For 30 years Dr. Peter Dunn and Dr. Linda Whittingham, ornithologists at UW-Milwaukee, conducted long-term research projects on the mating habits and success of Tree Swallows at the Field Station. This research resulted in over 30 publications. 85 swallow nest boxes in two large grids were maintained as part of those long-term research projects.

Dozens of those nest boxes were used every year by the Tree Swallows and a few by Eastern Bluebirds; they constituted a major housing facility for the birds of the Field Station and Cedarburg Bog. Drs. Dunn and Whittingham recently retired and moved from the area and the fate of the nest box facility was uncertain. The boxes are old; some need repair or replacement; and all the boxes need to be cleaned out each year before the start of the nesting season. Without continued maintenance, this major nesting habitat would be lost to this population of birds that have for so long called the Field Station home. With the approval and support of the Field Station, the Friends of Cedarburg Bog have adopted maintenance of the next box system as one of our projects to support bird habitat in the area.

In late February of 2024 a group of FOCB volunteers cleaned 82 Tree Swallow boxes to prepare them for the 2024 nesting season. Some of the boxes required repair and six of the boxes were beyond repair and needed replacement. FOCB volunteers provided materials and constructed new boxes for those that needed to be replaced. Over the next few years, all of the old boxes will need to be replaced to maintain nest box grid.

Evidence of Tree Swallow nesting in 2023 was found in 41 of the 82 usable boxes, a 50% box occupancy rate. It is impossible to know how many swallows actually fledged from these nests as the boxes were not monitored during the nest season in 2023. Tree Swallows have only one brood per season, with on average four to six chicks per nest; however, the fledge rate for these birds is undoubtedly less than the hatch rate. Bluebirds occupied three of the 82 nest boxes. Eastern Bluebirds often raise two broods in the same nesting season and given that they also average five or six or more hatchlings per brood, these nest boxes were most probably productive. In 2024, the Friends of the Cedarburg Bog plan to monitor these nest boxes in order to more accurately estimate the fledging success for both Tree Swallows and Eastern Bluebirds.

When it comes to reports documenting the impact of human activities upon the environment, most of the news these days is bad news. Nest boxes are definitely good news. The ongoing nationwide recovery of the Wood Duck and the Eastern Bluebird is in large measure due to humans building and erecting nest boxes. Constructed nest boxes for Tree Swallows nationwide have also been shown to slow the decline of this vulnerable species. Based on estimates of probable numbers of fledglings from the various boxes in and around the Cedarburg Bog over the past ten years, it appears that the Cedarburg Bog Nest Box Initiative is fulfilling its mission to increase or at a minimum hold steady the population numbers of Wood Ducks, Tree Swallows, Eastern Bluebirds, and possibly Hooded Mergansers.

Many thanks to Kira Dayton, John Hurth, Braden Meyer, Richard Albert, Thomas Thornton, Bob Strand, Jim Reinartz, and Michael & Jane Sebzda for their volunteer assistance with nest box maintenance this past season and to Tom Thorton and Jim Reinartz for building boxes for those that needed to be replaced. Anyone interested in volunteering to work with the Nest Box Initiative in 2024 should send a message to the Friends of the Cedarburg Bog website:


New tree swallow bird box