Glaciers and Shorebirds, an Unlikely Relationship

The Brooks Range of northern Alaska is not an icy place. Many of my clients on backcountry trips, mis-led by postcard-views from Southeast Alaska and the Alaska Range are surprised to find the Brooks largely unglaciated. There are, in fact, just a handful of glaciers, primarily in the eastern part of the range, in the Arctic National Wildlife Refuge. The alpine glaciers in this region, pour off the highest peaks, and wind only short distances down the valleys before petering out in a chaos of jumbled moraines and meltwater.

Turns out, these rivers of ice, are pretty damn important.

I’d never really thought much about the impact of these remnant glaciers on the arctic environment, but, fortunately for me (and all of us) a few people have. Turns out, these rivers of ice, are pretty damn important. Thanks to the
work of an interdisciplinary team of scientists from the University of Alaska, Fairbanks, USFWS, and the University of Texas, Austin, we now have a better understanding of the impact of the Brooks Range glaciers on the downstream environment.

Since I’m a bird-centric fellow, I’ll start with them. If I’d thought about species of birds that might be affected by glaciers, I’d probably have come up with a list of alpine species: Rock Ptarmigan, Snow Buntings, Gray-crowned Rosy-finches, Horned Larks and the like. But I’d be wrong. The species that are most impacted by the presence or absence of glaciers are species with a markedly different range: the shorebirds that breed and stage for migration on the arctic coast.

In the arctic, shorebirds are most abundant on the river deltas close to the coast. (Check on my previous post for more about that.) No real surprise there. They use these habitats for breeding, but also as important stop-over and staging areas during migration. Tens of thousands of shorebirds depend on these river deltas at one time of year or another.

There on the mudflats, the shorebirds forage for invertebrates. Freshwater inverts, are actually more abundant than marine inverts in the mudflat habitats of the river deltas. (I presume that the constant flow of fresh water from the rivers keeps, the saline ocean water at bay.)

OK, now stick with me here for a moment. In the mostly-freshwater, aquatic environment of the river deltas, there are two dominant groups of invertebrates: the Oligochaete (a class of annelid worms) and the Chironomidae (midges). Now, the life-history of these two classes of critters dictate that they spend multiple years in mudflat habitats. Midges, for example, spend at least three years in the mud before pupating and growing to adulthood. Marine invertebrates, on the other hand, are largely unpredictable and ephemeral, occurring on the mud after storm surges, or other high-water events.

So you got that, right? Just in case, I’ll summarize: the freshwater bugs are more reliable and available than their marine counterparts. This means they are a more dependable food source for the invertebrate-munching shorebirds.

Now, here’s the kicker: those reliable, freshwater inverts, the midges and worms, are WAY more abundant on the deltas of glacially fed rivers.

Boom! I hope you realize how cool this finding is. So we’ve got these small glaciers, high up in the mountains, 40 or 50 miles from the coast and they have an extraordinary effect not just on the structure of the coast, but on the critters that live there. So cool.

Though the exact mechanics of different abundances in invertebrates is still a mystery, it likely has something to do with the sediment load and makeup of the glacial rivers. But what it means is that the shorebirds fare better when they are foraging on the glacially influenced deltas. The birds know it too, and prefer to use the reliable foraging areas more often than the non-glacial river deltas.

Cool stuff, and really drives home the way wildly disparate features of the environment are related.

All this super-cool science has a really depressing subtext: Brooks Range glaciers are melting at such a rapid rate that they are going to be completely gone in less than 50 years.

But of course, all this super-cool science has a really depressing subtext: Brooks Range glaciers are melting at such a rapid rate that they are going to be completely gone in less than 50 years.

Now that sucks. As the glaciers disappear, what happens down on the deltas? Presumably the invert populations will decline to levels similar to those found on non-glacial rivers. Which means a huge decline in the overall availability of food for breeding and migrating shorebirds. Which means starving shorebirds.

And that really, really sucks.

(The information in this post was pulled from this fascinating paper (if you are interested in such things, you can find the pdf HERE):

Nolan, M., R. Churchwell, J. Adams, J. McClelland, K. D. Tape, S. Kendall, A. Powell, K. Dunton, D. Payer, and P. Martin. Predicting the impact of glacier loss on fish, birds, floodplains, and estuaries in the Arctic National Wildlife Refuge, p. 49-55. In C. N. Medley, C. N., G. Patterson, and M. J. Parker [eds.], Observing, Studying, and Managing for Change – Proceedings of the Fourth Interagency Conference on Research in the Watershed. US Geological Survey Scientific Investigations Report 2011-5169, Reston, VA.