Osprey nesting report released 

From the Iowa Department of Natural Resources

Ospreys 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, which 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 two 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 toward the end of the nesting season. Some opportunistic reports of nesting activity are also accepted if no formal data are available.

There were 50 osprey nests monitored during the 2024 nesting season. Of these 50 nests, 39 were active, and 11 were inactive. Seven new nests were reported this year. Of the 39 active nests, 25 were reported as successful (at least one young survived to fledging), five were reported as failed, and nine had no outcome reported.

In 2024, 23.1% of monitored active nests had an unknown outcome (i.e. do not know if the nest successfully fledged young or failed). This rate is lower than last year (36.4% unknown outcome nests in 2023). Volunteers help to improve reporting, and the DNR will continue to work with monitors to reduce the percentage of unknown outcome nests in future years. More complete reporting improves the certainty of our trend data for this species.

Based on available data, 64.1% of monitored active nests were successful (25 nests) and a minimum total of 47 young were fledged. This is a notable increase from last year where 48.5% of monitored active nests were successful (16 nests) and a minimum total of 26 young were fledged. An average of 1.57 young were produced per known-outcome active nest, the third highest fledge rate since 2016. The Spirit Lake area continues to see fluctuations in the number of active nests. In 2018, there were a record five active nests, which decreased to only one active nest in 2023 but this year saw an increase to three active nests recorded in the area. Additional years of nesting data and additional nest searching will help us better 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 more than 75% of the 2024 active Iowa nest sites were on cell towers. DNR will continue to work with partners on managing this potential conflict.

Contact the Volunteer Wildlife Monitoring Program Coordinator if you are interested in helping with monitoring in the future at vwmp@dnr.iowa.gov.