Marine ecology is complicated, yet there is one pattern that is quite consistent: cold water is more productive than warm water. There is more food in cold ocean systems than in warm ones. However, we shouldn’t confuse productivity with diversity, as evidenced by the incredible species diversity in tropical coral reefs. But if you are thinking of places with impressive concentrations of biomass—the ones that are full of shearwaters, whales, and penguins/alcids—these are cooler areas. Two of the most productive such areas are in the Americas: the Humboldt and California current systems.

But what happens when a typically cold and productive area becomes warm? This is at the heart of the discussion right now, as El Niño is in its early throes. ENSO (El Niño Southern Oscillation) is a multiyear oscillation which occurs along the Equatorial Pacific. During the positive phase (called El Niño), the water warms; during the negative phase (called La Niña), the water becomes cooler than normal. Specifically, El Niño occurs when water on the American side of the tropical Pacific becomes warmer than normal due to a shift in the overall wind regime. It is a natural cycle that has happened historically. However, predictions and current observation suggest that the one forming right now is a going to be a doozy.

It is this type of short-term climate shift that influences the beak size of Galápagos “finches” and results in breeding failure in many seabirds. Warm water usually creates more rain. In the Galápagos, this makes grass grow, and grass has small seeds, which smaller-billed “finches” may eat more efficiently. Meanwhile the warm, relatively hypoxic (low-oxygen) water is unproductive, so there is less food for seabirds to eat. Local whales also struggle finding enough food. A minor El Niño can be a short-lived nuisance to long-lived seabirds, but a major El Niño can cause adult mortality and, thus, profoundly affect population sizes. This is particularly true of resident birds such as Galápagos Penguin and Flightless Cormorant.

This map shows how ocean surface temperatures differed from the long-tern average on 4 Jul 2023. Note the red and maroon areas around the Galápagos Islands and off Peru and Ecuador, where the water was 5°C (9°F) warmer than normal—a major deviation. 2023’s El Niño is currently predicted to continue strengthening; once there has been an average increase of greater than 1.5°C (2.7°F) for three months along the Equator west of the Galápagos, the event will be called as a “major El Niño”, and this is the current expectation. But an additional pattern happening now is perhaps even more disturbing: the ocean is warmer than ever outside of the region of ENSO. Yellow to red coloration on this map is widespread. What a major El Niño looks like in an overly warm ocean is unknown, but it seems we are about to find out.

You may have heard that major El Niño events tend to provide a wet and warm winter to California, which may be good in the long-term for many of the terrestrial birds and other wildlife there. And while El Niño does shift rainfall patterns, its larger and more immediate effect is on marine life. Food becomes so scarce in a warm ocean that marine birds move away from their regular ranges in search of food. This is happening right now, and in spectacular fashion.

Since colder water has more food, you might expect that many of these hungry Humboldt Current birds would be heading south. Indeed, when water began to warm off Peru earlier this year, they did. Chile recorded record numbers of Waved Albatross and Masked and Nazca boobies. The last species is only a recent addition to country’s avifauna. But it is currently (July 2023) the middle of winter in the far south. Weather conditions are rough, and fewer birders are looking for out-of-range birds offshore. Thus, we don’t know if this southward movement of birds has continued, but we will starting in October, when pelagic trips begin again. Perhaps unintuitively, then, the big story right now is in Galápagos and coastal Ecuador clear up to Costa Rica.

Starting with the Galápagos, there have been three first records for the islands: Christmas Shearwater, Kermadec Petrel, Grey Gull. While I was in the Galápagos in June, I noticed many flying fish, which are usually absent at this time of year when water tends to be cold. Fewer seabirds were breeding, and in some areas where Blue-footed Boobies are usually plentiful, they were absent. We saw nearly no whales, but last year when the water was cold, we saw many. We saw Sooty Terns on two occasions, but usually we see none. And seeing a Striped Marlin, a warm-water fish species, was locally unusual. Other observers are reporting similar observations.

The birding in coastal Ecuador and Colombia is, in a word, insane right now. There are photos of coastal rocks covered by Peruvian Boobies and Inca Terns in places where a single bird would be rare in any other year. A single report of 200 Inca Terns in Ecuador, plus many other reports, suggests that there are thousands right now in Ecuador. A report of 50 at Isla Bocagrande in Colombia is unprecedented. At least one Inca Tern has made it as far north as Costa Rica.

Peruvian Boobies are so far north that the first of many records for Costa Rica have been reported in eBird, and the reports are of multiple birds. The species is common off Ecuador and parts of Colombia right now.

In this photo from Costa Rica, a Peruvian Booby is flanked by two Blue-footed Boobies on the left and two Brown Boobies on the right. In comparison to the former, note Peruvian Booby’s clean white head/neck, more extensively dark mantle, dark eyes, wholly dark tail, grayer feet, and pink-tinged bill.

Guanay Cormorant, a classic Humboldt Current seabird, typically makes a northward incursion during El Niño years. But this year they are in Ecuador in record numbers, and some have reached Colombia.

Ecuador hosted its first Red-legged Cormorant. Rather, its first Red-legged Cormorants: multiple birds have been reported.

Another bird likely moving farther north than the norm was a Salvin’s Albatross seen off Colombia. I expect more unusual records will occur as this El Niño continues.

Mortality events have also been noted with, especially, Sooty Shearwater. Dead birds have washed up from northern South America to Central America. How much of the die-off is due to starvation and how much to avian flu is not clear.

So that’s what’s happening in the tropics, but what should people in the ABA Area be looking for? A strong El Niño often causes warm water to appear near Baja California, and this can create wide-ranging effects, including northward movement for birds to the West Coast of the U.S. and even Canada. Perhaps we should be diligent about looking for Wedge-rumped Storm-Petrel off southern California. Folks in Florida and the Southeast should be watching, too, as some of the vagrants in Panama could easily cross to the Caribbean. I don’t believe than an Inca Tern on the Dry Tortugas is out of the question. I doubt that Peruvian Boobies will range north to California, but I could see Inca Tern making a go of it, and perhaps Swallow-tailed Gull should be on our radar. This is mostly guesswork, of course, and what is perhaps more likely is that the star bird of the event will be something not mentioned here at a truly unexpected place.

Editor’s Note: Just an hour after this article was published, a Swallow-tailed Gull was reported from Santa Barbara Co, California!

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Alvaro Jaramillo trained as a biologist with a focus in Evolutionary Ecology but was derailed from academia by international travel. He now runs Alvaro’s Adventures, a birding tour company focused on great birding, wine, and food. He is author of several books, including Birds of Chile and the ABA Field Guide to Birds of California.