Status and trends of landbird populations in the Northern Colorado Plateau Network: 2020 field season

Roberts, Samuel; Tymkiw, Elizabeth; Ladin, Zachary; Shriver, Greg

doi:10.36967/nrr-2284628

In 2020, the University of Delaware, in cooperation with the National Park Service (NPS), partially completed the fifteenth year of a habitat-based landbird monitoring program in NPS units of the Northern Colorado Plateau Network (NCPN). This program is designed to provide rigorous population trend data for most diurnal, regularly occurring breeding landbird species throughout the network. This information is useful for land managers and supports the National Park Service’s goal of long-term monitoring of biological indicators in network parks. Due to park closures and safety precautions related to the COVID-19 pandemic, a reduced survey effort was employed in 2020. Only sagebrush-shrubland transects were visited, and point counts were not conducted at Pipe Spring National Monument. In 2020, university biologists surveyed 15 locations in sagebrush-shrubland habitat within five NPS units. (In a typical year, 45 surveys are conducted—15 in each of the three following habitat types: low-elevation riparian, pinyon-juniper, and sagebrush shrubland.) Over 15 years of data collection, 14,483 point-count surveys have been conducted in 11 NCPN units, detecting 173 unique species. During the 2020 field season, 210 point-count surveys were conducted, detecting 73 unique species. Using data from 2005–2015 and 2017–2019 in low-elevation riparian and pinyon-juniper habitats, and data from 2005–2015 and 2017–2020 in sagebrush-shrubland habitat, 121 population-density trends were estimated across the three habitats. Eleven of the estimated density trends were significant (p-value <0.05), including nine negative trends and two positive trends. There were sufficient sample sizes to estimate the densities of 63 species in at least one of the three habitats surveyed. In 2020, we made a change to our species trend-estimation process. Annual density estimates were only included for species in habitats with at least 10 detections within the distance cut-off (125 meters). In previous years, annual density estimates did not have to meet a detection threshold to be included in trend estimates. As a result, some previous annual density estimates were based on a low number (<10) of annual detections. In distance sampling, this can lead to inaccurate estimates. Due to this change in methods, some trend estimates from 2019 are no longer presented. Others have changed in significance. Thus, all trend estimates in this report should replace those found in reports from previous years.

Status and trends of landbird populations in the Northern Colorado Plateau Network: 2020 field season

Series