From Subtle Skulker to Skylarking Songster

One of my favorite birds of the Southwest is the Cassin’s Sparrow. At first glance, it seems unassuming: a small, brown bird with subtle streaking and a long tail. To the casual observer, it can often be overlooked as just another “little brown bird”. But its life history is anything but ordinary. During the summer breeding season, the male Cassin’s Sparrow often delivers his song while performing a remarkable “skylarking” display, fluttering upward from a shrub or grass stalk before parachuting back down with wings and tail spread. Thus, for a short period of time each summer, this otherwise shy sparrow is one of the most conspicuous songsters of the grasslands. 

This species is also known for its nomadic tendencies, appearing in abundance one year and seemingly vanishing the next. In arid grasslands, Cassin’s Sparrows often track pulses of rainfall and vegetation growth, arriving in numbers when summer monsoon rains transform dry rangelands into lush seas of grass teeming with insects. Given how fleeting the summer monsoon can be in Arizona and New Mexico, it’s no surprise that Cassin’s Sparrows are easy to miss most of the year. But if you spend time in the wide-open grasslands of the Southwest in summer, you might hear the sweet, cascading whistles drifting down from above you, reminding you not to judge a book by its cover. 

Cassin’s Sparrows thrive in semi-arid grasslands with scattered shrubs—habitats typical of the Chihuahuan Desert grasslands of southern Arizona and New Mexico. They favor landscapes with a mix of bunchgrasses and low woody plants such as mesquite, yucca, cactus, or hackberry. These shrubs provide song perches and nest cover, while the grasses conceal their nests, which are placed on the ground. These needs illustrate an important principle of grassland ecology: structural diversity matters. Cassin’s Sparrows avoid dense shrublands but also struggle in landscapes that have lost their grass layer. They tend to favor native grasslands and are rarely found in cultivated fields.  

The Cassin’s Sparrow is currently considered as species of Least Concern, but populations fluctuate dramatically from year to year, making long-term trends difficult to measure. This also makes it a uniquely interesting species to monitor as an indicator of climate variability and vegetation productivity trends. Recently, at the Appleton-Whittell Research Ranch where Cassin’s Sparrows can typically be found, we collaborated with Sonoran Joint Venture and Arizona State University to initiate exciting new research into this species and other grassland birds. Taking advantage of the nearby Motus receiving station, over a dozen birds were outfitted with Motus transmitter tags, which automatically “ping” receiver stations whenever they are within range. With hundreds of other Motus stations already deployed across the country, this innovative technology enables researchers to efficiently track migration patterns of birds, leading to important ecological findings that can help inform conservation and management. 

In many areas, the biggest threats come from the loss or degradation of native grasslands, including shrub encroachment, invasive grasses, and changes in grazing management. That’s where conservation on working lands becomes crucial. Much of the remaining grassland habitat in the Southwest occurs on private ranches and leased grazing lands, and programs such as the Audubon Conservation Ranching (ACR) initiative help ranchers manage these landscapes in ways that benefit birds and livestock alike. Practices such as adaptive grazing management, maintaining native grasses, and process-based restoration can help sustain the mosaic of grass and shrub structure that many grasslands bird species such as the Cassin’s Sparrow need to thrive. The ACR initiative has been well-established across much of the country for over a decade, but recently expanded to include Audubon Southwest under our Wings Over Working Lands program. As the Senior Manager of this program, I am always excited to share my appreciation for these “little brown birds” with the diverse stakeholders we work with on a daily basis. Their presence reminds us that healthy grasslands are dynamic systems, shaped by rainfall, grazing, and stewardship.