Landbird monitoring in the Chihuahuan Desert Network: annual report, 2010

White, Chris; Bennetts, Robert

In 2010, landbirds were surveyed within six of seven Chihuahuan Desert Inventory & Monitoring Network (CHDN) parks. Sample points were located along a transect for linear features (e.g., most riparian habitats) or a grid for areal features. A total of 66 transects or grids were surveyed in 2010. Survey efforts were focused on the breeding season, when increased territorial behavior by songbirds results in higher detection rates and greater sampling efficiency. The window of primary breeding and, therefore, sampling was from April through June, with adjustments made for individual park visits based on latitude and elevation. We used point-transect surveys to estimate and monitor landbird population parameters. Surveys were generally conducted once for each transect or grid to facilitate estimates of occupancy, which rely on an encounter-history matrix derived from repeated visits, rather than a detection function to account for detectability. We sampled a total of 713 points on 66 transects or grids. Of these, 541 points were sampled in grassland habitat and 172 in riparian habitat. We recorded a total of 7,626 birds of 107 species on our survey points. Amistad National Recreation Area had the highest number of birds counted (n = 2,908). White Sands National Monument had the lowest number of birds detected (n = 102), though only two transects were surveyed and technicians were unable to access much of the area. We observed the greatest number of species at Big Bend National Park (n = 69) and the fewest at White Sands (n = 14). Species richness and community composition varied widely among the parks surveyed. The number of individuals or species detected is influenced not only by the number of survey points, but also by the size and diversity of available habitats. Cliff swallow was the most commonly detected species within the CHDN (n = 954). Nine species were detected only once during surveys. Six species (black-throated sparrow, blue grosbeak, northern mockingbird, mourning dove, ash-throated flycatcher, Scott’s oriole) were detected at all six parks, whereas numerous species were detected at one or very few parks. The Rocky Mountain Bird Observatory (RMBO), our primary cooperator for this project, manages the network’s bird monitoring data. Other networks using RMBO also use this service and have found it to be efficient and effective. This enables CHDN data to be in the same database as those of several other networks and organizations, which in turn allows for a more comprehensive regional assessment.

Landbird monitoring in the Chihuahuan Desert Network: annual report, 2010

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