Nest material kleptoparasitism likely evolved in birds to reduce the cost of searching for and collecting material themselves. Although nest material kleptoparasitism has been reported commonly in colonially nesting species, reports for solitary breeding species are infrequent, especially for neotropical migratory species. Here we report potential and actual nest material kleptoparasitism in the Worm-eating Warbler (Helmitheros vermivorum). We deployed video camera systems at passerine nests (n = 81) in east-central Arkansas during summers 2011–2012. In one video, we observed a Worm-eating Warbler stealing nesting material from a Hooded Warbler (Setophaga citrina) nest. One day later, we later observed a Worm-eating Warbler landing within 0.5 m of the same warbler nest when the female was incubating, which possibly deterred a second theft of nesting material. In a third video recording, we observed another Worm-eating Warbler landing within 1 m of an Indigo Bunting (Passerina cyanea) nest. As far as we could determine, neither of these latter two nest visits resulted in nest material kleptoparasitism. Potential benefits of nest material kleptoparasitism include reduced competition for limited nest materials, easy access to suitable material, reduced travel distance, and reduction of nest predation risk; however, costs include risk of attack by host or introducing parasites to one’s nest. Importantly, this behavior could ultimately affect the behavioral and life history evolution of a species. We suggest further work should be conducted to determine the prevalence of nest material kleptoparasitism in Worm-eating Warblers and other solitary breeding passerines, including efforts to quantify the benefits and costs of this behavior.

We recorded our Worm-eating Warbler observations while conducting an intensive study on the nesting ecology of passerines in bottomland hardwood forests. These observations were made at two study sites located in east-central Arkansas, USA: Saint Francis National Forest (N 34° 38' 44.840", W 90° 40' 9.974") and Trusten Holder Wildlife Management Area (N 33° 59' 21.584", W 91° 20' 53.917") (Fig. 1). Saint Francis is composed of over 8,500 ha of bottomland and upland forests (Benson et al. 2009) and Trusten Holder is comprised of over 4,000 ha of bottomland hardwood forest (AGFC 2020). In the larger research project (i.e., the intensive nesting ecology study), we established an approximately 72-ha grid at each site. We conducted nest searches for all understory passerine species from early May through late July 2011–2012 and deployed video camera systems recording 24 h/day at 81 nests of 10 different species. Camera systems consisted of a Supercircuits mono-power infrared camera (PC177IR-1color, Liberty Hill, TX), a micro-digital video recorder (DVR; AKR-100S, Korea), and a 12-V deep-cycle marine battery. We reviewed approximately 13,500 hours (i.e., 562.5 days) of video with camera systems deployed between 1-13 days per nest.