(SBA) - Osprey are a migratory raptor species that breed in Iowa. Osprey experienced population declines in the mid-20th Century. The Iowa DNR began the Osprey restoration program in 1997 and involved translocating young birds from Minnesota and Wisconsin to strategic locations across Iowa. The last year that birds were released was 2016 and currently, the objective is to monitor nesting activity. There are three main areas in the state where Osprey have become well established: the Iowa City to Waterloo corridor, Des Moines and vicinity, and Spirit Lake and vicinity (though this area is least stable). There are also three nesting pairs on the western border of Iowa south of Sioux City.
Monitoring of nest sites is accomplished primarily by volunteers. Volunteers are assigned to a particular nest or nests and new nests are reported opportunistically. Volunteers visit each nest multiple times during the breeding season and try to gather information on nest activity at the start of the nesting season and whether the pair is successful in fledging young towards the end of the nesting season. Some opportunistic reports of nesting activity are also accepted if no formal data are available.
Statewide map showing 2023 Osprey nest locations (33 active, 9 inactive, 1 not monitored).
We improved our analysis methodologies and updated historic records in 2023, thus some historic values presented in this report may appear different than previous reports. There were 42 Osprey nests monitored during the 2023 nesting season. Of these 42 nests, 33 were active and 9 were inactive. Three new nests were reported this year. Of the 33 active nests, 16 were reported as successful (at least one young survived to fledging), 4 were reported as failed, 1 was gone/removed, and 12 had no outcome reported.
In 2023, 36.4% of monitored active nests had an unknown outcome (i.e. we do not know if the nest successfully fledged young or failed). This rate is the highest over the last 5 years of monitoring and exceeded the 2021 rate of 27.6%, thus comparison of 2023 values to data from previous years should be done with caution. We will work with volunteers to attempt to reduce the percentage of unknown outcome nests in future years.
Summary of 2019-2023 Osprey nesting results.
Based on available data, 48.5% of monitored active nests were successful (16 nests) and a minimum total of 26 young were fledged, though 12 nests had unknown outcomes so more young may have been produced. An average of 1.30 young were produced per known-outcome active nest. The Spirit Lake area continues to see fluctuations in the number of active nests. In 2018, there were a record 5 active nests, which decreased to 2 active nests by 2020. A slight increase was seen in 2022 with 3 active nests, but in 2023 only 1 active nest was recorded in the area. Additional years of nesting data and additional nest searching will help us understand the stability of this segment of the population.
In future years, the DNR will continue to monitor Osprey nest sites with the partnership of volunteers. An ongoing challenge is that Osprey like nesting on cell phone towers. Osprey don’t generally cause damage to the towers but conflicts can arise when work must be done on a tower during the nesting season, especially since 72.7% of the 2023 active Iowa nest sites were on cell towers. We will continue to work with partners on managing this potential conflict.
The average number of Osprey young fledged per known-outcome nest from 2016-2023.
Finally, a huge thank you to all the volunteers who are vital to tracking the recovery of this species! You are invaluable. Please contact the Volunteer Wildlife Monitoring Program Coordinator if you are interested in helping with monitoring in the future; vwmp@dnr.iowa.gov.
