Following Curlews across the West: Grasslands, Agricultural Lands and Intertidal Mudflats

Photo by Mikki Brinkmeyer

The fate of a wildlife species is at times dependent on its ability to persist across a large landscape that may be losing priority habitat, or experiencing degradation. The Long-billed Curlew, a migratory North American shorebird, is one such species that has declined throughout its range. Grasslands are dwindling where curlews breed while wetlands and other foraging habitats may be disappearing on their wintering grounds.

In the late 1970s, Roland Redmond and colleagues conducted seminal research on a curlew breeding area near Boise, Idaho, an area now designated as the Long-billed Curlew Habitat Area of Critical Environmental Concern. This area has again been studied since 2007 in a collaboration between the Boise State University’s Intermountain Bird Observatory, Idaho Department of Fish and Game, and Bureau of Land Management. After documenting stark population decreases - estimates fell from 2000 to 200 individuals in less than 40 years (this site is likely facing more anthropogenic threats than elsewhere) - we expanded the project across the Intermountain West in a collaborative effort to more fully explore annual life history and issues vital for conservation.

Stephanie Coates collects data from a curlew for her thesis project. 

As part of a Master’s thesis, in 2015, we began examining habitat variables, predator communities, and disturbance regimes at six breeding sites across the Intermountain West. Adding to satellite transmitter data collected in 2013-2014, we also deployed an additional 15 satellite transmitters in Idaho, Wyoming, and Montana, and we are currently tracking a total of 19 curlews from as they move about their wintering grounds in southern California and northwestern Mexico. One of the most striking patterns we’re seeing is that curlews from many breeding areas are converging on a region including southeastern California and northwestern Mexico, using both inland and coastal areas during the non-breeding season. Many individuals are using intertidal mudflats while many others are using agricultural and/or grassland areas.

One common thread we are observing between breeding and wintering grounds is the importance of working lands, and specifically, flood-irrigated fields. Curlews maintain and defend territories during the breeding season, and usually return to the same territory they held in the previous year. It was evident from transmitter data at our site near Boise that while not on incubation duty, adults often left their dry grassland territories presumably to forage for insects and other prey in nearby agricultural lands. At some sites, we monitored many curlews nesting in flood-irrigated pastures. For example, though flooding did sometimes lead to nest failure/abandonment, private pastures in southwestern Wyoming are supporting the highest known population of curlews in the state.

Long-billed Curlew migration paths in 2013, 2014 and 2015. 

Even more obvious is the use of agricultural fields on the wintering grounds. For some individuals, transmitter data maps trace their paths frequently, and sometimes exclusively, through areas with a patchwork of crops. In fact, in the time since we began tracking them, most individuals wintering in California’s Central and Imperial Valleys have never visited the coast.

Recently, we were excited to see three curlews with satellite transmitters (one each from Idaho, Montana, and Wyoming) transmitting signals from the exact same agricultural field in California’s Imperial Valley southeast of the Salton Sea! On the ground, this type of event represents a spectacular sight. When one of our collaborators with California Department of Fish and Wildlife recently checked on a transmitter location in the Central Valley, he found an estimated 2,100 curlews foraging in a single alfalfa field. While it is not uncommon to see flocks of several hundred curlews concentrated within patches of dense resources, that many is phenomenal.

Our study is not unique in observing birds using flood-irrigated fields. Multiple observations on curlews as well as research on other species of waterbirds support the notion that this type of land-use can be beneficial for birds. In light of the ongoing drought in the West, managing water resources to mutually benefit people and wildlife will likely become increasingly difficult. However, by providing adequate functional equivalents to native habitats like seasonally flooded wetlands that no longer exist, working lands offer a compromise. Understanding the Long-billed Curlew’s compatibility with these habitats is an important stepping-stone for conservation efforts. (Learn more about conservation strategies for Long-billed Curlews here.)


Read more articles from the Fall 2015 e-Newsletter: