St. Croix Creature Feature: Prothonotary warbler

A brilliant little bird with a big confusing name finds its particular nesting needs along the St. Croix River.




7 minute read

“The brilliant Prothonotary Warbler bounces along branches like a golden flashlight in the dim understory of swampy woodlands. This golden ray of light is unique among warblers with its beady black eye and blue-gray wings. It is also one of two warblers that build their nests in holes in standing dead trees. Often called a “swamp warbler” in the southeast, it also occurs surprisingly far to the north along rivers. Its population is declining, due to loss of forested wetlands in the U.S. and mangroves on its wintering grounds.”

Cornell Lab of Ornithology

I love the prothonotary warbler for many reasons: its bright yellow head and body, its diminutive size but bold personality, its bizarre name — and because I’ve only seen the bird when I’m in a canoe or kayak. It prefers to nest in floodplain forest, with the St. Croix River representing a northern extreme of its breeding range.

So I also love it because its presence along the St. Croix is another example of the watershed as a transition and tension zone. Here in the northwest corner of its range, the prothonotary warbler nests and raises young, as do northern breeding birds like the veery.

The birds are notable because they are one of only two warbler species that nest in tree cavities, in the prothonotary warbler’s case, only using cavities excavated by woodpeckers or other birds. Most of those cavities are in dead or dying trees, which points to a potential problem: dead and dying trees are often cut from areas people use for safety reasons, or timber is harvested and leaves nothing behind. Letting trees die naturally is essential for prothonotary warblers, and the St. Croix’s significant protected silver maple-dominated lowlands can be a refuge for prothonotary warblers.

Prothonotary warblers nest in what is the definition of floodplain forest, especially large tracts of it:

“The most common features shared by all nesting sites include low-lying, flat terrain, standing or slow-moving waters, a dense forest canopy (50%–75% cover), and a sparse understory (Petit 1999). The species’ preference for nesting over water is believed to be related to higher insect availability (e.g., mayflies and dragonflies) and lower mammalian predation due to the relative inaccessibility of flooded stands (Petit and Petit 1996; Hoover 2006). Several studies have suggested the warbler is area sensitive, avoiding forest stands that are less than 100 ha in size and riparian edges less than 30 m wide (e.g., Whitcomb et al. 1981; Kahl et al. 1985).”

Minnesota Breeding Bird Atlas

The future of this bird species is not safe, unfortunately. The population has dropped by a third since the 1970s. It is picky about where it breeds, and it’s a type of habitat this imperiled by dams, climate change, development, logging, and other forces.

“Flood-control measures that result in drying of seasonally flooded areas reduce habitat availability and suitability (Petit 1999, Gannon 2005). Logging practices that remove cavity trees or decaying snags negatively impact this species (Petit 1999). Logging, insect infestations, or other disturbances that create open areas within bottomland hardwood forests may facilitate exotic plant establishment. Reed canary grass (Phalaris arundinacea), for instance, can dominate the ground layer, impede tree regeneration, and ultimately convert bottomland hardwoods to a habitat unsuitable for Prothonotary Warblers (Kreitinger and Paulios 2007). Brown-headed Cowbird parasitism is also a concern because parasitized nests suffer decreased hatching success, high nestling mortality, and low fledging rates (Petit 1999, Hoover 2003). Parasitism rates have been as high as 29% in Wisconsin (Flaspohler 2006), 43% in Arkansas (Gannon 2005), and 41-50% in southern Illinois (Hoover 2003).”

Prothonotary Warbler (Protonotaria citrea) Species Guidance, Wisconsin DNR

Water levels on the Lower St. Croix River, where the prothonotary warbler finds its floodplain nesting grounds, are manipulated and artificially elevated by a dam on the Mississippi River. The first dam on the Mississippi below the St. Croix’s mouth, operated by the U.S. Army Corps of Engineers, not only maintains a navigable channel on the Mississippi, but keeps the St. Croix about three to four feet higher than natural or historic. This results in reduced floodplain.

On the other end of the prothonotary warbler’s migration in Central America, where it spends the winter, the mangrove forests it depends on are also imperiled by logging and agriculture.

The sensitivity of the species and the many threats it faces has inspired several warnings about the bird’s status. It is a Species of Greatest Conservation Need in Minnesota, and The authoritative Partners in Flight program has assigned it a relatively high score of 14 out of 20 on its conservation assessment, putting it on a watch list of “species of continental concern.”

Audubon Minnesota released an action plan for protecting prothonotary warblers in 2014. It called for protection of large blocks of floodplain, among other measures. Nest boxes can also be built and installed in suitable habitat to replace lost tree cavity options.


Photos on the St. Croix River

Click to view larger versions of the images. All photos by Greg Seitz, St. Croix 360

Song and calls


Cold war connection

The excitement of seeing a prothonotary warbler was the downfall of one man investigated for Communist ties in early ears of America’s Cold War with the Soviet Union. His fate was the result of questioning by a future U.S. president.

Alger Hiss, a prominent state department official, had been accused of being a Communist by Whittaker Chambers, who had participated in the party in the 1930s but turned on his former comrades after World War II. Chambers said Hiss had been involved in what he called the “Communist underground.” Hiss denied it outright, saying he didn’t even know Chambers. The House un-American Activities Committee needed to figure out who was lying, so they sought to prove Chambers knew Hiss as well as Chambers claimed. As evidence, Chambers said he remembered that Hiss and his wife was a birder and Chambers even remembered one of his notable sightings.

“They used to get up early in the morning and go to Glen Echo, out the canal, to observe birds,” Chambers told the committee. “I recall once they saw, to their great excitement, a prothonotary warbler.”

That seemed like pretty specific knowledge that only a close friend might have heard. Rep. Richard Nixon, who would serve as president two decades later, pursued the line of inquiry. At a subsequent hearing, he set a trap for Hiss:

Mr. NIXON. What hobby, if any, do you have, Mr. Hiss?
Mr. HISS. Tennis and amateur ornithology.
Mr. NIXON. Is your wife interested in ornithology?
Mr. HISS. I also like to swim and also like to sail. My wife is interested in ornithology, as I am, through my interest. Maybe I am using too big a word to say an ornithologist because I am pretty amateur, but I have been interested in it since I was in Boston. I think anybody who knows me would know that.
Mr. McDOWELL. Did you ever see a prothonotary warbler?
Mr. HISS. I have right here on the Potomac. Do you know that place?
The CHAIRMAN. What is that?
Mr. NIXON. Have you ever seen one?
Mr. HISS. Did you see it in the same place?
Mr. McDOWELL. I saw one in Arlington.
Mr. HISS. They come back and nest in those swamps. Beautiful yellow head, a gorgeous bird.

The exchange reportedly changed the committee’s entire direction. Where most had been inclined to believe Hiss that he didn’t know Chambers, his credibility was now damaged.

Ultimately, Hiss was convicted of perjury and sentenced to five years in prison, where he served almost two years. Senator Joseph McCarthy was inspired by the Hiss case to claim the entire State Department was infiltrated by Communists, and he began his own investigations that would come to redefine the term “witch hunt.” Publicity from the investigation raised Richard Nixon’s profile, leading to him being picked as Dwight Eisenhower’s vice presidential candidate in 1952, working in the White House until his defeat by John Kennedy in 1961.

That name

The prothonotary warbler was originally given the name by French-speaking people in Louisiana. Most birders believe it’s because of the “bright yellow robes worn by papal clerks, known as prothonotaries, in the Roman Catholic church,” as Audubon says.

But one birding blogger has a different theory. Rick Wright says there’s little chance the early Cajuns were familiar with an obscure position in the church that had been eliminated by the late 1700s. It was more likely a reference to their form of colonial government.

An institution that would be called on to play a critical role in the economic and political life of the future state, the notariat was transferred to Louisiana from France at the beginning of the eighteenth century. Indeed, it was with the royal decree of 1717 establishing the first civil government in Louisiana that the powers and functions of the French notary were transplanted in the new colony. From that point on, all parties involved in a real estate transaction were obliged to record the contract in the presence of a notary.

In Quebec, and presumably in Louisiana, too, notaries, who became “an essential component in Louisiana’s civil legal system,” were required to deposit copies of all notarized documents and transactions in a central depot — overseen by a protonotary. The protonotaire would thus have been a significant and well-known figure in the Francophone community.

The Prothonotary Warbler: You Sure About That? – Birding New Jersey

Wright goes on to argue that the prothonotary of early Louisiana would have been a nosy busybody, perhaps “given to saying the same thing over and over just to hear themselves talk. And there is no bird anywhere whose song is more monotonous than the tweet-tweet-tweet-tweet of a Prothonotary Warbler.”

Links and resources


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6 responses to “St. Croix Creature Feature: Prothonotary warbler”

  1. Troy Howard Avatar
    Troy Howard

    The prothonotary range has been spreading northward along the St. Croix for a couple of decades and are more common than they used to be – at least in our area. Good article!

  2. Sarah Lilja Avatar

    Great information and photographs!

  3. Nancy Cole Avatar
    Nancy Cole

    Loved the multi media Creature Feature of the p.warbler!

  4. Suz Snyder Avatar
    Suz Snyder

    Now I won’t cut down the dead tree on our shoreline on the St Croix. Great article.

  5. Loralee D. Avatar
    Loralee D.

    Loved this article and the cold war connection. I think I saw 3 or 4 flitting among tree branches over the weekend – brilliant yellow that didn’t seem warbler like.

  6. Josh Leonard Avatar
    Josh Leonard

    Great article and impressive artistic representation of the P. Warbler. I love them so – especially since I have only seen them from a canoe or kayak too 🙂


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St. Croix Creature Feature: Prothonotary warbler