The name prothonotary warbler has been described as originating from the yellow color similarity shared with the robes of the Roman Catholic church’s papal clerks, referred to as prothonotaries (1). The bright yellow/orange plumage of the prothonotary warbler and its preference for hardwood swamps with cavity nesting sites are characteristics that set this warbler apart from other warblers. These identification qualities are reflected in its nickname “The Golden Swamp Warbler” (2).

Lifespan average is 2.44 years, with a record of over 8 years (1). Each brood averages 4 to 5 eggs, with 1 to 3 broods (1). Double brooding often occurs at higher rates in the more southern portion of the breeding range (13). Incubation lasts 12 to 14 days (4). Prothonotary warblers are the only Eastern wood-warblers that nest in cavities (1).

Nest sites are selected by the male and completed by the female (1, 4). Males establish a territory averaging between 3-4 acres, being more likely to return annually to sites with higher quality habitat (1, 4). Poor nest site selection can result in mortality due to improper shading or flooding, although it has been reported that fledglings can swim (1, 4, 15).

Visual identification and song recordings can be found at The Cornell Lab All About Birds and Audubon Guide to North American Birds.

Why is habitat loss important?

As humans destroy and degrade natural areas, the quantity and quality of habitat is lessened. The loss of habitat means that wildlife does not have access to the basic resources needed to live, such as food, shelter, and areas to safely raise young. The degree to which humans have globally altered habitat is so large that habitat degradation and destruction is currently the main driver of biodiversity loss and extinction of species (16, 17). Wetland habitat, which prothonotary warblers depend on, has historically been severely impacted by human activity, with estimates of up to 87% wetland area lost since the eighteenth century (18).

What does the future look like for prothonotary warblers?

While the current population is relatively stable, the effects of climate change and habitat loss will likely cause fluctuations in future population numbers (1, 9, 14).

Because they depend on a few key habitat areas in their non-breeding range, especially northern Colombia, land-use changes and climate change effects in these regions could have a serious impact on the population (6). Prothonotary warblers have mainly been studied in their breeding range. This means future research in their migratory stopover and non-breeding ranges is needed to fully understand population dynamics and the extent of climate change threats (6).

Increasing temperatures are known to shift the latitudinal ranges of bird species (19). A map prediction of what this climate shift could mean for the breeding range of prothonotary warblers can be found at Audubon’s Guide to North American Birds (20). How climate change will affect interactions with competitive species in the breeding range, such as brown-headed cowbirds (Molothrus ater) and house wrens (Troglodytes aedon), as their ranges change is also not yet fully understood (1, 12, 15).

Prothonotary warblers have demonstrated some beneficial strategies that could positively influence population numbers with the challenges of a changing climate. When preferred aquatic invertebrate food sources are unavailable, they supplement their diet by seeking out terrestrial invertebrates, like mayflies (Ephemeroptera) (21). As timing of migration and insect hatching shift due to climate change, this could become an important foraging strategy. Earlier migration times and warmer spring temperatures may contribute to instances of double brooding, potentially doubling an individual’s number of offspring in one year (13). Prothonotary warblers also have a relatively high tolerance for human interaction, readily accepting nest boxes and allowing nesting sites to be closely monitored (5, 14).

Prothonotary warblers are not currently considered threatened or endangered, but taking action now to maintain their population is vital for long-term preservation of the species.

What plans exist to protect prothonotary warblers?

Although prothonotary warblers are a United States species of conservation concern, a national strategy does not exist (11). However, specific states have developed individual conservation plans to manage habitat and stabilize regional breeding populations (22). Researchers at Virginia Commonwealth University have also successfully increased the local breeding population of prothonotary warblers through the efforts of a 30-year nest box program at a study site along the James River (23). Other conservation groups include the Lower Mississippi Valley Joint Venture and the Prothonotary Warbler Working Group (3, 24).

Prothonotary warblers also nest in Canada, where they are designated as Endangered because only a dozen nesting pairs remain along the northern shore of Lake Erie (14). The Ontario recovery strategy involves protection and restoration of habitat and nesting sites, with special attention on limiting the spread of invasive plants and insects that alter forest composition (14).

Like other migratory birds, the transboundary nature of prothonotary warblers means that international cooperation is essential to study and protect this species.

1. Petit, L. J. (2020). Prothonotary warbler (Protonotaria citrea), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology. https://doi.org/10.2173/bow.prowar.01

2. Dunn, J., & Garrett, K. (1997). Peterson Field Guides: A field guide to warblers of North America. Houghton Mifflin.

3. Lower Mississippi Valley Joint Venture. (2020). Mississippi Alluvial Valley forest-breeding landbird population goals & quantitative habitat objectives. https://www.lmvjv.org/landbird-plans

4. Walkinshaw, L. H. (1953). Life-history of the prothonotary warbler. The Wilson Bulletin, 65(3), 152-168. https://www.jstor.org/stable/4158203

5. Mueller, A. J., Twedt, D. J., & Bowers, E. K. (2019). Rapid adoption of nest boxes by prothonotary warblers (Protonotaria citrea) in mesic deciduous forest. Canadian Journal of Zoology, 97(12), 1109-1115. https://doi.org/10.1139/cjz-2019-0059

6. Tonra, C. M., Hallworth, M. T., Boves, T. J., Reese, J., Bulluck, L. P., Johnson, M., Viverette, C., Percy, K., Ames, E. M., Matthews, A., Slevin, M. C., Wilson R. R., & Johnson, E. I. (2019). Concentration of widespread breeding population in a few critically important nonbreeding areas: Migratory connectivity in the prothonotary warbler. The Condor, 121(2), 1-15. https://doi.org/10.1093/condor/duz019

7. Wolfe, J. D., Johnson, M. D., & Ralph, C. J. (2013). Greater mass increases annual survival of prothonotary warblers wintering in northeastern Costa Rica. The Condor, 115(1), 163-167. https://doi.org/10.1525/cond.2012.120084

8. Bulluck, L., Ames, E., Bayly, N., Reese, J., Viverette, C., Wright, J., Caguazango, A., Tonra, C. (2019). Habitat-dependent occupancy and movement in a migrant songbird highlights the importance of mangroves and forested lagoons in Panama and Columbia. Ecology and Evolution, 9(19), 11064-11077. https://doi.org/10.1002/ece3.5610

9. Prothonotary warbler: Protonotaria citrea. (2020, October 23). IUCN Red List. Retrieved March 28, 2022, from https://www.iucnredlist.org/species/22721765/137344170

10. USFWS. (2020). Migratory Bird Treaty Act protected species (10.13 list). https://www.fws.gov/birds/management/managed-species/migratory-bird-treaty-act-protected-species.php#alphabetical

11. USFWS. (2021). Birds of conservation concern 2021 report. https://www.fws.gov/media/birds-conservation-concern-2021pdf

12. Flaspohler, D. J. (1996). Nesting success of the prothonotary warbler in the upper Mississippi River bottomlands. Wilson Ornithological Society, 108(3), 457-466. http://www.jstor.org/stable/4163713

13. Bulluck, L., Huber, S., Viverette, C., & Blem, C. (2013). Age-specific responses to spring temperature in a migratory songbird: older females attempt more broods in warmer springs. Ecology and Evolution, 3(10), 3298-3306. https://doi.org/10.1002/ece3.673

14. Ontario Ministry of Natural Resources. (2021). Prothonotary warbler recovery strategy. https://www.ontario.ca/page/prothonotary-warbler-recovery-strategy

15. Cooper, R. J., Wood, L. A., Gannon, J. J., & Wilson, R. R. (2009). Effects of timber harvest and other factors on a floodplain forest indicator species, the prothonotary warbler. Wetlands, 29(2), 574-585. https://doi.org/10.1672/08-139.1

16. Cardinale, B. J., Duffy, J. E., Gonzalez, A., Hooper, D. U., Perrings, C., Venail, P., Narwani, A., Mace, G. M., Tilman, D., Wardle D. A., Kinzig, A. P., Daily, G. C., Loreau, M., Grace, J. B., Larigauderie, A., Srivastava, D. S., & Naeem, S. (2012). Biodiversity loss and its impact on humanity. Nature, 486, 59-67. https://doi.org/10.1038/nature11148

17. Pimm, S. L., & Raven, P. (2000). Extinction by numbers. Nature, 403, 843-845. https://doi.org/10.1038/35002708

18. Davidson, N. C. (2016). Wetland losses and the status of wetland-dependent species. In C. Finlayson, G. Milton, R. Prentice, & N. Davidson (Eds.), The wetland book (pp. 1-14). Springer. https://doi.org/10.1007/978-94-007-6173-5_197-1

19. McCaslin, H. M., & Heath, J. A. (2020). Patterns and mechanisms of heterogeneous breeding distribution shifts of North American migratory birds. Journal of Avian Biology, 51(3), 1-13. https://doi.org/10.1111/jav.02237

20. Prothonotary Warbler. (n.d.). Audubon: Guide to North American birds. Retrieved April 2, 2022, from https://www.audubon.org/field-guide/bird/prothonotary-warbler

21. Dodson, J. C., Moy, N. J., & Bulluck, L. P. (2016). Prothonotary warbler nestling growth and condition in response to variation in aquatic and terrestrial prey availability. Ecology and Evolution, 6(20), 7462-7474. https://doi.org/10.1002/ece3.2400

22. Wisconsin Department of Natural Resources [WDNR]. (2012). Wisconsin prothonotary warbler species guidance. https://dnr.wi.gov/files/PDF/pubs/er/ER0688.pdf

23. Prothonotary warblers. (n.d.). Virginia Commonwealth University Rice Rivers Center. Retrieved April 2, 2022, from https://ricerivers.vcu.edu/research/prothonotary-warblers/

24. Home. (n.d.). Prothonotary Warbler Working Group. Retrieved April 2, 2022, from https://prowwg.wixsite.com/home

Want to get more involved? Check out the links below! You can…

• Build your own prothonotary warbler nest box: Nest Watch: All About Birdhouses

• Help researchers gather data: eBird

• Learn more about the threats to birds: Silent Skies: Billions of North American Birds Have Vanished

• Help all birds: The Cornell Lab of Ornithology’s Seven Simple Actions to Help Birds

• Read about birds: The Birder’s Library

• Vote: Vote for the Birds