How Many Fish Does it Take to Grow a Loon? 

A lot. But size is more important.

There are four species of loons that commonly breed in North America: Common, Yellow-billed, Pacific, and Red-throated Loons.

Common Loons are probably the best known. They nest in large lakes throughout the northern contiguous states, Canada, and Alaska. Their lovely, ethereal calls are known to almost everyone (from ambient nature soundtracks if not from personal experience). Yellow-billed Loons are the largest of the bunch. They look much like Common Loons, but with a bright yellow bill that points upward at an arrogant tilt. This species prefers to breed in large lakes in the arctic, and are a favorite of visiting birders. The Pacific is elegant to the extreme. With breeding plumage like smooth silk, the Pacific Loon has been known to convert even the most cynical observer into a slack-jawed gaper. This species breeds in lakes and ponds across the northern boreal forest and arctic of Canada and Alaska.

Last, we come to the comparatively diminutive Red-throated Loon. Lovely, in a more subtle way, Red-throats are dressed in grays and buff with a flash of blood-red beneath their chins. They breed on small ponds (very small by loon standards), along the coasts of northern North America, Asia and Europe. And it’s this species, that I’m going to focus on here.

Dan Rizzolo is a biologist currently wrapping up his Ph.D. For the past several years, he has been researching loons, and the Red-throated loon in particular.

Red-throats warrant the attention Dan has given them. The species has been declining, dramatically in recent decades, and aside from the constant, vague, and insidious bugaboo of climate change, no one has been able to assign a specific cause.

Loons are tough birds to study. They breed, scattered across vast and difficult to access areas, and spend their winters in the ocean, moving constantly as they follow food. Dan has dedicated several long and grueling summers to these loons, living for months at a time at remote field camps in Alaska’s arctic, tromping hundreds of miles across the wet tundra in hip boots, and suffering through epic swarms of mosquitoes. Most people can’t put up with the conditions for long, but Rizzolo is not most people.

Dan’s field work is mostly complete, and he’s starting to piece together the results. His first paper on his loon work has just been published in the ornithological journal “The Auk”. It’s entitled: Fast and efficient: Postnatal growth and energy expenditure in an Arctic-breeding waterbird, the Red-throated Loon (Gavia stellata).

The title gets right to the point. It takes a lot of input to grow a loon chick, but it happens fast. Unlike other species, Red-throats don’t actually nest on lakes where they forage. Instead, the adults fly great distances to their preferred foraging areas just off the coast. More than a dozen times per day they make the journey, returning each time, fish in bill, to the waiting beaks of their young. This takes a lot of energy, but to minimize the effort, the chicks grow fast and fledge early, becoming independent after reaching only 60% of their parents’ size. The whole process from hatching to fledging takes only 49 days on average, an incredibly short period for a large bird living in a cold and difficult environment.

Impressive, no doubt, but this high input over a short period means that the parents need to focus on prey items with a lot of energy content (think of the piscine equivalent of chocolate cheesecake). Fish with great names like Rainbow Smelt, Least Cisco, and (my favorite) Slender Eelblenny, make up the bulk of their diet during the breeding season. When such prey is not available, the whole formula falls apart and the loons’ reproductive success plummets.

The adults know the chance of failure looms like a specter over each breeding attempt and, when prey abundance is low, will favor their own survival over that of their chicks. It sucks for the chicks who end up starving in their nests, but it means the parents will get another shot the following year. Loons are long-lived and this strategy, however distasteful to us, has worked for millennia.

Through his work, Dan has added a piece into the Red-throated Loon’s maddeningly complicated puzzle. We now know that breeding success depends on high energy food. But the birds are declining and I wanted a clear answer as to why, so I sent Dan an email and I asked him.

Dan was hesitant to step out on the limb I offered. But he did elucidate just how incredibly complicated the arctic food web is. The fish I mentioned in the previous paragraph live primarily in the Alaska Coastal Current which is driven by the enormous freshwater outflows from the Yukon and Kuskokwim Rivers. The relatively warm and low-salt water just happens to provide the right combination of conditions for these forage fish. But the Chukchi Sea, where Dan’s work took place, is changing. Water is flowing differently between the Bering and Chukchi Seas, and glacial melt in the state’s interior could impact flows and temperatures in the Yukon River. How all that is going to affect the coastal current and its fish is a best-guess scenario.

“There are no seabird colonies north of Cape Lisburne.” Dan tells me. The necessary cliffs and scree slopes required by nesting alcids is replaced by coastal tundra. This makes loons some of the few marine fish-dependent species in the northern part of Alaska. “Red-throated loons are an excellent sentinel species for monitoring ocean conditions in the Chukchi since they depend on marine fishes for their reproductive success.”

Dan’s work on Red-throated Loons doesn’t just tell us about Red-throated Loons. This research provides a window into the ocean environment of the entire Chukchi Sea. Meaning, through a better understanding of this gray and red waterbird, we can enhance our knowledge of fisheries stocks, marine conditions, and how that changing environment is impacting wildlife and human uses of the resources.

The implications of scientific research often reach far beyond the titles of the paper. This is something that policy-makers and cynical members of the public should keep in mind.

Big thanks to Dan Rizzolo for answering my questions and making many of the connections I’ve discussed here.

The natural history information on loons I’ve provided here come from the Birds of North America Accounts. The research featured in this post comes from the following article:

Rizzolo, Daniel J., J. A. Schmutz, and J.R. Speakman. 2015. Fast and efficient: Postnatal growth and energy expenditure in an Arctic-breeding waterbird, the Red-throated Loon (Gavia stellata). The Auk, 132(3): 657-670.