Locating the holy (g)rail of birds

As the tide rose, the salt flats became stickier to walk through, increasing the effort required for each step. The physical exertion was antithetical to the view before me—an expansive marsh with gradients of green grasses and sedges winding through the salt pannes, bursting with songs of Seaside Sparrows and Red-winged Blackbirds. Wading birds and shorebirds foraged in mixed flocks where water was beginning to pool. After taking a moment to drink some water and enjoy the scene before me, I trudged on—only about 250 meters until I got to the truck.

A high marsh habitat with glasswort in the foreground and black needlerush in the background. These systems require fire to prevent encroachment by woody shrubs and maintain an open, grassy setting.

That’s when I heard it. After searching for nearly six weeks, I was starting to lose hope I’d ever hear the elusive and threatened Black Rail. But, in a patch of short black needlerush, one began to ‘kickeedoo’ incessantly for nearly two minutes straight. I was beside myself. This was the first Black Rail I had ever heard. It was just one of many birds we heard last summer.

In 2020, we joined the efforts of the NOAA RESTORE Firebird project (Firebird), which seeks to understand the influences of high marsh management—specifically prescribed fire—on Black and Yellow Rails along the northern Gulf of Mexico coastline. The Eastern Black Rail, the subspecies that occurs in the eastern half of the United States, was listed as threatened under the Endangered Species Act last year. We completed a pilot season in 2021, to locate areas occupied by Black Rails in the region and to identify the most efficient survey methods. Our efforts were focused on high marsh habitats, the area nestled in between the mucky, low marshes and the uplands which are infrequently inundated with water. For our surveys, we tested the effects of different playback types, time of day, wind speed, lunar phase, and barometric pressure on responses.

After we finished surveys in late July, we used occupancy models to determine detection probability, or the likelihood of detecting an individual on a single visit. Occupancy models are ideal for species like the Black Rail because they account for imperfect detection. Within candidate models, we incorporated covariates that included environmental factors, such as wind and temperature that were measured at the start of each survey. We also included the type of playback used in addition to the time of the survey; the two factors we were especially interested in. We then ranked models to determine which factors affected Black Rail detections.

We made a total of 900 visits to the 147 sites between March 15 and July 31. Black Rails were first heard in early April, but responses peaked in June (Figure 1). The probability of detecting a Black Rail on any given survey was 0.21 ± 0.05. Across the 147 sites, 0.15 were occupied. Ranked models indicated that no one factor was especially important for determining occupancy and there were no significant effects regarding playback type (Figure 2) or survey time (Figure 3), two factors we were especially interested in.

Figure 1: Seasonal responses of Black Rails during the 2021 breeding season.

Figure 2: Black Rail responses according to 3 different playback call types.

Figure 3: Black Rail responses according to time of day.

Our detection and occupancy results were on par with other studies, and although we didn’t learn very much from the individual models, we came out with a lot of practical knowledge about Black Rail habitat, behavior, and vocal patterns in the Big Bend region that will inform our survey efforts for the next several years as we continue to unfurl the secretive ways of the Black Rail.

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