Studying birds that nest in grasslands on the firing ranges and runways of active military installations is not for the faint of heart, but it proved to be a successful strategy to help solve some perplexing migration mysteries.
Basic questions regarding the timing and choice of migration routes, and what that means for conservation of grassland bird populations have been surprisingly difficult to answer—until now. Research by VCE biologists recently published in Ecology and Evolution sheds light on the annual movements of two grassland bird species and yields surprising results that may help transform the way we manage grassland bird populations, both across international borders and throughout their annual cycle.
With support from the U.S. Department of Defense Legacy Resource Management Program, VCE’s Jason Hill and Rosalind Renfrew carried out the most extensive examination of the nonbreeding movement ecology for Grasshopper Sparrows (Ammodramus savannarum) and Eastern Meadowlarks (Sturnella magna) to date. Filling in fundamental knowledge gaps, their research will pave the way for cooperative endeavors to slow the decline of these grassland birds in the Midwest and Eastern United States.
To investigate the migratory patterns of these two species, Jason and Roz—with help from field crews, colleagues, and installation managers—captured and fitted backpack-style geolocators on 180 Grasshopper Sparrows and 29 Eastern Meadowlarks at Konza Prairie in Kansas, and at six U.S. Department of Defense installations across the species’ breeding ranges.
While that sounds difficult enough, the really hard part was re-capturing the very same Grasshopper Sparrows one year later to remove those geolocators and download their data! Eastern Meadowlark backpacks, thankfully, transmitted data through satellites. The team was able to retrieve location data on 34 Grasshopper Sparrows and five Eastern Meadowlarks.
Data retrieved from the geolocators held many surprises. Among the most astonishing findings was that Grasshopper Sparrows do not begin fall migration in August as biologists had previously assumed; they actually stay put on the breeding grounds until October. The data also revealed that Grasshopper Sparrows make short, nearly daily migration flights, and that the North American Great Lakes region likely serves as a migratory divide between Midwest and East Coast populations. Data from Eastern Meadowlarks provided evidence of a diversity of individual movement behaviors, ranging from year-round residency in the same location to short‐ and long‐distance migration strategies.
The study reveals where and when these grassland birds travel each year between their breeding seasons, and highlights where research is needed on the stopover and nonbreeding grounds, especially for Grasshopper Sparrows in Mexico and the Caribbean Islands. For an immersive experience, you can interact with those results on VCE’s Grassland Bird Migration Project page.