energy value of popcorn the chum line seems overall like a gimmicky endeavor for gulls.
Evolution favors those who are energetically efficient. The real winners in the chum line, then, are not the gulls that manage to grab a kernel of popcorn, but those who manage to maximize their net energy payoff. For some birds, that may mean avoiding the chumming altogether. There’s also consideration of species, as bigger Western Gulls may have an advantage fighting for a popcorn but waste more energy keeping up with the boat. It’s a puzzle so complicated that only decades of study and a complex mathematical equation could model it. Most likely, we will never perfect the equation of chumming.
It’s difficult to keep track of individual gulls, especially on a pelagic where birds fly in and out like popcorn. The simple act of chumming, however, carries evolutionary weight. To watch the gulls fighting for popcorn is to watch as individual variation in each gull determines its successive fate in the chum line, and, eventually, its fitness. In light of that, the wind on the exterior of the ship is worth braving.