ORIGINAL ARTICLE Mobbing behavior and fatal attacks on snakes by Fasciated Antshrikes (Cymbilaimus lineatus) Ioana Chiver 1,2 • Ce´sar A. Jaramillo 3 • Eugene S. Morton 4,5 Received: 16 May 2016 / Revised: 12 February 2017 / Accepted: 20 March 2017 Ó Dt. Ornithologen-Gesellschaft e.V. 2017 Abstract Birds often mob potential predators, which alerts other prey individuals of the danger and drives the predator away. Participation in, or increased intensity of mobbing is often associated with breeding activity suggesting an important function in the defense of nests and young. Less is known about bird mobbing of snakes, however, although these are important predators of birds, particularly at nests in tropical forests. Here, we report observations of mobbing behavior, some escalating into fatal attacks, of snakes by individuals of a tropical bird species, the Fasciated Antshrike (Cymbilaimus lineatus). In addition, we con- ducted snake-model presentations when Fasciated Antshrike pairs had active nests, and when not nesting, to examine the extent that pairs maintain a mobbing response outside of the nesting period. Pairs approached the snake model on average within 59 s (range 15–120 s) and 0.9 m (0.1–5 m) with no difference with nesting status. Our observations of mobbing behavior and fatal attacks suggest that passerines can also present a threat to potential snake predators and that mobbing is likely important in influ- encing predation rate. Mobbing when not nesting may be important in predator deterrence in bird species with year- round residency, and could influence territory quality and reproductive success. Forest birds that hunt large insects or other potentially dangerous prey may have morphological and cognitive specializations that help them to effectively mount a successful attack against predatory snakes. Keywords Year-round territoriality Á Tropical passerines Á Nesting success Á Interspecific communication Zusammenfassung Hassen und to¨dliche Angriffe auf Schlangen durch Zebraameisenwu¨ rger (Cymbilaimus lineatus) Ha¨ufig hassen Vo¨gel auf potenzielle Pra¨datoren, wodurch andere Beuteindividuen vor der Gefahr gewarnt und der Beutegreifer vertrieben werden. Die Beteiligung am Hassen beziehungsweise eine versta¨rkte Hassintensita¨t steht oft mit Brutaktivita¨ten im Zusammenhang, was auf eine wichtige Funktion bei der Verteidigung von Nestern und Jungvo¨ geln hindeutet. Weniger ist u¨ber Vo¨gel bekannt, welche auf Schlangen hassen, dabei stellen diese in Tropenwa¨ldern bedeutende Pra¨datoren, speziell von Nestern, dar. Hier schildern wir Beobachtungen von Hassverhalten auf Schlangen durch Individuen einer tropischen Vogelart, dem Zebraameisenwu¨rger (Cymbilaimus lineatus), von denen manche zu to¨dlichen Angriffen eskalierten. Daru¨ber hinaus fu¨hrten wir Versuche mit Schlangenattrappen durch, sowohl an Communicated by O. Kru¨ger. & Ioana Chiver ichiver@gmail.com Ce´sar A. Jaramillo jaramilc@si.edu Eugene S. Morton mortone@si.edu 1 183 Harding Avenue, Gamboa, Republic of Panama 2 Present Address: Department of Integrative Biology and Physiology, University of California, Los Angeles, 610 Charles E. Young Dr. East, Los Angeles, CA 90025, USA 3 Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Panama 4 Hemlock Hill Field Station, 22318 Teepleville Flats Road, Cambridge Springs, PA, USA 5 Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada 123 J Ornithol DOI 10.1007/s10336-017-1452-9