On the Move! Long-Billed Curlew Winter Migration

Reading Time: 5 minutes

By Erica Gaeta / Seasonal Field Technician at Terra Peninsular

Long-billed curlews (Numenius americanus) are on the move once again! As their short breeding season concludes, most curlews are making their way back to their non-breeding grounds throughout Mexico and southwestern United States.

During the 2019 long-billed curlew breeding season (March to June), Intermountain Bird Observatory (IBO) trapped and fitted curlews with satellite transmitters (PPT) throughout the western United States, and Canada with the support of Bird Studies Canada Project.

As of this year, IBO and partners are now tracking 36 curlews with 14 new individuals! These new individuals will be contributing to the ongoing long-billed curlew tracking database, which allows IBO and partners to gain a better understanding of migration patterns, migratory connectivity, and identification of important stopover and wintering areas.

As for us at Terra Peninsular, we have begun to track 9 curlews who have recently arrived to the Colorado River Delta and Northern Gulf of California coastal habitats (shown in the map below). Our partners at Pronatura Noroeste, working in our study area of the Mexicali Valley in Sonora and Baja California, Mexico, have occasionally observed 1-20 curlews in agriculture fields, but no large flocks. Yet to arrive are last year’s 2018-2019 wintering curlews fitted with transmitters who utilized fields in the Mexicali Valley.

Not too far from the Mexicali Valley agriculture sites is long-billed curlew named “HP” and “61” who both utilized agriculture fields in the valley near San Luis Rio Colorado last season.

“HP” (named after her alpha flag, female trapped in Saratoga, Wyoming in 2017; shown on the maps above), “61” (named after the last 2-digits of his aluminum band, male trapped in New Fork, Wyoming in 2017; shown the map above) currently are both in the Northern Gulf of California, Mexico. Last year both “HP” and “61” arrived at the same coastal area, and once it was October-November, they moved to agriculture habitat. They then spent the rest of the wintering season utilizing agriculture fields until it was time to migrate north.

It appears that many curlews are currently at their stopover sites, so this might just be where “HP” and “61” refuel before migrating slightly north to the Mexicali Valley. Other factors for delaying arrival to the Mexicali Valley may be due to food availability. Our partner from Pronatura Noroeste, Juan Butron, mentioned that during this time of the season common crops available in the Mexicali Valley are alfalfa, cotton, and corn. During our recent study we observed alfalfa as the most frequent crop type used by curlews, but they also utilized other crops such as wheat and asparagus, which are currently out of season till October-November. It will be interesting to see if these curlews move to the Mexicali Valley once again. 

“HX” (female, trapped in Island Park, Idaho in 2017; shown on the map below) unlike “HP” and “61”, has not arrived to the Northern Gulf of California. Last season she utilized coastal habitat in the Northern Gulf of California and Colorado River Delta for the entire non-breeding season. Her delayed arrival and current location causes some concern. Satellite transmitter technology gives us the ability to further investigate and understand the threats that impact curlews during their migration and throughout the annual cycle.

“HX” began her migration south late June. The last signal detected was in an urban area in southern Utah. While it is still early to determine the fate of “HX”, the odds do not look good. In the past IBO has observed curlew mortality caused by illegal shooting, car collisions, and predation events. IBO determines the fate by retrieving the transmitter using telemetry and once found they determine the fate of the long-billed curlew. Join us as we track curlews by clicking the link provided by IBO https://schall11.github.io/curlew_vision/#