A Prothonotary Warbler Nest Box Trail in Northwest Wisconsin


Herbert Wagner


The prothonotary warbler (Protonotaria citrea) is a rare gem among Wisconsin bird life. Strikingly beautiful, this flashy insect eater has bright yellow or orange-yellow plumage with blue-gray wings and an olive colored back. Its unusual name is derived from Catholic church hierarchy whose protonotarii or scribes to the Pope wore golden robes. (8)

People who have observed prothonotary warblers in the wild sometimes report that under the right light conditions they appear almost luminous. Older works refer to this bird as the golden swamp warbler which is also a clue to its breeding habitat. Wisconsin is the northern edge of this neotropical migrant's summer breeding range which winters in Central and South America. Wisconsin DNR defines it as a Species of Greatest Conservation Need (8) and Partners in Flight calls it a species of continental concern. (6)

Wisconsin Range

Although most commonly found in southern and central Wisconsin, the prothonotary warbler is also present in the northwest part of the state. It has been documented along the lower St. Croix River in Polk, Pierce and St. Croix counties, (14) and has been reported along the upper St. Croix River as far north as Burnett County. (11) That is the adjoining county west from where I write this at my photovoltaic powered home near Totogatic River.

In 2009, the Totogatic River was designated by the Wisconsin legislature as an official state Wild and Scenic River due to its pristine natural condition and remoteness. It is the largest tributary of the famed Namekagon River and joins that stream near its confluence with the St. Croix. These two streams comprise the federally protected St. Croix National Scenic Riverway where many rare and usual species are known to exist. (17)

Although the prothonotary warbler has been reported within 50 miles it is unknown whether its range extends into the Totogatic River watershed. Possibly it does as an unrecognized summer resident or as an occasional visitor. Research shows that vagrant prothonotary warblers are routinely reported much farther north and west of their normally accepted range (9). Since they have been reported just one county away and the bottomlands along Totogatic River offers potential breeding habitat for this species, it's possible they may be here too.

Studies Needed

One way to determine the presence of prothonotary warblers is to establish a system of nest boxes for them. This is practicable since this bird is a secondary cavity nester, meaning that it uses natural tree cavities or those excavated by other birds or animals. (1) Placing nest boxes for them in suitable habitat may draw and hold them during the breeding season where they can be observed. Such a nest box program would be a worthwhile land stewardship enhancement. One that would provide additional nesting opportunities for this uncommon species while determining whether or not prothonotary warblers are present in parts of Northwest Wisconsin where they have not yet been documented.

Research of this type is important because in Wisconsin good population studies of the prothonotary warbler are lacking and its status is not well known. This is largely due to the inaccessibility and unfavorable conditions of its breeding habitat: swamps, miry sloughs, and log-choked river bottoms swarming with cut grass, stinging nettles, venomous insects and poison ivy รณ places and things most people gladly avoid.

Although in general decline, there is also the possibly that with global warming the prothonotary warbler may be expanding its range northerly. The official Wisconsin DNR occurrence map for this species cautions that it is only a general reference of sightings and not meant to be an accurate range map. (13) For these reasons the Wisconsin Bird Conservation Initiative recommends additional surveys of this relatively rare bird be conducted in potential habitat areas in order to better understand its status and requirements. (2)

Habitat Requirements

According to the literature, the prothonotary warbler is declining over much of its range. (12) This is due to widespread habitat loss, the lack of and vulnerability of natural nesting cavities in trees, and parasitism by the brown-headed cowbird. (5)

Prothonotary warbler breeding habitat is restricted to lowland hardwood swamps and river floodplain forests that seasonally overflow their banks. These birds prefer woods with a sparse understory and require trees with hollow cavities for breeding. Nests are usually placed near or low over calm or slow moving water, often in areas that are periodically flooded. (12)

Good forest management practices for this species include retaining snags and cavity trees during logging operations in lowland forests. But since the prothonotary warbler easily adapts to human-supplied nest boxes, placing the structures in suitable habitat can enhance the nesting success of this species. (8)

Lowland Hardwood Forest

In Wisconsin it has been estimated that only 8% of the original presettlement river floodplain forests remain intact today. (10) Agriculture, grazing, draining, channeling, dam building and logging has disrupted or destroyed the rest. Although river floodplains are relatively rare in northern Wisconsin, (3) they do extend into the far northwestern part of the state along the St. Croix River and its tributaries. This is especially true along Totogatic River in Burnett, Washburn and Douglas counties. In fact, the name Totogatic stems from totosh, the Ojibwe Indian word for the female breast, meaning something soft or yielding. According to Schoolcraft the term is rendered geographical by the addition of a suffix. In Ojibwe a totogun is a peculiar type of soft or dancing bog and Totogatic River is translated as soft or boggy river. (15)

The name is apt. Along much of its length this stream flows through low lying bottomlands that are often flooded during high water events. These occur during the spring snow melt period and after periods of high rainfall. The surrounding uplands are porous sandy jack pine barrens which rapidly release water into adjacent swamps and streams. (16)

In Burnett County along the lower Totogatic River the Dismal Swamp is one such large floodplain area. Another large floodplain occupied the site of the present Minong Flowage. Other areas of extensive bottomland hardwood forest are found along Totogatic River upstream of Minong Flowage for many miles to the Colton Dam.

In many ways these far northern bottomlands resemble lowland forests found farther south in Wisconsin along the lower St. Croix, Chippewa, Wisconsin and Mississippi rivers. Dominant tree species here include silver and red maple, green and black ash, willow, basswood and American elm. There are many decayed fallen trees and dead snags available for foraging by insect eating birds. (16)

Although dams exist both upstream and downstream of the project area, the natural flood pulse cycle here appears to be intact. During high water events low lying parts of this property are covered by a slow moving river enlargement with arm-like embayments. This temporary water body forms a shallow flowing lake that spills onto hundreds of acres of adjacent lowland hardwood forest. (16)

River corridors with seasonally flooded hardwood forest provide critical habitat for migrating birds in the fall and spring seasons. (2) They also support a rich and abundant variety of breeding birds. In the upper Mississippi River floodplain forest almost twice as many bird species are present compared to adjacent upland areas. (7) From personal observation I can report similar conditions here. But whether the the prothonotary warbler is already a summer resident or can be attracted to nest here remains to be discovered.

Nest Box Construction

Although there seems to be a trend towards plastic nest box materials using PVC pipe, I chose to use traditional wooden construction. The type adopted here is a pattern provided by the Natural Resources Conservation Service based on a Minnesota DNR design. (1) It is simple and easy to build. All you need is a drill, hand tools, a 3/4 inch thick by 6 inch wide board, a handful of galvanized nails, and something to mount the box on. One four foot long pine or cedar board contains enough material to make one nest box with almost no waste.

Pieces are easily cut to length with a handsaw and then 1/4 inch vent holes are drilled into the floor panel and upper part of the side walls. The top edge of the entrance hole is located one inch below the top of the front panel and should be 1-1/8 inch in diameter. This is large enough to admit warblers but too small for entry by the parasitic brown-headed cowbird.

One side wall of the nest box is left loose and pivots open on two loosely fitted nails towards the top with a third loosely fitted nail to hold it closed at the bottom. This allows access to the interior of the box for cleaning purposes. The only addition I made to the design was to nail a shingle over the roof to better protect it from rain. I expect these nest boxes (made of rough cut red pine) to last several years.

After the boxes were completed they were mounted on 10 foot lengths of 3/4 inch diameter conduit pipe. The assemblies were then stuck 4 feet into the ground on my property along the edge of a flood-prone hardwood swamp bordering Totogatic River. This height puts the nest box opening approximately six feet above the ground or water level. This is high enough to keep the boxes from being flooded during high water events, but still within the bird's requirements. This height also makes them easy to inspect and clean. The nest boxes are all placed as close as possible to existing trails so they will be easy to visit. If prothonotary warblers are not present or do not use the boxes, they are also suitable for other species, including the black-capped chickadee, the white-breasted nuthatch, and even flying squirrels. (1)

Monitoring & Upkeep

Future plans for the nest boxes beginning in the spring of 2012 include the following. Early in the season they will be inspected, cleaned and repaired if necessary. Then during the spring breeding season beginning in May they will be regularly monitored for use by prothonotary warblers or other species. Due to the bright yellow plumage of the prothonotary warbler and its distinctive song (described as "sweet sweet sweet sweet sweet") identification should be fairly easy. (4) Photographs will be taken and all findings recorded in my "Woods Notes" series of field notebooks begun in 2005 and currently up to volume seven.

While there is no guarantee that the prothonotary warbler will nest here, I feel there is a fairly good chance of success based on its reported proximity and favorable habitat and already known biodiversity of plants and animals in this floodplain area. If prothonotary warblers find this place, I'm pretty sure they'll like it.

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This webpage was created October 3, 2011 on a recycled Mac PowerBook computer (1998 model) using electricity generated by the sun!