(Iowa Capital Dispatch) The Iowa Department of Natural Resources’ results from 2025 moonlit surveys of owls and nightjars show that some of the bird populations are declining.
DNR’s Monitoring of Owls and Nightjars, or MOON, survey has monitored population trends of nocturnal owls and nightjars, another nocturnal bird. Many of the species are listed as threatened in the state or as species of greatest conservation need, since 2016.
Each year the department tries to grow the number of survey routes, which consist of 10 survey stops. In 2025, DNR had 18 MOON survey routes, but the department said it hopes to grow the number of MOON survey routes so there is one in each of Iowa’s 24 bird conservation areas.
Only a handful of routes show long-term data, as a majority of the routes were added in 2024. According to the 2025 report, maximum counts from those long-term routes show that barred owls are “stable to decreasing” while Eastern whip-poor-wills, a species of greatest conservation need, and Chuck-will’s-widows, a threatened species in Iowa, are decreasing.
Surveys are conducted during two periods of the year, in May and June, when the moon is illuminated 50% or more at night during the birds’ breeding seasons. At each stop along the route, surveyors listen for owl and nightjar calls for six minutes, then broadcast recorded calls of Eastern screech-owls and barn owls and listen again, to increase the likelihood of detecting these species.
The survey monitors for a total of 11 species, eight species of owls and three species of nightjar. Of the monitored species, only the barred owl, great horned owl and Northern saw-whet owl are without species of greatest conservation need or state threatened designations.
The survey notes that because only a handful of routes have long-term survey data, there are unclear trends for many of the species monitored.
Data for 2025 show that Eastern whip-poor-wills were detected on 67% of routes, Chuck-will’s widows on just 6% of routes, the common nighthawk on 22% of routes, barred owl on 94% of routes, barn owls on 17% of routes, Eastern screech owls on 33% of routes and great horned owls on 61% of routes.
“Repeated annual surveys will allow us to detect species trends over time for all routes,” the report said. “Although we can only make inferences at the scale of the survey, there are some concerning negative population trends emerging from our long-term routes, particularly with nightjars.”
The report said additional data will be necessary for the department to make “specific links” between owl and nightjar populations and habitat management in the state, but the long-term route data showing declines in Eastern whip-poor-will and Chuck-will’s-widow indicate that those areas “may need additional habitat management.”
The report said forest management strategies like invasive shrub removal or understory thinning, could increase open canopy areas in the forest which can help support those species.
The MOON survey is one of several wildlife monitoring programs under DNR, some of which are open to volunteers, like frog and toad surveys or peregrine falcon nesting reports.
