Why African Penguins Shouldn’t Listen to Their Instincts
Thanks to overfishing and climate change, the birds are caught in an ecological trap that could lead to starvation.
The African penguin, sometimes called the “jackass penguin” for the way its squawks resemble donkey brays, hasn’t had the best century. People have gathered their eggs for supper and disturbed their nest sites to scrape up guano for use in fertilizers. Oil disasters, like the MV Apollo Sea spill in 1994 and the MV Treasure wreck in 2000, have taken out thousands of these birds at a pop. And throughout it all, overfishing has been drastically reducing the amount of food left for the little wobblers.
Since the late 1970s, African penguin populations have declined more than 50 percent; as of 2015, only around 50,000 mature birds were thought to remain. And now, according to a study published in February in Current Biology, the endangered birds may have yet another problem standing in the way of their recovery—their own brains. More specifically, their instincts are working against them.
Imagine you’re a juvenile penguin, no more than a year old. You are two feet tall and weigh less than a gallon of milk. Everything wants to eat you. On land, along Africa’s southern and southwestern coasts, it’s mongooses, caracals, genets, and leopards. At sea, it’s sharks, Cape fur seals, and orcas.
Your own tummy is rumbling, too. You look around for Mom and Dad, but they’re nowhere to be found. They’ve been bringing back fewer and fewer fish these last few weeks. It’s as if they’re trying to tell you something.
Finally your instinct kicks in and tells you to get your feathered butt into the ocean. Hit the breakers and turn right, it says, and just keep swimming until the water is cold and green and smells like a place where there are surely voluminous clouds of sardines and anchovies.
But instead, after days at sea, you arrive at a desolate stretch of ocean. The spot feels, looks, and smells right, but no fish. Whether you know it or not, juvenile African penguins like yourself have been coming here for as long as anyone can remember. But none of that changes the fact that the fish aren’t here now. You are still hungry―and now you may starve.
Scientists call this unfortunate turn of events an “ecological trap” in which you have been betrayed by your own instincts.
Ecological traps occur whenever environmental conditions change suddenly and a species has not yet adapted to them. For instance, when sea turtles hatch, their instincts tell them to follow the faint glow of moonlight reflecting off the ocean. However, modern lighting from houses, hotels, and roads can lure the little reptiles in the opposite direction. This is why many beachside communities now have laws about nighttime lighting.
So, what’s mucking up the penguins’ routine? According to the study’s lead author, Richard Sherley, a marine ecologist at the University of Exeter in the United Kingdom, it’s a one-two punch of fishing and climate change. Not only are there now fewer fish in the sea, so to speak, but the ones that are left have shifted to more suitable habitats.
The problem is, young penguins appear to choose their foraging sites based not on where fish are, but instead on where fish should be. Any fisherman can appreciate this conundrum. Fish live inconspicuously below the waterline. The only thing you can do is throw your line into areas that seem like they’ll be productive, ones with characteristics you know fish like—be they shade, depth, temperature, or what-have-you.
For African penguins, one of these fish-finding cues is the presence of a substance known as dimethyl sulfide, or DMS. “This is an important info-chemical in the oceans that is produced by phytoplankton when it is under stress from grazers or in turbid water,” says Sherley. (Not only penguins can detect DMS, by the way. So can humans: It’s the smell produced by cooking cabbage, corn, and seafood.)
The problem is, the DMS-emitting phytoplankton are right where they’ve always been, which means that stretch of ocean produces the right signals, says Sherley. It’s just that the fish have moved on.
Sherley and his team tracked 54 juvenile African penguins with satellite transmitters from 2011 to 2013. They found that birds foraging in “trap” areas were significantly less likely to survive to adulthood. By plotting their data into a projection model, the authors estimate that the reproduction rates of penguin populations swimming to trap areas are half as high as populations that don’t.
Perhaps worst of all, Sherley says that even when the juvenile penguins scrape together enough fish to survive, they might end up breeding back at their same colony. This means the ecological trap can echo on down through the generations.
The only good news is that we’re already doing a lot to protect African penguins. Most of their breeding sites in South Africa sit within national parks and nature preserves, and the Namibian Islands’ Marine Protected Area safeguards more than 3,500 square miles of ocean, including all penguin breeding localities and key foraging habitats. However, Sherley’s paper points out that this area, vast as it is, doesn’t include the waters where juvenile penguins forage. Sardine fishing persists there uninhibited. And progress on the climate front may not happen quickly enough to remedy the fish-penguin dynamic (especially with the uncertainties surrounding President Trump’s climate “plan”).
One thing, though, is clear. If conditions continue as they are, Sherley says the penguins will qualify for critically endangered status by the year 2030. After that, they’ll be swimming toward extinction.
This article was made possible by a grant from the Jonathan & Maxine Marshall Fund for Environmental Journalism.
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