Brett Reece

Every year over a hundred volunteers and DNR staff head out to spy on Iowa’s Bald Eagles. Thankfully the eagles usually don’t mind and we get valuable data that helps us to evaluate how these birds are doing in the state.

Volunteers help with two surveys: The Bald Eagle Midwinter Survey and the Bald Eagle Nest Monitoring Survey. The midwinter survey takes place in early January each year and requires surveyors to drive a standardized route, counting all eagles seen along the way. During the nest monitoring survey, volunteers collectively watch between 250 and 350 nests around the state and report on a nest’s activity and success in producing and fledging eaglets.

Some important background to have before reading last year’s results is that 2022 was the worst nesting season in many years for Iowa’s Bald Eagles. For the first time in the history of the survey the average number of young fledged per nest dropped below the important threshold of 1; only an average of 0.88 young were fledged per nest. This is thought to be the result of the Highly Pathogenic Avian Influenza outbreak.

A total 1,663.5 miles of waterway were surveyed in January of 2023 and over 2,900 eagles were counted using these waterways! That works out to almost 2 eagles per river mile surveyed. The most eagles were counted on the Mississippi and Des Moines Rivers though the highest density (eagles per mile) was on the Iowa River.

One of the important things we keep an eye on, as it is a good indicator of population health, is the proportion of the count made up of immature eagles. Since the survey started in 1991, that proportion has hovered around 30% and 2023 was consistent with that at 32%.

From late winter to summer 2023, another army of volunteers around the state monitored 329 bald eagle nest sites. They observed from a distance and recorded whether the nest was active and, if so, if it was successful fledging eaglets. A total of 66% of the active monitored nests were successful, 12% failed (the remaining had an unknown outcome). There was an average of 1.77 fledglings produced per nest which is one of the highest rates in recent years. This represented a very good recovery after 2022’s poor nesting season!

In addition, there was one very surprising observation – a nest that fledged 4 young! Usually, bald eagles only lay 1-3 eggs with the most common being 2 fledglings per nest. We had never even heard of a nest hatching 4 young, much less raising them all to fledging! However, a very diligent nest monitor was able to capture this very rare phenomenon. Congrats to the parents of the fab four for a job very well done!

2023 was characterized by a return to normal after a year of extremes in 2022. The midwinter survey count was just below the average and the nest monitoring survey had an average number of successful nests and a high number of young produced. Taking into account the success rate, the overall number of known active territories and the average number of young produced by nest, a possible 720 young eagles were fledged by Iowa’s nests!

This paints a picture of a resilient and healthy bald eagle population in Iowa, which is great news for our nation’s symbol! For now, we will continue to monitor both wintering and breeding eagles to help us to monitor the Bald Eagle’s recovery. A huge and very heart-felt thank you to the many volunteers and staff who help to make this monitoring possible!