Status of Osprey in Iowa

Osprey are a migratory raptor species that breed in Iowa. They are piscivorous (eat fish) and their populations declined steeply during the 1950s and 60s because of the pesticide DDT. Iowa DNR began its osprey restoration program in 1997 which involved translocating young birds from Minnesota and Wisconsin to strategic locations across Iowa. Birds were last released in 2016 and the current objective of the program is to monitor osprey 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. There are also two nesting pairs on the western border of Iowa south of Sioux City and a new nest site was found in Marshall County in 2021.

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 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.

At the start of 2021, there were 45 osprey nests that were designated as routinely active (active in recent years especially 2020) or with unknown status (no updates on the nest recently) and three new nests were reported in 2021. A total of 42 nests were reported on during or after the 2021 nesting season (Table 1). Thirteen of these 42 nests were reported as inactive, with 29 having some osprey activity on or near the nest. Of the active nests, 8 had no reported outcome, 6 failed to produce young and 15 were successful in producing young.

In 2021, 27.6% of monitored nests that were active had an unknown outcome (i.e. we do not know if the nest successfully fledged young or failed). This is the highest rate of unknown nest fate reported in survey history, thus comparison of 2021 values to data from previous years should be done with caution.

Based on the data we do have, 51.7% of monitored active nests were successful. A minimum total of 26 young were fledged in 2021 with an average of 1.24 young produced per known-outcome active nest (Figure 2). In 2018, there were 5 active nests in the Spirit Lake area, since then the number has decreased, with only two active nests documented in the area in 2021.

Osprey prefer a nest site with a commanding view and over half of Iowa’s osprey nest 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. We will continue to work with partners on managing this potential conflict.

In future years, the DNR will continue to monitor osprey nest sites with the partnership of volunteers, and may focus extra attention on the Spirit Lake area. A huge thank you to all the volunteers who are vital to tracking the recovery of this species! You are invaluable. We do have a number of nests that need monitors in 2022 so please contact the Volunteer Wildlife Monitoring Program coordinator if you are interested in helping, vwmp@dnr.iowa.gov.