Shorebirds vs. Songbirds: The Battle for the North Slope

Shorebird-Songbird

I take full blame for the mis-leading title of this post. And I’ll be forthcoming about that right up front. The North Slope is not some avian battleground with passerines sending vocal barrages of songs into the waiting bayonet-bills of the shorebirds. As interesting as that might sound, the birds of the arctic actually seem to tolerate one another with relative ease.

So why the click-bait title? Well earlier this summer I was paddling a packraft down the Aichilik River with a couple of clients. We started several miles into the Brooks Range and floated all the way through the coastal plain and out to the coast. As usual, I was paying attention to the birds along the way.

In the mountains, with the exceptions of the riverside Spotted Sandpipers and Semipalmated Plovers, there was not a shorebird to be found.

In the mountains, the avifauna was dominated by passerines. The willows along the river were full of singing Tree and White-crowned Sparrows, Wilson’s and Yellow Warblers, American Robins, Redpolls, and Gray-cheeked Thrushes. From the nearby tundra we could hear Smith’s Longspurs. With the exceptions of the riverside Spotted Sandpipers and Semipalmated Plovers, there was not a shorebird to be found.

But as we paddled out of the mountains and away from the tall willows that occur there, things began to change. At our first camp in the plains, about halfway to the coast, the songbirds had been reduced to a few White-crowned and Tree Sparrows, Redpolls and a lone Robin calling from the now-shrunken willows. But in the surrounding tundra, a mix of dry, mountain aven covered areas and saturated wet areas, there were American Golden Plovers, Semipalmated and Stilt Sandpipers.

Another day of paddling found us camped just a mile from the coast, the pressure ridges of the shore-fast sea ice clearly visible to the north. It was cold and nasty. A spitting rain was driven by a 25 knot wind with temperatures in the 30s. And yet, it wasn’t hard to find shorebirds. They were everywhere. Semipalmated, Pectoral, Buff-breasted, and Stilt Sandpipers, Red and Red-necked Phalaropes, and more. Just one lonely songbird species remained: the hardy Lapland Longspur.

Back at home, I took a look at some papers written on shorebird distributions of the north slope, and sure enough, my observations played out rather neatly. Shorebird abundances go way up the further toward the coast one gets.

Shorebird distibutionCheck out this cool figure from Saalfeld et al, (a 2013 paper in Ecosphere entitled: Predicting breeding shorebird distributions on the Arctic Coastal Plain of Alaska). There it is, the same pattern I just described of increasing densities of shorebirds as one moves out of the mountains and toward the coast. Nifty. 

The change is habitat driven. The varied habitats from rocky, alpine tundra, to 10 foot tall willows available in the mountains provides a great diversity of habitat for the songbirds. The friendly, dry substrates, perfect for nesting passerines, becomes increasingly rare, or even absent as you travel north. That diversity of dry nest sites, is steadily replaced by wetter and wetter tundra. That wet tundra, dotted with polygons, is perfect to support a broad array of shorebirds. The less damp areas are occupied by American Golden and Semipalmated Plovers while the saturated tundra and pond edges are perfect for water-loving species like the phalaropes.

It’s a fascinating change over the course of just 20 or 30 miles, and shows the importance of each and every habitat type on the north slope.