Grassland Bird Population Trends (1990–2016)

This dataset draws from the North American Breeding Bird Survey (BBS), archived on Zenodo (record #7101686), and tracks annual counts of 18 grassland-dependent bird species across hundreds of survey routes spanning U.S. states and Canadian provinces (state/province codes 4-81). Covering 4,243 route-year observations with 24 variables, it provides one of the longest-running population time series for birds tied to grassland and agricultural landscapes. The most striking pattern is the near-total absence of several species from most routes: Long-billed Curlews (LBCU), Baird's Sparrows (BAIS), and Grasshopper Sparrows (GRSP) all show a median count of zero, meaning they were simply not detected on the majority of surveyed routes -- a statistical fingerprint of severe range contraction. By contrast, the Western Meadowlark (WEME) still achieves a median of 38 birds per route but swings wildly (up to 447), suggesting it clings to a shrinking patchwork of strongholds rather than a stable, broad distribution. This data matters because grassland birds are among the fastest-declining bird groups in North America, and the BBS remains the primary evidence base for conservation listings and habitat policy across the continent.

• Horned Lark, once the most abundant grassland bird per route, dropped from 75 to 31 birds/route (59% decline)
• Western Meadowlark fell from 72 to 57 birds/route, a 21% decline over 27 years
• Chestnut-collared Longspur peaked at 13.6/route in 1992 then collapsed to 3.7 by 2016
• Clay-colored Sparrow and Vesper Sparrow remained relatively stable, bucking the broader decline
• Lark Bunting showed extreme year-to-year volatility, swinging from 27.5/route (1992) to 0.8 (2010)